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  • 51. Fitzsimmons, Kathryn E.
    et al.
    Cohen, Timothy J.
    Hesse, Paul P.
    Jansen, John
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Nanson, Gerald C.
    May, Jan-Hendrik
    Barrows, Timothy T.
    Haberlah, David
    Hilgers, Alexandra
    Kelly, Tegan
    Larsen, Joshua
    Lomax, Johanna
    Treble, Pauline
    Late Quaternary palaeoenvironmental change in the Australian drylands2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 74, s. 78-96Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we synthesise existing palaeoenvironmental data from the arid and semi-arid interior of the Australian continent for the period 40-0 ka. Moisture is the predominant variable controlling environmental change in the arid zone. Landscapes in this region respond more noticeably to changes in precipitation than to temperature. Depending on their location, arid zone records broadly respond to tropical monsoon-influenced climate regimes, the temperate latitude westerly systems, or a combination of both. The timing and extent of relatively arid and humid phases vary across the continent, in particular between the westerly wind-controlled temperate latitudes, and the interior and north which are influenced by tropically sourced precipitation. Relatively humid phases in the Murray-Darling Basin on the semi-arid margins, which were characterised by large rivers most likely fed by snow melt, prevailed from 40 ka to the Last Glacial Maximum (LGM), and from the deglacial to the mid Holocene. By contrast, the Lake Eyre basin in central Australia remained relatively dry throughout the last 40 ka, with lake high stands at lake Frome around 35-30 ka, and parts of the deglacial period and the mid-Holocene. The LGM was characterised by widespread relative aridity and colder conditions, as evidenced by extensive desert dune activity and dust transport, lake level fall, and reduced but episodic fluvial activity. The climate of the deglacial period was spatially divergent. The southern part of the continent experienced a brief humid phase around similar to 17-15 ka, followed by increased dune activity around similar to 14-10 ka. This contrasts with the post-LGM persistence of arid conditions in the north, associated with a lapsed monsoon and reflected in lake level lows and reduced fluvial activity, followed by intensification of the monsoon and increasingly effective precipitation from similar to 14 ka. Palaeoenvironmental change during the Holocene was also spatially variable. The early to mid-Holocene was, however, generally characterised by moderately humid conditions, demonstrated by lake level rise, source-bordering dune activity, and speleothem growth, persisting at different times across the continent. Increasingly arid conditions developed into the late Holocene, particularly in the central arid zone.

  • 52. Flink, Anne E.
    et al.
    Noormets, Riko
    Fransner, Oscar
    Hogan, Kelly A.
    O'Regan, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Past ice flow in Wahlenbergfjorden and its implications for late Quaternary ice sheet dynamics in northeastern Svalbard2017Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 163, s. 162-179Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wahlenbergfjorden is a fjord situated in the western part of Nordaustlandet in northern Svalbard. It leads into the 400 m deep Hinlopen Strait located between Nordaustlandet and Spitsbergen. High-resolution multibeam bathymetric and sub-bottom data, as well as sediment cores are used to study the past extent and dynamics of glaciers in Wahlenbergfjorden and western Nordaustlandet. The submarine landform assemblage in Wahlenbergfjorden consists of landforms characteristic of subglacial, ice marginal and proglacial conditions. Glacial lineations indicate that Wahlenbergfjorden was occupied by streaming ice during the LGM and most likely acted as an ice stream onset zone. Westward ice flow in the fjord merged with the ice stream in Hinlopen Strait. Absence of ice recessional landforms in outer Wahlenbergfjorden suggests relatively fast deglaciation, possibly by flotation of the glacier front in the deeper parts of the fjord. The inner part of Wahlenbergfjorden and Palanderbukta are characterized by De Geer moraines, indicating episodic retreat of a grounded glacier front. In Palanderbukta, longer still stands of the glacier terminus resulted in the formation of larger terminal moraine ridges. The inner part of Wahlenbergfjorden was deglaciated prior to 11.3 +/- 55 Cal. ka BP. The submarine landform assemblages in front of Bodleybreen, Etonbreen, Idunbreen, Frazerbreen and Aldousbreen confirm that these glaciers have surged at least once during the Holocene.

  • 53. Flink, Anne Elina
    et al.
    Noormets, Riko
    Kirchner, Nina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Benn, Douglas I.
    Luckman, Adrian
    Lovell, Harold
    The evolution of a submarine landform record following recent and multiple surges of Tunabreen glacier, Svalbard2015Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 108, s. 37-50Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study focuses on the glacial landform record associated with recent surge events of Tunabreen - a calving tidewater glacier in Tempelfjorden, Spitsbergen. Submarine geomorphology and recent terminal fluctuations of Tunabreen's glacier front were studied using high-resolution multibeam-bathymetric data and a range of published and remote-sensing sources, including topographic maps, satellite images and aerial photographs. The retreat moraines in the inner part of Tempelfjorden have been correlated with glacier terminus positions during retreat from the 2004 surge maximum. Glacier surface velocity and ice-front positions derived from high-resolution TerraSAR-X satellite data show ice movements at the glacier front during minor advances of the front in winter when calving is suppressed. This suggests that the moraines have formed annually during quiescent phase winter advances. Tunabreen has experienced three surges since the Little Ice Age (LIA). This is in contrast with most Svalbard surging glaciers which have long quiescent phases and have typically only undergone one or two surges during this time. The landform record in Tempelfjorden is distinguished from previously studied glacier-surge landsystems by four, well-preserved sets of landform assemblages generated by the LIA advance and three subsequent surges, all of which partly modify earlier landform records. Based on the unique landform record in Tempelfjorden, a new conceptual landsystem model for frequently surging glaciers has been put forward improving our understanding of the dynamics of the surging glaciers and, most importantly, how they can be distinguished from the climatically-controlled glaciers in the geological record.

  • 54.
    Fu, Ping
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK). Purdue University.
    Stroeven, Arjen P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Harbor, Jonathan M.
    Hättestrand, Clas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Heyman, Jakob
    Caffee, Marc W.
    Zhou, Liping
    Paleoglaciation of Shaluli Shan, southeastern Tibetan Plateau2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 64, s. 121-135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reconstructing the paleoglaciation of the Tibetan Plateau is critical to understanding linkages between regional climate changes and global climate changes, and here we focus on the glacial history of the Shaluli Shan, an area of the southeastern Tibetan Plateau that receives much of its precipitation from monsoon flow. Based on field investigation, geomorphological mapping, and Be-10 exposure dating of moraines, we identify glacial deposits from the Late Glacial, with minimum ages at 13.0 +/- 1.2 -17.1 +/- 1.6 ka, global Last Glacial Maximum (gLGM) at 21.6 +/- 2.0 ka, and pre-gLGM at 102.3 +/- 10.0-183.6 +/- 17.0 ka. These ages are consistent with and significantly extend the known range from most prior chronological work using terrestrial cosmogenic nuclides in this area, and include a set of dates for the Kuzhaori moraine that raise questions about prior chronologies based on the electron spin resonance technique. Ice caps about 4000 km(2) in size covered the Haizishan Plateau and the Xinlong Plateau during the global LGM, with large glaciers extending far down outlet valleys. The presence of ice cap glaciation, here, contrasts strongly to glaciation elsewhere in the Shaluli Shan and more central regions of the Tibetan Plateau where ice expansion remained constricted to valleys. This work provides important insights into the paleoclimate pattern and monsoon evolution of the Tibetan Plateau over past glacial cycles and indicates that the Shaluli Shan has a glacial chronology more consistent with the Northern Hemisphere paleo-ice sheets than other areas of the Tibetan Plateau.

  • 55.
    Fyfe, Ralph M.
    et al.
    Plymouth University, UK.
    Twiddle, Claire
    University of Aberdeen, UK.
    Sugita, Shinya
    Tallinn University, Estonia.
    Gaillard, Marie-José
    Linnéuniversitetet, Fakulteten för Hälso- och livsvetenskap (FHL), Institutionen för biologi och miljö (BOM).
    Barratt, Philip
    Queen's University of Belfast, UK.
    Caseldine, Christopher J.
    University of Exeter, UK.
    Dodson, John
    Institute for Environmental Research, Australia.
    Edwards, Kevin J.
    University of Aberdeen, UK.
    Farrell, Michelle
    University of Hull, UK.
    Froyd, Cynthia
    Swansea University, UK.
    Grant, Michael J.
    Wessex Archaeology, UK;Kingston University, UK.
    Huckerby, Elizabeth
    Oxford Archaeology North, UK.
    Innes, James B.
    Durham University, UK.
    Shaw, Helen
    Lancaster University, UK.
    Waller, Martyn
    Kingston University, UK.
    The Holocene vegetation cover of Britain and Ireland: overcoming problems of scale and discerning patterns of openness2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 73, s. 132-148Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The vegetation of Europe has undergone substantial changes during the course of the Holocene epoch, resulting from range expansion of plants following climate amelioration, competition between taxa and disturbance through anthropogenic activities. Much of the detail of this pattern is understood from decades of pollen analytical work across Europe, and this understanding has been used to address questions relating to vegetation-climate feedback, biogeography and human impact. Recent advances in modelling the relationship between pollen and vegetation now make it possible to transform pollen proportions into estimates of vegetation cover at both regional and local spatial scales, using the Landscape Reconstruction Algorithm (LRA), i.e. the REVEALS (Regional Estimates of VEgetation Abundance from Large Sites) and the LOVE (Local VEgetation) models. This paper presents the compilation and analysis of 73 pollen stratigraphies from the British Isles, to assess the application of the LRA and describe the pattern of landscape/woodland openness (i.e. the cover of low herb and bushy vegetation) through the Holocene. The results show that multiple small sites can be used as an effective replacement for a single large site for the reconstruction of regional vegetation cover. The REVEALS vegetation estimates imply that the British Isles had a greater degree of landscape/woodland openness at the regional scale than areas on the European mainland. There is considerable spatial bias in the British Isles dataset towards wetland areas and uplands, which may explain higher estimates of landscape openness compared with Europe. Where multiple estimates of regional vegetation are available from within the same region inter-regional differences are greater than intra-regional differences, supporting the use of the REVEALS model to the estimation of regional vegetation from pollen data. (C) 2013 Elsevier Ltd. All rights reserved.

