Endre søk
Begrens søket
2345 201 - 239 of 239
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 201.
    Stoetter, Tabea
    et al.
    Univ Bern, Switzerland.
    Bastviken, David
    Linköpings universitet, Institutionen för tema, Tema Miljöförändring. Linköpings universitet, Filosofiska fakulteten.
    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 concentrations2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 191, s. 337-347Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 202. Stokes, Chris R.
    et al.
    Tarasov, Lev
    Blomdin, Robin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Purdue University, USA.
    Cronin, Thomas M.
    Fisher, Timothy G.
    Gyllencreutz, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Hättestrand, Clas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Heyman, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Hindmarsh, Richard C. A.
    Hughes, Anna L. C.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Kirchner, Nina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Livingstone, Stephen J.
    Margold, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. 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.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Teller, James T.
    On the reconstruction of palaeo-ice sheets: Recent advances and future challenges2015Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 125, s. 15-49Artikkel, forskningsoversikt (Fagfellevurdert)
    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.

  • 203.
    Stranne, Christian
    et al.
    Univ Gothenburg, Dept Earth Sci, S-41320 Gothenburg, Sweden..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Bjork, Goran
    Univ Gothenburg, Dept Earth Sci, S-41320 Gothenburg, Sweden..
    Arctic Ocean perennial sea ice breakdown during the Early Holocene Insolation Maximum2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, s. 123-132Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (similar to 6000-10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth's orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere sea ice ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bolling Allerod period (c. 12,700-14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover. (C) 2013 The Authors. Published by Elsevier Ltd. All rights reserved.

  • 204. Stranne, Christian
    et al.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Björk, Göran
    Arctic Ocean perennial sea ice breakdown during the Early Holocene Insolation Maximum2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, s. 123-132Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (similar to 6000-10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth's orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere sea ice ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bolling Allerod period (c. 12,700-14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.

  • 205.
    Stroeven, Arjen
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Fabel, Derek
    The University of Glasgow, Department of Geographical and Earth Sciences.
    Codilean, Alexandru T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Clague, John J.
    Simon Fraser University, Centre for Natural Hazard Research.
    Miguens-Rodriguez, Maria
    Scottish Universities Environmental Research Centre, GU-SUERC Cosmogenic Isotope Laboratory.
    Xu, Sheng
    Scottish Universities Environmental Research Centre, SUERC-AMS.
    Investigating the glacial history of the northern sector of the Cordilleran Ice Sheet with cosmogenic 10Be concentrations in quartz2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, s. 3630-3643Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exposure durations of glacial landforms in widely separated areas of central Yukon Territory affected bythe northern sector of the Cordilleran Ice Sheet (CIS) and alpine glaciers have been determined usingcosmogenic 10Be in quartz. The aim of our research is to test previous reconstructions of glacial historyand to begin to address the paucity of chronological control for the lateral and vertical extent of thenorthern CIS. Chronological evidence for CIS expansion predating the Last Glacial Maximum comes fromminimum surface exposure durations of c 100 ka for two bedrock samples within the Reid glacial limit,indicating a possible marine Oxygen Isotope Stage (OIS) 6 age for this event, and from minimumexposure durations of about 40 ka for boulders on moraines constructed by alpine glaciers on a nunatakwithin the McConnell glacial limit (OIS 2), indicating a possible OIS 4 age. High elevation minimumsurface exposure durations within the McConnell limit indicate that some areas formerly mapped asnunataks were covered by cold-based ice prior to 30 ka. Montane glaciation in the Mackenzie Mountains,outside the McConnell glacial limit, was contemporaneous with nearby CIS advance at 17 ka, with CISretreat by 15 ka. Deglaciation of the Tintina Trench, a major ice discharge route, was completed by 12 ka.At this time ice in an adjacent discharge route to the south was still entering higher-elevation valleys inthe Pelly Mountains. A Lateglacial readvance may have peaked at ca 10 ka in the Ogilvie Mountains.Considerable variation in ages from individual landforms, and possible complex histories, requireadditional cosmogenic nuclide measurements to confirm interpretations.

  • 206.
    Stroeven, Arjen P.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Fabel, Derek
    Margold, Martin
    Clague, John J.
    Xu, Sheng
    Investigating absolute chronologies of glacial advances in the NW sector of the Cordilleran Ice Sheet with terrestrial in situ cosmogenic nuclides2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, s. 429-443Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Geologic mapping in Yukon Territory, Canada, over the past 100 years has revealed a consistent pattern of diminishing Cordilleran Ice Sheet (CIS) extent during successively younger glaciations. Although this pattern is generally accepted, there is still much uncertainty about the number of glaciations, their ages, and the dynamics of the different lobes that constituted the digitate ice sheet margin, their subglacial thermal regimes, and ice thicknesses. We address uncertainties in the timing of glaciation using cosmogenic nuclide exposure dating at key localities that straddle several major lobes of the CIS in west-central Yukon Territory. Differences in exposure duration within what are thought to be the same map units are perhaps due to inheritance (older than expected), but more likely result from postglacial shielding (younger than expected) or surface erosion. Despite a significant spread in exposure durations on moraines and within map units, and tending to rely on longest exposure durations on moraines due to postglacial degradation and shielding, our results indicate that the McConnell glacial advance occurred during Marine Oxygen Isotope Stage (MIS) 2, judging from oldest minimum apparent exposure ages of 15.7 +/- 1.5 and 17.7 +/- 1.6 ka, a Gladstone glacial advance occurred before 51.8 +/- 4.7 ka (MIS 4) and Reid glacial advances before 79.8 +/- 7.3 and 82.8 +/- 7.5 ka (consistent with MIS 6). Traces of even older glacial advances predate 100 ka (107.5 +/- 9.9-154.3 +/- 14.2 ka).

  • 207.
    Stroeven, Arjen P.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Hättestrand, Clas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Kleman, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Heyman, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Fabel, Derek
    Fredin, Ola
    Goodfellow, Bradley W.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Lund University, Sweden.
    Harbor, Jonathan M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Purdue University, USA.
    Jansen, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. University of Potsdam, Germany.
    Olsen, Lars
    Caffee, Marc W.
    Fink, David
    Lundqvist, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Rosqvist, Gunhild C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. University of Bergen, Norway.
    Strömberg, Bo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Jansson, Krister N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Deglaciation of Fennoscandia2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, nr SI, s. 91-121Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating. This is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every 1000 years between 22 and 13 cal kyr BP and every hundred years between 11.6 and final ice decay after 9.7 cal kyr BP. Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins. For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin. Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas. For example, the LGM extent of the ice sheet in northwestern Russia was located far east and it occurred at a later time than the rest of the ice sheet, at around 17-15 cal kyr BP. We also propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages. Retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet, with the lowest rates on the high-elevation and maritime Norwegian margin. Retreat rates compared to the climatic information provided by the Greenland ice core record show a general correspondence between retreat rate and climatic forcing, although a close match between retreat rate and climate is unlikely because of other controls, such as topography and marine versus terrestrial margins. Overall, the time slice reconstructions of Fennoscandian Ice Sheet deglaciation from 22 to 9.7 cal kyr BP provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the Fennoscandian Ice Sheet, and are an important resource for testing and refining ice sheet models.

  • 208. Trachsel, Mathias
    et al.
    Kamenik, Christian
    Grosjean, Martin
    McCarroll, Danny
    Moberg, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Brázdil, Rudolf
    Büntgen, Ulf
    Dobrovolný, Petr
    Esper, Jan
    Frank, David C.
    Friedrich, Michael
    Glaser, Rüdiger
    Larocque-Tobler, Isabelle
    Nicolussi, Kurt
    Riemann, Dirk
    Multi-archive summer temperature reconstruction for the European Alps, AD 1053-19962012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 46, s. 66-79Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a multi-archive, multi-proxy summer temperature reconstruction for the European Alpscovering the period AD 1053-1996 using tree-ring and lake sediment data. The new reconstruction isbased on nine different calibration approaches and errors were estimated conservatively. Summertemperatures of the last millennium are characterised by two warm (AD 1053-1171 and 1823-1996) andtwo cold phases (AD 1172-1379 and 1573-1822). Highest pre-industrial summer temperatures of the12th century were 0.3 degC warmer than the 20th century mean but 0.35 degC colder than proxy derivedtemperatures at the end of the 20th century. The lowest temperatures at the end of the 16th centurywere ~1 degC lower than the 20th century mean.

