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  • 151. Löwemark, Ludvig
    et al.
    Chao, Weng-Si
    Gyllencreutz, Richard
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Hanebuth, Till J. J.
    Chiu, Pin-Yao
    Yang, Tien-Nan
    Su, Chih-Chieh
    Chuang, Chih-Kai
    Leon Dominguez, Dora Carolina
    Jakobsson, Martin
    Stockholms universitet, Institutionen för geologiska vetenskaper.
    Variations in glacial and interglacial marine conditions over the last two glacial cycles off northern Greenland2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, no SI, p. 164-177Article in journal (Refereed)
    Abstract [en]

    Five sediment cores from the Lomonosov Ridge and the Morris Jesup Rise north of Greenland show the history of sea-ice coverage and primary productivity over the last two glacial cycles. Variations in Manganese content, benthic and planktonic foraminifera, bioturbation, and trace fossil diversity are interpreted to reflect differences in sea-ice cover and sediment depositional conditions between the identified interglacials. Marine Isotope Stage (MIS) 1 and MIS 2 are represented by thin (<< 5 cm) sediment units while the preceding interglacial MIS 5 and glacial MIS 6 are characterized by thick (10 -20 cm) deposits. Foraminiferal abundances and bioturbation suggest that MIS 1 was generally characterized by severe sea-ice conditions north of Greenland while MISS appears to have been considerably warmer with more open water, higher primary productivity, and higher sedimentation rates. Strengthened flow of Atlantic water along the northern continental shelf of Greenland rather than development of local polynyas is here suggested as a likely cause for the relatively warmer marine conditions during MIS 5 compared to MIS 1. The cores also suggest distinct differences between the glacial intervals MIS 2 and MIS 6. While MIS 6 is distinguished by a relatively thick sediment unit poor in foraminifera and with low Mn values, MIS 2 is practically missing. We speculate that this could be the effect from a paleocrystic sea-ice cover north of Greenland during MIS 2 that prevented sediment delivery from sea ice and icebergs. In contrast, the thick sequence deposited during MIS 6 indicates a longer glacial period with dynamic intervals characterized by huge drifting icebergs delivering ice rafted debris (IRD). A drastic shift from thinner sedimentary cycles where interglacial sediment parameters indicate more severe sea-ice conditions gave way to larger amplitude cycles with more open water indicators was observed around the boundary between MIS 7/8. This shift is in agreement with a sedimentary regime shift previously identified in the Eurasian Basin and may be an indicator for the growth of larger ice sheets on the Eurasian landmass during the penultimate glacial period.

  • 152. Mangerud, Jan
    et al.
    Goehring, Brent M.
    Lohne, Öystein S.
    Svendsen, John Inge
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences. University of Bergen, Norway.
    Collapse of marine-based outlet glaciers from the Scandinavian Ice Sheet2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 67, p. 8-16Article in journal (Refereed)
    Abstract [en]

    We present a reconstruction of the timing and retreat rates of more than 2000 m thick Younger Dryas (YD) fjord glaciers in western Norway using a detailed chronology of 10 Be exposure ages from lateral moraines and 14 C dated end moraines. A primary conclusion is that ice margins retreated up the 120 e 170 km long fjords at mean rates of 240e340 m yr1 during the early Holocene. We further show that part of the south-western sector of the Scandinavian Ice Sheet collapsed in two distinct steps. The first step occurred between 19.5 and 18.5 ka BP as break up of the Norwegian Channel Ice Stream, which drained the ice sheet during the Last Glacial Maximum (LGM). The second step was the rapid retreat up the fjords mentioned above, dated to 11.6 e11.1 ka BP. During the interveningw 7000 years no net retreat occurred despite oscillations of the ice margin. This stepwise ice margin retreat strongly contrasts with the more monotonic decay of the ice sheet as a whole, indicating that water depths set the pace for climate-triggered ice margin retreat in this part of the ice sheet. Calving and melting of marine margins has dominated mass-loss from modern ice sheets in recent decades; however, the mechanisms and longterm (100 e 1000 yr) rate of ice-front retreat is less certain and empirical examples such as those given here may help in developing better numerical models.

  • 153.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jansen, John D.
    Codilean, Alexandru T.
    Preusser, Frank
    Gurinov, Artem L.
    Fujioka, Toshiyuki
    Fink, David
    Repeated megafloods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000 years2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 187, p. 41-61Article in journal (Refereed)
    Abstract [en]

    Cataclysmic outburst floods transformed landscapes and caused abrupt climate change during the last deglaciation. Whether such events have also characterized previous deglaciations is not known. Arctic marine cores hint at megafloods prior to Oxygen Isotope Stage (OIS) 2, but the overprint of successive glaciations means that geomorphological traces of ancient floods remain scarce in Eurasia and North America. Here we present the first well-constrained terrestrial megaflood record to be linked with Arctic archives. Based on cosmogenic-nuclide exposure dating and optically stimulated luminescence dating applied to glacial-lake sediments, a 300-m deep bedrock spillway, and giant eddy-bars > 200-m high, we reconstruct a history of cataclysmic outburst floods from glacial Lake Vitim, Siberia, to the Arctic Ocean over the past 60,000-years. Three megafloods have reflected the rhythm of Eurasian glaciations, leaving traces that stretch more than 3500 km to the Lena Delta. The first flood was coincident with deglaciation from OIS-4 and the largest meltwater spike in Arctic marine-cores within the past 100,000 years (isotope-event 3.31 at 55.5 ka). The second flood marked the lead up to the local Last Glacial Maximum, and the third flood occurred during the last deglaciation. This final 3000 km(3) megaflood stands as one of the largest freshwater floods ever documented, with peak discharge of 4.0-6.5 million m(3)s(-1), mean flow depths of 120-150 m, and average flow velocities up to 21 ms(-1)

  • 154.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jansen, John D.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Gurinov, Artem L.
    Codilean, Alexandru T.
    Fink, David
    Preusser, Frank
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Reznichenko, Natalya V.
    Mifsud, Charles
    Extensive glaciation in Transbaikalia, Siberia, at the Last Glacial Maximum2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 132, p. 161-174Article in journal (Refereed)
    Abstract [en]

    Successively smaller glacial extents have been proposed for continental Eurasia during the stadials of the last glacial period leading up to the Last Glacial Maximum (LGM). At the same time the large mountainous region east of Lake Baikal, Transbaikalia, has remained unexplored in terms of glacial chronology despite clear geomorphological evidence of substantial past glaciations. We have applied cosmogenic Be-10 exposure dating and optically stimulated luminescence to establish the first quantitative glacial chronology for this region. Based on eighteen exposure ages from five moraine complexes, we propose that large mountain ice fields existed in the Kodar and Udokan mountains during Oxygen Isotope Stage 2, commensurate with the global LGM. These ice fields fed valley glaciers (>100 km in length) reaching down to the Chara Depression between the Kodar and Udokan mountains and to the valley of the Vitim River northwest of the Kodar Mountains. Two of the investigated moraines date to the Late Glacial, but indications of incomplete exposure among some of the sampled boulders obscure the specific details of the post-LGM glacial history. In addition to the LGM ice fields in the highest mountains of Transbaikalia, we report geomorphological evidence of a much more extensive, ice-cap type glaciation at a time that is yet to be firmly resolved.

  • 155.
    Margold, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Durham University, UK.
    Stokes, Chris R.
    Clark, Chris D.
    Reconciling records of ice streaming and ice margin retreat to produce a palaeogeographic reconstruction of the deglaciation of the Laurentide Ice Sheet2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 189, p. 1-30Article, review/survey (Refereed)
    Abstract [en]

    This paper reconstructs the deglaciation of the Laurentide Ice Sheet (LIS; including the Innuitian Ice Sheet) from the Last Glacial Maximum (LGM), with a particular focus on the spatial and temporal variations in ice streaming and the associated changes in flow patterns and ice divides. We build on a recent inventory of Laurentide ice streams and use an existing ice margin chronology to produce the first detailed transient reconstruction of the ice stream drainage network in the LIS, which we depict in a series of palaeogeographic maps. Results show that the drainage network at the LGM was similar to modern-day Antarctica. The majority of the ice streams were marine terminating and topographically controlled and many of these continued to function late into the deglaciation, until the ice sheet lost its marine margin. Ice streams with a terrestrial ice margin in the west and south were more transient and ice flow directions changed with the build-up, peak-phase and collapse of the Cordilleran-Laurentide ice saddle. The south-eastern marine margin in Atlantic Canada started to retreat relatively early and some of the ice streams in this region switched off at or shortly after the LGM. In contrast, the ice streams draining towards the north-western and north-eastern marine margins in the Beaufort Sea and in Baffin Bay appear to have remained stable throughout most of the Late Glacial, and some of them continued to function until after the Younger Dryas (YD). The YD influenced the dynamics of the deglaciation, but there remains uncertainty about the response of the ice sheet in several sectors. We tentatively ascribe the switching-on of some major ice streams during this period (e.g. M'Clintock Channel Ice Stream at the north-west margin), but for other large ice streams whose timing partially overlaps with the YD, the drivers are less clear and ice-dynamical processes, rather than effects of climate and surface mass balance are viewed as more likely drivers. Retreat rates markedly increased after the YD and the ice sheet became limited to the Canadian Shield. This hard-bed substrate brought a change in the character of ice streaming, which became less frequent but generated much broader terrestrial ice streams. The final collapse of the ice sheet saw a series of small ephemeral ice streams that resulted from the rapidly changing ice sheet geometry in and around Hudson Bay. Our reconstruction indicates that the LIS underwent a transition from a topographically-controlled ice drainage network at the LGM to an ice drainage network characterised by less frequent, broad ice streams during the later stages of deglaciation. These deglacial ice streams are mostly interpreted as a reaction to localised ice-dynamical forcing (flotation and calving of the ice front in glacial lakes and transgressing sea; basal de-coupling due to large amount of meltwater reaching the bed, debuttressing due to rapid changes in ice sheet geometry) rather than as conveyors of excess mass from the accumulation area of the ice sheet. At an ice sheet scale, the ice stream drainage network became less widespread and less efficient with the decreasing size of the deglaciating ice sheet, the final elimination of which was mostly driven by surface melt.

  • 156. Margold, Martin
    et al.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Clague, John J.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Timing of terminal Pleistocene deglaciation at high elevations in southern and central British Columbia constrained by Be-10 exposure dating2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 99, p. 193-202Article in journal (Refereed)
    Abstract [en]

    The Cordilleran Ice Sheet (CIS) covered most of British Columbia and southern Yukon Territory at the local Last Glacial Maximum (ILGM) during Marine Oxygen Isotope Stage 2. However, its subsequent demise is not well understood, particularly at high elevations east of its ocean-terminating margin. We present Be-10 exposure ages from two high-elevation sites in southern and central British Columbia that help constrain the time of initial deglaciation at these sites. We sampled granodiorite erratics at elevations of 2126-2230 m a.s.l. in the Marble Range and 1608-1785 m a.s.l. in the Telkwa Range at the western margin of the Interior Plateau. The erratics at both sites are near ice-marginal meltwater channels that delineate the local ice surface slope and thus the configuration of the ice sheet during deglaciation. The locations of the erratics and their relations to meltwater channels ensure that the resulting Be-10 ages date CIS deglaciation and not the retreat of local montane glaciers. Our sample sites emerged above the surface of the CIS as its divide migrated westward from the Interior Plateau to the axis of the Coast Mountains. Two of the four samples from the summit area of the Marble Range yielded apparent exposure ages of 14.0 +/- 0.7 and 15.2 +/- 0.8 ka. These ages are 1.8-3.0 ka younger than the well-established ILGM age of ca 17 ka for the Puget lobe of the CIS in Washington State; they are 1.7 ka younger than the ILGM age for the Puget lobe if a snow-shielding correction to their uncertainty-weighted mean age is applied. The other two samples yielded much older apparent exposure ages (20.6 +/- 1.4 and 33.0 +/- 1.5 ka), indicating the presence of inherited isotopes. Four samples collected from the summit area of the Telkwa Range in the Hazelton Mountains yielded well clustered apparent exposure ages of 10.1 +/- 0.6, 10.2 +/- 0.7, 10.4 +/- 0.5, and 11.5 +/- 1.1 ka. Significant present-day snow cover introduces a large uncertainty in the apparent exposure ages from this site. A snow-shielding correction based on present-day snow cover data increases the uncertainty-weighted mean exposure age of the Telkwa Range erratics to 12.4 +/- 0.7 ka, consistent with deglacial C-14 ages from areas near sea level to the west. Our exposure ages show a thinning of the southern portion of the CIS shortly after the ILGM and persistence of a remnant mountain ice cap in the central Coast Mountains into the Younger Dryas Chronozone. Our data also show that the summit area of the Marble Range was ice-covered during the ILGM. The presence of an ice body of considerable dimension in north-central British Columbia until, or possibly even after, the Younger Dryas highlights the need for geomorphological and geochronological studies of the ice dispersal centre over the Skeena Mountains in northwest British Columbia and the need for better understanding of the response of the CIS to Lateglacial climate fluctuations.