  • 56.
    Gallagher, S. J.
    et al.
    Univ Melbourne, Sch Earth Sci, Melbourne, Vic 3010, Australia.
    Reuning, L.
    Rhein Westfal TH Aachen, Geol Inst, EMR Energy & Mineral Resources Grp, Wuellnerstr 2, D-52056 Aachen, Germany.
    Himmler, T.
    Geol Survey Norway, Postal Box 6315 Torgarden, N-7491 Trondheim, Norway.
    Henderiks, Jorijntje
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleobiologi.
    De Vleeschouwer, D.
    Univ Bremen, MARUM Ctr Marine & Environm Sci, D-28334 Bremen, Germany;Univ Bremen, Dept Geosci, D-28334 Bremen, Germany.
    Groeneveld, J.
    Univ Bremen, MARUM Ctr Marine & Environm Sci, D-28334 Bremen, Germany;Univ Bremen, Dept Geosci, D-28334 Bremen, Germany.
    Lari, A. Rastegar
    Univ Western Australia, Sch Earth Sci, 35 Stirling Highway, Nedlands, WA 6009, Australia.
    Fulthorpe, C. S.
    Univ Texas Austin, Inst Geophys, 10100 Burnet Rd R2200, Austin, TX 78758 USA.
    Bogus, K.
    Univ Exeter, Coll Engn Math & Phys Sci, Camborne Sch Mines, Penryn TR10 9FE, Cornwall, England.
    The enigma of rare Quaternary oolites in the Indian and Pacific Oceans: A result of global oceanographic physicochemical conditions or a sampling bias?2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 200, s. 114-122Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Marine ooids are iconic indicators of shallow seawater carbonate saturation state, and their formation has traditionally been ascribed to physicochemical processes. The Indo-Pacific stands out as a region devoid of oolites, particularly during the Quaternary: the "ooid enigma". Here we present results from recent coring by the International Ocean Discovery Program (IODP Expedition 356) off west Australia that shows that ooid horizons are common in Pleistocene strata up to 730,000 years old. Extensive "ooid factories" were created due to the presence of long-lived tidally influenced flat topped tropical platforms suitable for intermittent ooid accretion over hundreds to thousands of years during highstands and times of lower sea level. This work suggests marine ooids may actually be more common in Indo-Pacific than previously reported. Past global ocean alkalinity was elevated during Pleistocene glacial periods and continental climate was generally more arid in the Indo-Pacific region compared to interglacials and the Holocene. Therefore, increased aridity associated with higher alkalinity conditions during the glacials facilitated ooid precipitation on adjacent tropical carbonate platforms particularly offshore from arid Australia. This confluence of factors suggests that more "ooid factories" may be encountered by further coring Indo-Pacific regions with Pleistocene flat long-lived carbonate shelves. However, Indo-Pacific Quaternary ooid occurrences outside Australia are rare, suggesting that the Northwest Shelf may be a unique archive of this non-skeletal precipitate. Further investigations into the petrography and geochemistry of pre-Holocene ooid occurrences will provide insights into their origin and the relative role of biotic, physicochemical and other factors in their formation. (C) 2018 Elsevier Ltd. All rights reserved.

  • 57. Garcia, Marga
    et al.
    Dowdeswell, Julian A.
    Ercilla, Gemma
    Jakobsson, Martin
    Recent glacially influenced sedimentary processes on the East Greenland continental slope and deep Greenland Basin2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 49, s. 64-81Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the morpho-sedimentary characterization and interpretations of the assemblage of landforms of the East Greenland continental slope and Greenland Basin, based on swath bathymetry and sub-bottom TOPAS profiles. The interpretation of landforms reveals the glacial influence on recent sedimentary processes shaping the seafloor, including mass-wasting and turbidite flows. The timing of landform development points to a predominantly glacial origin of the sediment supplied to the continental margin, supporting the scenario of a Greenland Ice Sheet extending across the continental shelf, or even to the shelf-edge, during the Last Glacial Maximum (LGM). Major sedimentary processes along the central section of the eastern Greenland Continental Slope, the Norske margin, suggest a relatively high glacial sediment input during the LGM that, probably triggered by tectonic activity, led to the development of scarps and channels on the slope and debris flows on the continental rise. The more southerly Kejser Franz Josef margin has small-scale mass-wasting deposits and an extensive turbidite system that developed in relation to both channelised and unconfined turbidity flows which transferred sediments into the deep Greenland Basin. (C) 2012 Elsevier Ltd. All rights reserved.

  • 58. Garcia, Marga
    et al.
    Dowdeswell, Julian A.
    Ercilla, Gemma
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Recent glacially influenced sedimentary processes on the East Greenland continental slope and deep Greenland Basin2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 49, s. 64-81Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    This paper presents the morpho-sedimentary characterization and interpretations of the assemblage of landforms of the East Greenland continental slope and Greenland Basin, based on swath bathymetry and sub-bottom TOPAS profiles. The interpretation of landforms reveals the glacial influence on recent sedimentary processes shaping the seafloor, including mass-wasting and turbidite flows. The timing of landform development points to a predominantly glacial origin of the sediment supplied to the continental margin, supporting the scenario of a Greenland Ice Sheet extending across the continental shelf, or even to the shelf-edge, during the Last Glacial Maximum (LGM). Major sedimentary processes along the central section of the eastern Greenland Continental Slope, the Norske margin, suggest a relatively high glacial sediment input during the LGM that, probably triggered by tectonic activity, led to the development of scarps and channels on the slope and debris flows on the continental rise. The more southerly Kejser Franz Josef margin has small-scale mass-wasting deposits and an extensive turbidite system that developed in relation to both channelised and unconfined turbidity flows which transferred sediments into the deep Greenland Basin.

  • 59. Gierga, Merle
    et al.
    Hajdas, Irka
    van Raden, Ulrike J.
    Gilli, Adrian
    Wacker, Lukas
    Sturm, Michael
    Bernasconi, Stefano M.
    Smittenberg, Rienk H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Long-stored soil carbon released by prehistoric land use: Evidence from compound-specific radiocarbon analysis on Soppensee lake sediments2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 144, s. 123-131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Compound-specific radiocarbon (C-14) analyses allow studying the fate of individual biomarkers in ecosystems. In lakes with small catchments, terrestrial biomarkers have the potential to be used for the dating of sediments that lack the traditionally targeted terrestrial macrofossils, if the specific organic compounds are deposited soon after production. On the other hand, if the biomarkers have been stored for a significant amount of time in the soils of the catchment before transported to the lake, their age can be used to reconstruct changes in average residence time of organic material on land through time. Here we present a study based on compound-specific C-14 analysis of the sedimentary record of Lake Soppensee, Switzerland, targeting long-chain n-alkanes of exclusive terrigenous origin, and comparing them with sediment ages obtained by high-resolution macrofossil dating. Additionally, we measured C-14 ages of bulk organic matter and carbonate samples to assess the hard water effect. Prior to 3100 cal BP n-alkanes had about the same age as the sediment or they were slightly older, indicating that the vast majority of the terrestrial organic carbon transported to the lake had a short residence time on land. In the samples younger than 3100 cal BP an increasing offset is observed, indicating liberation of old buried soil organic matter that must have accumulated over the previous millennia. Our results indicate that as long as stable ecosystem conditions have prevailed, the distribution and isotopic composition of the n-alkanes can be used as environmental proxies in small catchments with limited surface runoff, confirming a few earlier studies.

  • 60.
    Giesecke, Thomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleobiologi.
    Moving front or population expansion: How did Picea abies (L.) Karst. become frequent in central Sweden?2005Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 24, nr 23-24, s. 2495-2509Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Holocene increase in Picea abies around four central Swedish lakes was analysed using extended pollen counts over the sections comprising the tail of frequent, but discontinuous, occurrences and the beginning of the continuous curve. Simple landscape scenarios were simulated to test possible mechanisms of the spread and population expansion of P. abies in Scandinavia. Predicted patterns of pollen accumulation rates from the landscape scenarios were compared to patterns observed at the four sites to explore how the observed curves could have come about. Simulations of a moving front scenario indicate that pollen accumulation rates should rise faster than the exponential and logistic increase observed at the four sites. Exponential increase of pollen values at the sites is most likely due to locally increasing populations. However, the geography of expanding populations may influence the shape of the curve. Empirical and model results are discussed to gain new insights into the pattern and processes of the spread of P abies in central Sweden. Propagule pressure and self-fertilisation are considered as possible explanations of why small outpost populations that may have existed before the regional expansion of P. abies did not expand earlier.

  • 61. Giesecke, Thomas
    et al.
    Bennett, Keith D.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleobiologi.
    Birks, H. John B.
    Bjune, Anne E.
    Bozilova, Elisaveta
    Feurdean, Angelica
    Finsinger, Walter
    Froyd, Cynthia
    Pokorny, Petr
    Roesch, Manfred
    Seppa, Heikki
    Tonkov, Spasimir
    Valsecchi, Verushka
    Wolters, Steffen
    The pace of Holocene vegetation change: testing for synchronous developments2011Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 19-20, s. 2805-2814Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Mid to high latitude forest ecosystems have undergone several major compositional changes during the Holocene. The temporal and spatial patterns of these vegetation changes hold potential information to their causes and triggers. Here we test the hypothesis that the timing of vegetation change was synchronous on a sub-continental scale, which implies a common trigger or a step-like change in climate parameters. Pollen diagrams from selected European regions were statistically divided into assemblage zones and the temporal pattern of the zone boundaries analysed. The results show that the temporal pattern of vegetation change was significantly different from random. Times of change cluster around 8.2, 4.8, 3.7, and 1.2 ka, while times of higher than average stability were found around 2.1 and 5.1 ka. Compositional changes linked to the expansion of Corylus avellana and Alnus glutinosa centre around 10.6 and 9.5 ka, respectively. A climatic trigger initiating these changes may have occurred 0.5 to 1 ka earlier, respectively. The synchronous expansion of C avellana and A. glutinosa exemplify that dispersal is not necessarily followed by population expansion. The partly synchronous, partly random expansion of A. glutinosa in adjacent European regions exemplifies that sudden synchronous population expansions are not species specific traits but vary regionally.

  • 62. Glasser, Neil F.
    et al.
    Harrison, Stephan
    Schnabel, Christoph
    Fabel, Derek
    Jansson, Krister N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Younger Dryas and early Holocene age glacier advances in Patagonia2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 58, s. 7-17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reliable dating of Southern Hemisphere glacier fluctuations since the Last Glacial Maximum (LGM) is crucial to resolving debates about millennial-scale climate change. Here we present Be-10 dates for lateral, valley-mouth and cross-valley moraines formed between the contemporary South American North Patagonian Icefield (NPI) and its LGM position in four separate valleys around 47 degrees S. This is an area near the core of the precipitation-bearing southern westerly winds, where it is known that rapid shifts in climate occurred during Lateglacial times. The dates indicate that outlet glaciers advanced, or at least stabilised, to form large moraines east of an expanded NPI at 11.0 +/- 0.5/11.2 +/- 0.6, 11.5 +/- 0.6, 11.7 +/- 0.6 and 12.8 +/- 0.7 ka (Putnam southern-hemisphere production rates and Dunai scaling scheme, assumed boulder erosion rate of 2 mm/ka). Four of these ages are statistically indistinguishable and probably represent a single, regional ice advance. The dates indicate that glaciers in Patagonia were larger during these times than at any point since the LGM and provide evidence in Patagonia for glacier advances around the time of the European Younger Dryas (12.9-11.7 ka) and into the very early Holocene. Although palaeoclimatic records from this area are often contradictory, these glacier advances were probably associated with a period of cooling or regionally increased precipitation related to the changes in the position of the southern westerly winds.