  • 209. Unkel, I.
    et al.
    Björck, Svante
    Lund University.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Deglacial environmental changes on Isla de los Estados (54.4 degrees S), southeastern Tierra del Fuego2008Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 27, nr 15-16, s. 1541-1554Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The island of Isla de los Estados is situated at 54.5°S, 64°W, east of Argentinian Tierra del Fuego, and is located in a sensitive geographic position in relation to the zonal circulation between Antarctica and South America. Its terrestrial records of the last deglaciation, recording atmospheric conditions but within an oceanic setting, can help to clarify changes of regional circulation patterns, both atmospheric and marine. Here, we present geochemical analyses from 16–10 ka cal BP of a peat core from Lago Galvarne Bog at the northern coast of the island, and a lake sediment core from Laguna Cascada 3 km further south. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning on both cores as well as age–depth modeling based on AMS-14C dating. Deglaciation and onset of peat formation in the coastal areas began before 16 ka cal BP followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland. Data suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14.5 ka cal BP. The warming trend slows down until ca 13.5 ka cal BP, followed by arid conditions culminating around 12.8 ka cal BP. Our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10.6 ka cal BP, contemporaneous with the onset of the Antarctic thermal optimum. This indicates large-scale shifts in the placement of zonal flow and the Westerlies at the beginning of the Holocene.

  • 210.
    Unkel, Ingmar
    et al.
    GeoBiosphere Sci Ctr, SE-22362 Lund, Sweden..
    Björck, Svante
    GeoBiosphere Sci Ctr, SE-22362 Lund, Sweden..
    Wohlfarth, Barbara
    Stockholm Univ, Dept Geol & Geochem, SE-10691 Stockholm, Sweden..
    Deglacial environmental changes on Isla de los Estados (54.4 degrees S), southeastern Tierra del Fuego2008Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 27, nr 15-16, s. 1541-1554Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The island of Isla de los Estados is situated at 54.5 degrees S, 64 degrees W, east of Argentinian Tierra del Fuego, and is located in a sensitive geographic position in relation to the zonal circulation between Antarctica and South America. Its terrestrial records of the last deglaciation, recording atmospheric conditions but within an oceanic setting, can help to clarify changes of regional circulation patterns, both atmospheric and marine. Here, we present geochemical analyses from 16-10 ka cal BP of a peat core from Lago Galvarne Bog at the northern coast of the island, and a lake sediment core from Laguna Cascada 3 kin further south. The data comprise TC, TN, loss on ignition analyses and continuous XRF scanning on both cores as well as age-depth modeling based on AMS-C-14 dating. Deglaciation and onset of peat formation in the coastal areas began before 16 ka cal BP followed by a rapid glacial retreat and the start of lacustrine sedimentation further inland. Data Suggest initially windy conditions with permafrost succeeded by gradually warmer and wetter conditions until ca 14.5 ka cal BP. The warming trend slows down until ca 13.5 ka cal BP, followed by arid conditions culminating around 12.8 ka cal BP. Our data suggest fairly warm conditions and the establishment of denser peat and forest vegetation ca 10.6 ka cal BP, contemporaneous with the onset of the Antarctic thermal optimum. This indicates large-scale shifts in the placement of zonal flow and the Westerlies at the beginning of the Holocene. (C) 2008 Elsevier Ltd. All rights reserved.

  • 211. Urena, I.
    et al.
    Ersmark, E.
    Naturhistoriska riksmuseet, Enheten för bioinformatik och genetik.
    Samaniego, J. A.
    Galindo-Pellicena, M. A.
    Cregut-Bonnoure, E.
    Bolivar, H.
    Gomez-Olivencia, A.
    Rios-Garaizar, J.
    Garate, D.
    Dalén, L.
    Naturhistoriska riksmuseet, Enheten för bioinformatik och genetik.
    Arsuaga, J. L.
    Valdiosera, C. E.
    Unraveling the genetic history of the European wild goats2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 185, s. 189-198Artikkel i tidsskrift (Fagfellevurdert)
  • 212.
    van der Plas, Geert W.
    et al.
    Univ Ghent, Dept Biol, Limnol Unit, KL Ledeganckstr 35, B-9000 Ghent, Belgium.
    De Cort, Gijs
    Univ Ghent, Dept Biol, Limnol Unit, KL Ledeganckstr 35, B-9000 Ghent, Belgium;Royal Museum Cent Africa, Dept Earth Sci, B-3080 Tervuren, Belgium.
    Petek-Sargeant, Nik
    British Museum, Dept Africa Oceania & Amer, Great Russell St, London WC1B 3DG, England.
    Wuytack, Tabitha
    Univ Ghent, Dept Biol, Limnol Unit, KL Ledeganckstr 35, B-9000 Ghent, Belgium.
    Colombaroli, Daniele
    Univ Ghent, Dept Biol, Limnol Unit, KL Ledeganckstr 35, B-9000 Ghent, Belgium;Royal Holloway Univ London, Ctr Quaternary Res, Dept Geog, Egham TW20 0EX, Surrey, England.
    Lane, Paul J.
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Historisk-filosofiska fakulteten, Institutionen för arkeologi och antik historia, Arkeologi. Univ Cambridge, Dept Archaeol, Downing St, Cambridge CB2 3DZ, England.
    Verschuren, Dirk
    Univ Ghent, Dept Biol, Limnol Unit, KL Ledeganckstr 35, B-9000 Ghent, Belgium.
    Distinct phases of natural landscape dynamics and intensifying human activity in the central Kenya Rift Valley during the past 1300 years2019Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 218, s. 91-106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Socio-ecological stresses currently affecting the semi-arid regions of equatorial East Africa are driving environmental changes that need to be placed in a proper context of long-term human-climate-landscape interaction. Here we present a detailed reconstruction of past human influences on the landscape of the central Kenya Rift Valley, against the backdrop of natural climate-driven ecosystem dynamics over the past 1300 years. Proxy records of vegetation dynamics (pollen), animal husbandry (fungal spores), biomass burning (charcoal) and soil mobilization (clastic mineral influx) extracted from the continuous depositional archive of Lake Bogoria reveal six distinct phases of human activity. From ca 700 to 1430 CE, strong primary response of savanna woodland ecotonal vegetation to climatic moisture-balance variation suggests that anthropogenic influence on regional ecosystem dynamics was limited. The first unambiguous ecological signature of human activities involves a mid-15th century reduction of woodland/forest trees followed by the appearance of cereal pollen, both evidence for mixed farming. From the mid-17th century, animal husbandry became a significant ecological factor and reached near-modern levels by the mid-19th century, after severe early-19th century drought had substantially changed human-landscape interaction. A short-lived peak in biomass burning and evidence for soil mobilization in low-lying areas of the Bogoria catchment likely reflects the known 19th-century establishment of irrigation agriculture, while renewed expansion of forest and woodland trees reflect the return of a wetter climate and abandonment of other farmland. Since the mid-20th century, the principal signature of human activity within the Lake Bogoria catchment is the unprecedented increase in clastic sediment flux, reflecting widespread soil erosion associated with rapidly intensifying land use. (C) 2019 Elsevier Ltd. All rights reserved.