  • 157. Markovic, Slobodan B.
    et al.
    Hambach, Ulrich
    Stevens, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Kukla, George J.
    Heller, Friedrich
    Mccoy, William D.
    Oches, Eric A.
    Buggle, Bjoern
    Zoeller, Ludwig
    The last million years recorded at the Stari Slankamen (Northern Serbia) loess-palaeosol sequence: revised chronostratigraphy and long-term environmental trends2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 9-10, p. 1142-1154Article in journal (Refereed)
  • 158.
    Marquer, Laurent
    et al.
    Lund University, Sweden;Univ Toulouse Jean Jaures, France.
    Gaillard, Marie-José
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Sugita, Shinya
    Tallinn Univ, Estonia.
    Poska, Anneli
    Lund University, Sweden;Tallinn Univ Technol, Estonia.
    Trondman, Anna-Kari
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Mazier, Florence
    Univ Toulouse Jean Jaures, France.
    Nielsen, Anne Birgitte
    Lund University, Sweden.
    Fyfe, Ralph M.
    Univ Plymouth, UK.
    Jonsson, Anna Maria
    Lund University, Sweden.
    Smith, Benjamin
    Lund University, Sweden.
    Kaplan, Jed O.
    Ecole Polytech Fed Lausanne, Switzerland.
    Alenius, Teija
    Univ Helsinki, Finland;Univ Turku, Finland.
    Birks, H. John B.
    Univ Bergen, Norway;UCL, UK.
    Bjune, Anne E.
    Univ Bergen, Norway;Uni Res Climate, Norway.
    Christiansen, Jorg
    Univ Göttingen, Germany.
    Dodson, John
    Univ Wollongong, Australia;Chinese Acad Sci, Peoples Republic of China.
    Edwards, Kevin J.
    Univ Aberdeen, UK;Univ Cambridge, UK.
    Giesecke, Thomas
    Univ Göttingen, Germany.
    Herzschuh, Ulrike
    Univ Potsdam, Germany.
    Kangur, Mihkel
    Tallinn Univ, Estonia.
    Koff, Tiiu
    Tallinn Univ, Estonia.
    Latalowa, Maligorzata
    Univ Gdansk, Poland.
    Lechterbeck, Jutta
    Univ Stavanger, Norway.
    Olofsson, Jorgen
    Lund University, Sweden.
    Seppa, Heikki
    Univ Helsinki, Finland.
    Quantifying the effects of land use and climate on Holocene vegetation in Europe2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 171, p. 20-37Article in journal (Refereed)
    Abstract [en]

    Early agriculture can be detected in palaeovegetation records, but quantification of the relative importance of climate and land use in influencing regional vegetation composition since the onset of agriculture is a topic that is rarely addressed. We present a novel approach that combines pollen-based REVEALS estimates of plant cover with climate, anthropogenic land-cover and dynamic vegetation modelling results. This is used to quantify the relative impacts of land use and climate on Holocene vegetation at a sub-continental scale, i.e. northern and western Europe north of the Alps. We use redundancy analysis and variation partitioning to quantify the percentage of variation in vegetation composition explained by the climate and land-use variables, and Monte Carlo permutation tests to assess the statistical significance of each variable. We further use a similarity index to combine pollen based REVEALS estimates with climate-driven dynamic vegetation modelling results. The overall results indicate that climate is the major driver of vegetation when the Holocene is considered as a whole and at the sub-continental scale, although land use is important regionally. Four critical phases of land-use effects on vegetation are identified. The first phase (from 7000 to 6500 BP) corresponds to the early impacts on vegetation of farming and Neolithic forest clearance and to the dominance of climate as a driver of vegetation change. During the second phase (from 4500 to 4000 BP), land use becomes a major control of vegetation. Climate is still the principal driver, although its influence decreases gradually. The third phase (from 2000 to 1500 BP) is characterised by the continued role of climate on vegetation as a consequence of late-Holocene climate shifts and specific climate events that influence vegetation as well as land use. The last phase (from 500 to 350 BP) shows an acceleration of vegetation changes, in particular during the last century, caused by new farming practices and forestry in response to population growth and industrialization. This is a unique signature of anthropogenic impact within the Holocene but European vegetation remains climatically sensitive and thus may continue to respond to ongoing climate change. (C) 2017 Elsevier Ltd. All rights reserved.

  • 159.
    Marquer, Laurent
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Gaillard, Marie-José
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Sugita, Shinya
    Tallinn Univ, Estonia.
    Trondman, Anna-Kari
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Mazier, Florence
    Univ Toulouse, France.
    Nielsen, Anne Birgitte
    Lund University.
    Fyfe, Ralph
    Univ Plymouth, UK.
    Vad Odgaard, B.
    Aarhus University, Denmark.
    Alenius, T.
    University of Helsinki, Finland;University of Turku, Finland.
    Birks, H.J.B.
    University of Bergen, Norway;University College London, UK;University of Oxford, UK.
    Bjune, A.E.
    University of Bergen, Norway.
    Christiansen, J.
    University of Göttingen, Germany.
    Dodson, J.
    Australian Nuclear Science and Technology Organisation, Australia.
    Edwards, K.J.
    University of Aberdeen, UK.
    Giesecke, T.
    University of Göttingen, Germany.
    Herzschuh, U.
    Universität Potsdam, Germany.
    Kangur, M.
    Tallinn University, Estonia.
    Lorenz, S.
    Ernst-Moritz-Arndt-University, Germany.
    Poska, Anneli
    Lund University.
    Schult, M.
    Ernst-Moritz-Arndt-University, Germany.
    Seppä, H.
    University of Helsinki, Finland.
    Holocene changes in vegetation composition in northern Europe: why quantitative pollen-based vegetation reconstructions matter2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, no 90, p. 199-216Article in journal (Refereed)
    Abstract [en]

    We present pollen-based reconstructions of the spatio-temporal dynamics of northern European regional vegetation abundance through the Holocene. We apply the Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model using fossil pollen records from eighteen sites within five modern biomes in the region. The eighteen sites are classified into four time-trajectory types on the basis of principal components analysis of both the REVEALS-based vegetation estimates (RVs) and the pollen percentage (PPs). The four trajectory types are more clearly separated for RVs than PPs. Further, the timing of major Holocene shifts, rates of compositional change, and diversity indices (turnover and evenness) differ between RVs and PPs. The differences are due to the reduction by REVEALS of biases in fossil pollen assemblages caused by different basin size, and inter-taxonomic differences in pollen productivity and dispersal properties. For example, in comparison to the PPs, the RVs show an earlier increase in Corylus and Ulmus in the early-Holocene and a more pronounced increase in grassland and deforested areas since the mid-Holocene. The results suggest that the influence of deforestation and agricultural activities on plant composition and abundance from Neolithic times was stronger than previously inferred from PPs. Relative to PPs, RVs show a more rapid compositional change, a largest decrease in turnover, and less variable evenness in most of northern Europe since 5200 cal yr BP. All these changes are primarily related to the strong impact of human activities on the vegetation. This study demonstrates that RV-based estimates of diversity indices, timing of shifts, and rates of change in reconstructed vegetation provide new insights into the timing and magnitude of major human distribution on Holocene regional, vegetation, feature that are critical in the assessment of human impact on vegetation, land-cover, biodiversity, and climate in the past.

  • 160.
    Muschitiello, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schwark, L.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hammarlund, D.
    New evidence of Holocene atmospheric circulation dynamics based on lake sediments from southern Sweden: a link to the Siberian High2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 77, p. 113-124Article in journal (Refereed)
    Abstract [en]

    Oxygen (delta O-18) and carbon (delta C-13) isotope records of calcitic carbonate components (Chara sp. algal encrustations and Bithynia tentaculata gastropod opercula) from a lake-sediment succession on the Baltic Sea island of Gotland, south-eastern Sweden, have been obtained to investigate regional climate dynamics during the Holocene. The hydrological sensitivity of the small lake, particularly in terms of spring snowmelt contribution to the local water budget, provides a means of tracing past changes in the influence of snow-bearing easterly winds across the Baltic Sea Proper, which signifies the wintertime strength of the Siberian High. Repeated episodic depletions in O-18 at the centennial scale correlate with events of increased potassium concentration in the GISP2 ice-core record from Greenland, which indicates a coupling to large-scale fluctuations in atmospheric circulation patterns. A corresponding correlation with simultaneous depletions in C-13 suggests repeated responses of the local lake hydrology to snow-rich winters through decreasing water residence time, perhaps augmented by methanogenesis due to prolonged ice-cover seasons under the influence of an expanding Siberian High. Frequency analysis of the isotopic records reveals well-defined fluctuations at quasi-500-520-, 670-, 830- and 1430-yr periodicities, and a gradually stronger impact of Polar air outbreaks across the southern Baltic Sea region with time after ca 6000 cal. BP.

  • 161.
    Muschitiello, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Time-transgressive environmental shifts across Northern Europe at the onset of the Younger Dryas2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 109, p. 49-56Article in journal (Refereed)
    Abstract [en]

    Until lately, it has commonly been assumed that the last major reorganization of the North Atlantic ocean-atmosphere system, the Younger Dryas climatic reversal, spread synchronously on continental to hemispheric scales. This assumption arose because reliable chronologies, which would allow capturing the complexity surrounding local responses to abrupt climate change, were lacking. To better understand the temporal structure at the inception of the Younger Dryas across the North Atlantic, we revised, updated and compared the chronological framework of four Northern European sediment sequences (Lake Krakenes, Lake Madtjarn, Lake Gammelmose, Sluggan Bog) by applying classical Bayesian modelling. We found distinct and spatially consistent age differences between the inferred ages of the Allerod interstadial - Younger Dryas stadial pollen zone boundaries among the four sites. Our results suggest an earlier vegetation response at sites along latitude 56-54 degrees N as compared to sites located at 60 -58 degrees N. We explain this time lag by a gradual regional cooling that started as early as c. 12,900 -13,100 cal. BP. This phenomenon was probably linked to cooling around the Nordic Seas as a result of enhanced iceberg calving from the Fennoscandian Ice Sheet during the final stage of the Aneroid inter-stadial. By contrast, vegetation shifts at sites located further north occurred significantly later and in concert with the establishment of full stadial climate conditions (c. 12,600-12,750 cal. BP). Our study emphasizes the need to develop solid regional C-14 chronologies and to employ the same age modelling approach to determine the temporal and spatial response to a climatic shift.