  • 63. Glasser, Neil
    et al.
    Harrison, Stephan
    Jansson, Krister
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Topographic controls on glacier sediment–landform associations around the temperate North Patagonian Icefield.2009Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 28, s. 2817-2831Artikkel i tidsskrift (Fagfellevurdert)
  • 64.
    Goodfellow, Bradley W.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK). Stanford University, USA.
    A granulometry and secondary mineral fingerprint of chemical weathering in periglacial landscapes and its application to blockfield origins2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 57, s. 121-135Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A review of published literature was undertaken to determine if there was a fingerprint of chemical weathering in regoliths subjected to periglacial conditions during their formation. If present, this fingerprint would be applied to the question of when blockfields in periglacial landscapes were initiated. These blocky diamicts are usually considered to represent remnants of regoliths that were chemically weathered under a warm, Neogene climate and therefore indicate surfaces that have undergone only a few metres to a few 10s of metres of erosion during the Quaternary. Based on a comparison of clay and silt abundances and secondary mineral assemblages from blockfields, other regoliths in periglacial settings, and regoliths from non-periglacial settings, a fingerprint of chemical weathering in periglacial landscapes was identified. A mobile regolith origin under, at least seasonal, periglacial conditions is indicated where clay(%) ≤ 0.5*silt(%) + 8 across a sample batch. This contrasts with a mobile regolith origin under non-periglacial conditions, which is indicated where clay(%) ≥ 0.5*silt(%) − 6 across a sample batch with clay(%) ≥ 0.5*silt(%) + 8 in at least one sample. A range of secondary minerals, which frequently includes interstratified minerals and indicates high local variability in leaching conditions, is also commonly present in regoliths exposed to periglacial conditions during their formation. Clay/silt ratios display a threshold response to temperature, related to the freezing point of water, but there is little response to precipitation or regolith residence time. Lithology controls clay and silt abundances, which increase from felsic, through intermediate, to mafic compositions, but does not control clay/silt ratios. Use of a sedigraph or Coulter Counter to determine regolith granulometry systematically indicates lower clay abundances and intra-site variability than use of a pipette or hydrometer. In contrast to clay/silt ratios, secondary mineral assemblages vary according to regolith residence time, temperature, and/or precipitation. A microsystems model is invoked as a conceptual framework in which to interpret the concurrent formation of the observed secondary mineral ranges. According to the fingerprint of chemical weathering in periglacial landscapes, there is generally no evidence of blockfield origins under warm Neogene climates. Nearly all blockfields appear to be a product of Quaternary physical and chemical weathering. A more dominant role for periglacial processes in further bevelling elevated, low relief, non-glacial surface remnants in otherwise glacially eroded landscapes is therefore indicated.

  • 65. Goosse, H.
    et al.
    Roche, D. M.
    Mairesse, A.
    Berger, Marit
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Modelling past sea ice changes2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 79, s. 191-206Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A dominant characteristic of the available simulations of past sea ice changes is the strong link between the model results for modern and past climates. Nearly all the models have similar extent for pre-industrial conditions and for the mid-Holocene. The models with the largest extent at Last Glacial Maximum (LGM) are also characterized by large pre-industrial values. As a consequence, the causes of model biases and of the spread of model responses identified for present-day conditions appear relevant when simulating the past sea ice changes. Nevertheless, the models that display a relatively realistic sea-ice cover for present-day conditions often display contrasted response for some past periods. The difference appears particularly large for the LGM in the Southern Ocean and for the summer ice extent in the Arctic for the early Holocene (and to a smaller extent for the mid-Holocene). Those periods are thus key ones to evaluate model behaviour and model physics in conditions different from those of the last decades. Paleoclimate modelling is also an invaluable tool to test hypotheses that could explain the signal recorded by proxies and thus to improve our understanding of climate dynamics. Model analyses have been focused on specific processes, such as the role of atmospheric and ocean heat transport in sea ice changes or the relative magnitude of the model response to different forcings. The studies devoted to the early Holocene provide an interesting example in this framework as both radiative forcing and freshwater discharge from the ice sheets were very different compared to now. This is thus a good target to identify the dominant processes ruling the system behaviour and to evaluate the way models represent them.

  • 66.
    Gowan, Evan J.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. The Australian National University, Australia.
    Tregoning, Paul
    Purcell, Anthony
    Montillet, Jean-Philippe
    McClusky, Simon
    A model of the western Laurentide Ice Sheet, using observations of glacial isostatic adjustment2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 139, s. 1-16Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    We present the results of a new numerical model of the late glacial western Laurentide Ice Sheet, constrained by observations of glacial isostatic adjustment (GIA), including relative sea level indicators, uplift rates from permanent GPS stations, contemporary differential lake level change, and postglacial tilt of glacial lake level indicators. The later two datasets have been underutilized in previous GIA based ice sheet reconstructions. The ice sheet model, called NAICE, is constructed using simple ice physics on the basis of changing margin location and basal shear stress conditions in order to produce ice volumes required to match GIA. The model matches the majority of the observations, while maintaining a relatively realistic ice sheet geometry. Our model has a peak volume at 18,000 yr BP, with a dome located just east of Great Slave Lake with peak thickness of 4000 m, and surface elevation of 3500 m. The modelled ice volume loss between 16,000 and 14,000 yr BP amounts to about 7.5 m of sea level equivalent, which is consistent with the hypothesis that a large portion of Meltwater Pulse 1A was sourced from this part of the ice sheet. The southern part of the ice sheet was thin and had a low elevation profile. This model provides an accurate representation of ice thickness and paleo-topography, and can be used to assess present day uplift and infer past climate.

  • 67.
    Greenwood, Sarah L.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Clark, Chris D.
    University of Sheffield, Department of Geography.
    Reconstructing the last Irish Ice Sheet 1: changing flow geometries and ice flow dynamics deciphered from the glacial landform record2009Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 28, s. 3085-3100Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The glacial geomorphological record provides an effective means to reconstruct former ice sheets at ice sheet scale. In this paper we document our approach and methods for synthesising and interpreting a glacial landform record for its palaeo-ice flow information, applied to landforms of Ireland. New, countrywide glacial geomorphological maps of Ireland comprising >39,000 glacial landforms are interpreted for the spatial, glaciodynamic and relative chronological information they reveal. Seventy one ‘flowsets’ comprising glacial lineations, and 19 ribbed moraine flowsets are identified based on the spatial properties of these landforms, yielding information on palaeo-ice flow geometry. Flowset crosscutting is prevalent and reveals a highly complex flow geometry; major ice divide migrations are interpreted with commensurate changes in the flow configuration of the ice sheet. Landform superimposition is the key to deciphering the chronology of such changes, and documenting superimposition relationships yields a relative ‘age-stack’ of all Irish flowsets. We use and develop existing templates for interpreting the glaciodynamic context of each flowset – its palaeo-glaciology. Landform patterns consistent with interior ice sheet flow, ice stream flow, and with time-transgressive bedform generation behind a retreating margin, under a thinning ice sheet, and under migrating palaeo-flowlines are each identified. Fast ice flow is found to have evacuated ice from central and northern Ireland into Donegal Bay, and across County Clare towards the south-west. Ice-marginal landform assemblages form a coherent system across southern Ireland marking stages of ice sheet retreat. Time-transgressive, ‘smudged’ landform imprints are particularly abundant; in several ice sheet sectors ice flow geometry was rapidly varying at timescales close to the timescale of bedform generation. The methods and approach we document herein could be useful for interpreting other ice sheet histories. The flowsets and their palaeo-glaciological significance that we derive for Ireland provide a regional framework and context for interpreting results from local scale fieldwork, provide major flow events for testing numerical ice sheet models, and underpin a data-driven reconstruction of the Irish Ice Sheet that we present in an accompanying paper – Part 2.

  • 68.
    Greenwood, Sarah L.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Clark, Chris D.
    University of Sheffield, Department of Geography.
    Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics2009Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 28, s. 3101-3123Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheetproperties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel – Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.

  • 69.
    Greenwood, Sarah L.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Kleman, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Glacial landforms of extreme size in the Keewatin sector of the Laurentide Ice Sheet2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 15-16, s. 1894-1910Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Assemblages of glacial landforms of a 'mega-scale' are here identified in the Keewatin sector of the Laurentide Ice Sheet. Large till 'belts' or 'ridges', apparent only on satellite imagery and lying beneath the drumlins, flutes and ribbed moraine which comprise the known regional glacial landform record, form extensive and coherent patterns throughout the Keewatin region. Planform and crestline mapping from remotely sensed imagery yields a mapped population of >2500 individual landforms, whose dimensions are on average similar to 10 km long and similar to 1.5 km wide. Based on analysis of their morphology and morphometry, their spatial arrangement and pattern, and comparison with analogues and reference populations of glacial landform types, we interpret three morphological groups of different genetic origin. Two of these are examples of currently known landform types: i) a set of heavily overprinted, i.e. non-pristine, mega-scale glacial lineations, feeding from the heart of the Keewatin region north into Queen Maud Gulf; and ii) a 350 km long moraine zone, overrun by later ice flow paths, and likely associated with the terminal position of an ice sheet prior to the final deglacial episode. A third group, comprising a significant number of the Keewatin population, does not fit any existing category of glacial landforms. Here we report a major new finding: subglacial bedforms, of a mega-scale, transverse to the palaeo-ice flow direction. Mega-scale transverse bedforms have not been previously reported from any palaeo-(or contemporary) ice sheet. Close spatial integration with the ribbed moraine population in Keewatin suggests a similar mode of genesis. The Keewatin landforms indicate there is a fundamental transverse organisation of till at a scale beyond that of conventional transverse bedforms (ribbed moraine), and with as yet unknown implications for our understanding of subglacial processes and ice-bed coupling.

