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  • 1. Agren, A.
    et al.
    Haei, M.
    Kohler, S. J.
    Bishop, Kevin
    Dept. of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, P.O. Box 7050, 750 07 Uppsala, Sweden.
    Laudon, H.
    Regulation of stream water dissolved organic carbon (DOC) concentrations during snowmelt; the role of discharge, winter climate and memory effects2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, no 9, p. 2901-2913Article in journal (Refereed)
    Abstract [en]

    Using a 15 year stream record from a northern boreal catchment, we demonstrate that the inter-annual variation in dissolved organic carbon (DOC) concentrations during snowmelt was related to discharge, winter climate and previous DOC export. A short and intense snowmelt gave higher stream water DOC concentrations, as did long winters, while a high previous DOC export during the antecedent summer and autumn resulted in lower concentrations during the following spring. By removing the effect of discharge we could detect that the length of winter affected the modeled soil water DOC concentrations during the following snowmelt period, which in turn affected the concentrations in the stream. Winter climate explained more of the stream water DOC variations than previous DOC export during the antecedent summer and autumn.

  • 2.
    Alewell, C
    et al.
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Giesler, Reiner
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Leifeld, J
    Agroscope Reckenholz-Tanikon Research Station ART, Switzerland.
    Rollog, M
    Institute of Environmental Geosciences, University of Basel, Switzerland.
    Stable carbon isotopes as indicators for environmental change inpalsa peats2011In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, p. 1769-1778Article in journal (Refereed)
    Abstract [en]

    Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires.

    We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C.

    The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving.

  • 3.
    Almroth-Rosell, Elin
    et al.
    SMHI, Research Department, Oceanography.
    Edman, Moa
    SMHI, Research Department, Oceanography.
    Eilola, Kari
    SMHI, Research Department, Oceanography.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Sahlberg, Jörgen
    SMHI, Professional Services.
    Modelling nutrient retention in the coastal zone of an eutrophic sea2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 20, p. 5753-5769Article in journal (Refereed)
  • 4. Almén, Anna-Karin
    et al.
    Vehmaa, Anu
    Brutemark, Andreas
    Bach, Lennart
    Lischka, Silke
    Stuhr, Annegret
    Furuhagen, Sara
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Paul, Allanah
    Bermudez, J. Rafael
    Riebesell, Ulf
    Engström-Öst, Jonna
    Negligible effects of ocean acidification on Eurytemora affinis (Copepoda) offspring production2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 4, p. 1037-1048Article in journal (Refereed)
    Abstract [en]

    Ocean acidification is caused by increasing amounts of carbon dioxide dissolving in the oceans leading to lower seawater pH. We studied the effects of lowered pH on the calanoid copepod Eurytemora affinis during a mesocosm experiment conducted in a coastal area of the Baltic Sea. We measured copepod reproductive success as a function of pH, chlorophyll a concentration, diatom and dinoflagellate biomass, carbon to nitrogen (C : N) ratio of suspended particulate organic matter, as well as copepod fatty acid composition. The laboratory-based experiment was repeated four times during 4 consecutive weeks, with water and copepods sampled from pelagic mesocosms enriched with different CO2 concentrations. In addition, oxygen radical absorbance capacity (ORAC) of animals from the mesocosms was measured weekly to test whether the copepod's defence against oxidative stress was affected by pH. We found no effect of pH on offspring production. Phytoplankton biomass, as indicated by chlorophyll a concentration and dinoflagellate biomass, had a positive effect. The concentration of polyunsaturated fatty acids in the females was reflected in the eggs and had a positive effect on offspring production, whereas monounsaturated fatty acids of the females were reflected in their eggs but had no significant effect. ORAC was not affected by pH. From these experiments we conclude that E. affinis seems robust against direct exposure to ocean acidification on a physiological level, for the variables covered in the study. E. affinis may not have faced acute pH stress in the treatments as the species naturally face large pH fluctuations.

  • 5.
    Anderson, L. G.
    et al.
    Univ Gothenburg, Dept Chem, Gothenburg, Sweden..
    Björk, G.
    Univ Gothenburg, Dept Geosci, Gothenburg, Sweden..
    Jutterström, S.
    Univ Gothenburg, Dept Chem, Gothenburg, Sweden.;UNIFOB AS, Bjerknes Ctr Climate Res, Bergen, Norway..
    Pipko, I.
    Pacific Oceanol Inst FEB RAS, Vladivostok, Russia..
    Shakhova, N.
    Pacific Oceanol Inst FEB RAS, Vladivostok, Russia.;Univ Alaska, Int Arctic Res Ctr, Fairbanks, AK 99701 USA..
    Semiletov, I.
    Pacific Oceanol Inst FEB RAS, Vladivostok, Russia.;Univ Alaska, Int Arctic Res Ctr, Fairbanks, AK 99701 USA..
    Wåhlström, I.
    Univ Gothenburg, Dept Chem, Gothenburg, Sweden..
    East Siberian Sea, an Arctic region of very high biogeochemical activity2011In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, no 6, p. 1745-1754Article in journal (Refereed)
    Abstract [en]

    Shelf seas are among the most active biogeochemical marine environments and the East Siberian Sea is a prime example. This sea is supplied by seawater from both the Atlantic and Pacific Oceans and has a substantial input of river runoff. All of these waters contribute chemical constituents, dissolved and particulate, but of different signatures. Sea ice formation during the winter season and melting in the summer has a major impact on physical as well as biogeochemical conditions. The internal circulation and water mass distribution is significantly influenced by the atmospheric pressure field. The western region is dominated by input of river runoff from the Laptev Sea and an extensive input of terrestrial organic matter. The microbial decay of this organic matter produces carbon dioxide (CO2) that oversaturates all waters from the surface to bottom relative to atmospheric level, even when primary production, inferred from low surface water nutrients, has occurred. The eastern surface waters were under-saturated with respect to CO2 illustrating the dominance of marine primary production. The drawdown of dissolved inorganic carbon equals a primary production of similar to 0.8 +/- 2 mol C m(-2), which when multiplied by half the area of the East Siberian Sea, similar to 500 000 km(2), results in an annual primary production of 0.4 (+/- 1) x 10(12) mol C or similar to 4 (+/- 10) x 10(12) gC. Microbial decay occurs through much of the water column, but dominates at the sediment interface where the majority of organic matter ends up, thus more of the decay products are recycled to the bottom water. High nutrient concentrations and fugacity of CO2 and low oxygen and pH were observed in the bottom waters. Another signature of organic matter decomposition, methane (CH4), was observed in very high but variable concentrations. This is due to its seabed sources of glacial origin or modern production from ancient organic matter, becoming available due to sub-sea permafrost thaw and formation of so-called taliks. The decay of organic matter to CO2 as well as oxidation of CH4 to CO2 contribute to a natural ocean acidification making the saturation state of calcium carbonate low, resulting in under-saturation of all the bottom waters with respect to aragonite and large areas of under-saturation down to 50% with respect to calcite. Hence, conditions for calcifying organisms are very unfavorable.

  • 6. Anderson, Leif G.
    et al.
    Ek, Jörgen
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Ericson, Ylva
    Humborg, Christoph
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Ulfsbo, Adam
    Export of calcium carbonate corrosive waters from the East Siberian Sea2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 7, p. 1811-1823Article in journal (Refereed)
    Abstract [en]

    The Siberian shelf seas are areas of extensive biogeochemical transformation of organic matter, both of marine and terrestrial origin. This in combination with brine production from sea ice formation results in a cold bottom water of relative high salinity and partial pressure of carbon dioxide (pCO(2)). Data from the SWERUS-C3 expedition compiled on the icebreaker Oden in July to September 2014 show the distribution of such waters at the outer shelf, as well as their export into the deep central Arctic basins. Very high pCO(2) water, up to similar to 1000 mu atm, was observed associated with high nutrients and low oxygen concentrations. Consequently, this water had low saturation state with respect to calcium carbonate down to less than 0.8 for calcite and 0.5 for aragonite. Waters undersaturated in aragonite were also observed in the surface in waters at equilibrium with atmospheric CO2; however, at these conditions the cause of undersaturation was low salinity from river runoff and/or sea ice melt. The calcium carbonate corrosive water was observed all along the continental margin and well out into the deep Makarov and Canada basins at a depth from about 50 m depth in the west to about 150 m in the east. These waters of low aragonite saturation state are traced in historic data to the Canada Basin and in the waters flowing out of the Arctic Ocean north of Greenland and in the western Fram Strait, thus potentially impacting the marine life in the North Atlantic Ocean.

  • 7. Anderson, Leif G.
    et al.
    Jorgen, E. K.
    Ericson, Ylva
    Humborg, Christoph
    Semiletov, Igor
    Sundbom, Marcus
    Ulfsbo, Adam
    Export of calcium carbonate corrosive waters from the East Siberian Sea2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 7, p. 1811-1823Article in journal (Refereed)
    Abstract [en]

    The Siberian shelf seas are areas of extensive biogeochemical transformation of organic matter, both of marine and terrestrial origin. This in combination with brine production from sea ice formation results in a cold bottom water of relative high salinity and partial pressure of carbon dioxide (pCO(2)). Data from the SWERUS-C3 expedition compiled on the icebreaker Oden in July to September 2014 show the distribution of such waters at the outer shelf, as well as their export into the deep central Arctic basins. Very high pCO(2) water, up to similar to 1000 mu atm, was observed associated with high nutrients and low oxygen concentrations. Consequently, this water had low saturation state with respect to calcium carbonate down to less than 0.8 for calcite and 0.5 for aragonite. Waters undersaturated in aragonite were also observed in the surface in waters at equilibrium with atmospheric CO2; however, at these conditions the cause of undersaturation was low salinity from river runoff and/or sea ice melt. The calcium carbonate corrosive water was observed all along the continental margin and well out into the deep Makarov and Canada basins at a depth from about 50 m depth in the west to about 150 m in the east. These waters of low aragonite saturation state are traced in historic data to the Canada Basin and in the waters flowing out of the Arctic Ocean north of Greenland and in the western Fram Strait, thus potentially impacting the marine life in the North Atlantic Ocean.

  • 8.
    Baltar, Federico
    et al.
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Legrand, Catherine
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Pinhassi, Jarone
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Cell-free extracellular enzymatic activity is linked to seasonal temperature changes: a case study in the Baltic Sea2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 9, p. 2815-2821Article in journal (Refereed)
    Abstract [en]

    Extracellular enzymatic activities (EEA) are a crucial step on the degradation of organic matter. Dissolved (cell-free) extracellular enzymes in seawater can make up a significant contribution of the bulk EEA. However, the factors controlling the proportion of dissolved EEA in the marine environment remain unknown. Here we studied the seasonal changes in the proportion of dissolved relative to total EEA (of alkaline phosphatase [APase], β-glucosidase, [BGase], and leucine aminopeptidase, [LAPase]), in the Baltic Sea for 18 months. The proportio n of dissolved EEA ranged between 37-100%, 0-100%, 34-100% for APase, BGase and LAPase, respectively. A consistent seasonal pattern in the proportion of dissolved EEA was found among all the studied enzymes, with values up to 100% during winter and <40% du ring summer. A significant negative relation was found between the 21proportion of dissolved EEA and temperature, indicating that temperature might be a critical factor controlling the proportion of dissolved relative to total EEA in marine environments. Our results suggest a strong decoupling of hydrolysis rates from mi crobial dynamics in cold waters. This implies that under cold conditions, cell-free enzymes can contribute to substrate availability at large distances from the producing cell, increasing the dissociation between the hydrolysis of organic compounds and the actual microbes producing the enzymes. This also indicates that global warming could come to affect the hydrolysis of organic matter by reducing the hydrolytic activity of cell-free enzymes.