  • 162.
    Muschitiello, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sundqvist, Hanna S.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Davies, Frazer J.
    Renssen, Hans
    Arctic climate response to the termination of the African Humid Period2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 125, p. 91-97Article in journal (Refereed)
    Abstract [en]

    The Earth's climate response to the rapid vegetation collapse at the termination of the African Humid Period (AHP) (5.5-5.0 kyr BP) is still lacking a comprehensive investigation. Here we discuss the sensitivity of mid-Holocene Arctic climate to changes in albedo brought by a rapid desertification of the Sahara. By comparing a network of surface temperature reconstructions with output from a coupled global climate model, we find that, through a system of land-atmosphere feedbacks, the end of the AHP reduced the atmospheric and oceanic poleward heat transport from tropical to high northern latitudes. This entails a general weakening of the mid-latitude Westerlies, which results in a shift towards cooling over the Arctic and North Atlantic regions, and a change from positive to negative Arctic Oscillation-like conditions. This mechanism would explain the sign of rapid hydro-climatic perturbations recorded in several reconstructions from high northern latitudes at 5.5-5.0 kyr BP, suggesting that these regions are sensitive to changes in Saharan land cover during the present interglacial. This is central in the debate surrounding Arctic climate amplification and future projections for subtropical precipitation changes.

  • 163. Möller,
    Severnaya Zemlya, Arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to late Quaternary (vol 25, pg 21)2007In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 26, no 7-8, p. 1148-1191Article in journal (Refereed)
    Abstract [en]

    Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79 degrees N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences that occur at altitudes up to 140 m a.s.l. Chronologic control is provided by AMS C-14, electron-spin resonance, green-stimulated luminescence, and aspartic-acid geochronology. Major glaciations followed by deglaciation and marine inundation occurred during MIS 10-9, MIS 8-7, MIS 6-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of >2000m only 200km from the deep Arctic Ocean, consistent with published evidence of ice grounding at similar to 1000m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice did not impact Severnaya Zemlya and barely graced northernmost Taymyr Peninsula. (c) 2007 Elsevier Ltd. All rights reserved.

  • 164. Möller, P.
    et al.
    Alexanderson, H.
    Funder, S.
    Hjort, C.
    The Taimyr Peninsula and the Severnaya Zemlya archipelago, Arctic Russia: a synthesis of glacial history and palaeo-environmental change during the Last Glacial cycle (MIS 5e-2)2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 107Article in journal (Refereed)
    Abstract [en]

    We here suggest a glacial and climate history of the Taimyr Peninsula and Severnaya Zemlya archipelago in arctic Siberia for the last about 150 000 years (ka). Primarily it is based on results from seven field seasons between 1996 and 2012, to a large extent already published in papers referred to in the text and on data presented by Russian workers from the 1930s to our days and by German colleagues working there since the 1990s. Although glaciations even up here often started in the local mountains, their culminations in this region invariably seems to have centred on the shallow Kara Sea continental shelf - most likely due to expanding marine ice-shelves grounding there, as a combined effect of thickening ice and eustatically lowered sea-levels. The most extensive glaciation so far identified in this region (named the Taz glaciation) took place during Marine Isotope Stage 6 (MIS 6), i.e. being an equivalent to the late Saale/Illinoian glaciations. It reached c. 400 km southeast of the Kara Sea coast, across and well beyond the Byrranga Mountain range and ended c. 130 ka. It was followed by the MIS 5e (Karginsky/Eemian) interglacial, with an extensive marine transgression to 140 m above present sea level - facilitated by strong isostatic downloading during the preceding glaciation. During the latest (Zyryankan/Weichselian/Wisconsinan) glacial cycle followed a series of major glacial advances. The earliest and most extensive, culminating C. 110-100 ka (MIS 5d-5e), also reached south of the Byrranga mountains and its post-glacial marine limit there was c. 100 m a.s.l. The later glacial phases (around 70-60 ka and 20 ka) terminated at the North Taimyr Ice Marginal Zone (NTZ), along or some distance inland from the present northwest coast of Taimyr. They dammed glacial lakes, which caused the Taimyr River to flow southwards where to-day it flows northwards into the Kara Sea. The c. 20 ka glacial phase, contemporary with the maximum (LGM) glaciation in NW Europe, was this glacial cycle's least extensive one up here probably an effect of precipitation shadow caused by the major glaciations to the west. From the Kara Sea shelf this advance only reached c. 100 km inland, over some limited parts of NW Taimyr. The Severnaya Zemlya islands were only locally glaciated at this time. The lowlands south of the Byrranga Mountains have been a terrestrial "Mammoth steppe" environment during the last c. 50 ka and periglacial permafrosted sediments here have preserved excellent information on its megafauna and vegetation. The latter, according to new DNA-data, had considerably more (for grazing animals nourishing) flowering plants growing than earlier pollen-based (grass dominated) spectra have suggested. (C) 2014 Elsevier Ltd. All rights reserved.

  • 165. Möller, Per
    et al.
    Lubinski, D.
    Ingólfsson, Ó.
    Forman, S. L
    Siedenkrantz, M-S
    Bolshiyanov, D. Yu.
    Lokrantz, H.
    Antonov, O.
    Pavlov, ´M.
    Ljung, Karl
    Zeeberg, J. J.
    Andreev, A.
    Severnaya Zemlya, Arctic Russia: a nucleation area for Kara Sea ice sheets during the Middle to Late Quaternary2006In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 25, no 21-22, p. 2894-2936Article in journal (Refereed)
    Abstract [en]

    Quaternary glacial stratigraphy and relative sea-level changes reveal at least four expansions of the Kara Sea ice sheet over the Severnaya Zemlya Archipelago at 79 degrees N in the Russian Arctic, as indicated from tills interbedded with marine sediments, exposed in stratigraphic superposition, and from raised-beach sequences that occur at altitudes up to 140 m a.s.l. Chronologic control is provided by AMS C-14, electron-spin resonance, green-stimulated luminescence, and aspartic-acid geochronology. Major glaciations followed by deglaciation and marine inundation occurred during MIS 10-9, MIS 8-7, MIS 6-5e and MIS 5d-3. The MIS 6-5e event, associated with the high marine limit, implies ice-sheet thickness of > 2000m only 200km from the deep Arctic Ocean, consistent with published evidence of ice grounding at similar to 1000m water depth in the central Arctic Ocean. Till fabrics and glacial tectonics record repeated expansions of local ice caps exclusively, suggesting wet-based ice cap advance followed by cold-based regional ice-sheet expansion. Local ice caps over highland sites along the perimeter of the shallow Kara Sea, including the Byrranga Mountains, appear to have repeatedly fostered initiation of a large Kara Sea ice sheet, with exception of the Last Glacial Maximum (MIS 2), when Kara Sea ice did not impact Severnaya Zemlya and barely graced northernmost Taymyr Peninsula.

  • 166. Norstrom, E.
    et al.
    Neumann, F. H.
    Scott, L.
    Smittenberg, R. H.
    Holmstrand, H.
    Lundqvist, S.
    Snowball, Ian
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Natural Resources and Sustainable Development.
    Sundqvist, H. S.
    Risberg, J.
    Bamford, M.
    Late Quaternary vegetation dynamics and hydro-climate in the Drakensberg, South Africa2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 105, p. 48-65Article in journal (Refereed)
    Abstract [en]

    A multi-proxy study of a sediment sequence from Braamhoek wetland, covering the last c. 16,000 years, reveals a record of regional climate and vegetation dynamics in the Drakensberg region, South Africa, including signals from both the organic sediment fraction (fossil pollen, charcoal, n-alkane abundance, n-alkane delta C-13, TOC) and the inorganic fraction (mineral magnetic properties). The reconstruction, supported by a robust chronology, indicates two major periods of increased regional wetness during the late Pleistocene to early Holocene phase (c. 13,800-12,600 cal yr BP; c. 10,200-8500 cal yr BP) and one during the late Holocene (c. 2000 cal yr BP to present). Drier conditions are recorded during the Younger Dryas (c. 12,600-11,300 cal yr BP) and mid-Holocene (c. 7000-2000 cal yr BP). A major decline in fynbos vegetation during the early Holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern South Africa from c. 8500 cal yr BP. Comparison with records from interior of South Africa show relatively high inter-site variability, however, the Braamhoek moisture proxies do co-vary with the speleothem isotope records from Makapansgat, suggesting a similar hydro-climate evolution in eastern and interior parts of the summer rainfall region during the studied period. On multi-millennial time scales, an inverse hydro-climatological pattern is evident between these two South African records and reconstructions from tropical locations in southeast Africa. Such a rainfall dipole between eastern tropical and southern Africa, has previously been identified on shorter time scales, i.e. on inter-annual to millennial scales. The Braamhoek study suggests that a similar dipole pattern is acting also on a multi-millennial perspective. These long-term precipitation anomalies are tentatively coupled to teleconnections from multi-millennial changes in the dynamics of the Indian Ocean Dipole (IOD) and El Nino-Southern Oscillation (ENSO). 

  • 167.
    Norström, Elin
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Neumann, F. H.
    Scott, L.
    Smittenberg, Rienk
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Holmstrand, Henry
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Lundqvist, S.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Snowball, I.
    Sundqvist, Hanna
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bamford, M.
    Late Quaternary vegetation dynamics and hydro-climate in the Drakensberg, South Africa2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 105, p. 48-65Article in journal (Refereed)
    Abstract [en]

    Abstract A multi-proxy study of a sediment sequence from Braamhoek wetland, covering the last c. 16,000 years, reveals a record of regional climate and vegetation dynamics in the Drakensberg region, South Africa, including signals from both the organic sediment fraction (fossil pollen, charcoal, n-alkane abundance, n-alkane δ13C, TOC) and the inorganic fraction (mineral magnetic properties). The reconstruction, supported by a robust chronology, indicates two major periods of increased regional wetness during the late Pleistocene to early Holocene phase (c. 13,800–12,600 cal yr BP; c. 10,200–8500 cal yr BP) and one during the late Holocene (c. 2000 cal yr BP to present). Drier conditions are recorded during the Younger Dryas (c. 12,600–11,300 cal yr BP) and mid-Holocene (c. 7000–2000 cal yr BP). A major decline in fynbos vegetation during the early Holocene suggests a shift towards warmer temperatures and possibly towards less pronounced winter rains in eastern South Africa from c. 8500 cal yr BP. Comparison with records from interior of South Africa show relatively high inter-site variability, however, the Braamhoek moisture proxies do co-vary with the speleothem isotope records from Makapansgat, suggesting a similar hydro-climate evolution in eastern and interior parts of the summer rainfall region during the studied period. On multi-millennial time scales, an inverse hydro-climatological pattern is evident between these two South African records and reconstructions from tropical locations in southeast Africa. Such a rainfall dipole between eastern tropical and southern Africa, has previously been identified on shorter time scales, i.e. on inter-annual to millennial scales. The Braamhoek study suggests that a similar dipole pattern is acting also on a multi-millennial perspective. These long-term precipitation anomalies are tentatively coupled to teleconnections from multi-millennial changes in the dynamics of the Indian Ocean Dipole (IOD) and El Niño-Southern Oscillation (ENSO).

  • 168.
    O'Regan, Matt
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Glacial geological implications of overconsolidated sediments on the Lomonosov Ridge and Yermak Plateau2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3532-3544Article in journal (Refereed)
    Abstract [en]

    With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (790–950 thousand years ago – ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf.