  • 70.
    Gribenski, Natacha
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Jansson, Krister N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Lukas, Sven
    Stroeven, Arjen P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Harbor, Jonathan M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Purdue University, USA.
    Blomdin, Robin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Ivanov, Mikhail N.
    Heyman, Jakob
    Petrakov, Dmitry A.
    Rudoy, Alexei
    Clifton, Tom
    Lifton, Nathaniel A.
    Caffee, Marc W.
    Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 149, s. 288-305Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Southern part of the Russian Altai Mountains is recognized for its evidence for catastrophic glacial lake outbursts. However, little is known about the late Pleistocene paleoglacial history, despite the interest in such reconstructions for constraining paleoclimate. In this study, we present a detailed paleoglaciological reconstruction of the Chagan Uzun Valley, in the Russian Altai Mountains, combining for the first time detailed geomorphological mapping, sedimentological logging, and in situ cosmogenic 10Be and 26Al surface exposure dating of glacially-transported boulders. The Chagan Uzun Valley exhibits the most impressive glacial landforms of this sector of the Altai, with extensive lobate moraine belts deposited in the intramontane Chuja Basin, reflecting a series of pronounced former glacial advances. Observations of “hillside-scale” folding and extensive faulting of pre-existing soft sediments within the outer moraine belts, together with the geomorphology, strongly indicate that these moraine belts were formed during surge-like events. Identification of surge-related features is essential for paleoclimate inference because these features correspond to a glacier system that is not in equilibrium with the contemporary climate, but instead largely influenced by various internal and external factors. Therefore, no strict relationship can be established between climatic variables and the pronounced distal glacial extent observed in the Chagan Uzun Valley/Chuja basin. In contrast, the inner (up-valley) glacial landforms of the Chagan Uzun valley were likely deposited during retreat of temperate valley glaciers, close to equilibrium with climate, and so most probably triggered by a general warming. Cosmogenic ages associated with the outermost, innermost, and intermediate stages all indicate deposition times clustered around 19 ka. However, the actual deposition time of the outermost moraine may slightly predate the 10Be ages due to shielding caused by subsequent lake water coverage. This chronology indicates a Marine Isotope Stage (MIS) 2 last maximum extent of the Chagan Uzun Glacier, and an onset of the deglaciation around 19 ka. This is consistent with other regional paleoclimate proxy records and with the Northern Hemisphere glaciation chronology. Finally, this study also highlights the highly dynamic environment in this area, with complex interactions between glacial events and the formation and drainage of lakes.

  • 71.
    Gribenski, Natacha
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Lukas, Sven
    Stroeven, Arjen P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Jansson, Krister N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Harbor, Jonathan M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Purdue University, USA.
    Blomdin, Robin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Ivanov, Mikhail N.
    Heyman, Jakob
    Petrakov, Dmitry A.
    Rudoy, Alexei
    Clifton, Tom
    Lifton, Nathaniel A.
    Caffee, Marc W.
    Reply to comment received from J. Herget et al. regarding "Complex patterns of glacier advances during the late glacial in the Chagan Uzun Valley, Russian Altai" by Gribenski et al. (2016), Quaternary Science Reviews 149, 288-3052017Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 168, s. 219-221Artikkel i tidsskrift (Fagfellevurdert)
  • 72.
    Gurjazkaite, Karolina
    et al.
    Linköpings universitet, Institutionen för tema, Tema Miljöförändring. Linköpings universitet, Filosofiska fakulteten.
    Routh, Joyanto
    Linköpings universitet, Institutionen för tema, Tema Miljöförändring. Linköpings universitet, Filosofiska fakulteten.
    Djamali, Morteza
    Univ Avignon, France.
    Vaezi, Alireza
    Univ Tehran, Iran.
    Poher, Yoann
    Univ Avignon, France.
    Beni, Abdolmajid Naderi
    Iranian Natl Inst Oceanog and Atmospher Sci, Iran.
    Tavakoli, Vahid
    Univ Tehran, Iran.
    Kylin, Henrik
    Linköpings universitet, Institutionen för tema, Tema Miljöförändring. Linköpings universitet, Filosofiska fakulteten.
    Vegetation history and human-environment interactions through the late Holocene in Konar Sandal, SE Iran2018Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 194, s. 143-155Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Jiroft valley, situated on banks of the Halil Rud developed as an important agricultural and trading center during the Early Bronze Age. Known for its famous steatite sculptures and clay pottery, the first settlement in Konar Sandal collapsed around 3rd millennium BCE. A second shorter, but major phase of occupation in the settlement occurred towards the end of 2nd millennium BCE. A 250-cm long peat sequence near the archaeological complex at Konar Sandal was investigated to reconstruct the human environment history using palynological, sedimentological and geochemical data. With a basal age of 4 ka, the core traces the hydroclimatic changes and human activities that started just after large scale abandonment of Konar Sandal and extends from the late Bronze Age to the Mongol invasion. The results show that Jiroft had an arid dry climate dominated by the Saharo-Sindian open pseudo-savanna vegetation. However, due to human clearance and intensified agro-sylvo-pastoral activities, and climatic factors, the land-cover shifted from open xeric scrublands to a more open degraded landscape. The principal human occupation was cereal cultivation and herding. However, it is likely that during the more arid periods, communities retreated and abandoned agriculture, facilitating successional processes. Such droughts occurred around 4.0-3.8 ka and 3.4-2.8 ka and are related to the Siberian Anticyclonic system. Declining Artemisia and shrubs indicate milder climates ca. 3.8-3.4 ka and 2.8-0.6 ka. The latter period that started with the rule of the Persian empires (550-650 BCE), and continued through the Islamic era, coincides with intensive human activities, and the highest degradation of vegetation. (C) 2018 Elsevier Ltd. All rights reserved.

  • 73.
    Gyllencreutz, Richard
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Kissel, K
    Late Glacial and Holocene sediment sources and transport patterns in the Skagerrak interpreted from mineral magnetic properties and grain size data2006Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 25, nr 11-12, s. 1247-1263Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lateglacial and Holocene changes in circulation, sedimentation and provenance in north-eastern Skagerrak were studied using high-resolution mineral magnetic and grain size data from the 32-m-long IMAGES core MD99-2286. Ages are given in calibrated thousand years BP (‘cal. kyr’). Between 12 and 11.3 cal. kyr, a calving ice front occupied the Oslo Fjord, and sedimentation was strongly influenced by meltwater carrying re-deposited glacial sediments from southern Norway and western Sweden. Between 11.3 and 10.3 cal. kyr, sedimentation was dominated by re-deposited glacial sediments transported by meltwater outflow across south-central Sweden. After the Otteid-Stenselva outlet was closed at 10.3 cal. kyr, glacial marine sedimentation changed to normal marine sedimentation. At 8.5 cal. kyr, a hydrographic shift, marking the onset of modern circulation in the Skagerrak–Kattegat, occurred as a result of increased Atlantic inflow, transgression of former land areas, and opening of the English Channel and the Danish Straits. After 8.5 cal. kyr, sedimentation was governed by input from the Atlantic Ocean and the North Sea, with varying contributions from the South Jutland Current, Baltic Current, and currents along the coasts of western Sweden and southern Norway. From 0.9 cal. kyr until present, the sedimentation was totally dominated by southern North Sea and Atlantic Ocean sources.

  • 74. Haberle, Simon
    et al.
    Bennett, Keith
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Paleobiologi.
    Postglacial formation and dynamics of North Patagonian Rainforest in the Chonos Archipelago, Southern Chile2004Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, nr 23-24, s. 2433-2452Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pollen analysis of continuous sediment cores from two lakes in the northern Chonos Archipelago (44°S) in southern Chile shows a complete postglacial record of vegetation change. The fossil records indicate that deglaciation was complete in the northern Chonos by at least 13,600 14C yr BP. Ericaceous heath and grassland persisted for more than 600 years after deglaciation under the influence of dry/cold climates and frequent burning. Nothofagus-Pilgerodendron-Podocarpus forest, with modern analogues in the southern Chonos Archipelago, was established across the northern islands by 12,400 14C yr BP under increasingly warm and wet climates. There is no evidence for a return to cooler climates during the Younger Dryas chronozone. The rise of Tepualia stipularis and Weinmannia trichosperma as important forest components between 10,600 and 6000 14C yr BP may be associated with climates that were warmer than present. The collapse of Pilgerodendron communities during this time may have been triggered by a combination of factors related to disturbance frequency including tephra deposition events, fire and climate change. After 6000 14C yr BP Pilgerodendron recovers and Nothofagus-Pilgerodendron-Tepualia forest persists until the present. European logging and burning activity may have increased the susceptibility of North Patagonian Rainforest to invasion by introduced species and to future collapse of the long-lived Pilgerodendron communities.

  • 75. Hahn, A
    et al.
    Kliem, P
    Ohlendorf, C
    Zolitschka, B
    Rosen, Peter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Climate induced changes as registered in inorganic and organic sediment components from Laguna Potrok Aike (Argentina) during the past 51 ka2013Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 71, s. 154-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Total organic carbon, total inorganic carbon, biogenic silica content and total organic carbon/total nitrogen ratios of the Laguna Potrok Aike lacustrine sediment record are used to reconstruct the environmental history of south-east Patagonia during the past 51 ka in high resolution. High lake level conditions are assumed to have prevailed during the Last Glacial, as sediments are carbonate-free. Increased runoff linked to permafrost and reduced evaporation due to colder temperatures and reduced influence of Southern Hemispheric Westerlies (SHIN) may have caused these high lake levels with lake productivity being low and organic matter mainly of algal or cyanobacterial origin. Aquatic moss growth and diatom blooms occurred synchronously with southern hemispheric glacial warming events such as the Antarctic A-events, the postglacial warming following the LGM and the Younger Dryas chronozone. During these times, a combination of warmer climatic conditions with related thawing permafrost could have increased the allochthonous input of nutrients and in combination with warmer surface waters increased aquatic moss growth and diatom production. The SHW were not observed to affect southern Patagonia during the Last Glacial. The Holocene presents a completely different lacustrine system because (a) permafrost no longer inhibits infiltration nor emits meltwater pulses and (b) the positioning of the SHW over the investigated area gives rise to strong and dry winds. Under these conditions total organic carbon, total organic carbon/total nitrogen ratios and biogenic silica cease to be first order productivity indicators. On the one hand, the biogenic silica is influenced by dissolution of diatoms due to higher salinity and pH of the lake water under evaporative stress characterizing low lake levels. On the other hand, total organic carbon and total organic carbon/total nitrogen profiles are influenced by reworked macrophytes from freshly exposed lake level terraces during lowstands. Total inorganic carbon remains the most reliable proxy for climatic variations during the Holocene as high precipitation of carbonates can be linked to low lake levels and high autochthonous production. The onset of inorganic carbon precipitation has been associated with the southward shift of the SHW over the latitudes of Laguna Potrok Aike. The refined age-depth model of this record suggests that this shift occurred around 9.4 cal. ka BP. (c) 2012 Elsevier Ltd. All rights reserved.

  • 76.
    Hanslik, Daniela
    et al.
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Jakobsson, Martin
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Backman, Jan
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Björck, Svante
    Sellén, Emma
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    O'Regan, Matt
    Stockholm Univ, Dept Geol Sci, S-10691 Stockholm, Sweden..
    Fornaciari, Eliana
    Univ Padua, Dept Geosci, I-35100 Padua, Italy..
    Skog, Göran
    Lund Univ, Dept Earth & Ecosyst Sci, Div Geol, Radiocarbon Dating Lab, Lund, Sweden..
    Quaternary Arctic Ocean sea ice variations and radiocarbon reservoir age corrections2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, s. 3430-3441Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A short sediment core from a local depression forming an intra basin on the Lomonosov Ridge, was retrieved during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). It contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. The Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Calibration of the radiocarbon ages, using modeled reservoir corrections from previous studies and the microfossil abundance record of the studied core, results in marine reservoir ages of 1400 years or more, at least during the last deglaciation. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Lateglacial to the Holocene, suggesting circulation and ventilation changes. (C) 2010 Elsevier Ltd. All rights reserved.