  • 9.
    Baltar, Federico
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. University of Otago, New Zealand.
    Legrand, Catherine
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Pinhassi, Jarone
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Cell-free extracellular enzymatic activity is linked to seasonal temperature changes: a case study in the Baltic Sea2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 9, p. 2815-2821Article in journal (Refereed)
    Abstract [en]

    Extracellular enzymatic activities (EEA) are a crucial step on the degradation of organic matter. Dissolved (cell-free) extracellular enzymes in seawater can make up a significant contribution of the bulk EEA. However, the factors controlling the proportion of dissolved EEA in the marine environment remain unknown. Here we studied the seasonal changes in the proportion of dissolved relative to total EEA (of alkaline phosphatase [APase], β-glucosidase, [BGase], and leucine aminopeptidase, [LAPase]), in the Baltic Sea for 18 months. The proportio n of dissolved EEA ranged between 37-100%, 0-100%, 34-100% for APase, BGase and LAPase, respectively. A consistent seasonal pattern in the proportion of dissolved EEA was found among all the studied enzymes, with values up to 100% during winter and <40% du ring summer. A significant negative relation was found between the 21proportion of dissolved EEA and temperature, indicating that temperature might be a critical factor controlling the proportion of dissolved relative to total EEA in marine environments. Our results suggest a strong decoupling of hydrolysis rates from mi crobial dynamics in cold waters. This implies that under cold conditions, cell-free enzymes can contribute to substrate availability at large distances from the producing cell, increasing the dissociation between the hydrolysis of organic compounds and the actual microbes producing the enzymes. This also indicates that global warming could come to affect the hydrolysis of organic matter by reducing the hydrolytic activity of cell-free enzymes.

  • 10. Bartsch, Annett
    et al.
    Widhalm, Barbara
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Palmtag, Juri
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Siewert, Matthias Benjamin
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Can C-band synthetic aperture radar be used to estimate soil organic carbon storage in tundra?2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 19, p. 5453-5470Article in journal (Refereed)
    Abstract [en]

    A new approach for the estimation of soil organic carbon (SOC) pools north of the tree line has been developed based on synthetic aperture radar (SAR; ENVISAT Advanced SAR Global Monitoring mode) data. SOC values are directly determined from backscatter values instead of upscaling using land cover or soil classes. The multi-mode capability of SAR allows application across scales. It can be shown that measurements in C band under frozen conditions represent vegetation and surface structure properties which relate to soil properties, specifically SOC. It is estimated that at least 29 Pg C is stored in the upper 30 cm of soils north of the tree line. This is approximately 25% less than stocks derived from the soil-map-based Northern Circumpolar Soil Carbon Database (NCSCD). The total stored carbon is underestimated since the established empirical relationship is not valid for peatlands or strongly cryoturbated soils. The approach does, however, provide the first spatially consistent account of soil organic carbon across the Arctic. Furthermore, it could be shown that values obtained from 1 km resolution SAR correspond to accounts based on a high spatial resolution (2 m) land cover map over a study area of about 7 x 7 km in NE Siberia. The approach can be also potentially transferred to medium-resolution C-band SAR data such as ENVISAT ASAR Wide Swath with similar to 120m resolution but it is in general limited to regions without woody vegetation. Global Monitoring-mode-derived SOC increases with unfrozen period length. This indicates the importance of this parameter for modelling of the spatial distribution of soil organic carbon storage.

  • 11.
    Bastviken, David
    et al.
    Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Sundgren, Ingrid
    Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Natchimuthu, Sivakiruthika
    Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Reyier, Henrik
    Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
    Gålfalk, Magnus
    Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Technical Note: Cost-efficient approaches to measure carbon dioxide (CO2) fluxes and concentrations in terrestrial and aquatic environments using mini loggers2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, no 12, p. 3849-3859Article in journal (Refereed)
    Abstract [en]

    Fluxes of CO2 are important for our understanding of the global carbon cycle and greenhouse gas balances. Several significant CO2 fluxes in nature may still be unknown as illustrated by recent findings of high CO2 emissions from aquatic environments, previously not recognized in global carbon balances. Therefore, it is important to develop convenient and affordable ways to measure CO2 in many types of environments. At present, direct measurements of CO2 fluxes from soil or water, or CO2 concentrations in surface water, are typically labor intensive or require costly equipment. We here present an approach with measurement units based on small inexpensive CO2 loggers, originally made for indoor air quality monitoring, that were tested and adapted for field use. Measurements of soil-atmosphere and lake-atmosphere fluxes, as well as of spatiotemporal dynamics of water CO2 concentrations (expressed as the equivalent partial pressure, pCO(2aq)) in lakes and a stream network are provided as examples. Results from all these examples indicate that this approach can provide a cost- and labor-efficient alternative for direct measurements and monitoring of CO2 flux and pCO(2aq) in terrestrial and aquatic environments.

  • 12. Baumgartner, M.
    et al.
    Schilt, A.
    Eicher, O.
    Schmitt, J.
    Schwander, J.
    Spahni, R.
    Fischer, H.
    Stocker, T. F.
    High-resolution interpolar difference of atmospheric methane around the Last Glacial Maximum2012In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 9Article in journal (Refereed)
    Abstract [en]

    Reconstructions of past atmospheric methane concentrations are available from ice cores from both Greenland and Antarctica. The difference observed between the two polar methane concentration levels represents a valuable constraint on the geographical location of the methane sources. Here we present new high-resolution methane records from the North Greenland Ice Core Project (NGRIP) and the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land (EDML) ice cores covering Termination 1, the Last Glacial Maximum, and parts of the last glacial back to 32 000 years before present. Due to the high resolution of the records, the synchronisation between the ice cores from NGRIP and EDML is considerably improved, and the interpolar concentration difference of methane is determined with unprecedented precision and temporal resolution. Relative to the mean methane concentration, we find a rather stable positive relative interpolar difference throughout the record with its minimum value of 3.7+/-0.7% between 21 900-21 200 years before present, which is higher than previously estimated in this interval close to the Last Glacial Maximum. This implies that Northern Hemisphere boreal wetland sources were never completely shut off during the peak glacial, as suggested from previous bipolar methane concentration records. Starting at 21 000 years before present, i.e. several millennia prior to the transition into the Holocene, the relative interpolar difference becomes even more positive and stays at a fairly stable level of 6.5+/-0.8% during Termination 1. We thus find that the boreal and tropical methane sources increased by approximately the same factor during Termination 1. We hypothesise that latitudinal shifts in the Intertropical Convergence Zone (ITCZ) and the monsoon system contribute, either by dislocation of the methane source regions or, in case of the ITCZ, also by changing the relative atmospheric volumes of the Northern and Southern Hemispheres, to the subtle variations in the relative interpolar concentration difference on glacial/interglacial as well as on millennial time scales.

  • 13. Bauwens, M.
    et al.
    Stavrakou, T.
    Müller, J. -F
    Van Schaeybroeck, B.
    De Cruz, L.
    De Troch, R.
    Giot, O.
    Hamdi, R.
    Termonia, P.
    Laffineur, Q.
    Amelynck, C.
    Schoon, N.
    Heinesch, B.
    Holst, T.
    Arneth, A.
    Ceulemans, R.
    Sanchez-Lorenzo, A.
    Guenther, A.
    Recent past (1979–2014) and future (2070–2099) isoprene fluxes over Europe simulated with the MEGAN–MOHYCAN model2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 12, p. 3673-3690Article in journal (Refereed)
    Abstract [en]

    Isoprene is a highly reactive volatile organic compound emitted by vegetation, known to be a precursor of secondary organic aerosols and to enhance tropospheric ozone formation under polluted conditions. Isoprene emissions respond strongly to changes in meteorological parameters such as temperature and solar radiation. In addition, the increasing CO2 concentration has a dual effect, as it causes both a direct emission inhibition as well as an increase in biomass through fertilization. In this study we used the MEGAN (Model of Emissions of Gases and Aerosols from Nature) emission model coupled with the MOHYCAN (Model of HYdrocarbon emissions by the CANopy) canopy model to calculate the isoprene fluxes emitted by vegetation in the recent past (1979–2014) and in the future (2070–2099) over Europe at a resolution of 0.1° × 0.1°. As a result of the changing climate, modeled isoprene fluxes increased by 1.1%yr−1 on average in Europe over 1979–2014, with the strongest trends found over eastern Europe and European Russia, whereas accounting for the CO2inhibition effect led to reduced emission trends (0.76%yr−1). Comparisons with field campaign measurements at seven European sites suggest that the MEGAN–MOHYCAN model provides a reliable representation of the temporal variability of the isoprene fluxes over timescales between 1h and several months. For the 1979–2014 period the model was driven by the ECMWF ERA-Interim reanalysis fields, whereas for the comparison of current with projected future emissions, we used meteorology simulated with the ALARO regional climate model. Depending on the representative concentration pathway (RCP) scenarios for greenhouse gas concentration trajectories driving the climate projections, isoprene emissions were found to increase by +7% (RCP2.6), +33% (RCP4.5), and +83% (RCP8.5), compared to the control simulation, and even stronger increases were found when considering the potential impact of CO2 fertilization: +15% (RCP2.6), +52% (RCP4.5), and +141% (RCP8.5). However, the inhibitory CO2 effect goes a long way towards canceling these increases. Based on two distinct parameterizations, representing strong or moderate inhibition, the projected emissions accounting for all effects were estimated to be 0–17% (strong inhibition) and 11–65% (moderate inhibition) higher than in the control simulation. The difference obtained using the two CO2parameterizations underscores the large uncertainty associated to this effect.

  • 14. Berggren, Martin
    et al.
    Klaus, Marcus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Selvam, Balathandayuthabani Panneer
    Ström, Lena
    Laudon, Hjalmar
    Jansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Quality transformation of dissolved organic carbon during water transit through lakes: contrasting controls by photochemical and biological processes2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 2, p. 457-470Article in journal (Refereed)
    Abstract [en]

    Dissolved organic carbon (DOC) may be removed, transformed, or added during water transit through lakes, resulting in changes in DOC composition and pigmentation (color). However, the process-based understanding of these changes is incomplete, especially for headwater lakes. We hypothesized that because heterotrophic bacteria preferentially consume noncolored DOC, while photochemical processing removes colored fractions, the overall changes in DOC color upon water passage through a lake depend on the relative importance of these two processes, accordingly. To test this hypothesis we combined laboratory experiments with field studies in nine boreal lakes, assessing both the relative importance of different DOC decay processes (biological or photochemical) and the loss of color during water transit time (WTT) through the lakes. We found that influence from photo-decay dominated changes in DOC quality in the epilimnia of relatively clear headwater lakes, resulting in systematic and selective net losses of colored DOC. However, in highly pigmented brown-water lakes (absorbance at 420 nm > 7 m(-1)) biological processes dominated, and there was no systematic relationship between color loss and WTT. Moreover, in situ data and dark experiments supported our hypothesis on the selective microbial removal of nonpigmented DOC, mainly of low molecular weight, leading to persistent water color in these highly colored lakes. Our study shows that brown headwater lakes may not conform to the commonly reported pattern of the selective removal of colored constituents in freshwaters, as DOC can show a sustained degree of pigmentation upon transit through these lakes.

  • 15. Bermudez, Rafael
    et al.
    Winder, Monika
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Stuhr, Annegret
    Almen, Anna-Karin
    Engström-Öst, Jonna
    Riebesell, Ulf
    Effect of ocean acidification on the structure and fatty acid composition of a natural plankton community in the Baltic Sea2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 24, p. 6625-6635Article in journal (Refereed)
    Abstract [en]

    Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of offshore mesocosms and subjected to a CO2 gradient ranging from natural concentrations (similar to 347 mu atm fCO(2)) up to values projected for the year 2100 (similar to 1333 mu atm fCO(2)). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO(2). Although this coastal plankton community was tolerant of high pCO(2) levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.