  • 169.
    O'Regan, Matthew
    et al.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Kirchner, Nina
    Stockholm Univ, Dept Phys Geog & Quaternary Geol, S-10691 Stockholm, Sweden..
    Glacial geological implications of overconsolidated sediments on the Lomonosov Ridge and Yermak Plateau2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3532-3544Article in journal (Refereed)
    Abstract [en]

    With the coupled use of multibeam swath bathymetry, high-resolution subbottom profiling and sediment coring from icebreakers in the Arctic Ocean, there is a growing awareness of the prevalence of Quaternary ice-grounding events on many of the topographic highs found in present water depths of <1000 m. In some regions, such as the Lomonosov Ridge and Yermak Plateau, overconsolidated sediments sampled through either drilling or coring are found beneath seismically imaged unconformities of glacigenic origin. However, there exists no comprehensive analysis of the geotechnical properties of these sediments, or how their inferred stress state may be related to different glacigenic processes or types of ice-loading. Here we combine geophysical, stratigraphic and geotechnical measurements from the Lomonosov Ridge and Yermak Plateau and discuss the glacial geological implications of overconsolidated sediments. The degree of overconsolidation, determined from measurements of porosity and shear strength, is shown to result from consolidation and/or deformation below grounded ice and, with the exception of a single region on the Lomonosov Ridge, cannot be explained by erosion of overlying sediments. We demonstrate that the amount and depth of porosity loss associated with a middle Quaternary (similar to 790-950 thousand years ago - ka) grounding on the Yermak Plateau is compatible with sediment consolidation under an ice sheet or ice rise. Conversely, geotechnical properties of sediments from beneath late Quaternary ice-groundings in both regions, independently dated to Marine Isotope Stage (MIS) 6, indicate a more transient event commensurate with a passing tabular iceberg calved from an ice shelf. (C) 2010 Elsevier Ltd. All rights reserved.

  • 170. Patton, Henry
    et al.
    Hubbard, Alun
    Andreassen, Karin
    Auriac, Amandine
    Whitehouse, Pippa L.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Shackleton, Calvin
    Winsborrow, Monica
    Heyman, Jakob
    Hall, Adrian M.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Deglaciation of the Eurasian ice sheet complex2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 169, p. 148-172Article in journal (Refereed)
    Abstract [en]

    The Eurasian ice sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum with a span of over 4500 km and responsible for around 20 m of eustatic sea-level lowering. Whilst recent terrestrial and marine empirical insights have improved understanding of the chronology, pattern and rates of retreat of this vast ice sheet, a concerted attempt to model the deglaciation of the EISC honouring these new constraints is conspicuously lacking. Here, we apply a first-order, thermo-mechanical ice sheet model, validated against a diverse suite of empirical data, to investigate the retreat of the EISC after 23 ka BP, directly extending the work of Patton et al. (2016) who modelled the build-up to its maximum extent. Retreat of the ice sheet complex was highly asynchronous, reflecting contrasting regional sensitivities to climate forcing, oceanic influence, and internal dynamics. Most rapid retreat was experienced across the Barents Sea sector after 17.8 ka BP when this marine-based ice sheet disintegrated at a rate of similar to 670 gigatonnes per year (Gt a(-1)) through enhanced calving and interior dynamic thinning, driven by oceanic/atmospheric warming and exacerbated by eustatic sea-level rise. From 14.9 to 12.9 ka BP the EISC lost on average 750 Gt a(-1), peaking at rates >3000 Gt a(-1), roughly equally partitioned between surface melt and dynamic losses, and potentially contributing up to 2.5 m to global sea-level rise during Meltwater Pulse 1A. Independent glacio-isostatic modelling constrained by an extensive inventory of relative sea-level change corroborates our ice sheet loading history of the Barents Sea sector. Subglacial conditions were predominately temperate during deglaciation, with over 6000 subglacial lakes predicted along with an extensive subglacial drainage network. Moreover, the maximum EISC and its isostatic footprint had a profound impact on the proglacial hydrological network, forming the Fleuve Manche mega-catchment which had an area of similar to 2.5 x 10(6) km(2) and drained the present day Vistula, Elbe, Rhine and Thames rivers through the Seine Estuary. During the Bolling/Allerod oscillation after c. 14.6 ka BP, two major proglacial lakes formed in the Baltic and White seas, buffering meltwater pulses from eastern Fennoscandia through to the Younger Dryas when these massive proglacial freshwater lakes flooded into the North Atlantic Ocean. Deglaciation temporarily abated during the Younger Dryas stadial at 12.9 ka BP, when remnant ice across Svalbard, Franz Josef Land, Novaya Zemlya, Fennoscandia and Scotland experienced a short-lived but dynamic re-advance. The final stage of deglaciation converged on present day ice cover around the Scandes mountains and the Barents Sea by 8.7 ka BP, although the phas-lagged isostatic recovery still continues today.

  • 171. Patton, Henry
    et al.
    Hubbard, Alun
    Andreassen, Karin
    Winsborrow, Monica
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    The build-up, configuration, and dynamical sensitivity of the Eurasian ice-sheet complex to Late Weichselian climatic and oceanic forcing2016In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 153, p. 97-121Article in journal (Refereed)
    Abstract [en]

    The Eurasian ice-sheet complex (EISC) was the third largest ice mass during the Last Glacial Maximum (LGM), after the Antarctic and North American ice sheets. Despite its global significance, a comprehensive account of its evolution from independent nucleation centres to its maximum extent is conspicuously lacking. Here, a first-order, thermomechanical model, robustly constrained by empirical evidence, is used to investigate the dynamics of the EISC throughout its build-up to its maximum configuration. The ice flow model is coupled to a reference climate and applied at 10 km spatial resolution across a domain that includes the three main spreading centres of the Celtic, Fennoscandian and Barents Sea ice sheets. The model is forced with the NGRIP palaeo-isotope curve from 37 ka BP onwards and model skill is assessed against collated flowsets, marginal moraines, exposure ages and relative sea level history. The evolution of the EISC to its LGM configuration was complex and asynchronous; the western, maritime margins of the Fennoscandian and Celtic ice sheets responded rapidly and advanced across their continental shelves by 29 ka BP, yet the maximum aerial extent (5.48 x 10(6) km(2)) and volume (7.18 x 10(6) km(3)) of the ice complex was attained some 6 ka later at c. 22.7 ka BP. This maximum stand was short-lived as the North Sea and Atlantic margins were already in retreat whilst eastern margins were still advancing up until c. 20 ka BR High rates of basal erosion are modelled beneath ice streams and outlet glaciers draining the Celtic and Fennoscandian ice sheets with extensive preservation elsewhere due to frozen subglacial conditions, including much of the Barents and Kara seas. Here, and elsewhere across the Norwegian shelf and. North Sea, high pressure subglacial conditions would have promoted localised gas hydrate formation.

  • 172.
    Paus, Aage
    et al.
    Univ Bergen, Norway.
    Haflidason, Haflidi
    Univ Bergen, Norway.
    Routh, Joyanto
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Naafs, B. David A.
    Univ Bristol, England.
    Thoen, Mani W.
    Univ Bergen, Norway.
    Environmental responses to the 9.7 and 8.2 cold events at two ecotonal sites in the Dovre mountains, mid-Norway2019In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 205, p. 45-61Article in journal (Refereed)
    Abstract [en]

    We found strong signals of two cooling events around 9700 and 8200 cal yrs. BP in lakes Store Finnsjoen and Flafattjonna at Dovre, mid-Norway. Analyses included pollen in both lakes, and C/N-ratio, biomarkers (e.g. alkanes and br-GDGT5), and XRF scanning in Finnsjoen. The positions of these lakes close to ecotones (upper forest-lines of birch and pine, respectively) reduced their resilience to cold events causing vegetation regression at both sites. The global 8.2 event reflects the collapse of the Laurentide Ice Sheet. The 9.7 event with impact restricted to Scandinavia and traced by pollen at Dovre only, reflects the drainage of the Baltic Ancylus Lake. More detailed analysis in Finnsjoen shows that the events also caused increased allochtonous input (K, Ca), increased sedimentation rate, and decreased sediment density and aquatic production. br-GDGT-based temperatures indicate gradual cooling through the early Holocene. In Finnsjoen, ca. 3100 maxima-minima couplets in sediment density along the analysed sequence of ca. 3100 calibrated years show the presence of varves for the first time in Norway. Impact of the 9.7 and 8.2 events lasted ca. 60 and 370 years, respectively. Pine pollen percentages were halved and re-established in less than 60 years, indicating the reduction of pine pollen production and not vegetative growth during the 9.7 event. The local impact of the 8.2 event sensu lato (ca. 8420-8050 cal yrs. BP) divides the event into a precursor, an erosional phase, and a recovery phase. At the onset of the erosional phase, summer temperatures increased. (C) 2018 Elsevier Ltd. All rights reserved.

  • 173. Petherick, L.
    et al.
    Bostock, H.
    Cohen, T. J.
    Fitzsimmons, K.
    Tibby, J.
    Fletcher, M. -S
    Moss, P.
    Reeves, J.
    Mooney, S.
    Barrows, T.
    Kemp, J.
    Jansen, John
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Nanson, G.
    Dosseto, A.
    Climatic records over the past 30 ka from temperate Australia - a synthesis from the Oz-INTIMATE workgroup2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 74, p. 58-77Article in journal (Refereed)
    Abstract [en]

    Temperate Australia sits between the heat engine of the tropics and the cold Southern Ocean, encompassing a range of rainfall regimes and falling under the influence of different climatic drivers. Despite this heterogeneity, broad-scale trends in climatic and environmental change are evident over the past 30 ka. During the early glacial period (similar to 30-22 ka) and the Last Glacial Maximum (similar to 22-18 ka), climate was relatively cool across the entire temperate zone and there was an expansion of grasslands and increased fluvial activity in regionally important Murray Darling Basin. The temperate region at this time appears to be dominated by expanded sea ice in the Southern Ocean forcing a northerly shift in the position of the oceanic fronts and a concomitant influx of cold water along the southeast (including Tasmania) and southwest Australian coasts. The deglacial period (similar to 18-12 ka) was characterised by glacial recession and eventual disappearance resulting from an increase in temperature deduced from terrestrial records, while there is some evidence for climatic reversals (e.g. the Antarctic Cold Reversal) in high resolution marine sediment cores through this period. The high spatial density of Holocene terrestrial records reveals an overall expansion of sclerophyll woodland and rainforest taxa across the temperate region after similar to 12 ka, presumably in response to increasing temperature, while hydrological records reveal spatially heterogeneous hydro-climatic trends. Patterns after similar to 6 ka suggest higher frequency climatic variability that possibly reflects the onset of large scale climate variability caused by the El Nino/Southern Oscillation.

  • 174. Polyak, Leonid
    et al.
    Alley, Richard B.
    Andrews, John T.
    Brigham-Grette, Julie
    Cronin, Thomas M.
    Darby, Dennis A.
    Dyke, Arthur S.
    Fitzpatrick, Joan J.
    Funder, Svend
    Holland, Marika
    Jennings, Anne E.
    Miller, Gifford H.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Savelle, James
    Serreze, Mark
    St John, Kristen
    White, James W. C.
    Wolff, Eric
    History of sea ice in the Arctic2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 15-16, p. 1757-1778Article in journal (Refereed)
    Abstract [en]

    Arctic sea-ice extent and volume are declining rapidly. Several studies project that the Arctic Ocean may become seasonally ice-free by the year 2040 or even earlier. Putting this into perspective requires information on the history of Arctic sea-ice conditions through the geologic past. This information can be provided by proxy records from the Arctic Ocean floor and from the surrounding coasts. Although existing records are far from complete, they indicate that sea ice became a feature of the Arctic by 47 Ma, following a pronounced decline in atmospheric pCO(2) after the Paleocene-Eocene Thermal Optimum, and consistently covered at least part of the Arctic Ocean for no less than the last 13-14 million years. Ice was apparently most widespread during the last 2-3 million years, in accordance with Earth's overall cooler climate. Nevertheless, episodes of considerably reduced sea ice or even seasonally ice-free conditions occurred during warmer periods linked to orbital variations. The last low-ice event related to orbital forcing (high insolation) was in the early Holocene, after which the northern high latitudes cooled overall, with some superimposed shorterterm (multidecadal to millennial-scale) and lower-magnitude variability. The current reduction in Arctic ice cover started in the late 19th century, consistent with the rapidly warming climate, and became very pronounced over the last three decades. This ice loss appears to be unmatched over at least the last few thousand years and unexplainable by any of the known natural variabilities.