  • 77.
    Hanslik, Daniela
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Backman, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Björck, Svante
    Lund University, Department of Geology.
    Sellén, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    O'Regan, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologi och geokemi.
    Fornaciari, Eliana
    University of Padova, Department of Geosciences.
    Skog, Göran
    Lund University, Department of Geology.
    Quaternary Arctic Ocean sea ice variations and deep water isolation times2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, s. 3430-3441Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A short sediment core retrieved from a local depression forming an intra basin on the Lomonosov Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX) contains a record of the Marine Isotope Stages (MIS) 1-3 showing exceptionally high abundances of calcareous microfossils during parts of MIS 3. Based on radiocarbon dating, linear sedimentation rates of 7-9 cm/ka persist during the last deglaciation. Last Glacial Maximum (LGM) is partly characterized by a hiatus. Planktic foraminiferal abundance variations of Neogloboquadrina pachyderma sinistral and calcareous nannofossils reflect changes in Arctic Ocean summer sea ice coverage and probably inflow of subpolar North Atlantic water. Marine reservoir ages of 1400 years or more, at least during the last deglaciation, seem plausible from calibration of the radiocarbon ages using modeled reservoir corrections from previous studies in combination with the microfossil abundance record of the studied core. Paired benthic-planktic radiocarbon dated foraminiferal samples indicate a slow decrease in age difference between surface and bottom waters from the Late Glacial to the Holocene, suggesting circulation and ventilation changes.

  • 78. Harrison, Stephan
    et al.
    Glasser, Neil F.
    Duller, Geoff A. T.
    Jansson, Krister N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Early and mid-Holocene age for the Tempanos moraines, Laguna San Rafael, Patagonian Chile2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 31, s. 82-92Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Data about the nature and timing of Holocene events from the Southern Hemisphere, especially in southern South America, are required to provide insight into the extent and nature of past climate change in a region where land-based records are restricted. Here we present the first use of single grain Optically Stimulated Luminescence (OSL) dating of a moraine sequence recording glacial advance along the western side of the Patagonian Icefields. Dates from the Tempanos moraines at Laguna San Rafael (LSR) show that the San Rafael Glacier (SRG) advanced to maximum Holocene positions during the period 9.3 to 9.7 ka and at 5.7 ka. Outwash lying beneath the moraine in its northern portion, dated to 7.7 ka, indicates that the glacier front was also advanced at this time. Since these advances span both the regional early Holocene warm-dry phase (11.5 ka to 7.8 ka) and the subsequent cooling and rise in precipitation in the mid-late Holocene (since 6.6 ka) we infer that the advances of the SRG are not simply climate-driven, but that the glacier has also probably responded strongly to non-climatic stimuli such as internal ice dynamics and the transition between calving and non-calving. Many westwards-flowing glaciers in Patagonia were probably calving during much of the Late Pleistocene and Holocene, so we conclude that establishing robust glacial chronologies where climatic and non-climatic factors cannot be distinguished is likely to remain a challenge.

  • 79. Heiri, Oliver
    et al.
    Koinig, Karin A.
    Spoetl, Christoph
    Barrett, Sam
    Brauer, Achim
    Drescher-Schneider, Ruth
    Gaar, Dorian
    Ivy-Ochs, Susan
    Kerschner, Hanns
    Luetscher, Marc
    Moran, Andrew
    Nicolussi, Kurt
    Preusser, Frank
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Schmidt, Roland
    Schoeneich, Philippe
    Schwoerer, Christoph
    Sprafke, Tobias
    Terhorst, Birgit
    Tinner, Willy
    Palaeoclimate records 60-8 ka in the Austrian and Swiss Alps and their forelands2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 106, s. 186-205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The European Alps and their forelands provide a range of different archives and climate proxies for developing climate records in the time interval 60-8 thousand years (ka) ago. We review quantitative and semi-quantitative approaches for reconstructing climatic variables in the Austrian and Swiss sector of the Alpine region within this time interval. Available quantitative to semi-quantitative climate records in this region are mainly based on fossil assemblages of biota such as chironomids, cladocerans, co-leopterans, diatoms and pollen preserved in lake sediments and peat, the analysis of oxygen isotopes in speleothems and lake sediment records, the reconstruction of past variations in treeline altitude, the reconstruction of past equilibrium line altitude and extent of glaciers based on geomorphological evidence, and the interpretation of past soil formation processes, dust deposition and permafrost as apparent in loess-palaeosol sequences. Palaeoclimate reconstructions in the Alpine region are affected by dating uncertainties increasing with age, the fragmentary nature of most of the available records, which typically only incorporate a fraction of the time interval of interest, and the limited replication of records within and between regions. Furthermore, there have been few attempts to cross-validate different approaches across this time interval to confirm reconstructed patterns of climatic change by several independent lines of evidence. Based on our review we identify a number of developments that would provide major advances for palaeoclimate reconstruction for the period 60-8 ka in the Alps and their forelands. These include (1) the compilation of individual, fragmentary records to longer and continuous reconstructions, (2) replication of climate records and the development of regional reconstructions for different parts of the Alps, (3) the cross-validation of different proxy-types and approaches, and (4) the reconstruction of past variations in climate gradients across the Alps and their forelands. Furthermore, the development of downscaled climate model runs for the Alpine region 60-8 ka, and of forward modelling approaches for climate proxies would expand the opportunities for quantitative assessments of climatic conditions in Europe within this time-interval.

  • 80.
    Helmens, Karin F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    The Last Interglacial Glacial cycle (MIS 5-2) re-examined based on long proxy records from central and northern Europe2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 86, s. 115-143Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Current multi-proxy studies on a long sediment sequence preserved at Sokli (N Finland), i.e. in the central area of Fennoscandian glaciations, are drastically changing classic ideas of glaciations, vegetation and climate in northern Europe during the Late Pleistocene. The sediments in the Sokli basin have escaped major glacial erosion due to non-typical bedrock conditions. In this review, the Sokli record is compared in great detail with other long proxy records from central, temperate and northern, boreal Europe. These comprise the classic records of La Grande Pile (E France) and Oerel (N Germany) and more recently obtained records from Horoszki Duke (E Poland) and Lake Yamozero (NW Russia). The focus of the review is on pollen, lithology and macrofossil- and insect-based temperature inferences. The long records are further compared with recent proxy data from nearby terrestrial sites as well as with the rapidly accumulating high-resolution proxy data from the ocean realm. The comparison allows a re-examination of the environmental history and climate evolution of the Last Interglacial Glacial (LI-G) cycle (MIS 5-2). It shows that environmental and climate conditions during MIS 5 (ca 130-70 ka BP) were distinctly different from those during MIS 4-2 (ca 70-15 ka BP). MIS 5 is characterized by three long forested intervals (broadly corresponding to MIS 5e, 5c, 5a), both in temperate and northern boreal Europe. These mild periods were interrupted by two short, relatively cold and dry intervals (MIS 5d and 5b) with mountain-centered glaciation in Fennoscandia. Millennial scale climate events were superimposed upon these longer lasting climate fluctuations. The time interval encompassing MIS 4-2 shows open vegetation. It is characterized by two glacial maxima (MIS 4 and 2) with sub-continental scale glaciation over northern Europe and dry conditions in strongly continental eastern European settings. High amplitude climate oscillations of millennial duration characterized the climate variability of MIS 3. Mild climate conditions in early MIS 3 caused large-scale deglaciation of the Fennoscandian Ice Sheet, and ice-free conditions with Betula-dominated vegetation (including tree birch) persisted over large parts of Fennoscandia, possibly interrupted by glaciation, during major part of MIS 3 till ca 35 ka BP. Overall, MIS 5 was mostly mild with warmest or peak interglacial conditions at the very start during MIS 5e. MIS 4-2 was mostly cold with most extreme or peak glacial conditions in the closing phase during MIS 2. This points to a subdivision of the last climate cycle into an early, overall mild interglacial half and a late, overall cold glacial half, each with duration of ca 50 ka. This review also shows that the climate variability in central and northern Europe during the LI-G cycle was mostly in degrees of continentality with major shifts in winter temperature and precipitation values; summer temperatures, on the other hand, remained largely unchanged. It points to the waxing and waning of sea-ice over the North Atlantic Ocean as a possible characteristic feature of the Late Pleistocene. The present compilation, based on long terrestrial sequences, high-resolution multi-proxy data from the oceans, and quantified paleo-climate data, strongly favors a definition of entire Marine Oxygen Isotope Stage 5 as the Last Interglacial similar as in the original marine stratigraphy and the stratigraphy at La Grande Pile in France. The proxy-based climate data places the start of the Last Glacial at the base of MIS 4 and the northwest European Pleniglacial. It shows that the division between the Eemian (MIS 5e) and the Early Weichselian (MIS 5d-a) is not useful, as not relevant from a climate point of view.

  • 81.
    Helmens, Karin F.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Salonen, J. Sakari
    Plikk, Anna
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Engels, Stefan
    Valiranta, Minna
    Kylander, Malin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Brendryen, Jo
    Renssen, Hans
    Major cooling intersecting peak Eemian Interglacial warmth in northern Europe2015Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 122, s. 293-299Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The degree of climate instability on the continent during the warmer-than-present Eemian Interglacial (around ca. 123 kyr ago) remains unsolved. Recently published high-resolution proxy data from the North Atlantic Ocean suggest that the Eemian was punctuated by abrupt events with reductions in North Atlantic Deep Water formation accompanied by sea-surface temperature cooling. Here we present multiproxy data at an unprecedented resolution that reveals a major cooling event intersecting peak Eemian warmth on the North European continent. Two independent temperature reconstructions based on terrestrial plants and chironomids indicate a summer cooling of the order of 2-4 degrees C. The cooling event started abruptly, had a step-wise recovery, and lasted 500-1000 yr. Our results demonstrate that the common view of relatively stable interglacial climate conditions on the continent should be revised, and that perturbations in the North Atlantic oceanic circulation under warmer-than-present interglacial conditions may also lead to abrupt and dramatic changes on the adjacent continent.