  • 16. Bischoff, Juliane
    et al.
    Sparkes, Robert B.
    Selver, Ayca Dogrul
    Spencer, Robert G. M.
    Gustafsson, Orjan
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Wagner, Dirk
    Rivkina, Elizaveta
    van Dongen, Bart E.
    Talbot, Helen M.
    Source, transport and fate of soil organic matter inferred from microbial biomarker lipids on the East Siberian Arctic Shelf2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 17, p. 4899-4914Article in journal (Refereed)
    Abstract [en]

    The Siberian Arctic contains a globally significant pool of organic carbon (OC) vulnerable to enhanced warming and subsequent release by both fluvial and coastal erosion processes. However, the rate of release, its behaviour in the Arctic Ocean and vulnerability to remineralisation is poorly understood. Here we combine new measurements of microbial biohopanoids including adenosylhopane, a lipid associated with soil microbial communities, with published glycerol dialkyl glycerol tetraethers (GDGTs) and bulk delta C-13 measurements to improve knowledge of the fate of OC transported to the East Siberian Arctic Shelf (ESAS). The microbial hopanoid-based soil OC proxy R’(soil) ranges from 0.0 to 0.8 across the ESAS, with highest values nearshore and decreases offshore. Across the shelf R’(soil) displays a negative linear correlation with bulk delta C-13 measurements (r(2) = -0.73, p = < 0 : 001). When compared to the GDGT-based OC proxy, the branched and isoprenoid tetraether (BIT) index, a decoupled (non-linear) behaviour on the shelf was observed, particularly in the Buor-Khaya Bay, where the R’(soil) shows limited variation, whereas the BIT index shows a rapid decline moving away from the Lena River outflow channels. This reflects a balance between delivery and removal of OC from different sources. The good correlation between the hopanoid and bulk terrestrial signal suggests a broad range of hopanoid sources, both fluvial and via coastal erosion, whilst GDGTs appear to be primarily sourced via fluvial transport. Analysis of ice complex deposits (ICDs) revealed an average R’(soil) of 0.5 for the Lena Delta, equivalent to that of the Buor-Khaya Bay sediments, whilst ICDs from further east showed higher values (0.6-0.85). Although R’(soil) correlates more closely with bulk OC than the BIT, our understanding of the endmembers of this system is clearly still incomplete, with variations between the different East Siberian Arctic regions potentially reflecting differences in environmental conditions (e.g. temperature, pH), but other physiological controls on microbial bacteriohopanepolyol (BHP) production under psychrophilic conditions are as yet unknown.

  • 17. Bischoff, Juliane
    et al.
    Sparkes, Robert B.
    Selver, Ayca Dogrul
    Spencer, Robert G. M.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Wagner, Dirk
    Rivkina, Elizaveta
    van Dongen, Bart E.
    Talbot, Helen M.
    Source, transport and fate of soil organic matter inferred from microbial biomarker lipids on the East Siberian Arctic Shelf2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 17, p. 4899-4914Article in journal (Refereed)
    Abstract [en]

    The Siberian Arctic contains a globally significant pool of organic carbon (OC) vulnerable to enhanced warming and subsequent release by both fluvial and coastal erosion processes. However, the rate of release, its behaviour in the Arctic Ocean and vulnerability to remineralisation is poorly understood. Here we combine new measurements of microbial biohopanoids including adenosylhopane, a lipid associated with soil microbial communities, with published glycerol dialkyl glycerol tetraethers (GDGTs) and bulk delta C-13 measurements to improve knowledge of the fate of OC transported to the East Siberian Arctic Shelf (ESAS). The microbial hopanoid-based soil OC proxy R'(soil) ranges from 0.0 to 0.8 across the ESAS, with highest values nearshore and decreases offshore. Across the shelf R'(soil) displays a negative linear correlation with bulk delta C-13 measurements (r(2) = -0.73, p = < 0 : 001). When compared to the GDGT-based OC proxy, the branched and isoprenoid tetraether (BIT) index, a decoupled (non-linear) behaviour on the shelf was observed, particularly in the Buor-Khaya Bay, where the R'(soil) shows limited variation, whereas the BIT index shows a rapid decline moving away from the Lena River outflow channels. This reflects a balance between delivery and removal of OC from different sources. The good correlation between the hopanoid and bulk terrestrial signal suggests a broad range of hopanoid sources, both fluvial and via coastal erosion, whilst GDGTs appear to be primarily sourced via fluvial transport. Analysis of ice complex deposits (ICDs) revealed an average R'(soil) of 0.5 for the Lena Delta, equivalent to that of the Buor-Khaya Bay sediments, whilst ICDs from further east showed higher values (0.6-0.85). Although R'(soil) correlates more closely with bulk OC than the BIT, our understanding of the endmembers of this system is clearly still incomplete, with variations between the different East Siberian Arctic regions potentially reflecting differences in environmental conditions (e.g. temperature, pH), but other physiological controls on microbial bacteriohopanepolyol (BHP) production under psychrophilic conditions are as yet unknown.

  • 18.
    Bonaglia, Stefano
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hylén, Astrid
    Rattray, Jayne E.
    Kononets, Mikhail Y.
    Ekeroth, Nils
    Roos, Per
    Thamdrup, Bo
    Brüchert, Volker
    Hall, Per O. J.
    The fate of fixed nitrogen in marine sediments with low organic loading: an in situ study2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 2, p. 285-300Article in journal (Refereed)
    Abstract [en]

    Over the last decades, the impact of human activities on the global nitrogen (N) cycle has drastically increased. Consequently, benthic N cycling has mainly been studied in anthropogenically impacted estuaries and coasts, while in oligotrophic systems its understanding is still scarce. Here we report on benthic solute fluxes and on rates of denitrification, anammox, and dissimilatory nitrate reduction to ammonium (DNRA) studied by in situ incubations with benthic chamber landers during two cruises to the Gulf of Bothnia (GOB), a cold, oligotrophic basin located in the northern part of the Baltic Sea. Rates of N burial were also inferred to investigate the fate of fixed N in these sediments. Most of the total dissolved fixed nitrogen (TDN) diffusing to the water column was composed of organic N. Average rates of dinitrogen (N-2) production by denitrification and anammox (range: 53-360 mu mol Nm(-2) day(-1)) were comparable to those from Arctic and subarctic sediments worldwide (range: 34-344 mu mol Nm(-2) day(-1)). Anammox accounted for 18-26% of the total N2 production. Absence of free hydrogen sulfide and low concentrations of dissolved iron in sediment pore water suggested that denitrification and DNRA were driven by organic matter oxidation rather than chemolithotrophy. DNRA was as important as denitrification at a shallow, coastal station situated in the northern Bothnian Bay. At this pristine and fully oxygenated site, ammonium regeneration through DNRA contributed more than one-third to the TDN efflux and accounted, on average, for 45% of total nitrate reduction. At the offshore stations, the proportion of DNRA in relation to denitrification was lower (0-16% of total nitrate reduction). Median value and range of benthic DNRA rates from the GOB were comparable to those from the southern and central eutrophic Baltic Sea and other temperate estuaries and coasts in Europe. Therefore, our results contrast with the view that DNRA is negligible in cold and well-oxygenated sediments with low organic carbon loading. However, the mechanisms behind the variability in DNRA rates between our sites were not resolved. The GOB sediments were a major source (237 kt yr(-1), which corresponds to 184% of the external N load) of fixed N to the water column through recycling mechanisms. To our knowledge, our study is the first to document the simultaneous contribution of denitrification, DNRA, anammox, and TDN recycling combined with in situ measurements.

  • 19. Bonnet, Sophie
    et al.
    Caffin, Mathieu
    Berthelot, Hugo
    Grosso, Olivier
    Benavides, Mar
    Helias-Nunige, Sandra
    Guieu, Cecile
    Stenegren, Marcus
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Foster, Rachel Ann
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    In-depth characterization of diazotroph activity across the western tropical South Pacific hotspot of N-2 fixation (OUTPACE cruise)2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 13, p. 4215-4232Article in journal (Refereed)
    Abstract [en]

    Here we report N-2 fixation rates from a similar to 4000 km transect in the western and central tropical South Pacific, a particularly undersampled region in the world ocean. Water samples were collected in the euphotic layer along a west to east transect from 160 degrees E to 160 degrees W that covered contrasting trophic regimes, from oligotrophy in the Melanesian archipelago (MA) waters to ultraoligotrophy in the South Pacific Gyre (GY) waters. N-2 fixation was detected at all 17 sampled stations with an average depth-integrated rate of 631 +/- 286 mu mol Nm(-2) d(-1) (range 196-1153 mu mol Nm(-2) d(-1)) in MA waters and of 85 +/- 79 mu mol Nm(-2) d(-1) (range 18-172 mu mol Nm(-2) d(-1)) in GY waters. Two cyanobacteria, the larger colonial filamentous Trichodesmium and the smaller UCYN-B, dominated the enumerated diazotroph community (>80 %) and gene expression of the nifH gene (cDNA > 10(5) nifH copies L-1) in MA waters. Single-cell isotopic analyses performed by nanoscale secondary ion mass spectrometry (nanoSIMS) at selected stations revealed that Trichodesmium was always the major contributor to N-2 fixation in MA waters, accounting for 47.1-83.8% of bulk N-2 fixation. The most plausible environmental factors explaining such exceptionally high rates of N-2 fixation in MA waters are discussed in detail, emphasizing the role of macro- and micro-nutrient (e.g., iron) availability, seawater temperature and currents.

  • 20.
    Borg, Hans
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Sundbom, Marcus
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Long-term trends of water chemistry in mountain streams in Sweden - slow recovery from acidification2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 1, p. 173-184Article in journal (Refereed)
    Abstract [en]

    The water chemistry of streams and precipitation in the province of Jamtland, northern Sweden has been monitored since the 1980s to study long-term trends, occurrence of acid episodes, and effects of liming. The acidity in precipitation increased in the 1970s, followed by a loss of acid neutralizing capacity (ANC) and low pH in the streams. Sulfur deposition began to decrease in the 1980s, until approximately 2000, after which the decrease levelled out. Stream water sulfate concentration followed the precipitation trend but decreased more slowly and since the late 1990s a subtle increase was observed. Sulfate concentrations in the snow typically have been higher than or equal to the stream sulfate levels. However, during the period of rapid deposition decrease and also since 2005 stream sulfate has sometimes exceeded snow sulfate, indicating desorption of stored soil sulfate, possibly because of climate-related changes in runoff routes through the soil profiles, following shorter periods of frost. From 1982 to 2000, total organic carbon (TOC) increased by approximately 0.1 mg L-1 yr(-1). The mean trends in sulfate and TOC from approximately 1990 until today were generally opposite. Acidic episodes with pH 4.0 at flow peaks occurred frequently in the unlimed streams, despite relatively well-buffered waters at baseflow. To evaluate the main causes for the loss of ANC during episodes, the changes in major ion concentrations during high flow episodes were evaluated. The most important factors contributing to ANC loss were dilution of base cations (Na+, K+, Ca2+, Mg2+), enrichment of organic anions and enrichment of sulfate. Wetland liming started in 1985 after which the earlier observed extreme peak values of iron, manganese and aluminium, did not reoccur. The studied area is remote from emission sources in Europe, but the critical load of acidity is still exceeded. The long-term recovery observed in the unlimed streams is thus slow, and severe acidic episodes still occur.

  • 21. Bouton, Anthony
    et al.
    Vennin, Emmanuelle
    Boulle, Julien
    Pace, Aurelie
    Bourillot, Raphael
    Thomazo, Christophe
    Brayard, Arnaud
    Desaubliaux, Guy
    Goslar, Tomasz
    Yokoyama, Yusuke
    Dupraz, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Visscher, Pieter T.
    Linking the distribution of microbial deposits from the Great Salt Lake (Utah, USA) to tectonic and climatic processes2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 19, p. 5511-5526Article in journal (Refereed)
    Abstract [en]

    The Great Salt Lake is a modern hypersaline lake, in which an extended modern and ancient microbial sedimentary system has developed. Detailed mapping based on aerial images and field observations can be used to identify non-random distribution patterns of microbial deposits, such as paleoshorelines associated with extensive polygons or fault-parallel alignments. Although it has been inferred that climatic changes controlling the lake level fluctuations explain the distribution of paleoshorelines and polygons, straight microbial deposit alignments may underline a normal fault system parallel to the Wasatch Front. This study is based on observations over a decimetre to kilometre spatial range, resulting in an integrated conceptual model for the controls on the distribution of the microbial deposits. The morphology, size and distribution of these deposits result mainly from environmental changes (i.e. seasonal to long-term water level fluctuations, particular geomorphological heritage, fault-induced processes, groundwater seepage) and have the potential to bring further insights into the reconstruction of paleoenvironments and paleoclimatic changes through time. New ra-diocarbon ages obtained on each microbial macrofabric described in this study improve the chronological framework and question the lake level variations that are commonly assumed.