  • 175. Reeves, Jessica M.
    et al.
    Barrows, Timothy T.
    Cohen, Timothy J.
    Kiem, Anthony S.
    Bostock, Helen C.
    Fitzsimmons, Kathryn E.
    Jansen, John D.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kemp, Justine
    Krause, Claire
    Petherick, Lynda
    Phipps, Steven J.
    Climate variability over the last 35,000 years recorded in marine and terrestrial archives in the Australian region: an OZ-INTIMATE compilation2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 74, p. 21-34Article in journal (Refereed)
    Abstract [en]

    The Australian region spans some 600 of latitude and 500 of longitude and displays considerable regional climate variability both today and during the Late Quaternary. A synthesis of marine and terrestrial climate records, combining findings from the Southern Ocean, temperate, tropical and arid zones, identifies a complex response of climate proxies to a background of changing boundary conditions over the last 35,000 years. Climate drivers include the seasonal timing of insolation, greenhouse gas content of the atmosphere, sea level rise and ocean and atmospheric circulation changes. Our compilation finds few climatic events that could be used to construct a climate event stratigraphy for the entire region, limiting the usefulness of this approach. Instead we have taken a spatial approach, looking to discern the patterns of change across the continent. The data identify the clearest and most synchronous climatic response at the time of the Last Glacial Maximum (LGM) (21 +/- 3 ka), with unambiguous cooling recorded in the ocean, and evidence of glaciation in the highlands of tropical New Guinea, southeast Australia and Tasmania. Many terrestrial records suggest drier conditions, but with the timing of inferred snowmelt, and changes to the rainfall/runoff relationships, driving higher river discharge at the LGM. In contrast, the deglaciation is a time of considerable south-east to north-west variation across the region. Warming was underway in all regions by 17 ka. Post-glacial sea level rise and its associated regional impacts have played an important role in determining the magnitude and timing of climate response in the north-west of the continent in contrast to the southern latitudes. No evidence for cooling during the Younger Dryas chronozone is evident in the region, but the Antarctic cold reversal clearly occurs south of Australia. The Holocene period is a time of considerable climate variability associated with an intense monsoon in the tropics early in the Holocene, giving way to a weakened monsoon and an increasingly El Nino-dominated ENSO to the present. The influence of ENSO is evident throughout the southeast of Australia, but not the southwest. This climate history provides a template from which to assess the regionality of climate events across Australia and make comparisons beyond our region.

  • 176. Reeves, Jessica M.
    et al.
    Bostock, Helen C.
    Ayliffe, Linda K.
    Barrows, Timothy T.
    De Deckker, Patrick
    Devriendt, Laurent S.
    Dunbar, Gavin B.
    Drysdale, Russell N.
    Fitzsimmons, Kathryn E.
    Gagan, Michael K.
    Griffiths, Michael L.
    Haberle, Simon G.
    Jansen, John D.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Krause, Claire
    Lewis, Stephen
    McGregor, Helen V.
    Mooney, Scott D.
    Moss, Patrick
    Nanson, Gerald C.
    Purcell, Anthony
    van der Kaars, Sander
    Palaeoenvironmental change in tropical Australasia over the last 30,000 years - a synthesis by the OZ-INTIMATE group2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 74, p. 97-114Article in journal (Refereed)
    Abstract [en]

    The tropics are the major source of heat and moisture for the Australasian region. Determining the tropics' response over time to changes in climate forcing mechanisms, such as summer insolation, and the effects of relative sea level on exposed continental shelves during the Last Glacial period, is an ongoing process of re-evaluation. We present a synthesis of climate proxy data from tropical Australasia spanning the last 30,000 years that incorporates deep sea core, coral, speleothem, pollen, charcoal and terrestrial sedimentary records. Today, seasonal variability is governed largely by the annual migration of the inter-tropical convergence zone (ITCZ), influencing this region most strongly during the austral summer. However, the position of the ITCZ has varied through time. Towards the end of Marine Isotope Stage (MIS) 3, conditions were far wetter throughout the region, becoming drier first in the south. Universally cooler land and sea-surface temperature (SST) were characteristic of the Last Glacial Maximum, with drier conditions than previously, although episodic wet periods are noted in the fluvial records of northern Australia. The deglacial period saw warming first in the Coral Sea and then the Indonesian seas, with a pause in this trend around the time of the Antarctic Cold Reversal (c. 14.5 ka), coincident with the flooding of the Sunda Shelf. Wetter conditions occurred first in Indonesia around 17 ka and northern Australia after 14 ka. The early Holocene saw a peak in marine SST to the northwest and northeast of Australia. Modern vegetation was first established on Indonesia, then progressively south and eastward to NE Australia. Flores and the Atherton Tablelands show a dry period around 11.6 ka, steadily becoming wetter through the early Holocene. The mid-late Holocene was punctuated by millennial-scale variability, associated with the El Nino-Southern Oscillation; this is evident in the marine, coral, speleothem and pollen records of the region.

  • 177. Rosenberg, Thomas M.
    et al.
    Preusser, Frank
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Risberg, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Plikk, Anna
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kadi, Khalid A.
    Matter, Albert
    Fleitmann, Dominik
    Middle and Late Pleistocene humid periods recorded in palaeolake deposits of the Nafud desert, Saudi Arabia2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 70, p. 109-123Article in journal (Refereed)
    Abstract [en]

    Present climate in the Nafud desert of northern Saudi Arabia is hyper-arid and moisture brought by north-westerly winds scarcely reaches the region. The existence of abundant palaeolake sediments provides evidence for a considerably wetter climate in the past. However, the existing chronological framework of these deposits is solely based on radiocarbon dating of questionable reliability, due to potential post-depositional contamination with younger C-14. By using luminescence dating, we show that the lake deposits were not formed between 40 and 20 ka as suggested previously, but approximately ca 410 ka, 320 ka, 200 ka, 125 ka, and 100 ka ago. All of these humid phases are in good agreement with those recorded in lake sediments and speleothems from southern Arabia. Surprisingly, no Holocene lake deposits were identified. Geological characteristics of the deposits and diatom analysis suggest that a single, perennial lake covered the entire south-western Nafud ca 320 ka ago. In contrast, lakes of the 200 ka, 125 ka, and 100 ka humid intervals were smaller and restricted to interdune depressions of a preexisting dune relief. The concurrent occurrence of humid phases in the Nafud, southern Arabia and the eastern Mediterranean suggests that moisture in northern Arabia originated either from the Mediterranean due to more frequent frontal depression systems or from stronger Indian monsoon circulation, respectively. However, based on previously published climate model simulations and palaecolimate evidence from central Arabia and the Negev desert, we argue that humid climate conditions in the Nafud were probably caused by a stronger African monsoon and a distinct change in zonal atmospheric circulation.

  • 178.
    Rosqvist, G.
    et al.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Jonsson, C.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Yam, R.
    Karlén, W.
    Stockholms universitet, Institutionen för naturgeografi och kvartärgeologi (INK).
    Shemesh, A.
    Diatom oxygen isotopes in pro-galcial lake sediments from northern Sweden: A 5000 year record of atmospheric circulation.2004In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, no 7-8, p. 851-859Article in journal (Refereed)
    Abstract [en]

    We use a pro-glacial oxygen isotope record of diatom silica (δ18Odiatom) and a sedimentary proxy for glacier flutuations to determine centennial-millennial scale climate change during the last 5000 yeras in northern Sweden. We show that the lake water isotopic composition åredominantly reflects the isotopic composition of the precipitation. Superimposed on a general depletion trend of 3.5‰ over the past 5000 years we found that the isotopic composition of precipitation became depleted (> 1‰ excursions) during four occasions centered at 4400, 3000, 2000 and, after 1200 cal yr BP. Climate simultaneously sustained a positive glacier mass balance, taht caused the catchment glacier to advance. A peristan cgange in the atmopheric circulation pattern could potentially have caused the registered chnages in the δ18Odiatom because different air masses hold characteristics δ18O signatures of their precipitation. The glacier mass balance primarily responds to the influence of summer temperature on ablation. We suggest that the most likely cause for the recorded chnages in both these proxies is a steadily increasing but fluctuating dominance of colder and δ18O depleted air masses from the north/northeast during the past 5000 years. Theδ18Odiatom depletion and glacier events all occur at times of relative ice-rafted-debris maxima in the North Atlanic, consistent with cold conditions and changes in surface wind directions. Our results confirm that changes towards a predominace of north/northeasterly winds occured at these time intervals.

  • 179.
    Rosqvist, G.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jonsson, C.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Yam, R.
    Karlén, W.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Shemesh, A.
    Diatom oxygen isotopes in pro-galcial lake sediments from northern Sweden: A 5000 year record of atmospheric circulation.2004In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, no 7-8, p. 851-859Article in journal (Refereed)
    Abstract [en]

    We use a pro-glacial oxygen isotope record of diatom silica (δ18Odiatom) and a sedimentary proxy for glacier flutuations to determine centennial-millennial scale climate change during the last 5000 yeras in northern Sweden. We show that the lake water isotopic composition åredominantly reflects the isotopic composition of the precipitation. Superimposed on a general depletion trend of 3.5‰ over the past 5000 years we found that the isotopic composition of precipitation became depleted (> 1‰ excursions) during four occasions centered at 4400, 3000, 2000 and, after 1200 cal yr BP. Climate simultaneously sustained a positive glacier mass balance, taht caused the catchment glacier to advance. A peristan cgange in the atmopheric circulation pattern could potentially have caused the registered chnages in the δ18Odiatom because different air masses hold characteristics δ18O signatures of their precipitation. The glacier mass balance primarily responds to the influence of summer temperature on ablation. We suggest that the most likely cause for the recorded chnages in both these proxies is a steadily increasing but fluctuating dominance of colder and δ18O depleted air masses from the north/northeast during the past 5000 years. Theδ18Odiatom depletion and glacier events all occur at times of relative ice-rafted-debris maxima in the North Atlanic, consistent with cold conditions and changes in surface wind directions. Our results confirm that changes towards a predominace of north/northeasterly winds occured at these time intervals.

  • 180. Rosqvist, Gunhild C
    et al.
    Leng, Melanie J.
    Goslar, Tomasz
    Sloane, Hilary J.
    Bigler, Christian
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Cunningham, Laura
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dadal, Anna
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bergman, Jonas
    Berntsson, Annika
    Jonsson, Christina
    Wastegard, Stefan
    Shifts in precipitation during the last millennium in northern Scandinavia from lacustrine isotope records2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 66, p. 22-34Article in journal (Refereed)
    Abstract [en]

    Here we present delta P-18(diatom) data from two high-latitude lakes; one has short residence time and a water isotopic composition (delta O-18(lake)) that fluctuate due to seasonal variations in precipitation and temperature, and the other has delta O-18(lake) that is influenced by longer lake water residence times and evaporation. The delta O-18(diatom) records reveal common responses to precipitation forcing over the past millennium. Relatively wet summers are inferred from delta O-18(diatom) between 1000 and 1080 AD, 1300 and 1440 AD, and during the early 19th century, coincided with periods of high cloud cover inferred from tree-ring carbon isotopes, and other data for high Arctic Oscillation index. While relatively dry summers with increasing influence of winter snow are indicated between 1600 and 1750 AD. The co-response between carbon isotopes in trees and oxygen isotopes in diatoms strengthens the relationship between cloud cover and precipitation and the hypothesis that these changes were the result of significant regional shifts in atmospheric circulation. (C) 2012 Elsevier Ltd. All rights reserved.