  • 82.
    Helmens, Karin F.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Valiranta, Minna
    Engels, Stefan
    Shala, Shyhrete
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Large shifts in vegetation and climate during the early weichselian (mis 5d c) inferred from multi proxy evidence at Sokli (Northern Finland)2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 41, s. 22-38Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For decades, detailed studies on Early Weichselian deposits have been made in central Europe. In contrast, these studies are rare in Fennoscandia in northern Europe. We here integrate an extensive multi-proxy data set obtained on sediments of MIS 5d-c age that form part of a long sediment record preserved at Sokli in northern Finland. We make a detailed interpretation of the vegetation and depositional history for MIS 5d-c using pollen, macrofossils, diatoms and other siliceous microfossils, insect remains, and sediment characteristics, and combine these data with recently published estimates on July temperatures based on chironomids and selected plant indicator species in order to make inferences of paleo-climate regimes. The fossil record obtained on the seven meter thick MIS 5d-c deposit at Sokli is exceptionally rich in species due to the large variety of habitats associated with an overall fluvial depositional environment. A braided river system flanked by steppe-tundra vegetation is inferred for MIS 5d. Mean July temperatures of at least 12-14 degrees C are indicated by chironomids and plant indicator species and are in agreement with the presence of conifers and birch trees as recorded by macrofossils. The reconstructed environmental conditions suggest strong continental climate conditions at Sokli during MIS 5d. The gradual infilling of an oxbow lake and subsequent return to stream channel deposition is traced in great detail in the overlying gyttja and gravelly sediment of MIS 5c age. The terrestrial pollen and plant macrofossil record from the gyttja shows the establishment of birch forest followed by the spread of pine and then spruce. Rich plant indicator species assemblages indicate that the boreal environment at Sokli during MIS 5c experienced July temperatures several degrees higher than the present-day value of 13 degrees C. The high summer temperatures and presence of larch suggest more continental conditions. More open vegetation returned at Sokli during late MIS 5c and was followed by glaciation by the Fennoscandian Ice Sheet (MIS 5b). Despite the major differences in zonal vegetation types during MIS 5d-c, differences in reconstructed July temperatures are minor and suggest that winter temperatures combined with precipitation values mostly determined the stadial-interstadial climate variability. The most compelling conclusion from our study is that forest development during MIS 5c was remarkably similar to that recorded for the Eemian (MIS 5e) and Holocene Interglacials at the high-latitude site Sokli, and also to that inferred from MIS 5c sediments on the northern European mainland. Our results question the definition of MIS 5c in the terrestrial record of Europe as an interstadial interval of the last glacial cycle and suggest inclusion of MIS 5c together with the Eemian (MIS 5e) in an interglacial complex.

  • 83.
    Helmens, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Risberg, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Jansson, Krister N.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Weckström, Jan
    Berntsson, Annika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Kaislahti Tillman, Päivi
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Johansson, Peter W.
    Wastegård, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Early MIS 3 glacial lake evolution, ice-marginal retreat pattern and climate at Sokli (northeastern Fennoscandia)2009Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 28, nr 19-20, s. 1880-1894Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lake development at Sokli, northern Finland, is traced through the analysis of diatoms and other siliceous micro-fossils in a 2-meter thick minerogenic, laminated clay-silt deposit dated to the early part of Marine Isotope Stage (MIS) 3. Fluctuating water levels and changes in lake extent depicted by the siliceous micro-fossil record, together with lithology, suggest that an important part of the sediment sequence was deposited in a glacial lake. The proxy-based glacial lake evolution is tested using a Digital Elevation Model and geomorphologic evidence including eskers dated to the early MIS 3 Tulppio Interstadial at Sokli. Despite the apparent ice-dammed nature of the lake, the sediment is relatively rich in fossils and there are limited signs of re-deposition of older fossil material. The siliceous micro-fossil record together with data from other proxies previously analysed in the same sediment samples provides a coherent picture of past environmental changes around the Sokli site. This is most probably due to the sheltered position of the coring-site in a lake embayment. Quantitative climate reconstructions based on the diatom record show mean July air temperatures as high as present-day values at Sokli, and the temperature ranges indicated by the diatom record are in agreement with temperature reconstructions based on chironomids. The position of Sokli in the northeastern portion of the central area of the Scandinavian glaciations and the northern retreat pattern implies that an important part of eastern Fennoscandia was deglaciated during the early MIS 3 warming event.

  • 84. Hessler, Ines
    et al.
    Dupont, Lydie
    Bonnefille, Raymonde
    Behling, Hermann
    Gonzalez, Catalina
    Helmens, Karin F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Hooghiemstra, Henry
    Lebamba, Judicael
    Ledru, Marie-Pierre
    Lezine, Anne-Marie
    Maley, Jean
    Marret, Fabienne
    Vincens, Annie
    Millennial-scale changes in vegetation records from tropical Africa and South America during the last glacial2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 21-22, s. 2882-2899Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To reconstruct the response of vegetation to abrupt climate changes during the last glacial we have compiled pollen records from the circum-Atlantic tropics between 23 degrees N and 23 degrees S from both marine and terrestrial sediment cores. Pollen data were grouped into mega-biomes to facilitate the comparison between the different records. Most tropical African records do not appear to register Dansgaard-Oeschger (D-O) variability, although there are vegetation changes during Heinrich Stadials (HS). There is a stronger signal of D-O and HS variability in the South American records. Records close to the modern northern and southern limits of the Intertropical Convergence Zone (ITCZ) show opposite trends in vegetation development during HS and D-O cycles. The pollen data from tropical South America corroborate the hypothesis of a southward shift in the migration pattern of the ITCZ and a reduction in the Atlantic Meridional Overturning Circulation (AMOC) during HS.

  • 85.
    Heyman, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Paleoglaciation of the Tibetan Plateau and surrounding mountains based on exposure ages and ELA depression estimates2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 91, s. 30-41Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Tibetan Plateau holds an ample record of past glaciations, and there is an extensive set of glacial deposits dated by exposure dating. Here a compilation is presented of 10Be exposure ages from 485 glacial deposits with 1855 individual samples on the Tibetan Plateau, and ELA depression estimates for the glacial deposits based on a simple toe to headwall ratio approach. To recalculate the Tibetan Plateau exposure ages, 10Be production rates from 24 calibration sites across the world are compiled and recalibrated yielding an updated global reference 10Be production rate. The recalculated exposure ages from the Tibetan Plateau glacial deposits are then divided into three groups based on exposure age clustering, to discriminate good (well-clustered) from poor (scattered) deglaciation ages. A major part of the glacial deposits have exposure ages affected by prior or incomplete exposure, complicating exposure age interpretations. The well-clustered deglaciation ages are primarily from mountain ranges along the margins of the Tibetan Plateau with a main peak between 10 and 30 ka, indicating glacial advances during the global LGM. A large number of deglaciation ages older than 30 ka indicates maximum glaciation predating the LGM, but the exposure age scatter generally prohibits accurate definition of the glacial chronology. The ELA depression estimates scatter significantly, but the main part is remarkably low. Average ELA depressions of 337 ± 197 m for the LGM and 494 ± 280 m for the pre-LGM indicate restricted glacier expansion.

  • 86.
    Heyman, Jakob
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Stroeven, Arjen P.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Caffee, Marc W.
    Hattestrand, Clas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Harbor, Jonathan M.
    Li, Yingkui
    Alexanderson, Helena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Zhou, Liping
    Hubbard, Alun
    Palaeoglaciology of Bayan Har Shan, NE Tibetan Plateau: exposure ages reveal a missing LGM expansion2011Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 30, nr 15-16, s. 1988-2001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined (10)Be exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in exposure ages for individual sites and within the recognised four morphostratigraphical groups. The exposure age disparity cannot be explained by differences in inheritance without using unrealistic assumptions but it can be explained by differences in post-depositional shielding which produces exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40-65 ka. More extensive glaciations occurred before 60-100 ka and 95-165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Hat Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is further supported by high-resolution glacier modelling experiments.

  • 87. Hoffmann, Gösta
    et al.
    Grützner, Christoph
    Reicherter, Klaus
    Preusser, Frank
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Geo-archaeological evidence for a Holocene extreme flooding event within the Arabian Sea (Ras al Hadd, Oman)2015Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 113, s. 123-133Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Arabian Sea is regarded as one of the least studied regions in terms of coastal hazards such as tropical cyclones and tsunamis. Parts of the coastline are developing rapidly, especially in Oman. This calls for a proper understanding of the natural processes that act on and affect it. This can be done by investigating the magnitude and impact of past events, in particular on human settlements. By doing this, future risks may not only be scientifically predicted and evaluated, but the damage caused by future events might even be mitigated. Evidence of past extreme wave events is preserved in the onshore stratigraphic record. In addition to this, the coastal zone of Oman is rich in archaeological remains. Presented here are the results of comprehensive mapping and analysis of extreme wave deposits of an archaeological site near Ras al-Hadd, suggesting that the Early Bronze Age site HD-6 was inundated at 4450 cal. BP. An event layer is identified between two settlement phases within the archaeological excavation. A contemporaneous sand bed with a maximum thickness of 0.4 m was mapped in the vicinity of the settlement. Ground penetrating radar surveys allow measurement of the thickness as well as identification of the internal facies architecture of the deposit. A high resolution digital elevation model reveals the coastal geomorphology. It is concluded that the causative event must have been a tsunami that was most likely generated within the Makran Subduction Zone. This interpretation does however, remain tentative at the moment Archaeological evidence indicates that the site was immediately re-occupied after the event, which attests to a certain resiliences of the Early Bronze Age coastal communities in the region.

  • 88. Hogan, K. A.
    et al.
    Dowdeswell, J. A.
    Noormets, R.
    Evans, J.
    Cofaigh, C. O.
    Jakobsson, M.
    Submarine landforms and ice-sheet flow in the Kvitoya Trough, northwestern Barents Sea2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, SI, s. 3545-3562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-resolution geophysical and sediment core data are used to investigate the pattern and dynamics of former ice flow in Kvitoya Trough, northwestern Barents Sea. A new swath-bathymetric dataset identifies three types of submarine landform in the study area (streamlined landforms, meltwater channels and cavities, iceberg scours). Subglacially produced streamlined landforms provide a record of ice flow through Kvitoya Trough during the last glaciation. Flow directions are inferred from the orientations of streamlined landforms (drumlins, crag-and-tail features). Ice flowed northward for at least 135 km from an ice divide at the southern end of Kvitoya Trough. A large channel-cavity system incised into bedrock in the southern trough indicates that subglacial meltwater was present at the former ice-sheet base. Modest landform elongation ratios and a lack of mega-scale glacial lineations suggest that, although ice in Kvitoya Trough was melting at the bed and flowed faster than the likely thin and cold-based ice on adjacent banks, a major ice stream probably did not occupy the trough. Retreat was relatively rapid after 14-13.5 C-14 kyr B.P. and probably progressed via ice sheet-bed decoupling in response to rising sea level. There is little evidence for still stands during ice retreat or of ice-proximal deglacial sediments. Relict iceberg scours in present-day water depths of more than 350 m in the northern trough indicate that calving was an important mass loss mechanism during retreat. (C) 2010 Elsevier Ltd. All rights reserved.