  • 22. Bragee, P.
    et al.
    Mazier, F.
    Nielsen, A. B.
    Rosén, Peter
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fredh, D.
    Brostrom, A.
    Graneli, W.
    Hammarlund, D.
    Historical TOC concentration minima during peak sulfur deposition in two Swedish lakes2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, no 2, p. 307-322Article in journal (Refereed)
    Abstract [en]

    Decadal-scale variations in total organic carbon (TOC) concentration in lake water since AD1200 in two small lakes in southern Sweden were reconstructed based on visible-near-infrared spectroscopy (VNIRS) of their recent sediment successions. In order to assess the impacts of local land-use changes, regional variations in sulfur, and nitrogen deposition and climate variations on the inferred changes in TOC concentration, the same sediment records were subjected to multi-proxy palaeolimnological analyses. Changes in lake-water pH were inferred from diatom analysis, whereas pollen-based land-use reconstructions (Landscape Reconstruction Algorithm) together with geochemical records provided information on catchment-scale environmental changes, and comparisons were made with available records of climate and population density. Our long-term reconstructions reveal that inferred lake-water TOC concentrations were generally high prior to AD1900, with additional variability coupled mainly to changes in forest cover and agricultural land-use intensity. The last century showed significant changes, and unusually low TOC concentrations were inferred at AD1930-1990, followed by a recent increase, largely consistent with monitoring data. Variations in sulfur emissions, with an increase in the early 1900s to a peak around AD1980 and a subsequent decrease, were identified as an important driver of these dynamics at both sites, while processes related to the introduction of modern forestry and recent increases in precipitation and temperature may have contributed, but the effects differed between the sites. The increase in lake-water TOC concentration from around AD1980 may therefore reflect a recovery process. Given that the effects of sulfur deposition now subside and that the recovery of lake-water TOC concentrations has reached pre-industrial levels, other forcing mechanisms related to land management and climate change may become the main drivers of TOC concentration changes in boreal lake waters in the future.

  • 23.
    Bragée, P.
    et al.
    Lund University.
    Mazier, F.
    Jean Jaures University, France.
    Nielsen, Anne Birgitte
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science. Lund University.
    Rosén, P.
    Umeå University.
    Fredh, D.
    Lund University.
    Broström, A.
    Lund University.
    Granéli, W.
    Lund University.
    Hammarlund, D.
    Lund University.
    Historical TOC concentration minima during peak sulfur deposition in two Swedish lakes2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, no 2, p. 307-322Article in journal (Refereed)
    Abstract [en]

    Decadal-scale variations in total organic carbon (TOC) concentration in lake water since AD1200 in two small lakes in southern Sweden were reconstructed based on visible-near-infrared spectroscopy (VNIRS) of their recent sediment successions. In order to assess the impacts of local land-use changes, regional variations in sulfur, and nitrogen deposition and climate variations on the inferred changes in TOC concentration, the same sediment records were subjected to multi-proxy palaeolimnological analyses. Changes in lake-water pH were inferred from diatom analysis, whereas pollen-based land-use reconstructions (Landscape Reconstruction Algorithm) together with geochemical records provided information on catchment-scale environmental changes, and comparisons were made with available records of climate and population density. Our long-term reconstructions reveal that inferred lake-water TOC concentrations were generally high prior to AD1900, with additional variability coupled mainly to changes in forest cover and agricultural land-use intensity. The last century showed significant changes, and unusually low TOC concentrations were inferred at AD1930-1990, followed by a recent increase, largely consistent with monitoring data. Variations in sulfur emissions, with an increase in the early 1900s to a peak around AD1980 and a subsequent decrease, were identified as an important driver of these dynamics at both sites, while processes related to the introduction of modern forestry and recent increases in precipitation and temperature may have contributed, but the effects differed between the sites. The increase in lake-water TOC concentration from around AD1980 may therefore reflect a recovery process. Given that the effects of sulfur deposition now subside and that the recovery of lake-water TOC concentrations has reached pre-industrial levels, other forcing mechanisms related to land management and climate change may become the main drivers of TOC concentration changes in boreal lake waters in the future.

  • 24.
    Breitbarth, E.
    et al.
    Department of Chemistry, University of Otago, Dunedin.
    Achterberg, E.P.
    National Oceanography Center Southampton, University of Southampton.
    Ardelan, M.V.
    Norwegian University of Science and Technology, Department of Chemistry, Trondheim.
    Baker, A.R.
    School of Environmental Sciences, University of East Anglia, Norwich.
    Buccarelli, E.
    Université Européenne de Bretagne.
    Chever, F.
    Université Européenne de Bretagne.
    Croot, P.L.
    IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Division Marine Biogeochemistry, Kiel.
    Duggen, S.
    IFM-GEOMAR, Leibniz-Institute of Marine Sciences, Division Dynamics of the Ocean Floor, Kiel.
    Gledhill, M.
    National Oceanography Center Southampton, University of Southampton.
    Hassellöv, Martin
    University of Gothenburg.
    Hassler, C.
    Centre for Australian Weather and Climate Research (CAWCR), Hobart.
    Hoffmann, L.J.
    Department of Chemistry, University of Otago, Dunedin.
    Hunter, K.A.
    Department of Chemistry, University of Otago, Dunedin.
    Hutchins, D.A.
    Department of Biological Sciences, University of Southern California, Los Angeles.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jickells, T.
    School of Environmental Sciences, University of East Anglia, Norwich.
    Lohan, M.C.
    Marine Institute, University of Plymouth.
    Nielsdóttir, M.C.
    National Oceanography Center Southampton, University of Southampton.
    Sarthou, G.
    Université Européenne de Bretagne.
    Schoemann, V.
    Ecologie des Systémes Aquatiques, Université Libre de Bruxelles.
    Trapp, J.M.
    University of Miami, Rosenstiel School of Marine and Atmospheric Science, Department of Marine and Atmospheric Chemistry, Miami.
    Turner, D.R.
    Department of Chemistry, University of Gothenburg.
    Ye, Y.
    Alfred Wegener Institute for Polar and Marine Research, Bremerhaven.
    Iron biogeochemistry across marine systems: progress from the past decade2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, no 3, p. 1075-1097Article in journal (Refereed)
    Abstract [en]

    Based on an international workshop (Gothenburg, 14-16 May 2008), this review article aims to combine interdisciplinary knowledge from coastal and open ocean research on iron biogeochemistry. The major scientific findings of the past decade are structured into sections on natural and artificial iron fertilization, iron inputs into coastal and estuarine systems, colloidal iron and organic matter, and biological processes. Potential effects of global climate change, particularly ocean acidification, on iron biogeochemistry are discussed. The findings are synthesized into recommendations for future research areas

  • 25.
    Breitbarth, E
    et al.
    Univ Gothenburg, Dept Chem Analyt & Marine Chem.
    Gelting, J
    Lulea Univ Technol, Div Appl Geol.
    Walve, Jakob
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Hoffmann, LJ
    Univ Gothenburg, Dept Chem Analyt & Marine Chem.
    Turner, DR
    Univ Gothenburg, Dept Chem Analyt & Marine Chem.
    Hassellov, M
    Univ Gothenburg, Dept Chem Analyt & Marine Chem.
    Ingri, J
    Lulea Univ Technol, Div Appl Geol.
    Dissolved iron (II) in the Baltic Sea surface water and implications for cyanobacterial bloom development2009In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 6, no 11, p. 2397-2420Article in journal (Refereed)
    Abstract [en]

    Iron chemistry measurements were conducted during summer 2007 at two distinct locations in the Baltic Sea (Gotland Deep and Landsort Deep) to evaluate the role of iron for cyanobacterial bloom development in these estuarine waters. Depth profiles of Fe(II) were measured by chemiluminescent flow injection analysis (CL-FIA). Up to 0.9 nmol Fe(II) L-1 were detected in light penetrated surface waters, which constitutes up to 20% to the dissolved Fe pool. This bioavailable iron source is a major contributor to the Fe requirements of Baltic Sea phytoplankton and apparently plays a major role for cyanobacterial bloom development during our study. Measured Fe(II) half life times in oxygenated water exceed predicted values and indicate organic Fe(II) complexation. Potential sources for Fe(II) ligands, including rainwater, are discussed. Fe(II) concentrations of up to 1.44 nmol L-1 were detected at water depths below the euphotic zone, but above the oxic anoxic interface. Mixed layer depths after strong wind events are not deep enough in summer time to penetrate the oxic-anoxic boundary layer. However, Fe(II) from anoxic bottom water may enter the sub-oxic zone via diapycnal mixing and diffusion.

  • 26.
    Breitbarth, Eike
    et al.
    Department of Chemistry, University of Otago, Dunedin.
    Gelting, Johan
    Walve, Jakob
    Department of Systems Ecology, Stockholm University.
    Hoffmann, Linn
    Department of Chemistry, University of Otago, Dunedin.
    Turner, David
    Department of Chemistry, Analytical and Marine Chemistry, Göteborg University.
    Hassellöv, Martin
    Department of Chemistry, Analytical and Marine Chemistry, Göteborg University.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dissolved iron (II) in the Baltic Sea surface water and implications for cyanobacterial bloom development2009In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 6, no Special issue, p. 2397-2420Article in journal (Refereed)
    Abstract [en]

    Iron chemistry measurements were conducted during summer 2007 at two distinct locations in the Baltic Sea (Gotland Deep and Landsort Deep) to evaluate the role of iron for cyanobacterial bloom development in these estuarine waters. Depth profiles of Fe(II) were measured by chemiluminescent flow injection analysis (CL-FIA). Up to 0.9 nmol Fe(II) L−1 were detected in light penetrated surface waters, which constitutes up to 20% to the dissolved Fe pool. This bioavailable iron source is a major contributor to the Fe requirements of Baltic Sea phytoplankton and apparently plays a major role for cyanobacterial bloom development during our study. Measured Fe(II) half life times in oxygenated water exceed predicted values and indicate organic Fe(II) complexation. Potential sources for Fe(II) ligands, including rainwater, are discussed. Fe(II) concentrations of up to 1.44 nmol L−1 were detected at water depths below the euphotic zone, but above the oxic anoxic interface. Mixed layer depths after strong wind events are not deep enough in summer time to penetrate the oxic-anoxic boundary layer. However, Fe(II) from anoxic bottom water may enter the sub-oxic zone via diapycnal mixing and diffusion.

  • 27. Breitbarth, Eike
    et al.
    Oschlies, A.
    National Oceanography Centre, Southampton, European Way, Southampton.
    LaRoche, J.
    Leibniz-Institute of Marine Sciences, IFM-GEOMAR, Dusternbrooker Weg 20, 24105 Kiel.
    Physiological constraints on the global distribution of Trichodesmium: effect of temperature on diazotrophy2007In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 4, no 1, p. 53-61Article in journal (Refereed)
    Abstract [en]

    The cyanobacterium Trichodesmium is an important link in the global nitrogen cycle due to its significant input of atmospheric nitrogen to the ocean. Attempts to incorporate Trichodesmium in ocean biogeochemical circulation models have, so far, relied on the observed correlation between temperature and Trichodesmium abundance. This correlation may result in part from a direct effect of temperature on Trichodesmium growth rates through the control of cellular biochemical processes, or indirectly through temperature influence on mixed layer depth, light and nutrient regimes. Here we present results indicating that the observed correlation of Trichodesmium with temperature in the field reflects primarily the direct physiological effects of temperature on diazotrophic growth of Trichodesmium. Trichodesmium IMS-101 (an isolate of T. erythraeum) could acclimate and grow at temperatures ranging from 20 to 34C.Maximum growth rates (μmax=0.25 day-1) and maximum nitrogen fixation rates (0.13 mmol N mol POC-1 h-1) were measured within 24 to 30C. Combining this empirical relationship with global warming scenarios derived from state-of-the-art climate models sets a physiological constraint on the future distribution of Trichodesmium that could significantly affect the future nitrogen input into oligotrophic waters by this diazotroph.