  • 181.
    Rosqvist, Gunhild C.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Leng, Melanie J.
    Goslar, Tomasz
    Sloane, Hilary J.
    Bigler, Christian
    Cunningham, Laura
    Dadal, Anna
    Bergman, Jonas
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Berntsson, Annika
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jonsson, Christina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Wastegård, Stefan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Shifts in precipitation during the last millennium in northern Scandinavia from lacustrine isotope records2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 66, p. 22-34Article in journal (Refereed)
    Abstract [en]

    Here we present delta P-18(diatom) data from two high-latitude lakes; one has short residence time and a water isotopic composition (delta O-18(lake)) that fluctuate due to seasonal variations in precipitation and temperature, and the other has delta O-18(lake) that is influenced by longer lake water residence times and evaporation. The delta O-18(diatom) records reveal common responses to precipitation forcing over the past millennium. Relatively wet summers are inferred from delta O-18(diatom) between 1000 and 1080 AD, 1300 and 1440 AD, and during the early 19th century, coincided with periods of high cloud cover inferred from tree-ring carbon isotopes, and other data for high Arctic Oscillation index. While relatively dry summers with increasing influence of winter snow are indicated between 1600 and 1750 AD. The co-response between carbon isotopes in trees and oxygen isotopes in diatoms strengthens the relationship between cloud cover and precipitation and the hypothesis that these changes were the result of significant regional shifts in atmospheric circulation.

  • 182. Rousseau, Denis-Didier
    et al.
    Boers, Niklas
    Sima, Adriana
    Svensson, Anders
    Bigler, Matthias
    Lagroix, France
    Taylor, Samuel
    Antoine, Pierre
    (MIS3 & 2) millennial oscillations in Greenland dust and Eurasian aeolian records - A paleosol perspective2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 169, p. 99-113Article in journal (Refereed)
    Abstract [en]

    Since their discovery, the abrupt climate changes that punctuated the last glacial period (similar to 110.6-14.62 ka) have attracted considerable attention. Originating in the North-Atlantic area, these abrupt changes have been recorded in ice, marine and terrestrial records all over the world, but especially in the Northern Hemisphere, with various environmental implications. Ice-core records of unprecedented temporal resolution from northern Greenland allow to specify the timing of these abrupt changes, which are associated with sudden temperature increases in Greenland over a few decades, very precisely. The continental records have, so far, been mainly interpreted in terms of temperature, precipitation or vegetation changes between the relatively warm “Greenland Interstadials” (GI) and the cooler “Greenland Stadials” (GS). Here we compare records from Greenland ice and northwestern European eolian deposits in order to establish a link between GI and the soil development in European mid latitudes, as recorded in loess sequences. For the different types of observed paleosols, we use the correlation with the Greenland records to propose estimates of the maximum time lapses needed to achieve the different degrees of maturation and development. To identify these time lapses more precisely, we compare two independent ice-core records: 6180 and dust concentration, indicating variations of atmospheric temperature and dustiness in the Greenland area, respectively. Our method slightly differs from the definition of a GI event duration applied in other studies, where the sharp end of the 8180 decrease alone defines the end of a Gl. We apply the same methodology to both records (i.e., the GIs are defined to last from the beginning of the abrupt 6180 increase or dust concentration decrease until the time when 6180 or dust recur to their initial value before the GI onset), determined both visually and algorithmically, and compare them to published estimates of GI timing and duration. The duration of the GI and consequently the maximum time for paleosol development varies between 200 and 4200 years when visually determined and between 200 and 4800 years when estimated algorithmically for GI 17 to 2, i.e. an interval running from 60 ka to 23 ka b2k (age before 2000 AD). Furthermore, we investigate the abruptness of the transition from stadial to interstadial conditions, which initiates the paleosol development. The average transition duration is 55.4 +/- 16.1 (56.8 +/- 19.6) years when determined visually, and 36.4 +/- 13.4 (60.00 +/- 21.2) years when determined algorithmically for the delta O-18 (dust concentration). The 6180 increases correspond to a mean temperature difference of 11.8 degrees C on the top of the Greenland ice sheet, associated with substantial reorganizations of the ecosystems in mid-latitude Europe. (C) 2017 Elsevier Ltd. All rights reserved.

  • 183.
    Ruskeeniemi, Timo
    et al.
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Engstrom, Jon
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Lehtimaki, Jukka
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Vanhala, Heikki
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Korhonen, Kimmo
    Geol Survey Finland, FI-02150 Espoo, Finland.
    Kontula, Anne
    Posiva Oy, FI-27160 Eurajoki, Finland.
    Liljedahl, Lillemor Claesson
    Swedish Nucl Fuel & Waste Management Co, Box 3091, SE-16903 Solna, Sweden.
    Naslund, Jens-Ove
    Swedish Nucl Fuel & Waste Management Co, Box 3091, SE-16903 Solna, Sweden.
    Pettersson, Rickard
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala Univ, Dept Earth Sci, SE-75236 Uppsala, Sweden.
    Subglacial permafrost evidencing re-advance of the Greenland Ice Sheet over frozen ground2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 199, p. 174-187Article in journal (Refereed)
    Abstract [en]

    Greenland Ice Sheet (GrIS) covers an area of 1.7 million km(2). It has been an important source of climate information and the air temperature history of Greenland is well known. However, the thermal history and temperature conditions of the Greenland bedrock are poorly known. There are only few records on the temperature of the proglacial bedrock and no records on bedrock temperature underneath the ice sheet. The Greenland Analogue Project (GAP) recently investigated hydrological, hydrogeological and geochemical processes in Kangerlussuaq, West Greenland. Because permafrost has a major hydrological impact in Arctic regions, the cryogenic structure of the bedrock was an important research topic. From previous studies it was already known that Kangerlussuaq is located within the zone of continuous permafrost. Temperature profiling in a new research borehole, extending horizontally 30 m underneath the ice sheet, revealed that permafrost is 350 m deep at the ice margin. This result raised the question how far the permafrost extends under the ice sheet? In order to investigate the thermal properties, we made a series of electromagnetic (EM) soundings at the ice margin area - on proglacial area and on the ice sheet - and detected, that subglacial permafrost extends at least 2 km from the ice margin to inland. We also observed a patchy unfrozen sediment layer between the ice and the frozen bedrock. Possible existence of subglacial sediments and their role in ice dynamics has been debated in many recent papers. Our successful campaign shows that geophysics can be used for bedrock investigations through thick ice, which is known to be challenging for electromagnetic methods. Our results provide the first direct evidence supporting the proposed Holocene ice re-advance over frozen ground, and contribute to the discussion on the rapid climate changes in past, to the future of the ice sheet under warming climate and hydrogeology at the ice margin.

  • 184. Schollaen, Karina
    et al.
    Heinrich, Ingo
    Neuwirth, Burkhard
    Krusic, Paul J.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    D'Arrigo, Rosanne D.
    Karyanto, Oka
    Helle, Gerhard
    Multiple tree-ring chronologies (ring width, delta C-13 and delta O-18) reveal dry and rainy season signals of rainfall in Indonesia2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 73, p. 170-181Article in journal (Refereed)
    Abstract [en]

    Climatic hazards, such as severe droughts and floods, affect extensive areas across monsoon Asia and can have profound impacts on the populations of that region. The area surrounding Indonesia, including large portions of the eastern Indian Ocean and Java Sea, plays a key role in the global climate system because of the enormous heat and moisture exchange that occurs between the ocean and atmosphere there. Here, we evaluate the influence of rainfall variability on multiple tree-ring parameters of teak (Tectona grandis) trees growing in a lowland rain forest in Central Java (Indonesia). We assess the potential of, annually resolved, tree-ring width, stable carbon (delta C-13) and oxygen (delta O-18) isotope records to improve our understanding of the Asian monsoon variability. Climate response analysis with regional, monthly rainfall data reveals that all three tree-ring parameters are significantly correlated to rainfall, albeit during different monsoon seasons. Precipitation in the beginning of the rainy season (Sep-Nov) is important for tree-ring width, confirming previous studies. Compared to ring width, the stable isotope records possess a higher degree of common signal, especially during portions of the peak rainy season (delta C-13: Dec-May; delta O-18: Nov-Feb) and are negatively correlated to rainfall. In addition, tree-ring delta O-18 also responds positively to peak dry season rainfall, although the delta O-13 rainy season signal is stronger and more time-stable. The correlations of opposite sign reflect the distinct seasonal contrast of the delta O-18 signatures in rainfall (O-18(Pre)) during the dry (O-18-enriched rain) and rainy (O-18-depleted rain) seasons. This difference in O-18(Pre) signal reflects the combination of two signals in the annual tree-ring delta O-18 record. Highly resolved intra-annual 8180 isotope analyses suggest that the signals of dry and rainy season can be distinguished clearly. Thereby reconstructions can improve our understanding of variations and trends of the hydrological cycle over the Indonesian archipelago.

  • 185. Schwalb, Antje
    et al.
    Dean, Walter
    Güde, Hans
    Hanisch, Sabine
    Sobek, Sebastian
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.
    Wessels, Martin
    Benthic ostracode ∂13C as sensor for early Holocene establishment of modern circulation patterns in Central Europe2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 66, no SI, p. 112-122Article in journal (Refereed)
    Abstract [en]

    Shells from adult specimen of the benthic ostracodes Limnocytherina sanctipatricii and Leucocythere mirabilis selected from a 8.7 m long piston core provide continuous stable oxygen and carbon records for the past approximately 16 ka. Oxygen isotopes from both species show identical values and track the general North Atlantic and European temperature history since deglaciation in great detail. Values of ostracode δ18O values suggest that about 16 cal ka the average annual air temperatures were about 11 °C colder than today. Carbon isotopic values from both species of ostracodes are similar during the Lateglacial and early Holocene, and show an overall decrease from −4‰ to −7‰ that is probably related to an increase in photosynthetic productivity in the water column, as suggested by an increase in organic carbon, delivering 13C-depleted organic matter to the bottom waters (carbon pump). About 9 cal ka only L. mirabilis δ13C values decreased about −2.5‰ within 300 years. Higher δ13C variability and ecological evidence suggests that L. mirabilis represents a summer signal, whereas L. sanctipatricii displays a more subdued annual average. After about 7 cal ka another −1.5% decrease for both species, accompanied by an increase in magnetic susceptibility, a decrease in carbonate content, and more positive bulk carbonate isotope values followed, suggesting higher detrital-clastic input into the lake. In order to provide a possible mechanism explaining the negative L. mirabilis δ13C-values, sediment pore water profiles of O2 and CH4 in short cores collected from sites distal to proximal to the Alpine Rhine River delta, were inspected. Sediments in cores from more proximal sites to the Rhine delta become anoxic at shallower sediment depth due to the decay of high allochthonous organic carbon input to the sediment, which greatly increases concentrations of methane in pore waters closer to the Rhine inflow. When methane is oxidized close to the sediment–water-interface, 13C-depleted carbon is added to pore water DIC that is then available for incorporation into ostracode shells. This mechanism suggests that about 9 cal ka the oxygen supply to the bottom waters, especially in summer, decreased. This stimulated methanogenesis close to the sediment–water-interface, and provided δ13C-depleted carbon to benthic dwellers. Independent evidence for methanogenesis is provided by the increase in concentration of tetrahymanol after about 9 cal ka coincident with the decrease in δ13C of L. mirabilis. We suggest that about 9 cal ka the northward retreat of the Northern Hemisphere Ice Sheets, and consequently the polar front, left the alpine region affected by a more oceanic climate, characterized by warmer winters as they occur today especially during the positive North Atlantic Oscillation Index phase. More frequently incomplete mixing of the water column may have shifted the decay of organic matter faster to anaerobic conditions in surficial sediments especially during summer. By about 7 cal ka the North Atlantic region had probably warmed sufficiently to increase precipitation in Central Europe and consequently detrital-clastic runoff to Lake Constance.