  • 89. Hogan, K. A.
    et al.
    Dowdeswell, J. A.
    Noormets, R.
    Evans, J.
    O'Cofaigh, C.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Submarine landforms and ice-sheet flow in the Kvitøya Trough, northwestern Barents Sea2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, s. 3545-3562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-resolution geophysical and sediment core data are used to investigate the pattern and dynamics of former ice flow in Kvitøya Trough, northwestern Barents Sea. A new swath-bathymetric dataset identifies three types of submarine landform in the study area (streamlined landforms, meltwater channels and cavities, iceberg scours). Subglacially produced streamlined landforms provide a record of ice flow through Kvitøya Trough during the last glaciation. Flow directions are inferred from the orientations of streamlined landforms (drumlins, crag-and-tail features). Ice flowed northward for at least 135 km from an ice divide at the southern end of Kvitøya Trough. A large channel-cavity system incised into bedrock in the southern trough indicates that subglacial meltwater was present at the former ice-sheet base. Modest landform elongation ratios and a lack of mega-scale glacial lineations suggest that, although ice in Kvitøya Trough was melting at the bed and flowed faster than the likely thin and cold-based ice on adjacent banks, a major ice stream probably did not occupy the trough. Retreat was relatively rapid after 14–13.5 14C kyr B.P. and probably progressed via ice sheet-bed decoupling in response to rising sea level. There is little evidence for still stands during ice retreat or of ice-proximal deglacial sediments. Relict iceberg scours in present-day water depths of more than 350 m in the northern trough indicate that calving was an important mass loss mechanism during retreat.

  • 90.
    Holmgren, Karin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Gogou, Alexandra
    Izdebski, Adam
    Luterbacher, Juerg
    Sicre, Marie-Alexandrine
    Xoplaki, Elena
    Mediterranean Holocene climate, environment and human societies2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, s. 1-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper introduces the reader to a special issue of articles that explores links and processes behind societal change, climate change and environmental change in a Holocene perspective in the Mediterranean region. All papers are, by purpose, co-authored by scientists representing different disciplines. The cross-cutting theme has been to reach beyond simple explanations of potential climate-society relationships and advance our understanding on how to improve research methods and theories in the field. The thirteen papers in this issue address these questions in three different ways, by i) conceptual/methodological approaches; ii) review papers; and iii) case studies.

  • 91.
    Hubbard, Alun
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK). Aberystwyth University, UK.
    Bradwell, Tom
    Golledge, Nicholas
    Hall, Adrian
    University of Edinburgh, UK.
    Patton, Henri
    Sugden, David
    Cooper, Rhys
    Stoker, Martyn
    Dynamic cycles, ice streams and their impact on the extent, chronology and deglaciation of the British–Irish ice sheet2009Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 28, nr 7-8, s. 758-776Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present results from a suite of forward transient numerical modelling experiments of the British and Irish Ice Sheet (BIIS), consisting of Scottish, Welsh and Irish accumulation centres, spanning the last Glacial period from 38 to 10 ka BP. The 3D thermomechanical model employed uses higher-order physics to solve longitudinal (membrane) stresses and to reproduce grounding-line dynamics. Surface mass balance is derived using a distributed degree-day calculation based on a reference climatology from mean (1961–1990) precipitation and temperature patterns. The model is perturbed from this reference state by a scaled NGRIP oxygen isotope curve and the SPECMAP sea-level reconstruction. Isostatic response to ice loading is computed using an elastic lithosphere/relaxed asthenosphere scheme. A suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities, to yield a subset of experiments that showed close correspondence to offshore and onshore ice-directional indicators, broad BIIS chronology, and the relative sea-level record. Three of these simulations are described in further detail and indicate that the separate ice centres of the modelled BIIS complex are dynamically interdependent during the build up to maximum conditions, but remain largely independent throughout much of the simulation. The modelled BIIS is extremely dynamic, drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time-scale. A series of binge/purge, advance/retreat, cycles are identified which correspond to alternating periods of relatively cold-based ice, (associated with a high aspect ratio and net growth), and wet-based ice with a lower aspect ratio, characterised by streaming. The timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling, but are modulated and phase-lagged to the oscillations within the NGRIP record of climate forcing. Phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate, resulting in major iceberg/melt discharge events into the North Sea and Atlantic Ocean. The broad chronology of the modelled BIIS indicates a maximum extent at 20 ka, with fast-flowing ice across its western and northern sectors that extended to the continental shelf edge. Fast-flowing streams also dominate the Irish Sea and North Sea Basin sectors and impinge onto SW England and East Anglia. From 19 ka BP deglaciation is achieved in less than 2000 years, discharging the freshwater equivalent of 2 m global sea-level rise. A much reduced ice sheet centred on Scotland undergoes subsequent retrenchment and a series of advance/retreat cycles into the North Sea Basin from 17 ka onwards, culminating in a sustained Younger Dryas event from 13 to 11.5 ka BP. Modelled ice cover is persistent across the Western and Central Highlands until the last remnant glaciers disappear around 10.5 ka BP.

  • 92. Hubberten, Hans W
    et al.
    Julian A. Dowdeswell, Mona Henriksen
    Martin Jakobsson, Svetlana Kuzmina
    Jan Mangerud, Per Möller
    Christine Siegert, Martin J. Siegert
    The periglacial climate andenvironment in northern Eurasia during the Last Glaciation2004Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 23, s. 1333-1357Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper summarizes the results of studies of the Late Weichselian periglacial environments carried out in key areas of northern Eurasia by several QUEEN teams (European Science Foundation (ESF) programme: ‘‘Quaternary Environment of the Eurasian North’’). The palaeoglaciological boundary conditions are defined by geological data on timing and extent of the last glaciation obtained in the course of the EU funded project ‘‘Eurasian Ice Sheets’’. These data prove beyond any doubt, that with the exception of the northwestern fringe of the Taymyr Peninsula, the rest of the Eurasian mainlandand Severnaya Zemlya were not affectedby the Barents–Kara Sea Ice Sheet during the Last Glacial Maximum (LGM). Inversedmod elling basedon these results shows that a progressive cooling which startedaround30 ka BP, causedice growth in Scandinavia and the northwestern areas of the Barents–Kara Sea shelf, due to a maritime climate with relatively high precipitation along the western flank of the developing ice sheets. In the rest of the Eurasian Arctic extremely low precipitation rates (less than 50mmyr 1), did not allow ice sheet growth in spite of the very cold temperatures. Palaeoclimatic and palaeoenvironmental conditions for the time prior to, during, and after the LGM have been reconstructed for the non-glaciated areas around the LGM ice sheet with the use of faunal and vegetation records, permafrost, eolian sediments, alluvial deposits and other evidences. The changing environment, from interstadial conditions around 30 ka BP to a much colder and drier environment at the culmination of the LGM at 20–15 ka BP, andthe beginning of warming around15 ka BP have been elaboratedfrom the fieldd ata, which fits well with the modelling results.

  • 93. Håkansson, Lena
    et al.
    Briner, Jason
    Alexanderson, Helena
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    Aldahan, Ala
    Possnert, Goran
    Be-10 ages from central east Greenland constrain the extent of the Greenland ice sheet during the Last Glacial Maximum2007Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 26, nr 19-21, s. 2316-2321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Traditional ice sheet reconstructions have suggested two distinctly different ice sheet regimes along the East Greenland continental margin during the Last Glacial Maximum (LGM): ice to the shelf break south of Scoresby Sund and ice extending no further than to the inner shelf at and north of Scoresby Sund. We report new Be-10 ages from erratic boulders perched at 250 m a.s.l. on the Kap Brewster peninsula at the mouth of Scoresby Sund. The average Be-10 ages, calculated with an assumed maximum erosion rate of 1 cm/ka and no erosion (respectively, 17.3 +/- 2.3 ka and 15.1 +/- 1.7 ka) overlap with a period of increased sediment input to the Scoresby Sund fan (19-15 ka). The results presented here suggest that ice reached at least 250 m a.s.l. at the mouth of Scoresby Sund during the LGM and add to a growing body of evidence indicating that LGM ice extended onto the outer shelf in northeast Greenland.

  • 94. Håkansson, Lena
    et al.
    Briner, Jason
    Alexanderson, Helena
    Aldahan, Ala
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Geovetenskapliga sektionen, Institutionen för geovetenskaper, Luft- och vattenlära.
    Possnert, Göran
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Jonfysik.
    10Be ages from central east Greenland constrain the extent of the Greenland ice sheet during the Last Glacial Maximum2007Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 26, nr 19-21, s. 2316-2321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Traditional ice sheet reconstructions have suggested two distinctly different ice sheet regimes along the East Greenland continental margin during the Last Glacial Maximum (LGM): ice to the shelf break south of Scoresby Sund and ice extending no further than to the inner shelf at and north of Scoresby Sund. We report new 10Be ages from erratic boulders perched at 250 m a.s.l. on the Kap Brewster peninsula at the mouth of Scoresby Sund. The average 10Be ages, calculated with an assumed maximum erosion rate of 1 cm/ka and no erosion (respectively, 17.3±2.3 ka and 15.1±1.7 ka) overlap with a period of increased sediment input to the Scoresby Sund fan (19–15 ka). The results presented here suggest that ice reached at least 250 m a.s.l. at the mouth of Scoresby Sund during the LGM and add to a growing body of evidence indicating that LGM ice extended onto the outer shelf in northeast Greenland.

  • 95. Izdebski, Adam
    et al.
    Holmgren, Karin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi.
    Weiberg, Erika
    Stocker, Sharon R.
    Büntgen, Ulf
    Florenzano, Assunta
    Gogou, Alexandra
    Leroy, Suzanne A. G.
    Luterbacher, Jürg
    Martrat, Belen
    Masi, Alessia
    Mercuri, Anna Maria
    Montagna, Paolo
    Sadori, Laura
    Schneider, Adam
    Sicre, Marie-Alexandrine
    Triantaphyllou, Maria
    Xoplaki, Elena
    Realising consilience: How better communication between archaeologists, historians and natural scientists can transform the study of past climate change in the Mediterranean2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, s. 5-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reviews the methodological and practical issues relevant to the ways in which natural scientists, historians and archaeologists may collaborate in the study of past climatic changes in the Mediterranean basin. We begin by discussing the methodologies of these three disciplines in the context of the consilience debate, that is, attempts to unify different research methodologies that address similar problems. We demonstrate that there are a number of similarities in the fundamental methodology between history, archaeology, and the natural sciences that deal with the past (palaeoenvironmental sciences), due to their common interest in studying societal and environmental phenomena that no longer exist. The three research traditions, for instance, employ specific narrative structures as a means of communicating research results. We thus present and compare the narratives characteristic of each discipline; in order to engage in fruitful interdisciplinary exchange, we must first understand how each deals with the societal impacts of climatic change. In the second part of the paper, we focus our discussion on the four major practical issues that hinder communication between the three disciplines. These include terminological misunderstandings, problems relevant to project design, divergences in publication cultures, and differing views on the impact of research. Among other recommendations, we suggest that scholars from the three disciplines should aim to create a joint publication culture, which should also appeal to a wider public, both inside and outside of academia.