  • 28. Broder, Lisa
    et al.
    Tesi, Tommaso
    Salvado, Joan A.
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Gustafsson, Orjan
    Fate of terrigenous organic matter across the Laptev Sea from the mouth of the Lena River to the deep sea of the Arctic interior2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 17, p. 5003-5019Article in journal (Refereed)
    Abstract [en]

    Ongoing global warming in high latitudes may cause an increasing supply of permafrost-derived organic carbon through both river discharge and coastal erosion to the Arctic shelves. Mobilized permafrost carbon can be either buried in sediments, transported to the deep sea or degraded to CO2 and outgassed, potentially constituting a positive feedback to climate change. This study aims to assess the fate of terrigenous organic carbon (TerrOC) in the Arctic marine environment by exploring how it changes in concentration, composition and degradation status across the wide Laptev Sea shelf. We analyzed a suite of terrestrial biomarkers as well as source-diagnostic bulk carbon isotopes (delta C-13, Delta C-14) in surface sediments from a Laptev Sea transect spanning more than 800 km from the Lena River mouth (< 10m water depth) across the shelf to the slope and rise (2000-3000m water depth). These data provide a broad view on different TerrOC pools and their behavior during cross-shelf transport. The concentrations of lignin phenols, cutin acids and high-molecular-weight (HMW) wax lipids (tracers of vascular plants) decrease by 89-99% along the transect. Molecular-based degradation proxies for TerrOC (e.g., the carbon preference index of HMW lipids, the HMW acids / alkanes ratio and the acid / aldehyde ratio of lignin phenols) display a trend to more degraded TerrOC with increasing distance from the coast. We infer that the degree of degradation of permafrost-derived TerrOC is a function of the time spent under oxic conditions during protracted cross-shelf transport. Future work should therefore seek to constrain cross-shelf transport times in order to compute a TerrOC degradation rate and thereby help to quantify potential carbon-climate feedbacks.

  • 29.
    Bröder, Lisa
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Tesi, Tommaso
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Institute of Marine Sciences – National Research Council, Italy.
    Salvadó, Joan A.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Fate of terrigenous organic matter across the Laptev Sea from the mouth of the Lena River to the deep sea of the Arctic interior2016In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, no 17, p. 5003-5019Article in journal (Refereed)
    Abstract [en]

    Ongoing global warming in high latitudes may cause an increasing supply of permafrost-derived organic carbon through both river discharge and coastal erosion to the Arctic shelves. Mobilized permafrost carbon can be either buried in sediments, transported to the deep sea or degraded to CO2 and outgassed, potentially constituting a positive feedback to climate change. This study aims to assess the fate of terrigenous organic carbon (TerrOC) in the Arctic marine environment by exploring how it changes in concentration, composition and degradation status across the wide Laptev Sea shelf. We analyzed a suite of terrestrial biomarkers as well as source-diagnostic bulk carbon isotopes (delta C-13, Delta C-14) in surface sediments from a Laptev Sea transect spanning more than 800 km from the Lena River mouth (< 10m water depth) across the shelf to the slope and rise (2000-3000m water depth). These data provide a broad view on different TerrOC pools and their behavior during cross-shelf transport. The concentrations of lignin phenols, cutin acids and high-molecular-weight (HMW) wax lipids (tracers of vascular plants) decrease by 89-99% along the transect. Molecular-based degradation proxies for TerrOC (e.g., the carbon preference index of HMW lipids, the HMW acids / alkanes ratio and the acid / aldehyde ratio of lignin phenols) display a trend to more degraded TerrOC with increasing distance from the coast. We infer that the degree of degradation of permafrost-derived TerrOC is a function of the time spent under oxic conditions during protracted cross-shelf transport. Future work should therefore seek to constrain cross-shelf transport times in order to compute a TerrOC degradation rate and thereby help to quantify potential carbon-climate feedbacks.

  • 30.
    Brüchert, Volker
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bröder, Lisa
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Sawicka, Joanna E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Tesi, Tommaso
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. nstitute of Marine Sciences, National Research Council, Italy.
    Joye, Samantha P.
    Sun, Xiaole
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Semiletov, Igor P.
    Samarkin, Vladimir A.
    Carbon mineralization in Laptev and East Siberian sea shelf and slope sediment2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 2, p. 471-490Article in journal (Refereed)
    Abstract [en]

    The Siberian Arctic Sea shelf and slope is a key region for the degradation of terrestrial organic material transported from the organic carbon-rich permafrost regions of Siberia. We report on sediment carbon mineralization rates based on O2 microelectrode profiling, intact sediment core incubations, 35 S-sulfate tracer experiments, porewater dissolved inorganic carbon (DIC), δ13 CDIC, and iron, manganese, and ammonium concentrations from 20 shelf and slope stations. This data set provides a spatial overview of sediment carbon mineralization rates and pathways over large parts of the outer Laptev and East Siberian Arctic shelf and slope, and allowed us to assess degradation rates and efficiency of carbon burial in these sediments. Rates of oxygen uptake and iron and manganese reduction were comparable to temperate shelf and slope environments, but bacterial sulfate reduction rates were comparatively low. In the topmost 20 to 50 cm of sediment, aerobic carbon mineralization dominated degradation and comprised on average 82% of the depthintegrated carbon mineralization. Oxygen uptake rates and 35 S-sulfate reduction rates were higher in the eastern East Siberian Sea shelf compared to the Laptev Sea shelf. DIC/NH4 + ratios in porewaters and the stable carbon isotope composition of remineralized DIC indicated that the degraded organic matter on the Siberian shelf and slope was a mixture of marine and terrestrial organic matter. Based on dual end member calculations, the terrestrial organic carbon contribution varied between 32% and 36%, with a higher contribution in the Laptev Sea than in the East Siberian Sea. Extrapolation of the measured degradation rates using  isotope end member apportionment over the outer shelf of the Laptev and East Siberian Sea suggests that about 16 Tg C per year are respired in the outer shelf sea floor sediment. Of the organic matter buried below the oxygen penetration depth, between 0.6 and 1.3 Tg C per year are degraded by anaerobic processes, with a terrestrial organic carbon contribution ranging between 0.3 and 0.5 Tg per year.

  • 31. Buendía, Corina
    et al.
    Kleidon, Axel
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Reu, Björn
    Porporato, Amilcare
    Evaluating the effect of nutrient redistribution by animals on the phosphorus cycle of lowland Amazonia2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 1, p. 279-295Article in journal (Refereed)
    Abstract [en]

    Phosphorus (P) availability decreases with soil age and potentially limits the productivity of ecosystems growing on old and weathered soils. Despite growing on ancient soils, ecosystems of lowland Amazonia are highly productive and are among the most biodiverse on Earth. P eroded and weathered in the Andes is transported by the rivers and deposited in floodplains of the lowland Amazon basin creating hotspots of P fertility. We hypothesize that animals feeding on vegetation and detritus in these hotspots may redistribute P to P-depleted areas, thus contributing to dissipate the P gradient across the landscape. Using a mathematical model, we show that animal-driven spatial redistribution of P from rivers to land and from seasonally flooded to terra firme (upland) ecosystems may sustain the P cycle of Amazonian lowlands. Our results show how P imported to land by terrestrial piscivores in combination with spatial redistribution of herbivores and detritivores can significantly enhance the P content in terra firme ecosystems, thereby highlighting the importance of food webs for the biogeochemical cycling of Amazonia.

  • 32.
    Burkhardt, J.
    et al.
    Institute for Crop Science and Resource Conservation, INRES-PE, University of Bonn, Karlrobert-Kreiten-Str. 13, 53115 Bonn, Germany.
    Flechard, C. R.
    Soils, Agronomy and Spatialization Unit, UMR-SAS, INRA, 65, rue de St-Brieuc, 35042 Rennes, France.
    Mattsson, Marie
    Plant and Soil Science Laboratory, University of Copenhagen (UoC), Faculty of Life Sciences, Thorvaldsensvej 40, 1871 Frederiksberg C, Copenhagen, Denmark.
    Gresens, F.
    Institute for Crop Science and Resource Conservation, INRES-PE, University of Bonn, Karlrobert-Kreiten-Str. 13, 53115 Bonn, Germany.
    Jongejan, P.A.C.
    Energy Research Centre of the Netherlands (ECN), Postbus 1, 1755 ZG Petten, The Netherlands.
    Erisman, J.W.
    Energy Research Centre of the Netherlands (ECN), Postbus 1, 1755 ZG Petten, The Netherlands.
    Weidinger, T.
    Department of Meteorology, Eötvös Loránd University (ELU), Budapest, Hungary.
    Meszaros, R.
    Department of Meteorology, Eötvös Loránd University (ELU), Budapest, Hungary.
    Nemitz, E.
    Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, Midlothian, EH26 0QB, UK.
    Sutton, M.A.
    Centre for Ecology and Hydrology (CEH), Edinburgh Research Station, Bush Estate, Penicuik, Midlothian, EH26 0QB, UK.
    Modelling the dynamic chemical interactions of atmospheric ammonia with leaf surface wetness in a managed grassland canopy2009In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 6, no 1, p. 67-84Article in journal (Refereed)
    Abstract [en]

    Ammonia exchange fluxes between grassland and the atmosphere were modelled on the basis of stomatal compensation points and leaf surface chemistry, and compared with measured fluxes during the GRAMINAE intensive measurement campaign in spring 2000 near Braunschweig, Germany. Leaf wetness and dew chemistry in grassland were measured together with ammonia fluxes and apoplastic NH4+ and H+ concentration, and the data were used to apply, validate and further develop an existing model of leaf surface chemistry and ammonia exchange. Foliar leaf wetness which is known to affect ammonia fluxes may be persistent after the end of rainfall, or sustained by recondensation of water vapour originating from the ground or leaf transpiration, so measured leaf wetness values were included in the model. pH and ammonium concentrations of dew samples collected from grass were compared to modelled values.

    The measurement period was divided into three phases: a relatively wet phase followed by a dry phase in the first week before the grass was cut, and a second drier week after the cut. While the first two phases were mainly characterised by ammonia deposition and occasional short emission events, regular events of strong ammonia emissions were observed during the post-cut period. A single-layer resistance model including dynamic cuticular and stomatal exchange could describe the fluxes well before the cut, but after the cut the stomatal compensation points needed to numerically match measured fluxes were much higher than the ones measured by bioassays, suggesting another source of ammonia fluxes. Considerably better agreement both in the direction and the size range of fluxes were obtained when a second layer was introduced into the model, to account for the large additional ammonia source inherent in the leaf litter at the bottom of the grass canopy. Therefore, this was found to be a useful extension of the mechanistic dynamic chemistry model by keeping the advantage of requiring relatively little site-specific information.