  • 186. Scott, L.
    et al.
    Neumann, F. H.
    Brook, G. A.
    Bousman, C. B.
    Norström, Elin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Metwally, A. A.
    Terrestrial fossil-pollen evidence of climate change during the last 26 thousand years in Southern Africa2012In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 32, p. 100-118Article in journal (Refereed)
    Abstract [en]

    In order to define criteria for long-term climate change models in Southern Africa, an overview of the available pollen data during the Late Quaternary is needed. Here we reassess the paleo-climatic conditions in southern Africa by synthesising available fossil pollen data that can provide new insights in environmental change processes. The data considered here include the latest as well as previously published information that has been difficult to assess. Available calibrated pollen sequences spanning the Late Pleistocene and Holocene were subjected to Principal Components Analysis (PCA) to monitor taxa sensitive to moisture and temperature fluctuations. The PCA values are presented graphically as indicators of climate variability for the region. The results cover different biomes that include the summer-rain region in the north and east, the winter-rain area in the south and the dry zone in the west. The PCA plots directly reflect major changes of terrestrial environments due to variations in temperature and moisture. Mostly sub-humid but fluctuating conditions are indicated during the cold Marine Isotope Stage (MIS) 2, which were followed by a dry phase soon after the beginning of the Holocene but before the middle Holocene in the northern, central and eastern parts of the sub-continent. Marked but non-parallel moisture changes occurred in different subregions during the Holocene suggesting that climatic forcing was not uniform over the entire region. Some events seemed to have had a more uniform effect over the sub-continent, e.g., a relatively dry summer rain event at c. two thousand years ago, which can possibly be related to the ENSO phenomenon. The role of anthropogenic activities in some of the most recent vegetation shifts is likely.

  • 187. Sellen, E.
    et al.
    O’Regan, M.
    Jakobsson, M.
    Spatial and temporal Arctic Ocean depositional regimes: a key to the evolution of ice drift and current patterns2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, SI, p. 3644-3664Article in journal (Refereed)
    Abstract [en]

    Sediment physical properties measured in cores from all the major ridges and plateaus in the central Arctic Ocean were studied in order to analyze the spatial and temporal consistency of sediment depositional regimes during the Quaternary. In total, six physiographically distinct areas are outlined. In five of these, cores can be correlated over large distances through characteristic patterns in sediment physical properties. These areas are (1) the southern Mendeleev Ridge, (2) the northern Mendeleev Ridge and Alpha Ridge, (3) the Lomonosov Ridge, (4) the Morris Jesup Rise and (5) the Yermak Plateau. Averaged downhole patterns in magnetic susceptibility, bulk density and lithostratigraphy were compiled to establish a composite stratigraphy for each area. In the sixth physiographic area, the Chukchi Borderland, repeated ice-grounding during recent glacial periods complicates the stratigraphy and prevents the compilation of a composite stratigraphy using the studied material. By utilizing published age models for the studied cores we are able to show that the northern Mendeleev Ridge and Alpha Ridge have the lowest average late Quaternary sedimentation rates, while intermediate sedimentation rates prevail on the southern Mendeleev Ridge and the Morris Jesup Rise. The second highest sedimentation rate is observed on the Lomonosov Ridge, whereas the average sedimentation rate on the Yermak Plateau is more than twice as high. The close correlation of physical properties within each area suggests uniform variations in sediment transport through time, at least throughout the later part of the Quaternary. The unique stratigraphic characteristics within each area is the product of similar past depositional regimes and are key for furthering our understanding of the evolution of ice drift and current patterns in the central Arctic Ocean. (C) 2010 Elsevier Ltd. All rights reserved.

  • 188.
    Sellén, Emma
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    O'Regan, Matthew
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Spatial and temporal ArcticOcean depositional regimes: a key to the evolution of ice and current patterns2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 25-26, p. 3644-3664Article in journal (Refereed)
    Abstract [en]

    Sediment physical properties measured in cores from all the major ridges and plateaus in the central Arctic Ocean were studied in order to analyze the spatial and temporal consistency of sediment depositional regimes during the Quaternary. In total, six physiographically distinct areas are outlined. In five of these, cores can be correlated over large distances through characteristic patterns in sediment physical properties. These areas are (1) the southern Mendeleev Ridge, (2) the northern Mendeleev Ridge and Alpha Ridge, (3) the Lomonosov Ridge, (4) the Morris Jesup Rise and (5) the Yermak Plateau. Averaged downhole patterns in magnetic susceptibility, bulk density and lithostratigraphy were compiled to establish a composite stratigraphy for each area. In the sixth physiographic area, the Chukchi Borderland, repeated ice-grounding during recent glacial periods complicates the stratigraphy and prevents the compilation of a composite stratigraphy using the studied material. By utilizing published age models for the studied cores we are able to show that the northern Mendeleev Ridge and Alpha Ridge have the lowest average late Quaternary sedimentation rates, while intermediate sedimentation rates prevail on the southern Mendeleev Ridge and the Morris Jesup Rise. The second highest sedimentation rate is observed on the Lomonosov Ridge, whereas the average sedimentation rate on the Yermak Plateau is more than twice as high. The close correlation of physical properties within each area suggests uniform variations in sediment transport through time, at least throughout the later part of the Quaternary. The unique stratigraphic characteristics within each area is the product of similar past depositional regimes and are key for furthering our understanding of the evolution of ice drift and current patterns in the central Arctic Ocean.

  • 189. Shackleton, Calvin
    et al.
    Patton, Henry
    Hubbard, Alun
    Winsborrow, Monica
    Kingslake, Jonathan
    Esteves, Mariana
    Andreassen, Karin
    Greenwood, Sarah L.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Subglacial water storage and drainage beneath the Fennoscandian and Barents Sea ice sheets2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 201, p. 13-28Article in journal (Refereed)
    Abstract [en]

    Subglacial hydrology modulates how ice sheets flow, respond to climate, and deliver meltwater, sediment and nutrients to proglacial and marine environments. Here, we investigate the development of subglacial lakes and drainage networks beneath the Fennoscandian and Barents Sea ice sheets over the Late Weichselian. Utilizing an established coupled climate/ice flow model, we calculate high-resolution, spatio-temporal changes in subglacial hydraulic potential from ice sheet build-up (similar to 37 ka BP) to complete deglaciation (similar to 10 ka BP). Our analysis predicts up to 3500 potential subglacial lakes, the largest of which was 658 km(2), and over 70% of which had surface areas <10 km(2), comparable with subglacial lake size distributions beneath the Antarctic Ice Sheet. Asynchronous evolution of the Fennoscandian Ice Sheet into the flatter relief of northeast Europe affected patterns of subglacial drainage, with up to 100 km(3) more water impounded within subglacial lakes during ice build-up compared to retreat. Furthermore, we observe frequent fill/drain cycles within clusters of subglacial lakes at the onset zones and margins of ice streams that would have affected their dynamics. Our results resonate with mapping of large subglacial channel networks indicative of high-discharge meltwater drainage through the Gulf of Bothnia and central Barents Sea. By tracking the migration of meltwater drainage outlets during deglaciation, we constrain locations most susceptible to focussed discharge, including the western continental shelf-break where subglacial sediment delivery led to the development of major trough mouth fans. Maps of hydraulic potential minima that persist throughout the Late Weichselian reveal potential sites for preserved subglacial lake sediments, thereby defining useful targets for further field investigation.

  • 190. Sime, Louise C.
    et al.
    Kohfeld, Karen E.
    Le Quere, Corinne
    Wolff, Eric W.
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Graham, Robert M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Bopp, Laurent
    Southern Hemisphere westerly wind changes during the Last Glacial Maximum: model-data comparison2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 64, p. 104-120Article in journal (Refereed)
    Abstract [en]

    The Southern Hemisphere (SH) westerly winds are thought to be critical to global ocean circulation, productivity, and carbon storage. For example, an equatorward shift in the winds, though its affect on the Southern Ocean circulation, has been suggested as the leading cause for the reduction in atmospheric CO2 during the Last Glacial period. Despite the importance of the winds, it is currently not clear, from observations or model results, how they behave during the Last Glacial. Here, an atmospheric modelling study is performed to help determine likely changes in the SH westerly winds during the Last Glacial Maximum (LGM). Using LGM boundary conditions, the maximum in SH westerlies is strengthened by similar to+1 m s(-1) and moved southward by similar to 2 degrees at the 850 hPa pressure level. Boundary layer stabilisation effects over equatorward extended LGM sea-ice can lead to a small apparent equatorward shift in the wind band at the surface. Further sensitivity analysis with individual boundary condition changes indicate that changes in sea surface temperatures are the strongest factor behind the wind change. The HadAM3 atmospheric simulations, along with published PMIP2 coupled climate model simulations, are then assessed against the newly synthesised database of moisture observations for the LGM. Although the moisture data is the most commonly cited evidence in support of a large equatorward shift in the SH winds during the LGM, none of the models that produce realistic LGM precipitation changes show such a large equatorward shift. In fact, the model which best simulates the moisture proxy data is the HadAM3 LGM simulation which shows a small poleward wind shift. While we cannot prove here that a large equatorward shift would not be able to reproduce the moisture data as well, we show that the moisture proxies do not provide an observational evidence base for it.

  • 191.
    Sparrenbom, Charlotte J.
    et al.
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Bennike, Ole
    Geol Survey Denmark & Greenland, DK-1350 Copenhagen, Denmark..
    Fredh, Daniel
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Randsalu-Wendrup, Linda
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Zwartz, Dan
    Victoria Univ Wellington, Antarctic Res Ctr, Wellington 6140, New Zealand..
    Ljung, Karl
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Björck, Svante
    Lund Univ, Dept Geol, SE-22362 Lund, Sweden..
    Lambeck, Kurt
    Australian Natl Univ, Res Sch Earth Sci, Canberra, ACT 0200, Australia..
    Holocene relative sea-level changes in the inner Bredefjord area, southern Greenland2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 69, p. 107-124Article in journal (Refereed)
    Abstract [en]

    In this paper we present new relative sea-level data from southern Greenland, a key area for understanding the Greenland Ice Sheet (GIS) response to climate change. Within fourteen lakes and marine lagoons from the inner part of Bredefjord (Nordre Sermilik) in southern Greenland, isolations revealed by stratigraphic and palaeoecological analyses are dated and relative sea levels reconstructed. Due to coastal emergence caused by the GIS retreat within the area, the relative sea-level fell rapidly in the early Holocene between at least c. 9600 and c. 7300 cal. yrs BP attaining a rate of 2 cm per year between 9600 and 8000 cal. yrs BP. Spatial variability in relative sea-level changes is show for southern Greenland from a comparison with the Nanortalik and the Qagortoq areas. The regression occurred about 2000 years later in the inner Bredefjord area, compared to the Nanortalik area, and about 1000 years later compared to the Qaqortoq area. This is a consequence of earlier deglaciation in areas located at the outer coast. Between c. 8000 cal. yrs BP and the present day, relative sea level was lower than today. The lowest relative sea level in the Inner Bredefjord area of between -5.4 and -15 m a.h.a.t. (above highest astronomical tide) was reached between 7000 and 1000 cal. yrs BP. The neoglacial readvance together with the collapse of the Laurentide peripheral bulge is probably responsible for the transgression in the Inner Bredefjord area, as has been indicated from the nearby sites Qagortoq and Nanortalik. Our relative sea-level reconstructions showing spatial variability within southern Greenland have implications for Glacial Isostatic Adjustment (GIA) modelling and the understanding of the GIS ice sheet dynamics. The early Holocene regression is consistent with the recession of the southern sector of the GIS from the shelf edge at c. 22 000 cal. yrs BP, reaching inland of the present day outer coast by c. 12 000 cal. yrs BP, and its present margin by c. 10 500 cal. yrs BP. (c) 2013 Elsevier Ltd. All rights reserved.