  • 213.
    van Hardenbroek, M
    et al.
    University of Utrecht, Netherlands .
    Heiri, O
    University of Utrecht, Netherlands .
    Parmentier, FJ W
    Vrije University of Amsterdam, Netherlands .
    Bastviken, David
    Linköpings universitet, Institutionen för tema, Tema vatten i natur och samhälle. Linköpings universitet, Filosofiska fakulteten.
    Ilyashuk, B P
    University of Bern, Switzerland .
    Wiklund, J A
    University of Waterloo, Canada .
    Hall, R I
    University of Waterloo, Canada .
    Lotter, A F
    University of Utrecht, Netherlands .
    Evidence for past variations in methane availability in a Siberian thermokarst lake based on delta C-13 of chitinous invertebrate remains2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 66, nr SI, s. 74-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding past methane dynamics in arctic wetlands and lakes is crucial for estimating future methane release. Methane fluxes from lake ecosystems have increasingly been studied, yet only few reconstructions of past methane emissions from lakes are available. In this study, we develop an approach to assess changes in methane availability in lakes based on delta C-13 of chitinous invertebrate remains and apply this to a sediment record from a Siberian thermokarst lake. Diffusive methane fluxes from the surface of ten newly sampled Siberian lakes and seven previously studied Swedish lakes were compared to taxon-specific delta C-13 values of invertebrate remains from lake surface sediments to investigate whether these invertebrates assimilated C-13-depleted carbon typical for methane. Remains of chironomid larvae of the tribe Orthocladiinae that, in the study lakes, mainly assimilate plant-derived carbon had higher delta C-13 than other invertebrate groups. delta C-13 of other invertebrates such as several chironomid groups (Chironomus, Chironomini, Tanytarsini, and Tanypodinae), cladocerans (Daphnia), and ostracods were generally lower. delta C-13 of Chironomini and Daphnia, and to a lesser extent Tanytarsini was variable in the lakes and lower at sites with higher diffusive methane fluxes. delta C-13 of Chironomini, Tanytarsini, and Daphnia were correlated significantly with diffusive methane flux in the combined Siberian and Swedish dataset (r = -0.72, p = 0.001, r = -0.53, p = 0.03, and r = -0.81, p andlt; 0.001, respectively), suggesting that delta C-13 in these invertebrates was affected by methane availability. In a second step, we measured delta C-13 of invertebrate remains from a sediment record of Lake S1, a shallow thermokarst lake in northeast Siberia. In this record, covering the past ca 1000 years, delta C-13 of taxa most sensitive to methane availability (Chironomini, Tanytarsini, and Daphnia) was lowest in sediments deposited from ca AD 1250 to ca AD 1500, and after AD 1970, coinciding with warmer climate as indicated by an independent local temperature record. As a consequence the offset in delta C-13 between methane-sensitive taxa and bulk organic matter was higher in these sections than in other parts of the core. In contrast, delta C-13 of other invertebrate taxa did not show this trend. Our results suggest higher methane availability in the study lake during warmer periods and that thermokarst lakes can respond dynamically in their methane output to changing environmental conditions.

  • 214. Van Meerbeeck, C. J.
    et al.
    Renssen, H.
    Roche, D. M.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Bohncke, S. J. P.
    Bos, J. A. A.
    Engels, S.
    Helmens, Karin F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Sanchez-Goni, M. F.
    Svensson, A.
    Vandenberghe, J.
    The nature of MIS 3 stadial-interstadial transitions in Europe: New insights from model-data comparisons2011Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 25-26, s. 3618-3637Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    15 abrupt warming transitions perturbed glacial climate in Greenland during Marine Isotope Stage 3 (MIS 3, 60-27 ka BP). One hypothesis states that the 8-16 degrees C warming between Greenland Stadials (GS) and Interstadials (GI) was caused by enhanced heat transport to the North Atlantic region after a resumption of the Atlantic Meridional Overturning Circulation (AMOC) from a weak or shutdown stadial mode. This hypothesis also predicts warming over Europe, a prediction poorly constrained by data due to the paucity of well-dated quantitative temperature records. We therefore use a new evidence from biotic proxies and a climate model simulation to study the characteristics of a GS-GI transition in continental Europe and the link to enhanced AMOC strength. We compare reconstructed climatic and vegetation changes between a stadial and subsequent interstadial - correlated to GS15 and GI14 (similar to 55 ka BP) - with a simulated AMOC resumption using a three-dimensional earth system model setup with early-MIS 3 boundary conditions. Over western Europe (12 degrees W-15 degrees E), we simulate twice the annual precipitation, a 17 degrees C warmer coldest month, a 8 degrees C warmer warmest month, 1300 degrees C-day more growing degree days with baseline 5 degrees C (GDD5) and potential vegetation allowing tree cover after the transition. However, the combined effect of frequent killing frosts, <20 mm summer precipitation and too few GDD5 after the transition suggest a northern tree limit lying at similar to 50 degrees N during GI14. With these 3 climatic limiting factors we provide a possible explanation for the absence of forests north of 48 degrees N during MIS 3 interstadials with mild summers. Finally, apart from a large model bias in warmest month surface air temperatures, our simulation is in reasonable agreement with reconstructed climatic and vegetation changes in Europe, thus further supporting the hypothesis.

  • 215. Vandergoes, MJ
    et al.
    Dieffenbacher-Krall, AC
    Newnham, RM
    Denton, GH
    Blaauw, Maarten
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleobiologi.
    Cooling and changing seasonality in the Southern Alps, New Zealand during the Antarctic Cold Reversal2008Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 27, nr 5-6, s. 589-601Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A comprehensively 14C AMS dated pollen and chironomid record from Boundary Stream Tarn provides the first chironomid-derived temperature reconstruction to quantify temperature change during Lateglacial times (17,500–10,000 cal yr BP) in the Southern Alps, New Zealand. The records indicate a ca 1000-year disruption to the Lateglacial warming trend and an overall cooling consistent with the Antarctic Cold Reversal (ACR). The main interval of chironomid-inferred summer temperature depression (2–3 °C) lasted about 700 years during the ACR. Following this cooling event, both proxies indicate a warming step to temperatures slightly cooler than present during the Younger Dryas chronozone (12,900–11,500 cal yr BP). These results highlight a direct linkage between Antarctica and mid-latitude terrestrial climate systems and the largely asynchronous nature of the interhemispheric climate system during the last glacial transition. The greater magnitude of temperature changes shown by the chironomid record is attributed to the response of the proxies to differences in seasonal climate with chironomids reflecting summer temperature and vegetation more strongly controlled by duration of winter or by minimum temperatures. These differences imply stronger seasonality at times during the Lateglacial, which may explain some of the variability between other paleoclimate records from New Zealand and have wider implications for understanding differences between proxy records for abrupt climate change.

  • 216. Villavicencio, Natalia
    et al.
    Werdelin, Lars
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    The Casa del Diablo cave (Puno, Peru) and the late Pleistocene demise of megafauna in the Andean Altiplano2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 195, s. 21-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During the Late Quaternary Extinction event South America lost ~83% of all its late Pleistocene megafaunal genera. As in other regions of the world, the debate about the possible drivers behind these extinctions revolves around the role of humans arriving into the continent and on the effect of the climatic changes characteristic of the Pleistocene-Holocene transition. The availability of precise chronological information, in order to estimate the timing of extinction of the different taxa affected, is critical for solving such debate. Here we present an updated study of the late Pleistocene mammalian deposits from Casa del Diablo Cave (CdD) in the Altiplano of Peru. The study includes an updated list of the mammalian faunas found in the cave and 11 taxon-specific XAD radiocarbon dates from extinct and extant megafauna bones.We compare this new chronology to the timing of major environmental changes and human arrival in the area, as well as with other megafaunal discoveries from the high Andes. The radiocarbon dates from CdD fall in the time window between 23 and 12.8 cal kyr BP. Compared to other records of extinct megafauna in the high Andes, the one from CdD presents in general younger occurrences. No temporal overlap between humans and extinct megafauna emerges from comparing first dates of appearance of humans in the Altiplano, and last appearance dates of extinct megafauna from CdD. However, the possibility of temporal overlap among the records becomes evident when we compare confidence intervals calculated to estimate true times of human arrival and megafaunal local extinctions.