  • 96.
    Izdebski, Adam
    et al.
    Jagiellonian University in Krakow, Institute of History.
    Holmgren, Karin
    Stockholm University, Department of Physical Geography.
    Weiberg, Erika
    Uppsala universitet, Humanistisk-samhällsvetenskapliga vetenskapsområdet, Historisk-filosofiska fakulteten, Institutionen för arkeologi och antik historia, Antikens kultur och samhällsliv.
    Stocker, Sharon R
    University of Cincinnati, Department of Classics.
    Büntgen, Ulf
    Florenzano, Assunta
    Gogou, Alexandra
    Leroy, Suzanne A.G.
    Luterbacher, Jürg
    Martrat, Belen
    Masi, Alessia
    Mercuri, Anna Maria
    Montagna, Paolo
    Sadori, Laura
    Schneider, Adam
    Sicre, Marie-Alexandrine
    Triantaphyllou, Maria
    Xoplaki, Elena
    Realising consilience: How better communication between archaeologists, historians and natural scientists can transform the study of past climate change in the Mediterranean2016Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 136, s. 5-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reviews the methodological and practical issues relevant to the ways in which natural scientists, historians and archaeologists may collaborate in the study of past climatic changes in the Mediterranean basin. We begin by discussing the methodologies of these three disciplines in the context of the consilience debate, that is, attempts to unify different research methodologies that address similar problems. We demonstrate that there are a number of similarities in the fundamental methodology between history, archaeology, and the natural sciences that deal with the past (“palaeoenvironmental sciences”), due to their common interest in studying societal and environmental phenomena that no longer exist. The three research traditions, for instance, employ specific narrative structures as a means of communicating research results. We thus present and compare the narratives characteristic of each discipline; in order to engage in fruitful interdisciplinary exchange, we must first understand how each deals with the societal impacts of climatic change. In the second part of the paper, we focus our discussion on the four major practical issues that hinder communication between the three disciplines. These include terminological misunderstandings, problems relevant to project design, divergences in publication cultures, and differing views on the impact of research. Among other recommendations, we suggest that scholars from the three disciplines should aim to create a joint publication culture, which should also appeal to a wider public, both inside and outside of academia.

  • 97. Jakobsson, M.
    et al.
    Nilsson, J.
    O'Regan, M.
    Backman, J.
    Löwemark, L.
    Dowdeswell, J. A.
    Mayer, L.
    Polyak, L.
    Colleoni, F.
    Anderson, L. G.
    Björk, G.
    Darby, D.
    Eriksson, B.
    Hanslik, D.
    Hell, Benjamin
    Marcussen, C.
    Sellén, Emma
    Wallin, T.
    An Arctic Ocean ice shelf during MIS 6 constrained by new geophysical and geological data2010Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, nr 25-26, s. 3505-3517Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The hypothesis of floating ice shelves covering the Arctic Ocean during glacial periods was developed in the 1970s. In its most extreme form, this theory involved a 1000 m thick continuous ice shelf covering the Arctic Ocean during Quaternary glacial maxima including the Last Glacial Maximum (LGM). While recent observations clearly demonstrate deep ice grounding events in the central Arctic Ocean, the ice shelf hypothesis has been difficult to evaluate due to a lack of information from key areas with severe sea ice conditions. Here we present new data from previously inaccessible, unmapped areas that constrain the spatial extent and timing of marine ice sheets during past glacials. These data include multibeam swath bathymetry and subbottom profiles portraying glaciogenic features on the Chukchi Borderland, southern Lomonosov Ridge north of Greenland, Morris Jesup Rise, and Yermak Plateau. Sediment cores from the mapped areas provide age constraints on the glaciogenic features. Combining these new geophysical and geological data with earlier results suggests that an especially extensive marine ice sheet complex, including an ice shelf, existed in the Amerasian Arctic Ocean during Marine Isotope Stage (MIS) 6. From a conceptual oceanographic model we speculate that the cold halocline of the Polar Surface Water may have extended to deeper water depths during MIS 6 inhibiting the warm Atlantic water from reaching the Amerasian Arctic Ocean and, thus, creating favorable conditions for ice shelf development. The hypothesis of a continuous 1000 m thick ice shelf is rejected because our mapping results show that several areas in the central Arctic Ocean substantially shallower than 1000 m water depth are free from glacial influence on the seafloor.

  • 98. Jakobsson, Martin
    et al.
    Anderson, John B.
    Nitsche, Frank O.
    Gyllencreutz, Richard
    Kirshner, Alexandra E.
    Kirchner, Nina
    O’Regan, Matthew
    Mohammad, Rezwan
    Eriksson, Bjorn
    Ice sheet retreat dynamics inferred from glacial morphology of the central Pine Island Bay Trough, West Antarctica2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 38, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pine Island Glacier drains portions of the West Antarctic Ice Sheet into the Amundsen Sea. During the Last Glacial Maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf. Unusually restricted sea-ice cover during the austral summer of 2010 allowed for a systematic multibeam swath-bathymetric and chirp sonar survey of the mid-shelf section of Pine Island Trough. The mapped glacial landforms reveal new information about the paleo-Pine Island Ice Stream’s dynamic retreat from the mid-shelf area and confirm previous suggestion of a retreat in distinct steps. The periods of grounding line stability during the overall retreat phase are marked by sediment accumulations, i.e. grounding zone wedges. These wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment. Considering a range of sediment flux rates from the paleo-Pine Island Ice Stream we estimate that the largest and most clearly defined grounding zone wedge, located at about 73 degrees S in the surveyed area, took between 600 and 2000 years to form. The ice stream retreated landward of this wedge before 12.3 cal ka BP. The swath-bathymetric imagery of landforms in Pine Island Trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break-up. The depths of grounding line wedges decrease in a landward direction, from 740 to 670 m, and record elevation of the grounding line as it stepped landward. In all, the grounding line elevation varied by only similar to 80 m over a distance of just over 100 km, implying a low ice sheet profile during retreat. Finally, we revisited seismic reflection profile NB9902, acquired along Pine Island Trough in 1999, in combination with the newly acquired swath-bathymetric imagery from 2010. Together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central Pine Island Trough where a high in dipping bedrock strata exists and the glacial trough is narrow, forming a bathymetric “bottle neck”. (C) 2011 Elsevier Ltd. All rights reserved.

  • 99.
    Jakobsson, Martin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Anderson, John B.
    Nitsche, Frank O.
    Gyllencreutz, Richard
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Kirshner, Alexandra E.
    Kirchner, Nina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi och kvartärgeologi (INK).
    O'Regan, Matthew
    Mohammad, Rezwan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Eriksson, Bjorn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Ice sheet retreat dynamics inferred from glacial morphology of the central Pine Island Bay Trough, West Antarctica2012Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 38, s. 1-10Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pine Island Glacier drains portions of the West Antarctic Ice Sheet into the Amundsen Sea. During the Last Glacial Maximum the glacier extended nearly 500 km from its present location onto the outer continental shelf. Unusually restricted sea-ice cover during the austral summer of 2010 allowed for a systematic multibeam swath-bathymetric and chirp sonar survey of the mid-shelf section of Pine Island Trough. The mapped glacial landforms reveal new information about the paleo-Pine Island Ice Stream's dynamic retreat from the mid-shelf area and confirm previous suggestion of a retreat in distinct steps. The periods of grounding line stability during the overall retreat phase are marked by sediment accumulations, i.e. grounding zone wedges. These wedges are here mapped in sufficient detail to characterize spatial dimensions and estimate the volume of deposited sediment. Considering a range of sediment flux rates from the paleo-Pine Island Ice Stream we estimate that the largest and most clearly defined grounding zone wedge, located at about 73 degrees S in the surveyed area, took between 600 and 2000 years to form. The ice stream retreated landward of this wedge before 12.3 cal ka BP. The swath-bathymetric imagery of landforms in Pine Island Trough includes glacial features that suggest that retreat between periods of grounding line stability may be associated with episodes of ice shelf break-up. The depths of grounding line wedges decrease in a landward direction, from 740 to 670 m, and record elevation of the grounding line as it stepped landward. In all, the grounding line elevation varied by only similar to 80 m over a distance of just over 100 km, implying a low ice sheet profile during retreat. Finally, we revisited seismic reflection profile NB9902, acquired along Pine Island Trough in 1999, in combination with the newly acquired swath-bathymetric imagery from 2010. Together these data show that the ice stream paused during its retreat to form grounding zone wedges at an area in central Pine Island Trough where a high in dipping bedrock strata exists and the glacial trough is narrow, forming a bathymetric bottle neck.

  • 100. Jakobsson, Martin
    et al.
    Andreassen, Karin
    Bjarnadottir, Lilja Run
    Dove, Dayton
    Dowdeswell, Julian A.
    England, John H.
    Funder, Svend
    Hogan, Kelly
    Ingolfsson, Olafur
    Jennings, Anne
    Larsen, Nikolaj Krog
    Kirchner, Nina
    Landvik, Jon Y.
    Mayer, Larry
    Mikkelsen, Naja
    Moller, Per
    Niessen, Frank
    Nilsson, Johan
    O’Regan, Matt
    Polyak, Leonid
    Norgaard-Pedersen, Niels
    Stein, Ruediger
    Arctic Ocean glacial history2014Inngår i: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 92, nr SI, s. 40-67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    While there are numerous hypotheses concerning glacial interglacial environmental and climatic regime shifts in the Arctic Ocean, a holistic view on the Northern Hemisphere’s late Quaternary ice-sheet extent and their impact on ocean and sea-ice dynamics remains to be established. Here we aim to provide a step in this direction by presenting an overview of Arctic Ocean glacial history, based on the present state-of-the-art knowledge gained from field work and chronological studies, and with a specific focus on ice-sheet extent and environmental conditions during the Last Glacial Maximum (LGM). The maximum Quaternary extension of ice sheets is discussed and compared to LGM. We bring together recent results from the circum-Arctic continental margins and the deep central basin; extent of ice sheets and ice streams bordering the Arctic Ocean as well as evidence for ice shelves extending into the central deep basin. Discrepancies between new results and published LGM ice-sheet reconstructions in the high Arctic are highlighted and outstanding questions are identified. Finally, we address the ability to simulate the Arctic Ocean ice sheet complexes and their dynamics, including ice streams and ice shelves, using presently available ice-sheet models. Our review shows that while we are able to firmly reject some of the earlier hypotheses formulated to describe Arctic Ocean glacial conditions, we still lack information from key areas to compile the holistic Arctic Ocean glacial history. (C) 2013 The Authors. Published by Elsevier Ltd.

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