  • 33.
    Bäckstrand, Kristina
    et al.
    Stockholm University.
    Crill, P. M.
    Stockholm University.
    Jackowicz-Korczyñski, M.
    Lund University.
    Mastepanov, M.
    Lund University.
    Christensen, T. R.
    Lund University.
    Bastviken, David
    Department of Geology and Geochemistry, Stockholm University.
    Annual carbon gas budget for a subarctic peatland, northern Sweden2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, p. 95-108Article in journal (Other academic)
    Abstract [en]

     Temperatures in the Arctic regions are rising, thawing permafrost and exposing previously stable soil organic carbon (OC) to decomposition. This can result in northern latitude soils, which have accumulated large amounts of OC potentially shifting from atmospheric C sinks to C sources with positive feedback on climate warming. In this paper, we estimate the annual net C gas balance (NCB) of the subarctic mire Stordalen, based on automatic chamber measurements of CO2 and total hydrocarbon (THC; CH4 and NMVOCs) exchange. We studied the dominant vegetation communities with different moisture and permafrost characteristics; a dry Palsa underlain by permafrost, an intermediate thaw site with Sphagnum spp. and a wet site with Eriophorum spp. where the soil thaws completely. Whole year accumulated fluxes of CO2 were estimated to 29.7, −35.3 and −34.9 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum sites (positive flux indicates an addition of C to the atmospheric pool). The corresponding annual THC emissions were 0.5, 6.2 and 31.8 gC m−2 for the same sites. Therefore, the NCB for each of the sites was 30.2, −29.1 and −3.1 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum site. On average, the whole mire was a CO2 sink of 2.6 gC m−2 and a THC source of 6.4 gC m−2 over a year. Consequently, the mire was a net source of C to the atmosphere by 3.9 gC m−2 (based on area weighted estimates for each of the three plant communities). Early and late snow season efflux of CO2 and THC emphasize the importance of winter measurements for complete annual C budgets. Decadal vegetation changes at Stordalen indicate that both the productivity and the THC emissions increased between 1970 and 2000. Considering the GWP100 of CH4, the net radiative forcing on climate increased 21% over the same time. In conclusion, reduced C compounds in these environments have high importance for both the annual C balance and climate.

  • 34.
    Bäckstrand, Kristina
    et al.
    Stockholms universitet, Institutionen för geologi och geokemi.
    Crill, Patrick, M.
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Jackowicz-Korczyński, Marcin
    Mastepanov, Mikhail
    Christensen, Torben, R.
    Bastviken, David
    Annual carbon gas budget for a subarctic peatland, northern Sweden2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, no 1, p. 95-108Article in journal (Refereed)
    Abstract [en]

    Temperatures in the Arctic regions are rising, thawing permafrost and exposing previously stable soil organic carbon (OC) to decomposition. This can result in northern latitude soils, which have accumulated large amounts of OC potentially shifting from atmospheric C sinks to C sources with positive feedback on climate warming. In this paper, we estimate the annual net C gas balance (NCB) of the subarctic mire Stordalen, based on automatic chamber measurements of CO2 and total hydrocarbon (THC; CH4 and NMVOCs) exchange. We studied the dominant vegetation communities with different moisture and permafrost characteristics; a dry Palsa underlain by permafrost, an intermediate thaw site with Sphagnum spp. and a wet site with Eriophorum spp. where the soil thaws completely. Whole year accumulated fluxes of CO2 were estimated to 29.7, −35.3 and −34.9 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum sites (positive flux indicates an addition of C to the atmospheric pool). The corresponding annual THC emissions were 0.5, 6.2 and 31.8 gC m−2 for the same sites. Therefore, the NCB for each of the sites was 30.2, −29.1 and −3.1 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum site. On average, the whole mire was a CO2 sink of 2.6 gC m−2 and a THC source of 6.4 gC m−2 over a year. Consequently, the mire was a net source of C to the atmosphere by 3.9 gC m−2 (based on area weighted estimates for each of the three plant communities). Early and late snow season efflux of CO2 and THC emphasize the importance of winter measurements for complete annual C budgets. Decadal vegetation changes at Stordalen indicate that both the productivity and the THC emissions increased between 1970 and 2000. Considering the GWP100 of CH4, the net radiative forcing on climate increased 21% over the same time. In conclusion, reduced C compounds in these environments have high importance for both the annual C balance and climate.

  • 35.
    Bäckstrand, Kristina
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Crill, Patrick, M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jackowicz-Korczyński, Marcin
    Mastepanov, Mikhail
    Christensen, Torben, R.
    Bastviken, David
    Annual carbon gas budget for a subarctic peatland, northern Sweden2010In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, no 1, p. 95-108Article in journal (Refereed)
    Abstract [en]

    Temperatures in the Arctic regions are rising, thawing permafrost and exposing previously stable soil organic carbon (OC) to decomposition. This can result in northern latitude soils, which have accumulated large amounts of OC potentially shifting from atmospheric C sinks to C sources with positive feedback on climate warming. In this paper, we estimate the annual net C gas balance (NCB) of the subarctic mire Stordalen, based on automatic chamber measurements of CO2 and total hydrocarbon (THC; CH4 and NMVOCs) exchange. We studied the dominant vegetation communities with different moisture and permafrost characteristics; a dry Palsa underlain by permafrost, an intermediate thaw site with Sphagnum spp. and a wet site with Eriophorum spp. where the soil thaws completely. Whole year accumulated fluxes of CO2 were estimated to 29.7, −35.3 and −34.9 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum sites (positive flux indicates an addition of C to the atmospheric pool). The corresponding annual THC emissions were 0.5, 6.2 and 31.8 gC m−2 for the same sites. Therefore, the NCB for each of the sites was 30.2, −29.1 and −3.1 gC m−2 respectively for the Palsa, Sphagnum and Eriophorum site. On average, the whole mire was a CO2 sink of 2.6 gC m−2 and a THC source of 6.4 gC m−2 over a year. Consequently, the mire was a net source of C to the atmosphere by 3.9 gC m−2 (based on area weighted estimates for each of the three plant communities). Early and late snow season efflux of CO2 and THC emphasize the importance of winter measurements for complete annual C budgets. Decadal vegetation changes at Stordalen indicate that both the productivity and the THC emissions increased between 1970 and 2000. Considering the GWP100 of CH4, the net radiative forcing on climate increased 21% over the same time. In conclusion, reduced C compounds in these environments have high importance for both the annual C balance and climate.

  • 36. Caffin, Mathieu
    et al.
    Moutin, Thierry
    Foster, Rachel Ann
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bouruet-Aubertot, Pascale
    Doglioli, Andrea Michelangelo
    Berthelot, Hugo
    Guieu, Cecile
    Grosso, Olivier
    Helias-Nunige, Sandra
    Leblond, Nathalie
    Gimenez, Audrey
    Petrenko, Anne Alexandra
    de Verneil, Alain
    Bonnet, Sophie
    N-2 fixation as a dominant new N source in the western tropical South Pacific Ocean (OUTPACE cruise)2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 8, p. 2565-2585Article in journal (Refereed)
    Abstract [en]

    We performed nitrogen (N) budgets in the photic layer of three contrasting stations representing different trophic conditions in the western tropical South Pacific (WTSP) Ocean during austral summer conditions (FebruaryMarch 2015). Using a Lagrangian strategy, we sampled the same water mass for the entire duration of each long-duration (5 days) station, allowing us to consider only vertical exchanges for the budgets. We quantified all major vertical N fluxes both entering (N-2 fixation, nitrate turbulent diffusion, atmospheric deposition) and leaving the photic layer (particulate N export). The three stations were characterized by a strong nitracline and contrasted deep chlorophyll maximum depths, which were lower in the oligotrophic Melanesian archipelago (MA, stations LD A and LD B) than in the ultra-oligotrophic waters of the South Pacific Gyre (SPG, station LD C). N-2 fixation rates were extremely high at both LD A (593 +/- 51 mu mol N m(-2) d(-1)) and LD B (706 +/- 302 mu mol N m(-2)d(-1)), and the diazotroph community was dominated by Trichodesmium. N-2 fixation rates were lower (59 +/- 16 mu mol N m(-2) d(-1)) at LD C, and the diazotroph community was dominated by unicellular N-2-fixing cyanobacteria (UCYN). At all stations, N-2 fixation was the major source of new N (> 90 %) before atmospheric deposition and upward nitrate fluxes induced by turbulence. N-2 fixation contributed circa 1318 % of primary production in the MA region and 3 in the SPG water and sustained nearly all new primary production at all stations. The e ratio (e ratio articulate carbon export / primary production) was maximum at LD A (9.7 ) and was higher than the e ratio in most studied oligotrophic regions (< 5), indicating a high efficiency of the WTSP to export carbon relative to primary production. The direct export of diazotrophs assessed by qPCR of the nifH gene in sediment traps represented up to 30.6 of the PC export at LD A, while their contribution was 5 and < 0.1 % at LD B and LD C, respectively. At the three studied stations, the sum of all N input to the photic layer exceeded the N output through organic matter export. This disequilibrium leading to N accumulation in the upper layer appears as a characteristic of the WTSP during the summer season.

  • 37. Castro-Morales, Karel
    et al.
    Kleinen, Thomas
    Kaiser, Sonja
    Zaehle, Sönke
    Kittler, Fanny
    Kwon, Min Jung
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Göckede, Mathias
    Year-round simulated methane emissions from a permafrost ecosystem in Northeast Siberia2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, no 9, p. 2691-2722Article in journal (Refereed)
    Abstract [en]

    Wetlands of northern high latitudes are ecosystems highly vulnerable to climate change. Some degradation effects include soil hydrologic changes due to permafrost thaw, formation of deeper active layers, and rising topsoil temperatures that accelerate the degradation of permafrost carbon and increase in CO2 and CH4 emissions. In this work we present 2 years of modeled year-round CH4 emissions into the atmosphere from a Northeast Siberian region in the Russian Far East. We use a revisited version of the process-based JSBACH-methane model that includes four CH4 transport pathways: plant-mediated transport, ebullition and molecular diffusion in the presence or absence of snow. The gas is emitted through wetlands represented by grid cell inundated areas simulated with a TOPMODEL approach. The magnitude of the summertime modeled CH4 emissions is comparable to ground-based CH4 fluxes measured with the eddy covariance technique and flux chambers in the same area of study, whereas wintertime modeled values are underestimated by 1 order of magnitude. In an annual balance, the most important mechanism for transport of methane into the atmosphere is through plants (61 %). This is followed by ebullition (similar to 35 %), while summertime molecular diffusion is negligible (0.02 %) compared to the diffusion through the snow during winter (similar to 4 %). We investigate the relationship between temporal changes in the CH4 fluxes, soil temperature, and soil moisture content. Our results highlight the heterogeneity in CH4 emissions at landscape scale and suggest that further improvements to the representation of large-scale hydrological conditions in the model will facilitate a more process-oriented land surface scheme and better simulate CH4 emissions under climate change. This is especially necessary at regional scales in Arctic ecosystems influenced by permafrost thaw.

  • 38. Chadburn, Sarah E.
    et al.
    Krinner, Gerhard
    Porada, Philipp
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Bartsch, Annett
    Beer, Christian
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Belelli Marchesini, Luca
    Boike, Julia
    Ekici, Altug
    Elberling, Bo
    Friborg, Thomas
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Johansson, Margareta
    Kuhry, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Kutzbach, Lars
    Langer, Moritz
    Lund, Magnus
    Parmentier, Frans-Jan W.
    Peng, Shushi
    Van Huissteden, Ko
    Wang, Tao
    Westermann, Sebastian
    Zhu, Dan
    Burke, Eleanor J.
    Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 22, p. 5143-5169Article in journal (Refereed)
    Abstract [en]

    It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that an improved simulation of photosynthesis would also lead to an improved simulation of soil carbon stocks. However, the stocks are also influenced by soil carbon burial (e.g. through cryoturbation) and the rate of heterotrophic respiration, which depends on the soil physical state. More detailed below-ground measurements are needed to fully evaluate biological and physical soil processes. Furthermore, even if these processes are well modelled, the soil carbon profiles cannot resemble peat layers as peat accumulation processes are not represented in the models. Thus, we identify three priority areas for model development: (1) dynamic vegetation including (a) climate and (b) nutrient limitation effects; (2) adding moss as a plant functional type; and an (3) improved vertical profile of soil carbon including peat processes.