  • 217. Väliranta, Minna
    et al.
    Birks, Hilary H.
    Helmens, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Engels, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Piirainen, Mikko
    Early Weichselian interstadial (MIS 5c) summer temperatures were higher than today in northern Fennoscandia2009Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 28, nr 9-10, s. 777-782Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Only fragmentary biostratigraphical interstaidial data exist from northern European high latitudes. The palaeoenvironmental interpretations for the early part of the Last Glaciation in northern Fennoscandia are mainly based on palynological evidence that suggests open birch woodland and a sub-arctic climate. Plant macrofossils from the Sokli sediment sequence in Finnish Lapland provide different evidence of interstadial climate conditions. The assemblage includes several species that currently have considerably more southern distribution ranges. This indicates that ca 100,000 years ago summer temperatures were warmer than today. The mean minimum July temperature may have been as high as 16 degrees C and the effective temperature sum may have been 1000 in day-degree units (d.d.), the modern values being 13 degrees C and 650 d.d., respectively. The contemporary astronomical forcing mechanisms may have resulted in a weaker north-south temperature gradient and a longer growing period, creating more favourable climate conditions compared with today.

  • 218.
    Wastegård, Stefan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Gudmundsdóttir, Esther R.
    Lind, Ewa M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Timms, Rhys G. O.
    Björck, Svante
    Hannon, Gina E.
    Olsen, Jesper
    Rundgren, Mats
    Towards a Holocene tephrochronology for the Faroe Islands, North Atlantic2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 195, s. 195-214Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Faroe Islands hold a key position in the North Atlantic region for tephra studies due to their relative proximity to Iceland. Several tephras have been described over the last 50 years in peat and lake sediment sequences, including the type sites for the Saksunarvatn and Mjauvotn tephras. Here we present a comprehensive overview of Holocene tephras found on the Faroe Island. In total 23 tephra layers are described including visible macrotephras such as the Saksunarvatn and Hekla 4 tephras and several cryptotephras. The importance of tephras originally described from the Faroe Islands is highlighted and previously unpublished results are included. In addition, full datasets for several sites are published here for the first time. The Saksunarvatn Ash, now considered to be the result of several eruptions rather than one major eruption, can be separated into two phases on the Faroe Islands; one early phase with two precursor eruptions with lower MgO concentrations (4.5-5.0 wt%) than the main eruption and a later phase with higher MgO concentrations (5.5-6.0 wt%), including the visible Saksunarvatn Ash. The Tjornuvik Tephra, previously considered to be a primary deposit, is now interpreted as a reworked tephra with material from at least two middle Holocene eruptions of Hekla. Several of the tephras identified on the Faroe Islands provide useful isochrons for climate events during the Holocene.

  • 219.
    Wastegård, Stefan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Veres, Daniel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK). Lucian Blaga University of Sibiu .
    Kliem, P.
    Hahn, A.
    Ohlendorf, C.
    Zolitschka, B.
    Towards a late Quaternary tephrochronological framework for the southernmost part of South America - the Laguna Potrok Aike tephra record2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, s. 81-90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A total of 18 tephra samples have been analysed from the composite sediment sequence from Site 2 of the Laguna Potrok Aike ICDP expedition 5022 from southern Patagonia, Argentina, which extends back to ca 51 ka cal BP. Analyses of the volcanic glass show that all layers but one are rhyolitic in composition, with SiO2 contents ranging between ca 74.5 and 78 wt% and suggest an origin in the Austral Andean Volcanic Zone (AVZ; 49-55 degrees S). Nonetheless, two main data clusters occur, one group with K2O contents between ca 1.5 and 2.0 wt%, indicating an origin in the Mt. Burney volcanic area, and one group with K2O contents between ca 2.7 and 3.9 wt%, tentatively correlated with Viedma/Lautaro and the Aguilera volcanoes in the northern part of the AVZ. The early Holocene Tephra, MB1 and the late Pleistocene Reclus R-1 tephra occur in the upper part of the sequence. Periods with significant tephra deposition occurred between ca 51-44 ka cal BP, and ca 31-25 ka cal BP, with a decrease in tephra layer frequency between these two periods.

  • 220.
    Weiberg, Erika
    et al.
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Historisk-filosofiska fakulteten, Institutionen för arkeologi och antik historia, Antikens kultur och samhällsliv.
    Unkel, Ingmar
    Kouli, Katerina
    Holmgren, Karin
    Avramidis, Pavlos
    Bonnier, Anton
    Dibble, Flint
    Finné, Martin
    Stockholm Univ, Dept Phys Geog, S-10691 Stockholm, Sweden; Navarino Environm Observ, Costa Navarino 24001, Messinia, Greece .
    Izdebski, Adam
    Katrantsiotis, Christos
    Stocker, Sharon R.
    Andwinge, Maria
    Baika, Kalliope
    Boyd, Meighan
    Heymann, Christian
    The socio-environmental history of the Peloponnese during the Holocene: Towards an integrated understanding of the past2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, s. 40-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Published archaeological, palaeoenvironmental, and palaeoclimatic data from the Peloponnese in Greece are compiled, discussed and evaluated in order to analyse the interactions between humans and the environment over the last 9000 years. Our study indicates that the number of human settlements found scattered over the peninsula have quadrupled from the prehistoric to historical periods and that this evolution occurred over periods of climate change and seismo–tectonic activity. We show that societal development occurs both during periods of harsh as well as favourable climatic conditions. At some times, some settlements develop while others decline. Well-known climate events such as the 4.2 ka and 3.2 ka events are recognizable in some of the palaeoclimatic records and a regional decline in the number and sizes of settlements occurs roughly at the same time, but their precise chronological fit with the archaeological record remains uncertain. Local socio-political processes were probably always the key drivers behind the diverse strategies that human societies took in times of changing climate. The study thus reveals considerable chronological parallels between societal development and palaeoenvironmental records, but also demonstrates the ambiguities in these correspondences and, in doing so, highlights some of the challenges that will face future interdisciplinary projects. We suggest that there can be no general association made between societal expansion phases and periods of advantageous climate. We also propose that the relevance of climatic and environmental regionality, as well as any potential impacts of seismo-tectonics on societal development, need to be part of the interpretative frameworks.

  • 221. Weiberg, Erika
    et al.
    Unkel, Ingmar
    Kouli, Katerina
    Holmgren, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Avramidis, Pavlos
    Bonnier, Anton
    Dibble, Flint
    Finné, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Izdebski, Adam
    Katrantsiotis, Christos
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Stocker, Sharon R.
    Andwinge, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Baika, Kalliopi
    Boyd, Meighan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Heymann, Christian
    The socio-environmental history of the Peloponnese during the Holocene: Towards an integrated understanding of the past2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, s. 40-65Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Published archaeological, palaeoenvironmental, and palaeoclimatic data from the Peloponnese in Greece are compiled, discussed and evaluated in order to analyse the interactions between humans and the environment over the last 9000 years. Our study indicates that the number of human settlements found scattered over the peninsula have quadrupled from the prehistoric to historical periods and that this evolution occurred over periods of climate change and seismo-tectonic activity. We show that societal development occurs both during periods of harsh as well as favourable climatic conditions. At some times, some settlements develop while others decline. Well-known climate events such as the 4.2 ka and 3.2 ka events are recognizable in some of the palaeoclimatic records and a regional decline in the number and sizes of settlements occurs roughly at the same time, but their precise chronological fit with the archaeological record remains uncertain. Local socio-political processes were probably always the key drivers behind the diverse strategies that human societies took in times of changing climate. The study thus reveals considerable chronological parallels between societal development and palaeoenvironmental records, but also demonstrates the ambiguities in these correspondences and, in doing so, highlights some of the challenges that will face future interdisciplinary projects. We suggest that there can be no general association made between societal expansion phases and periods of advantageous climate. We also propose that the relevance of climatic and environmental regionality, as well as any potential impacts of seismo-tectonics on societal development, need to be part of the interpretative frameworks.