  • 192. Statham, Mark J.
    et al.
    Edwards, Ceridwen J.
    Norén, Karin
    Stockholm University, Faculty of Science, Department of Zoology.
    Soulsbury, Carl D.
    Sacks, Benjamin N.
    Genetic analysis of European red foxes reveals multiple distinct peripheral populations and central continental admixture2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 197, p. 257-266Article in journal (Refereed)
    Abstract [en]

    Temperate terrestrial species in Europe were hypothesized to have been restricted to southern peninsular refugia (Iberia, Italy, Balkans) during the height of the last glacial period. However, recent analyses of fossil evidence indicate that some temperate species existed outside these areas during the last glacial maximum (LGM). Red foxes (Vulpes vulpes) in particular, could have been distributed across the southern half of the continent, potentially forming one continuous population. To investigate these hypotheses, we used 21 nuclear microsatellite loci and two fragments (768 bp) of mitochondrial DNA to characterize the population structure among a continent-wide sample of 288 European red foxes. We tested whether European red foxes clustered into discrete populations corresponding to the hypothetical peninsular refugia. Additionally, we sought to determine if distinct northern populations were formed after post-glacial recolonization. Our results indicated that only the foxes of Iberia appeared to have remained distinct over a considerable period of time (32–104 kya). Spanish red foxes formed their own genotypic cluster; all mtDNA haplotypes were endemic and closely related, and together both the mitochondrial and nuclear datasets indicated this population contributed little to postglacial recolonization of Northern Europe. In contrast, red foxes from Italy and the Balkans contributed significantly to, or were part of, a wider, admixed population stretching across mid-latitude Europe. In Northern Europe, we identified a Scandinavian population that had an ancestral relationship with red foxes to the south, and a more recent relationship with those to the east, in Russia. We also resolved two distinct populations on the islands of Ireland and Britain that had been separated from one another, and from those on the continent, since the late Pleistocene/mid Holocene (∼4–24 kya).

  • 193.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Oliver, Kevin I. C.
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Reimer, Paula J.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Synchronous records of pCO(2) and Delta C-14 suggest rapid, ocean-derived pCO(2) fluctuations at the onset of Younger Dryas2014In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 99, p. 84-96Article in journal (Refereed)
    Abstract [en]

    Just before the onset of the Younger Dryas (YD) cold event, several stomatal proxy-based pCO(2) records have shown a sharp increase in atmospheric CO2 concentration (pCO(2)) of between ca 50 and 100 ppm, followed by a rapid decrease of similar or even larger magnitude. Here we compare one of these records, a high-resolution pCO(2) record from southern Sweden, with the IntCal13 record of radiocarbon (Delta C-14). The two records show broadly synchronous fluctuations at the YD onset. Specifically, the IntCal13 record documents decreasing Delta C-14 just before the YD onset when pCO(2) peaks, consistent with a source of old CO2 from the deep ocean. We propose that this fluctuation occurred due to a major ocean flushing event. The cause of the flushing event remains speculative but could be related to the hypothesis of the glacial ocean as a thermobaric capacitor. We confirm that the earth system can produce such large multi-decadal timescale fluctuations in pCO(2) through simulating an artificial ocean flushing event with the GENIE Earth System Model. We suggest that sharp transitions of pCO(2) may have remained undetected so far in ice cores due to inter-firn gas exchange and time-averaging. The stomatal proxy record is a powerful complement to the ice core records for the study of rapid climate change.

  • 194.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    de Boer, Agatha M.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Oliver, Kevin I. C.
    Muschitiello, Francesco
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Response to: Comment on Synchronous records of pCO(2) and Delta C-14 suggest rapid, ocean-derived pCO(2) fluctuations at the onset of Younger Dryas (Steinthorsdottir et al., 2014, Quaternary Science Reviews 99, 84-96)2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 107, p. 270-273Article in journal (Refereed)
  • 195.
    Steinthorsdottir, Margret
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kylander, Malin E.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Blaauw, Maarten
    Reimer, Paula J.
    Stomatal proxy record of CO2 concentrations from the last termination suggests an important role for CO2 at climate change transitions2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 68, p. 43-58Article in journal (Refereed)
    Abstract [en]

    A new stomatal proxy-based record of CO2 concentrations ([CO2]), based on Betula nana (dwarf birch) leaves from the Hasseldala Port sedimentary sequence in south-eastern Sweden, is presented. The record is of high chronological resolution and spans most of Greenland Interstadial 1 (GI-1a to 1c, Allerod pollen zone), Greenland Stadial 1 (GS-1, Younger Dryas pollen zone) and the very beginning of the Holocene (Preboreal pollen zone). The record clearly demonstrates that i) [CO2] were significantly higher than usually reported for the Last Termination and ii) the overall pattern of CO2 evolution through the studied time period is fairly dynamic, with significant abrupt fluctuations in [CO2] when the climate moved from interstadial to stadial state and vice versa. A new loss-on-ignition chemical record (used here as a proxy for temperature) lends independent support to the Hasseldala Port [CO2] record. The large-amplitude fluctuations around the climate change transitions may indicate unstable climates and that tipping-point situations were involved in Last Termination climate evolution. The scenario presented here is in contrast to [CO2] records reconstructed from air bubbles trapped in ice, which indicate lower concentrations and a gradual, linear increase of [CO2] through time. The prevalent explanation for the main climate forcer during the Last Termination being ocean circulation patterns needs to re-examined, and a larger role for atmospheric [CO2] considered.

  • 196. Stevens, T.
    et al.
    Carter, A.
    Watson, T. P.
    Vermeesch, P.
    Ando, S.
    Bird, A. F.
    Lu, H.
    Garzanti, E.
    Cottam, M. A.
    Sevastjanova, I.
    Genetic linkage between the Yellow River, the Mu Us desert and the Chinese Loess Plateau2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 78, p. 355-368Article in journal (Refereed)
  • 197.
    Stevens, Thomas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Adamiec, Grzegorz
    Bird, Anna F.
    Lu, Huayu
    An abrupt shift in dust source on the Chinese Loess Plateau revealed through high sampling resolution OSL dating2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 82, p. 121-132Article in journal (Refereed)
  • 198.
    Stevens, Thomas
    et al.
    Centre for Quaternary Research, Department of Geography, Royal Holloway, University of London, UK.
    Markovic, Slobodan B.
    Zech, Michael
    Hambach, Ulrich
    Suemegi, Pal
    Dust deposition and climate in the Carpathian Basin over an independently dated last glacial-interglacial cycle2011In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, no 5-6, p. 662-681Article in journal (Refereed)
  • 199.
    Stoetter, Tabea
    et al.
    Univ Bern, Switzerland.
    Bastviken, David
    Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
    Bodelier, Paul L. E.
    Netherlands Inst Ecol NIOO KNAW, Netherlands.
    van Hardenbroek, Maarten
    Univ Bern, Switzerland; Univ Bern, Switzerland; Newcastle Univ, England.
    Rinta, Paeivi
    Univ Bern, Switzerland.
    Schilder, Jos
    Univ Bern, Switzerland; Univ Jyvaskyla, Finland.
    Schubert, Carsten J.
    EAWAG, Switzerland.
    Heiri, Oliver
    Univ Bern, Switzerland; Univ Bern, Switzerland.
    Abundance and delta C-13 values of fatty acids in lacustrine surface sediments: Relationships with in-lake methane concentrations2018In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 191, p. 337-347Article in journal (Refereed)
    Abstract [en]

    Proxy-indicators in lake sediments provide the only approach by which the dynamics of in-lake methane cycling can be examined on multi-decadal to centennial time scales. This information is necessary to constrain how lacustrine methane production, oxidation and emissions are expected to respond to global change drivers. Several of the available proxies for reconstructing methane cycle changes of lakes rely on interpreting past changes in the abundance or relevance of methane oxidizing bacteria (MOB), either directly (e.g. via analysis of bacterial lipids) or indirectly (e.g. via reconstructions of the past relevance of MOB in invertebrate diet). However, only limited information is available about the extent to which, at the ecosystem scale, variations in abundance and availability of MOB reflect past changes in in-lake methane concentrations. We present a study examining the abundances of fatty acids (FAs), particularly of C-13-depleted FM known to be produced by MOB, relative to methane concentrations in 29 small European lakes. 39 surface sediment samples were obtained from these lakes and FA abundances were compared with methane concentrations measured at the lake surface, 10 cm above the sediments and 10 cm within the sediments. Three of the FAs in the surface sediment samples, C-16(:1 omega 7c), C-16(:1 omega 5c/t), and C-18(:1 omega 7c) were characterized by lower delta C-13 values than the remaining FAs. We show that abundances of these FM, relative to other short-chain FAs produced in lake ecosystems, are related with sedimentary MOB concentrations assessed by quantitative polymerase chain reaction (qPCR). We observed positive relationships between methane concentrations and relative abundances of C-16:1 omega 7c, C-16:1 omega 5c/t, and C-18:1 omega 7c and the sum of these FAs. For the full dataset these relationships were relatively weak (Spearmans rank correlation (r(s)) of 0.34-0.43) and not significant if corrected for multiple testing. However, noticeably stronger and statistically significant relationships were observed when sediments from near-shore and deep-water oxic environments (r(s) = 0.57 to 0.62) and those from anoxic deep-water environment (r(s)= 0.55 to 0.65) were examined separately. Our results confirm that robust relationships exist between in-lake CH 4 concentrations and 13 C-depleted groups of FAs in the examined sediments, agreeing with earlier suggestions that the availability of MOB-derived, C-13-depleted organic matter for aquatic invertebrates increases with increasing methane concentrations. However, we also show that these relationships are complex, with different relationships observed for oxic and anoxic sediments and highest values measured in sediments deposited in oxic environments overlain with relatively methane-rich water. Furthermore, although all three C-13-depleted FA groups identified in our survey are known to be produced by MOB, they also receive contributions by other organism groups, and this will have influenced their distribution in our dataset. (C) 2018 Elsevier Ltd. All rights reserved.

  • 200. Stokes, Chris R.
    et al.
    Tarasov, Lev
    Blomdin, Robin
    Stockholm University, Faculty of Science, Department of Physical Geography. Purdue University, USA.
    Cronin, Thomas M.
    Fisher, Timothy G.
    Gyllencreutz, Richard
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hättestrand, Clas
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Heyman, Jakob
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Hindmarsh, Richard C. A.
    Hughes, Anna L. C.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Kirchner, Nina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Livingstone, Stephen J.
    Margold, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography. Durham University, UK.
    Murton, Julian B.
    Noormets, Riko
    Peltier, W. Richard
    Peteet, Dorothy M.
    Piper, David J. W.
    Preusser, Frank
    Renssen, Hans
    Roberts, David H.
    Roche, Didier M.
    Saint-Ange, Francky
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Teller, James T.
    On the reconstruction of palaeo-ice sheets: Recent advances and future challenges2015In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 125, p. 15-49Article, review/survey (Refereed)
    Abstract [en]

    Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-Sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.

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