  • 39. Charkin, A. N.
    et al.
    Dudarev, O. V.
    Semiletov, I. P.
    Kruhmalev, A. V.
    Vonk, J. E.
    Sanchez-Garcia, L.
    Karlsson, E.
    Gustafsson, O.
    Seasonal and interannual variability of sedimentation and organic matter distribution in the Buor-Khaya Gulf: the primary recipient of input from Lena River and coastal erosion in the southeast Laptev Sea2011In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, no 9, p. 2581-2594Article in journal (Refereed)
    Abstract [en]

    Climate warming is amplified in the land-sea system of the East Siberian Arctic, which also holds large pools of vulnerable carbon in permafrost. This coastal area is strongly influenced by sediment and carbon transport from both its large rivers and extensive erosion of Pleistocene permafrost along its coastline. This study is investigating the coastal fate of the sediment and organic carbon delivered to the Buor-Khaya Gulf, which is the first recipient of the overwhelming fluvial discharge from the Lena River and is additionally receiving large input from extensive erosion of the coastal ice-complex (permafrost a. k.a. Yedoma; loess soil with high organic carbon content). Both water column suspended particulate matter (SPM) and surface sediments were sampled at about 250 oceanographic stations in the Gulf in this multi-year effort, including one winter campaign, and analyzed for the distribution and sorting of sediment size, organic carbon content, and stable carbon isotope signals. The composition of the surface sediment suggests an overwhelmingly terrestrial contribution from both river and coastal erosion. The objective of this paper is to improve our understanding of the seasonal (i.e., winter vs summer) and interannual variability of these coastal sedimentation processes and the dynamics of organic carbon (OC) distribution in both the water column SPM and the surface sediments of the Buor-Khaya Gulf. Based on data collected during several years in the period 2000-2008, two different sedimentation regimes were revealed for the Buor-Khaya Gulf, the relative importance of each at a given time depend on hydrometeorological conditions, the Lena River water discharge and sea-ice regime: Type 1 erosion-accumulation and Type 2 accumulation. The Type 1 erosion-accumulation sedimentation regime is typical (2000-2006) for the ice-free period of the year (here considered in detail for August 2005). Under such conditions terrigenous sources of SPM and particulate organic carbon (POC) stem predominantly from river discharge, thermal erosion of coastal ice-complex and remobilized bottom sediments. The Type 2 accumulation sedimentation regime develops under ice-covered conditions, and only occasionally during the ice-free period (August 2008). In Type 2 winter, combined terrigenous and marine-biogenic SPM and POC sources are dominating due to relatively low overall terrigenous input (April 2007). In Type 2 summer, river alluvium becomes the major SPM and POC source (August 2008). The water column SPM and POC loadings vary by more than a factor of two between the two regimes. This study underscores the necessity of multi-year investigations to better understand the functioning of the primary recipient of terrestrially expulsed matter in the East Siberian Arctic.

  • 40. Charkin, A. N.
    et al.
    Dudarev, O. V.
    Semiletov, I. P.
    Kruhmalev, A. V.
    Vonk, J. E.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Sanchez-Garcia, L.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Karlsson, Emma
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Seasonal and interannual variability of sedimentation and organic matter distribution in the Buor-Khaya Gulf: the primary recipient of input from Lena River and coastal erosion in the southeast Laptev Sea2011In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, no 9, p. 2581-2594Article in journal (Refereed)
    Abstract [en]

    Climate warming is amplified in the land-sea system of the East Siberian Arctic, which also holds large pools of vulnerable carbon in permafrost. This coastal area is strongly influenced by sediment and carbon transport from both its large rivers and extensive erosion of Pleistocene permafrost along its coastline. This study is investigating the coastal fate of the sediment and organic carbon delivered to the Buor-Khaya Gulf, which is the first recipient of the overwhelming fluvial discharge from the Lena River and is additionally receiving large input from extensive erosion of the coastal ice-complex (permafrost a. k.a. Yedoma; loess soil with high organic carbon content). Both water column suspended particulate matter (SPM) and surface sediments were sampled at about 250 oceanographic stations in the Gulf in this multi-year effort, including one winter campaign, and analyzed for the distribution and sorting of sediment size, organic carbon content, and stable carbon isotope signals. The composition of the surface sediment suggests an overwhelmingly terrestrial contribution from both river and coastal erosion. The objective of this paper is to improve our understanding of the seasonal (i.e., winter vs summer) and interannual variability of these coastal sedimentation processes and the dynamics of organic carbon (OC) distribution in both the water column SPM and the surface sediments of the Buor-Khaya Gulf. Based on data collected during several years in the period 2000-2008, two different sedimentation regimes were revealed for the Buor-Khaya Gulf, the relative importance of each at a given time depend on hydrometeorological conditions, the Lena River water discharge and sea-ice regime: Type 1 erosion-accumulation and Type 2 accumulation. The Type 1 erosion-accumulation sedimentation regime is typical (2000-2006) for the ice-free period of the year (here considered in detail for August 2005). Under such conditions terrigenous sources of SPM and particulate organic carbon (POC) stem predominantly from river discharge, thermal erosion of coastal ice-complex and remobilized bottom sediments. The Type 2 accumulation sedimentation regime develops under ice-covered conditions, and only occasionally during the ice-free period (August 2008). In Type 2 winter, combined terrigenous and marine-biogenic SPM and POC sources are dominating due to relatively low overall terrigenous input (April 2007). In Type 2 summer, river alluvium becomes the major SPM and POC source (August 2008). The water column SPM and POC loadings vary by more than a factor of two between the two regimes. This study underscores the necessity of multi-year investigations to better understand the functioning of the primary recipient of terrestrially expulsed matter in the East Siberian Arctic.

  • 41. Chaudhary, Nitin
    et al.
    Miller, Paul A.
    Smith, Benjamin
    Modelling Holocene peatland dynamics with an individual-based dynamic vegetation model2017In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, no 10, p. 2571-2596Article in journal (Refereed)
    Abstract [en]

    Dynamic global vegetation models (DGVMs) are designed for the study of past, present and future vegetation patterns together with associated biogeochemical cycles and climate feedbacks. However, most DGVMs do not yet have detailed representations of permafrost and non-permafrost peatlands, which are an important store of carbon, particularly at high latitudes. We demonstrate a new implementation of peatland dynamics in a customized “Arctic” version of the LPJ-GUESS DGVM, simulating the long-term evolution of selected northern peatland ecosystems and assessing the effect of changing climate on peatland carbon balance. Our approach employs a dynamic multi-layer soil with representation of freeze-thaw processes and litter inputs from a dynamically varying mixture of the main peatland plant functional types: mosses, shrubs and graminoids. The model was calibrated and tested for a sub-Arctic mire in Stordalen, Sweden, and validated at a temperate bog site in Mer Bleue, Canada. A regional evaluation of simulated carbon fluxes, hydrology and vegetation dynamics encompassed additional locations spread across Scandinavia. Simulated peat accumulation was found to be generally consistent with published data and the model was able to capture reported long-term vegetation dynamics, water table position and carbon fluxes. A series of sensitivity experiments were carried out to investigate the vulnerability of high-latitude peatlands to climate change. We found that the Stordalen mire may be expected to sequester more carbon in the first half of the 21st century due to milder and wetter climate conditions, a longer growing season, and the CO2 fertilization effect, turning into a carbon source after mid-century because of higher decomposition rates in response to warming soils.

  • 42. Chi Fru, Ernest
    et al.
    Callac, Nolwenn
    Posth, Nicole
    Argyaki, Ariadne
    Ling, Y.-C.
    Ivarsson, Magnus
    Swedish Museum of Natural History, Department of Paleobiology.
    Broman, Curt
    Kilias, Stephanos
    Arsenic and high affinity phosphate uptake gene distribution in shallow submarine hydrothermal sediments2018In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189Article in journal (Refereed)
  • 43. Chierici, M.
    et al.
    Fransson, A.
    Calcium carbonate saturation in the surface water of the Arctic Ocean: undersaturation in freshwater influenced shelves2009In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 6, no 11, p. 2421-2431Article in journal (Refereed)
    Abstract [en]

    In the summer of 2005, we sampled surface water and measured pH and total alkalinity (A(T)) underway aboard IB Oden along the Northwest Passage from Cape Farewell (South Greenland) to the Chukchi Sea. We investigated the variability of carbonate system parameters, focusing particularly on carbonate concentration [CO32-] and calcium carbonate saturation states, as related to freshwater addition, biological processes and physical upwelling. Measurements on A(T), pH at 15 degrees C, salinity (S) and sea surface temperature (SST), were used to calculate total dissolved inorganic carbon (C-T), [CO32-] and the saturation of aragonite (Omega Ar) and calcite (Omega Ca) in the surface water. The same parameters were measured in the water column of the Bering Strait. Some surface waters in the Canadian Arctic Archipelago (CAA) and on the Mackenzie shelf (MS) were found to be undersaturated with respect to aragonite (Omega Ar<1). In these areas, surface water was low in AT and CT (<1500 mu mol kg(-1)) relative to seawater and showed low [CO32-]. The low saturation states were probably due to the likely the effect of dilution due to freshwater addition by sea ice melt (CAA) and river runoff (MS). High A(T) and C-T and low pH, corresponded with the lowest [CO32-], Omega Ar and Omega Ca, observed near Cape Bathurst and along the South Chukchi Peninsula. This was linked to the physical upwelling of subsurface water with elevated CO2. The highest surface Omega Ar and Omega Ca of 3.0 and 4.5, respectively, were found on the Chukchi Sea shelf and in the cold water north of Wrangel Island, which is heavily influenced by high CO2 drawdown and lower C-T from intense biological production. In the western Bering Strait, the cold and saline Anadyr Current carries water that is enriched in A(T) and C-T from enhanced organic matter remineralization, resulting in the lowest Omega Ar (similar to 1.2) of the area.

  • 44. Clymans, W.
    et al.
    Barao, L.
    Van der Putten, N.
    Wastegård, Sefan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gisladottir, G.
    Björck, S.
    Moine, B.
    Struyf, E.
    Conley, D. J.
    The contribution of tephra constituents during biogenic silica determination: implications for soil and palaeoecological studies2015In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, no 12, p. 3789-3804Article in journal (Refereed)
    Abstract [en]

    Biogenic silica (BSi) is used as a proxy by soil scientists to identify biological effects on the Si cycle and by palaeoecologists to study environmental changes. Alkaline extractions are typically used to measure BSi in both terrestrial and aquatic environments. The dissolution properties of volcanic glass in tephra deposits and their nanocrystalline weathering products are hypothesized to overlap those of BSi; however, data to support this behaviour are lacking. The potential that Si-bearing fractions dissolve in alkaline media (Si-Alk) that do not necessarily correspond to BSi brings the applicability of BSi as a proxy into question. Here, analysis of 15 samples reported as tephra-containing allows us to reject the hypothesis that tephra constituents produce an identical dissolution signal to that of BSi during alkaline extraction. We found that dissolution of volcanic glass shards is incomplete during alkaline dissolution. Simultaneous measurement of Al and Si used here during alkaline dissolution provides an important parameter to enable us to separate glass shard dissolution from dissolution of BSi and other Si-bearing fractions. The contribution from volcanic glass shards (between 0.2 and 4 wt % SiO2), the main constituent of distal tephra, during alkaline dissolution can be substantial depending on the total Si-Alk. Hence, soils and lake sediments with low BSi concentrations are highly sensitive to the additional dissolution from tephra constituents and its weathering products. We advise evaluation of the potential for volcanic or other non-biogenic contributions for all types of studies using BSi as an environmental proxy.