  • 222. Wennrich, Volker
    et al.
    Andreev, Andrei A.
    Tarasov, Pavel E.
    Fedorov, Grigory
    Zhao, Wenwei
    Gebhardt, Catalina A.
    Meyer-Jacob, Carsten
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Snyder, Jeffrey A.
    Nowaczyk, Norbert R.
    Schwamborn, Georg
    Chapligin, Bernhard
    Anderson, Patricia M.
    Lozhkin, Anatoly V.
    Minyuk, Pavel S.
    Koeberl, Christian
    Melles, Martin
    Impact processes, permafrost dynamics, and climate and environmental variability in the terrestrial Arctic as inferred from the unique 3.6 Myr record of Lake El'gygytgyn, Far East Russia - A review2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 147, s. 221-244Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lake El'gygytgyn in Far East Russia is a 3.6 Myr old impact crater lake. Located in an area that has never been affected by Cenozoic glaciations nor desiccation, the unique sediment record of the lake represents the longest continuous sediment archive of the terrestrial Arctic. The surrounding crater is the only impact structure on Earth developed in mostly acid volcanic rocks. Recent studies on the impactite, permafrost, and sediment sequences recovered within the framework of the ICDP "El'gygytgyn Drilling Project" and multiple pre-site surveys yielded new insight into the bedrock origin and cratering processes as well as permafrost dynamics and the climate and environmental history of the terrestrial Arctic back to the mid-Pliocene. Results from the impact rock section recovered during the deep drilling clearly confirm the impact genesis of the El'gygytgyn crater, but indicate an only very reduced fallback impactite sequence without larger coherent melt bodies. Isotope and element data of impact melt samples indicate a F-type asteroid of mixed composition or an ordinary chondrite as the likely impactor. The impact event caused a long-lasting hydrothermal activity in the crater that is assumed to have persisted for c. 300 kyr. Geochemical and microbial analyses of the permafrost core indicate a subaquatic formation of the lower part during lake-level highstand, but a subaerial genesis of the upper part after a lake-level drop after the Allerod. The isotope signal and ion compositions of ground ice is overprinted by several thaw freeze cycles due to variations in the talik underneath the lake. Modeling results suggest a modern permafrost thickness in the crater of c. 340 m, and further confirm a pervasive character of the talik below Lake El'gygytgyn. The lake sediment sequences shed new leight into the Pliocene and Pleistocene climate and environmental evolution of the Arctic. During the mid-Pliocene, significantly warmer and wetter climatic conditions in western Beringia than today enabled dense boreal forests to grow around Lake Ergygytgyn and, in combination with a higher nutrient flux into the lake, promoted primary production. The exceptional warmth during the mid-Pliocene is in accordance with other marine and terrestrial records from the Arctic and indicates a period of enhanced "Arctic amplification". The favourable conditions during the mid-Pliocene were repeatedly interrupted by climate deteriorations, e.g., during Marine Isotope Stage (MIS) M2, when pollen data and sediment proxies indicate a major cooling and the onset of local permafrost around the lake. A gradual vegetation change after c. 3.0 Ma points to the onset of a long-term cooling trend during the Late Pliocene that culminated in major temperature drops, first during MIS G6, and later during MIS 104. These cold events coincide with the onset of an intensified Northern Hemisphere (NH) glaciation and the largest extent of the Cordilleran Ice Sheet, respectively. After the Pliocene/Pleistocene transition, local vegetation and primary production in Lake El'gygtygyn experienced a major change from relatively uniform conditions to a high-amplitude glacial-to-interglacial cyclicity that fluctuated on a dominant 41 kyr obliquity band, but changed to a 100 kyr eccentricity dominance during the Middle Pleistocene transition (MPT) at c. 1.2-0.6 Ma. Periods of exceptional warming in the Pleistocene record of Lake El'gygytgyn with dense boreal forests around and peaks of primary production in the lake are assigned to so-called "super-interglacial" periods. The occurrence of these super-interglacials well corresponds to collapses of the West Antarctic Ice Sheet (WAIS) recorded in ice-free periods in the ANDRILL core, which suggests strong intrahemispheric teleconnections presumably driven by changes in the thermocline ocean circulation.

  • 223. Wilson, Rob
    et al.
    Anchukaitis, Kevin
    Briffa, Keith R.
    Buentgen, Ulf
    Cook, Edward
    D'Arrigo, Rosanne
    Davi, Nicole
    Esper, Jan
    Frank, Dave
    Gunnarson, Björn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Hegerl, Gabi
    Helama, Samuli
    Klesse, Stefan
    Krusic, Paul J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Linderholm, Hans W.
    Myglan, Vladimir
    Osborn, Timothy J.
    Rydval, Milos
    Schneider, Lea
    Schurer, Andrew
    Wiles, Greg
    Zhang, Peng
    Zorita, Eduardo
    Last millennium northern hemisphere summer temperatures from tree rings: Part I2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 134, s. 1-18Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Large-scale millennial length Northern Hemisphere (NH) temperature reconstructions have been progressively improved over the last 20 years as new datasets have been developed. This paper, and its companion (Part II, Anchukaitis et al. in prep), details the latest tree-ring (TR) based NH land air temperature reconstruction from a temporal and spatial perspective. This work is the first product of a consortium called N-TREND (Northern Hemisphere Tree-Ring Network Development) which brings together dendroclimatologists to identify a collective strategy for improving large-scale summer temperature reconstructions. The new reconstruction, N-TREND2015, utilises 54 records, a significant expansion compared with previous TR studies, and yields an improved reconstruction with stronger statistical calibration metrics. N-TREND2015 is relatively insensitive to the compositing method and spatial weighting used and validation metrics indicate that the new record portrays reasonable coherence with large scale summer temperatures and is robust at all time-scales from 918 to 2004 where at least 3 TR records exist from each major continental mass. N-TREND2015 indicates a longer and warmer medieval period (similar to 900 1170) than portrayed by previous TR NH reconstructions and by the CMIP5 model ensemble, but with better overall agreement between records for the last 600 years. Future dendroclimatic projects should focus on developing new long records from data-sparse regions such as North America and eastern Eurasia as well as ensuring the measurement of parameters related to latewood density to complement ring-width records which can improve local based calibration substantially.

  • 224.
    Witus, Alexandra E.
    et al.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Branecky, Carolyn M.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Anderson, John B.
    Rice Univ, Dept Earth Sci, Houston, TX 77005 USA..
    Szczucinski, Witold
    Adam Mickiewicz Univ, Inst Geol, PL-61606 Poznan, Poland..
    Schroeder, Dustin M.
    Univ Texas Austin, Inst Geophys, Austin, TX USA..
    Blankenship, Donald D.
    Univ Texas Austin, Inst Geophys, Austin, TX USA..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Meltwater intensive glacial retreat in polar environments and investigation of associated sediments: example from Pine Island Bay, West Antarctica2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 85, s. 99-118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are among the fastest changing portions of the cryosphere and the least stable ice streams in Antarctica. Here we show that the uppermost sediment unit in Pine Island Bay was deposited from a meltwater plume, a plumite, during the late stages of ice sheet retreat similar to 7-8.6 k cal yr BP and argue that this deposit records episodes of meltwater intensive sedimentation. The plumite is a hydraulically sorted, glacially sourced, draping deposit that overlies proximal glaci-marine sediments and thickens towards the modern grounding line. The uppermost sediment unit is interpreted as a product of non-steady-state processes in which low background sedimentation in large bedrock-carved basins alternates with episodic purging of sediment-laden water from these basins. The inner part of Pine Island Bay contains several basins that are linked by channels with a storage capacity on the order of 70 km(3) of stagnant water and significant sediment storage capacity. Purging of these basins is caused by changes in hydraulic potential and glacial reorganization. The sediment mobilized by these processes is found here to total 120 km3. This study demonstrates that episodes of meltwater-intensive sedimentation in Pine Island Bay occurred at least three times in the Holocene. The most recent episode coincides with rapid retreat of the grounding line in historical time and has an order of magnitude greater flux relative to the entire unit. We note that the final phase of ice stream retreat in Marguerite Bay was marked by a similar sedimentary event and suggest that the modern Thwaites Glacier is poised for an analogous meltwater-intensive phase of retreat. (C) 2013 Elsevier Ltd. All rights reserved.

  • 225. Witus, Alexandra E.
    et al.
    Branecky, Carolyn M.
    Anderson, John B.
    Szczucinski, Witold
    Schroeder, Dustin M.
    Blankenship, Donald D.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Meltwater intensive glacial retreat in polar environments and investigation of associated sediments: example from Pine Island Bay, West Antarctica2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 85, s. 99-118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Modern Pine Island and Thwaites Glaciers, which both drain into Pine Island Bay, are among the fastest changing portions of the cryosphere and the least stable ice streams in Antarctica. Here we show that the uppermost sediment unit in Pine Island Bay was deposited from a meltwater plume, a plumite, during the late stages of ice sheet retreat similar to 7-8.6 k cal yr BP and argue that this deposit records episodes of meltwater intensive sedimentation. The plumite is a hydraulically sorted, glacially sourced, draping deposit that overlies proximal glaci-marine sediments and thickens towards the modern grounding line. The uppermost sediment unit is interpreted as a product of non-steady-state processes in which low background sedimentation in large bedrock-carved basins alternates with episodic purging of sediment-laden water from these basins. The inner part of Pine Island Bay contains several basins that are linked by channels with a storage capacity on the order of 70 km(3) of stagnant water and significant sediment storage capacity. Purging of these basins is caused by changes in hydraulic potential and glacial reorganization. The sediment mobilized by these processes is found here to total 120 km3. This study demonstrates that episodes of meltwater-intensive sedimentation in Pine Island Bay occurred at least three times in the Holocene. The most recent episode coincides with rapid retreat of the grounding line in historical time and has an order of magnitude greater flux relative to the entire unit. We note that the final phase of ice stream retreat in Marguerite Bay was marked by a similar sedimentary event and suggest that the modern Thwaites Glacier is poised for an analogous meltwater-intensive phase of retreat.

  • 226. Wohlfarth, B
    et al.
    Gaillard, Marie-Jose
    Högskolan i Kalmar, Naturvetenskapliga institutionen.
    Häberli, W
    Kelts, K
    Environment and Climate in Southwestern Switzerland during the Last Termination, 15-10 ka BP1994Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 13, nr 4, s. 361-394Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Various records from sites ranging in altitude between 372 and 2290 m along a NW-SE transect through SW Switzerland were compiled and correlated within well defined chrono- and biostratigraphic units. Deglaciation of lowland areas is estimated at ca. 15,000-14,000 BP (minimum age), while the lower part of the Rhone valley and the Jura Mountains may have become ice free later. A significant climatic warming is clearly indicated by several palaeoecological records at ca. 12,600 BP. The compiled data give no clear evidence of a cooler phase between 12,200-12,000 BP. Oxygen isotope data point to a slight and progressive decrease in the deltaO-18 values between ca. 12,500-11,000 BP, which is followed by a marked drop at 11,000 BP. A very distinct change in lithology, rock glacier development and in mollusc and vegetation records characterises many low and high altitude sites ca. 300 years later, at 10,700 BP. Between 11,000 and 10,000 BP oxygen isotope records seem to respond more rapidly to the climatic shifts than the biostratigraphical records. Possible explanations for these time-lags are discussed. Our compilation shows that further multidisciplinary research in key sites would provide more precise palaeoclimatological information, both qualitatively and quantitatively. Higher time resolution and quantitative estimates of climatic parameters are needed to evaluate in detail the mechanisms and consequences of these rapid climatic changes in SW Switzerland.

  • 227. Wolff, E. W.
    et al.
    Barbante, C.
    Becagli, S.
    Bigler, M.
    Boutron, C. F.
    Castellano, E.
    de Angelis, M.
    Federer, U.
    Fischer, H.
    Fundel, F.
    Hansson, Margareta
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Hutterli, M.
    Jonsell, Ulf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Karlin, Torbjörn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Kaufmann, P.
    Lambert, F.
    Littot, G. C.
    Mulvaney, R.
    Roethlisberger, R.
    Ruth, U.
    Severi, M.
    Siggaard-Andersen, M. L.
    Sime, L. C.
    Steffensen, J. P.
    Stocker, T. F.
    Traversi, R.
    Twarloh, B.
    Udisti, R.
    Wagenbach, D.
    Wegner, A.
    Changes in environment over the last 800,000 years from chemical analysis of the EPICA Dome C ice core2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 1-2, s. 285-295Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The EPICA ice core from Dome C extends 3259 m in depth, and encompasses 800 ka of datable and sequential ice. Numerous chemical species have been measured along the length of the cores. Here we concentrate on interpreting the main low-resolution patterns of major ions. We extend the published record for non-sea-salt calcium, sea-salt sodium and non-sea-salt sulfate flux to 800 ka. The non-sea-salt calcium record confirms that terrestrial dust originating from South America closely mirrored Antarctic climate, both at orbital and millennial timescales. A major cause of the main trends is most likely climate in southern South America, which could be sensitive to subtle changes in atmospheric circulation. Sea-salt sodium also follows temperature, but With a threshold at low temperature. We re-examine the use of sodium as a sea ice proxy, concluding that it is probably reflecting extent, with high salt concentrations reflecting larger ice extents. With this interpretation, the sodium flux record indicates low ice extent operating as an amplifier in warm interglacials. Non-sea-salt sulfate flux is almost constant along the core, confirming the lack of change in marine productivity (for sulfur-producing organisms) in the areas of the Southern Ocean contributing to the flux at Dome C. For the first time we also present long records of reversible species such as nitrate and chloride, and show that the pattern of post-depositional losses described for shallower ice is maintained in older ice. It appears possible to use these concentrations to constrain snow accumulation rates in interglacial ice at this site, and the results suggest a possible correction to accumulation rates in one early interglacial. Taken together the chemistry records offer a number of constraints on the way the Earth system combined to give the major climate fluctuations of the late Quaternary period.

  • 228. Workman, C.
    et al.
    Dalen, L.
    Vartanyan, S.
    Shapiro, B.
    Kosintsev, P.
    Sher, A.
    Gotherstrom, A.
    Barnes, I.
    Population-level genotyping of coat colour polymorphism in woolly mammoth (Mammuthus primigenius)2011Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 17-18, s. 2304-2308Artikkel i tidsskrift (Fagfellevurdert)
  • 229. Workman, Claire
    et al.
    Dalen, Love
    Vartanyan, Sergey
    Shapiro, Beth
    Kosintsev, Pavel
    Sher, Andrei
    Gotherstrom, Anders
    Barnes, Ian
    Population-level genotyping of coat colour polymorphism in woolly mammoth (Mammuthus primigenius)2011Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 17-18, s. 2304-2308Artikkel i tidsskrift (Fagfellevurdert)
  • 230. Workman, Claire
    et al.
    Dalen, Love
    Vartanyan, Sergey
    Shapiro, Beth
    Kosintsev, Pavel
    Sher, Andrei
    Götherström, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Biologiska sektionen, Institutionen för ekologi och genetik, Evolutionsbiologi.
    Barnes, Ian
    Population-level genotyping of coat colour polymorphism in woolly mammoth (Mammuthus primigenius)2011Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 17-18, s. 2304-2308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Patterns in the spatial or temporal distribution of genotypes may be indicative of natural selection. Previous work on the woolly mammoth melanocortin-1 receptor (Mc1r) gene identified three polymorphic positions that suggest Pleistocene populations may have harboured both light- and dark-haired mammoths (Rompler et al., 2006, 313: 62). Here, we extend this work and present the first population-level analysis of a functional gene in an extinct species. We genotyped the Mc1r gene in 47 woolly mammoth samples excavated from sites across the central portion of the woolly mammoths' former range to examine the extent of variation of this polymorphism through time and across space. Only one individual was found to be heterozygous, indicating that the frequency of the 'light' mutant allele was very low. We conclude that light-coloured woolly mammoths would have been very rare, and may even have been non-existent if the 'light' mutant allele was strongly selected against in its homozygotic form. With the increasing availability of large-scale sequencing technologies, population-level datasets capable of identifying local adaptation will become increasingly attainable.