  • 45.
    Conrad, Sarah
    et al.
    Luleå University of Technology.
    Ingri, Johan
    Luleå University of Technology.
    Gelting, Johan
    Leleå University of Technology.
    Nordblad, Fredrik
    Luleå University of Technology.
    Engström, Emma
    Luleå University of Technology.
    Rodushkin, Ilia
    ALS Laboratory Group, Luleå.
    Andersson, Per
    Swedish Museum of Natural History, Research Division.
    Porcelli, Don
    Oxford University, Oxford.
    Gustafsson, Örjan
    Stockholm University, Stockholm.
    Semiletov, Igor
    University of Alaska, USA.
    Öhlander, Björn
    Luleå University of Technology.
    Distributionof Fe isotopes in particles and colloids in the salinity gradient along theLena River plume, Laptev Sea2019In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 16, p. 1305-1319Article in journal (Refereed)
    Abstract [en]

    Riverine Fe input is the primary Fe source to the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate (>0.22µm), colloidal (0.22µm – 1kDa), and truly dissolved (<1kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.15 to 57 µM with Fe dominantly as particulate Fe. The loss of > 99% of particulate Fe and about 90% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative δ56Fe values (relative to IRMM-14). The colloidal Fe phase showed negative δ56Fe values close to the river mouth (about -0.20‰) and positive δ56Fe values in the outermost stations (about +0.10‰).

    We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative δ56Fe values, representing chemically reactive ferrihydrites. While the positive δ56Fe values of the colloidal phase within the outer Lena River freshwater plume, might represent Fe-oxyhydroxides, which remain in the water column, and will be the predominant δ56Fe composition in the Arctic Ocean.

  • 46. Conrad, Sarah
    et al.
    Ingri, Johan
    Gelting, Johan
    Nordblad, Fredrik
    Engström, Emma
    Rodushkin, Ilia
    Andersson, Per S.
    Porcelli, Don
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Semiletov, Igor
    Öhlander, Björn
    Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea2019In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 16, no 6, p. 1305-1319Article in journal (Refereed)
    Abstract [en]

    Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate (> 0.22 mu m), colloidal (0.22 mu m-1 kDa), and truly dissolved (< 1 kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57 mu M with Fe dominantly as particulate Fe. The loss of > 99% of particulate Fe and about 90% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative delta Fe-56 values (relative to IRMM-14). The colloidal Fe phase showed negative delta Fe-56 values close to the river mouth (about -0.20 parts per thousand) and positive delta Fe-56 values in the outermost stations (about +0.10 parts per thousand). We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative delta Fe-56 values, representing chemically reactive ferrihydrites. The positive delta Fe-56 values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant delta Fe-56 composition in the Arctic Ocean.

  • 47.
    Conrad, Sarah
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ingri, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Gelting, Johan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nordblad, Fredrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Engström, Emma
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. ALS Laboratory Group, ALS Scandinavia AB, Luleå, Sweden .
    Rodushkin, Ilia
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. ALS Laboratory Group, ALS Scandinavia AB, Luleå, Sweden .
    Andersson, Per S.
    Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
    Porcelli, Don
    Department of Earth Sciences, Oxford University, Oxford, UK.
    Gustafsson, Örjan
    Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden.
    Semiletov, Igor
    International Arctic Research Center (IARC), University of Alaska, Fairbanks, AK, USA. Pacific Oceanological Institute (POI), Far Eastern Branch of the Russian Academy of Sciences (FEBRAS), Vladivostok, Russia. Tomsk National Research Politechnical University, Arctic Seas Carbon International Research Laboratory, Tomsk, Russia.
    Öhlander, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Distribution of Fe isotopes in particles and colloids in the salinity gradient along the Lena River plume, Laptev Sea2019In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 16, no 6, p. 1305-1319Article in journal (Refereed)
    Abstract [en]

     Riverine Fe input is the primary Fe source for the ocean. This study is focused on the distribution of Fe along the Lena River freshwater plume in the Laptev Sea using samples from a 600 km long transect in front of the Lena River mouth. Separation of the particulate ( >  0.22 μm), colloidal (0.22 μm–1 kDa), and truly dissolved (<  1 kDa) fractions of Fe was carried out. The total Fe concentrations ranged from 0.2 to 57μM with Fe dominantly as particulate Fe. The loss of >  99% of particulate Fe and about 90% of the colloidal Fe was observed across the shelf, while the truly dissolved phase was almost constant across the Laptev Sea. Thus, the truly dissolved Fe could be an important source of bioavailable Fe for plankton in the central Arctic Ocean, together with the colloidal Fe. Fe-isotope analysis showed that the particulate phase and the sediment below the Lena River freshwater plume had negative δ56Fe values (relative to IRMM-14). The colloidal Fe phase showed negative δ56Fe values close to the river mouth (about -0.20 ‰) and positive δ56Fe values in the outermost stations (about +0.10 ‰). We suggest that the shelf zone acts as a sink for Fe particles and colloids with negative δ56Fe values, representing chemically reactive ferrihydrites. The positive δ56Fe values of the colloidal phase within the outer Lena River freshwater plume might represent Fe oxyhydroxides, which remain in the water column, and will be the predominant δ56Fe composition in the Arctic Ocean.

  • 48.
    David, M.
    et al.
    Inst. National de la Recherche Agronomique, UMR Environnement et Grandes Cultures, Thiverval-Grignon, France.
    Loubet, B.
    Inst. National de la Recherche Agronomique, UMR Environnement et Grandes Cultures, Thiverval-Grignon, France.
    Cellier, P.
    Inst. National de la Recherche Agronomique, UMR Environnement et Grandes Cultures, Thiverval-Grignon, France.
    Mattsson, Marie
    Halmstad University, School of Business and Engineering (SET), Biological and Environmental Systems (BLESS).
    Schjoerring, J.K.
    Plant and Soil Science Laboratory, University of Copenhagen, Faculty of Life Sciences, Copenhagen, Denmark.
    Nemitz, E.
    Centre for Ecology and Hydrology (Edinburgh Research Station), Bush Estate, Penicuik, Midlothian ,UK.
    Roche, R.
    Inst. National de la Recherche Agronomique, UMR Environnement et Grandes Cultures.
    Riedo, M.
    Inst. fur Agrarokologie, Bundesforschungsanstalt fur Landwirtschaft (FAL), Braunschweig, Germany.
    Sutton, M.A.
    Centre for Ecology and Hydrology (Edinburgh Research Station), Bush Estate, Penicuik, Midlothian ,UK.
    Ammonia sources and sinks in an intensively managed grassland canopy2009In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 6, no 9, p. 1903-1915Article in journal (Refereed)
    Abstract [en]

    Grasslands represent canopies with a complex structure where sources and sinks of ammonia (NH3) may coexist at the plant level. Moreover, management practices such as mowing, hay production and grazing may change the composition of the sward and hence the source-sink relationship at the canopy level as well as the interaction with the atmosphere. There is therefore a need to understand the exchange of ammonia between grasslands and the atmosphere better, especially regarding the location and magnitude of sources and sinks. Fluxes of atmospheric NH3 within a grassland canopy were assessed in the field and under controlled conditions using a dynamic chamber technique (cuvette). These cuvette measurements were combined with extraction techniques to estimate the ammonium (NH+4 ) concentration and the pH of a given part of the plant or soil, leading to an estimated ammo- nia compensation point (Cp ). The combination of the cuvette and the extraction techniques was used to identify the poten- tial sources and sinks of NH3 within the different compart- ments of the grassland: the soil, the litter or senescent “litter leaves”, and the functioning “green leaves”. A set of six field experiments and six laboratory experiments were performed in which the different compartments were either added or removed from the cuvettes.The results show that the cuvette measurements agree with the extraction technique in ranking the strength of compartment sources. It suggests that in the studied grassland the green leaves were mostly a sink for NH3 with a compensation point around 0.1–0.4 μg m−3 and   an NH3 flux of 6 to 7 ng m−2 s−1. Cutting of the grass did not increase the NH3 fluxes of the green leaves. The litter was found to be the largest source of NH3 in the canopy, with a Cp of up to 1000μgm−3 NH3 andanNH3 fluxupto90ngm−2 s−1. The litter was found to be a much smaller NH3 source when dried (Cp =160 μg m−3 and FNH3 =35 ng m−2 s−1 NH3 ). Moreover emissions from the litter were found to vary with the relative humidity of the air. The soil was a strong source of NH3 in the period immediately after cutting (Cp =320 μg m−3 and FNH3 =60 ng m−2 s−1 ), which was nevertheless always smaller than the litter source. The soil NH3 emissions lasted, however, for less than one day, and were not observed with sieved soil. They could not be solely explained by xylem sap flow extruding NH+4 . These results indicate that future research on grassland-ammonia relationships should focus on the post-mowing period and the role of litter in interaction with meteorological conditions.

  • 49. Deng, J.
    et al.
    Li, C.
    Frolking, S.
    Zhang, Y.
    Bäckstrand, Kristina
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Crill, Patrick
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Assessing effects of permafrost thaw on C fluxes based on multiyear modeling across a permafrost thaw gradient at Stordalen, Sweden2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 17, p. 4753-4770Article in journal (Refereed)
    Abstract [en]

    Northern peatlands in permafrost regions contain a large amount of organic carbon (C) in the soil. Climate warming and associated permafrost degradation are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is uncertain. We incorporated a permafrost model, Northern Ecosystem Soil Temperature (NEST), into a biogeochemical model, DeNitrification-DeComposition (DNDC), to model C dynamics in high-latitude peatland ecosystems. The enhanced model was applied to assess effects of permafrost thaw on C fluxes of a subarctic peatland at Stordalen, Sweden. DNDC simulated soil freeze-thaw dynamics, net ecosystem exchange of CO2 (NEE), and CH4 fluxes across three typical land cover types, which represent a gradient in the process of ongoing permafrost thaw at Stordalen. Model results were compared with multiyear field measurements, and the validation indicates that DNDC was able to simulate observed differences in seasonal soil thaw, NEE, and CH4 fluxes across the three land cover types. Consistent with the results from field studies, the modeled C fluxes across the permafrost thaw gradient demonstrate that permafrost thaw and the associated changes in soil hydrology and vegetation not only increase net uptake of C from the atmosphere but also increase the annual to decadal radiative forcing impacts on climate due to increased CH4 emissions. This study indicates the potential of utilizing biogeochemical models, such as DNDC, to predict the soil thermal regime in permafrost areas and to investigate impacts of permafrost thaw on ecosystem C fluxes after incorporating a permafrost component into the model framework.

  • 50. Deng, J.
    et al.
    Li, C.
    Frolking, S.
    Zhang, Y.
    Bäckstrand, Kristina
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Crill, Patrick
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Assessing effects of permafrost thaw on C fluxes based on multiyear modeling across a permafrost thaw gradient at Stordalen, Sweden2014In: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, no 17, p. 4753-4770Article in journal (Refereed)
    Abstract [en]

    Northern peatlands in permafrost regions contain a large amount of organic carbon (C) in the soil. Climate warming and associated permafrost degradation are expected to have significant impacts on the C balance of these ecosystems, but the magnitude is uncertain. We incorporated a permafrost model, Northern Ecosystem Soil Temperature (NEST), into a biogeochemical model, DeNitrification-DeComposition (DNDC), to model C dynamics in high-latitude peatland ecosystems. The enhanced model was applied to assess effects of permafrost thaw on C fluxes of a subarctic peatland at Stordalen, Sweden. DNDC simulated soil freeze-thaw dynamics, net ecosystem exchange of CO2 (NEE), and CH4 fluxes across three typical land cover types, which represent a gradient in the process of ongoing permafrost thaw at Stordalen. Model results were compared with multiyear field measurements, and the validation indicates that DNDC was able to simulate observed differences in seasonal soil thaw, NEE, and CH4 fluxes across the three land cover types. Consistent with the results from field studies, the modeled C fluxes across the permafrost thaw gradient demonstrate that permafrost thaw and the associated changes in soil hydrology and vegetation not only increase net uptake of C from the atmosphere but also increase the annual to decadal radiative forcing impacts on climate due to increased CH4 emissions. This study indicates the potential of utilizing biogeochemical models, such as DNDC, to predict the soil thermal regime in permafrost areas and to investigate impacts of permafrost thaw on ecosystem C fluxes after incorporating a permafrost component into the model framework.

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