  • 231.
    Xu, Qinghai
    et al.
    Hebei Normal University, China.
    Zhang, Shengrui
    Chinese Academy of Sciences, China.
    Gaillard, Marie-José
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM).
    Li, Manyue
    Hebei Normal University, China.
    Cao, Xianyong
    Hebei Normal University, China ; Alfred Wegener Institute, Germany.
    Tian, Fang
    Hebei Normal University, China ; Alfred Wegener Institute, Germany.
    Li, Furong
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM).
    Studies of modern pollen assemblages for pollen dispersal- deposition- preservation process understanding and for pollen-based reconstructions of past vegetation, climate, and human impact: A review based on case studies in China2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 149, s. 151-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fossil pollen, as a direct proxy record of past vegetation, and indirect proxy record of past climate, plays an essential role in revealing and reconstructing past vegetation and climate. However, relationships between pollen, vegetation and climate are not linear, hence quantitative reconstructions of past vegetation and climate based on pollen records are not straightforward, and results may be highly contradictory and difficult to interpret. One of the main causes of discrepancies between results has been the lack of comprehensive and systematical studies on modern pollen dispersal and deposition processes, particularly on the quantification of these processes. Based on empirical studies performed in China over the last 30 years, this paper provides the state-of-the-art of the understanding of pollen dispersal and deposition processes in China and the remaining questions to be investigated. We show that major progress has been achieved in the study of modern pollen dispersal and deposition processes, and in the application of models of the pollen-vegetation-climate relationships for quantitative reconstruction of past vegetation and climate. However, several issues are not entirely solved or understood yet, such as how to quantify the reworking and re-deposition of pollen grains in quaternary alluvial sediments, the influence of pollen preservation on pollen assemblages, and human impact on vegetation. Even so, the progress made during the last decades makes it possible to achieve significantly more precise and informative reconstructions of past vegetation, land-use and climate in China than was possible earlier.

  • 232. Xuan, Chuang
    et al.
    Channell, James E. T.
    Polyak, Leonid
    Darby, Dennis A.
    Paleomagnetism of Quaternary sediments from Lomonosov Ridge and Yermak Plateau: implications for age models in the Arctic Ocean2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 32, s. 48-63Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Inclination patterns of natural remanent magnetization (NRM) in Quaternary sediment cores from the Arctic Ocean have been widely used for stratigraphic correlation and the construction of age models, however, shallow and negative NRM inclinations in sediments deposited during the Brunhes Chron in the Arctic Ocean appear to have a partly diagenetic origin. Rock magnetic and mineralogical studies demonstrate the presence of titanomagnetite and titanomaghemite. Thermal demagnetization of the NRM indicates that shallow and negative inclination components are largely “unblocked” below similar to 300 degrees C, consistent with a titanomaghemite remanence carrier. Following earlier studies on the Mendeleev Alpha Ridge, shallow and negative NRM inclination intervals in cores from the Lomonosov Ridge and Yermak Plateau are attributed to partial self-reversed chemical remanent magnetization (CRM) carried by titanomaghemite formed during seafloor oxidation of host (detrital) titanomagnetite grains. Distortion of paleomagnetic records due to seafloor maghemitization appears to be especially important in the perennially ice covered western (Mendeleev Alpha Ridge) and central Arctic Ocean (Lomonosov Ridge) and, to a lesser extent, near the ice edge (Yermak Plateau). On the Yermak Plateau, magnetic grain size parameters mimic the global benthic oxygen isotope record back to at least marine isotope stage 6, implying that magnetic grain size is sensitive to glacial interglacial changes in bottom-current velocity and/or detrital provenance. (C) 2011 Elsevier Ltd. All rights reserved.

  • 233.
    Yamoah, Kweku A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chabangborn, Akkaneewut
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Chulalongkorn University, Thailand.
    Chawchai, Sakonvan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Chulalongkorn University, Thailand.
    Schenk, Frederik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Smittenberg, Rienk H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    A 2000-year leaf wax-based hydrogen isotope record from Southeast Asia suggests low frequency ENSO-like teleconnections on a centennial timescale2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 148, s. 44-53Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Limited understanding of the complex dynamics of the tropical monsoon exists, partly due to inadequate paleo (hydro)-climate proxy data from monsoonal regions. This study presents a 2000-year long record of hydrogen isotope values of leaf wax (delta D-wax) from a sedimentary sequence recovered from Lake Pa Kho, Northern Thailand. Evaluation of present day rainfall patterns and water isotope data indicates that delta D-wax reflects the amount of rainfall and is also influenced by El Nino-Southern Oscillation (ENSO) dynamics. Over the last 2000 years, wettest conditions occurred between ca. 700 AD and ca. 1000 AD, whereas the driest intervals lasted from ca. 50 BCE to ca. 700 AD and from ca. 1300 AD to ca. 1500 AD. Further investigations to establish the spatiotemporal variability of ENSO within the wider tropical Asian-Pacific realm over centennial timescales revealed a low-frequency-tripole pattern between mainland SE Asia (MSEA), the tropical West Pacific, and the central-eastern Pacific, with a wetter than normal MSEA during El Nino-like climate conditions. This pattern stands in contrast to the annual event where El Nino cause drier conditions in MSEA. We hypothesize that on centennial timescales the land-sea contrast, which drives monsoon intensity in MSEA, is modulated by the latitudinal shift of the Walker circulation and associated ENSO dynamics.

  • 234.
    Yamoah, Kweku Kyei Afrifa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chabangborn, Akkaneewut
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chawchai, Sakonvan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Schenk, Frederik
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Smittenberg, Rienk
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    A 2000-year leaf wax-based hydrogen isotope record from Southeast Asia suggests low frequency ENSO-like teleconnections on a sub-millenial timescaleInngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457XArtikkel i tidsskrift (Fagfellevurdert)
  • 235. Yang, Tien-Nan
    et al.
    Lee, Teh-Quei
    Meyers, Philip A.
    Song, Sheng-Rong
    Kao, Shuh-Ji
    Löwemark, Ludvig
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chen, Rou-Fei
    Chen, Huei-Fen
    Wei, Kuo-Yen
    Fan, Cheng-Wei
    Shiau, Liang-Jian
    Chiang, Hong-Wei
    Chen, Yue-Gau
    Chen, Min-Te
    Variations in monsoonal rainfall over the last 21 kyr inferred from sedimentary organic matter in Tung-Yuan Pond, southern Taiwan2011Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 23-24, s. 3413-3422Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Changes in paleorainfall intensity linked to the strength of the East Asian (EA) summer monsoon since 21 cal kyr BP are inferred from the organic matter contents of a 15-m sediment core from Tung-Yuan Pond in southern Taiwan. High total organic carbon/total nitrogen (TOC/TN) values in association with increased TOC content suggest that more soil-derived material containing terrestrial organic matter (OM) was delivered to the lake during periods of increased runoff associated with extensive precipitation that resulted from intensified summer monsoons, whereas low values indicate OM possessing a dominant algal origin during weakened summer monsoons. Rainfall intensity in terms of the proportion of terrestrial OM was high in four periods: the last deglaciation (similar to 17.2 to similar to 12.2 ka), the early Holocene (similar to 10.6 to similar to 8.6 ka), the middle Holocene Thermal Optimum (similar to 7.7 to similar to 5 ka) and the late Holocene (similar to 4.2 to similar to 2 ka), whereas it was low in the intervening time periods. High TOC/TN values coincide with peak values of summer insolation, and thus the strongest EA summer monsoon during the early and middle Holocene: small drops in these ratios correspond to increasing and decreasing solar radiation in the deglacial period and the late Holocene, respectively. The four intervals with low TOC/TN ratios, as well as episodic drops of the ratios during the deglaciation and the early and late Holocene are concordant with the late last glacial (similar to 21 to similar to 17.2 ka), the Oldest (similar to 14.8 ka), the Older (similar to 13.3 ka) and the Younger Dryas (similar to 13 to similar to 11.5 ka), the 8.2 cold event (similar to 8.6-7.7 ka) and a late Holocene cold event (similar to 5-4.2 ka), and suggest a weakened EA summer monsoon during these times. Moreover, high frequency hydrological variability occurred during the early Holocene, heavy rainfall persisted during the middle Holocene, and precipitation intensity generally diminished after similar to 5 ka. The Tung-Yuan Pond sediment record indicates that the TOC/TN ratio can be used as a paleorainfall intensity proxy to trace variations in the EA summer monsoon strength in other small lakes. Crown Copyright

  • 236.
    Yi, Peng
    et al.
    Hohai Univ, State Key Lab Hydrol Water Resources & Hydraul En, Nanjing 210098, Jiangsu, Peoples R China;Joint Int Res Lab Global Change & Water Cycle, Nanjing 210098, Jiangsu, Peoples R China;Hohai Univ, Coll Hydrol & Water Resources, Nanjing 210098, Jiangsu, Peoples R China.
    Yu, Zhongbo
    Hohai Univ, State Key Lab Hydrol Water Resources & Hydraul En, Nanjing 210098, Jiangsu, Peoples R China;Joint Int Res Lab Global Change & Water Cycle, Nanjing 210098, Jiangsu, Peoples R China;Hohai Univ, Coll Hydrol & Water Resources, Nanjing 210098, Jiangsu, Peoples R China.
    Chen, Peng
    Hohai Univ, State Key Lab Hydrol Water Resources & Hydraul En, Nanjing 210098, Jiangsu, Peoples R China;Joint Int Res Lab Global Change & Water Cycle, Nanjing 210098, Jiangsu, Peoples R China;Hohai Univ, Coll Hydrol & Water Resources, Nanjing 210098, Jiangsu, Peoples R China.
    Aldahan, Ala
    United Arab Emirates Univ, Dept Geol, Al Ain 17551, U Arab Emirates.
    Hou, Xiaolin
    Chinese Acad Sci, State Key Lab Loess & Quaternary Geol, Inst Earth Environm, Xian AMS Ctr,Shaanxi Key Lab AMS Technol & Applic, Xian 710061, Shaanxi, Peoples R China;Tech Univ Denmark, Ctr Nucl Technol, Riso Campus, DK-4000 Roskilde, Denmark.
    Fan, Yukun
    Chinese Acad Sci, State Key Lab Loess & Quaternary Geol, Inst Earth Environm, Xian AMS Ctr,Shaanxi Key Lab AMS Technol & Applic, Xian 710061, Shaanxi, Peoples R China.
    Chen, Li
    Desert Res Inst, Div Hydrol Sci, Las Vegas, NV 89119 USA.
    Possnert, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, För teknisk-naturvetenskapliga fakulteten gemensamma enheter, Tandemlaboratoriet.
    Muscheler, Raimund
    Lund Univ, Dept Geol Quaternary Sci, S-22362 Lund, Sweden.
    Zhou, Weijian
    Chinese Acad Sci, State Key Lab Loess & Quaternary Geol, Inst Earth Environm, Xian AMS Ctr,Shaanxi Key Lab AMS Technol & Applic, Xian 710061, Shaanxi, Peoples R China.
    Sudicky, Edward
    Univ Waterloo, Dept Earth & Environm Sci, Waterloo, ON N2L 3G1, Canada.
    Schwartz, Frank
    Ohio State Univ, Sch Earth Sci, Columbus, OH 43210 USA.
    Murad, Ahmed
    United Arab Emirates Univ, Dept Geol, Al Ain 17551, U Arab Emirates.
    Late Holocene pathway of Asian Summer Monsoons imprinted in soils and societal implications2019Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 215, s. 35-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Asian Summer Monsoons (ASM) represent the main source of precipitation in China and East Asia with about one third of the world population and a region of widespread civilizations. Identifying the temporal and spatial patterns (pathways) of these monsoonal events during the Late Holocene to today has been a matter of debate amongst the scientific community. Here we show that the distribution patterns of the cosmogenic isotope Be-10 and oceanic I-127 in the topsoil across China exhibit imprints of the main ASM pathways. Our results indicate the monsoon pathway pattern persisted for several millennia or more and suggest a strong bond between Be-10 and water vapor transport patterns. Our data also reveal a(127)I distribution pattern controlled by the ASM pathways, rather than proximity to the sea or bedrock weathering. The persistent pathway of the ASM during the late Holocene, together with higher than average global soil iodine concentration, may have further strengthened the development of civilizations in this region of the world through reduction of iodine deficiency related diseases. (C) 2019 Elsevier Ltd. All rights reserved.

  • 237. Zale, R.
    et al.
    Huang, Y. -T
    Bigler, C.
    Wood, J. R.
    Dalén, L.
    Naturhistoriska riksmuseet, Enheten för bioinformatik och genetik.
    Wang, X. -R
    Segerstrom, U.
    Klaminder, J.
    Growth of plants on the Late Weichselian ice-sheet during Greenland interstadial-1?2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 185, s. 222-229Artikkel i tidsskrift (Fagfellevurdert)
  • 238.
    Zale, Rolf
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Huang, Y. -T
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Bigler, Christian
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wood, J. R.
    Dalén, L.
    Wang, Xiao-Ru
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Segerström, U.
    Klaminder, Jonatan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Growth of plants on the Late Weichselian ice-sheet during Greenland interstadial-1?2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 185, s. 222-229Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Unglaciated forelands and summits protruding from ice-sheets are commonly portrayed as areas where plants first establish at the end of glacial cycles. But is this prevailing view of ice-free refugia too simplistic? Here, we present findings suggesting that surface debris supported plant communities far beyond the rim of the Late Weichselian Ice-sheet during Greenland interstadial 1 (GI-1 or Bolling-Altered interstadial). We base our interpretations upon findings from terrigenous sediments largely resembling 'plant-trash' deposits in North America (known to form as vegetation established on stagnant ice became buried along with glacial debris during the deglaciation). In our studied deposit, we found macrofossils (N = 10) overlapping with the deglaciation period of the area (9.5-10 cal kyr BP) as well as samples (N = 2) with ages ranging between 12.9 and 13.3 cal kyr BP. The latter ages indicate growth of at least graminoids during the GI-1 interstadial when the site was near the geographic center of the degrading ice-sheet. We suggest that exposure of englacial material during GI-1 created patches of supraglacial debris capable of supporting vascular plants three millennia before deglaciation. The composition and resilience of this early plant community remain uncertain. Yet, the younger group of macrofossils, in combination with pollen and ancient DNA analyses of inclusions, imply that shrubs (Salix sp., Betula sp. and Ericaceae sp) and even tree species (Larix) were present in the debris during the final deglaciation stage. 

  • 239. Zolitschka, B.
    et al.
    Anselmetti, F.
    Ariztegui, D.
    Corbella, H.
    Francus, P.
    Luecke, A.
    Maidana, N. I.
    Ohlendorf, C.
    Schaebitz, F.
    Wastegård, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Environment and climate of the last 51,000 years - new insights from the Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO)2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, s. 1-12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this introductory paper we summarize the history and achievements of the Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO), an interdisciplinary project embedded in the International Continental Scientific Drilling Program (ICDP). The stringent multiproxy approach adopted in this research combined with radiocarbon and luminescence dating provided the opportunity to synthesize a large body of hydrologically relevant data from Laguna Potrok Aike (southern Patagonia, Argentina). At this site, lake level was high from 51 ka until the early Holocene when the Southern Hemisphere Westerlies (SHW) were located further to the north. At 9.3 ka cal. BP the SHW moved southward and over the latitude of the study area (52 degrees S) causing a pronounced negative water balance with a lake level decrease of more than 50 m. Two millennia later, the SHW diminished in intensity and lake level rose to a subsequent maximum during the Little Ice Age. Since the 20th century, a strengthening of the SHW increased the evaporative stress resulting in a more negative water balance. A comparison of our data with other hydrological fluctuations at a regional scale in south-eastern Patagonia, provides new insights and also calls for better chronologies and high-resolution records of climate variability.

2345 201 - 239 of 239
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf