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Sökning: WFRF:(Glasser Neil)

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1.
  • Andersen, J. L., et al. (författare)
  • Ice surface changes during recent glacial cycles along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica
  • 2020
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 249
  • Tidskriftsartikel (refereegranskat)abstract
    • Reconstructing past ice-sheet surface changes is key to testing and improving ice-sheet models. Data constraining the past behaviour of the East Antarctic Ice Sheet are sparse, limiting our understanding of its response to past, present and future climate change. Here, we report the first cosmogenic multinuclide (Be-10, Al-26, Cl-36) data from bedrock and erratics on nunataks along the Jutulstraumen and Penck Trough ice streams in western Dronning Maud Land, East Antarctica. Spanning elevations between 741 and 2394 m above sea level, the samples have apparent exposure ages between 2 ka and 5 Ma. The highest-elevation bedrock sample indicates (near-) continuous minimum exposure since the Pliocene, with a low apparent erosion rate of 0.15 +/- 0.03 m Ma(-1), which is similar to results from eastern Dronning Maud Land. In contrast to studies in eastern Dronning Maud Land, however, our data show clear indications of a thicker-than-present ice sheet within the last glacial cycle, with a thinning of similar to 35-120 m during the Holocene (similar to 2-11 ka). Difficulties in separating suitable amounts of quartz from the often quartz-poor rock-types in the area, and cosmogenic nuclides inherited from exposure prior to the last deglaciation, prevented robust thinning estimates from elevational profiles. Nevertheless, the results clearly demonstrate ice-surface fluctuations of several hundred meters between the current grounding line and the edge of the polar plateau for the last glacial cycle, a constraint that should be considered in future ice-sheet model simulations.
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2.
  • Bentley, Michael J., et al. (författare)
  • A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
  • 2014
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 100, s. 1-9
  • Tidskriftsartikel (refereegranskat)abstract
    • A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse la. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.
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3.
  • Glasser, Neil F., et al. (författare)
  • Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina
  • 2011
  • Ingår i: Quaternary Research. - : Cambridge University Press (CUP). - 0033-5894 .- 1096-0287. ; 75:3, s. 636-646
  • Tidskriftsartikel (refereegranskat)abstract
    • At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49 degrees S, 72 degrees W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide ((10)Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 +/- 1.7 ka, 22.4 +/- 2.3 ka, 34.4 +/- 3.4 ka to 37.6 +/- 3.4 ka (and possibly 60 +/- 3.5 ka), and 99 +/- 11 ka (1 sigma). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on (14)C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.
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4.
  • Glasser, Neil F., et al. (författare)
  • Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean
  • 2016
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
  • Tidskriftsartikel (refereegranskat)abstract
    • Large freshwater lakes formed in North America and Europe during deglaciation following the Last Glacial Maximum. Rapid drainage of these lakes into the Oceans resulted in abrupt perturbations in climate, including the Younger Dryas and 8.2 kyr cooling events. In the mid-latitudes of the Southern Hemisphere major glacial lakes also formed and drained during deglaciation but little is known about the magnitude, organization and timing of these drainage events and their effect on regional climate. We use 16 new single-grain optically stimulated luminescence (OSL) dates to define three stages of rapid glacial lake drainage in the Lago General Carrera/Lago Buenos Aires and Lago Cohrane/Pueyrredon basins of Patagonia and provide the first assessment of the effects of lake drainage on the Pacific Ocean. Lake drainage occurred between 13 and 8 kyr ago and was initially gradual eastward into the Atlantic, then subsequently reorganized westward into the Pacific as new drainage routes opened up during Patagonian Ice Sheet deglaciation. Coupled ocean-atmosphere model experiments using HadCM3 with an imposed freshwater surface hosing to simulate glacial lake drainage suggest that a negative salinity anomaly was advected south around Cape Horn, resulting in brief but significant impacts on coastal ocean vertical mixing and regional climate.
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5.
  • Glasser, Neil F., et al. (författare)
  • Younger Dryas and early Holocene age glacier advances in Patagonia
  • 2012
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 58, s. 7-17
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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6.
  • Glasser, Neil, et al. (författare)
  • The glacial geomorphology and Pleistocene history of South America between 38 degrees S and 56 degrees S
  • 2008
  • Ingår i: QUATERNARY SCIENCE REVIEWS. - : Elsevier. - 0277-3791. ; 27:3-4, s. 365-390
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents new mapping of the glacial geomorphology of southern South America between latitudes 38 degrees S and 56 degrees S, approximately the area covered by the former Patagonian Ice Sheets. Glacial geomorphological features, including glacial lineations, moraines, meltwater channels, trimlines, sandur and cirques, were mapped from remotely sensed images (Landsat 7 ETM +, pan-sharpened Landsat 7 and ASTER). The landform record indicates that the Patagonian Ice Sheets consisted of 66 main outlet glaciers, together with numerous local cirque glaciers and independent ice domes in the surrounding mountains. In the northern part of the mapped area, in the Chilean Lake District (38-42 degrees S), large piedmont glaciers developed on the western side of the Andes and the maximum positions of these outlet glaciers are, in general, marked by arcuate terminal moraines. To the east of the Andes between 38 degrees S and 42 degrees S, outlet glaciers were more restricted in extent and formed "alpine-style" valley glaciers. Along the eastern flank of the Andes south of similar to 45 degrees S a series of large fast-flowing outlet glaciers drained the ice sheet. The location of these outlet glaciers was topographically controlled and there was limited scope for interactions between individual lobes. West of the Andes at this latitude, there is geomorphological evidence for an independent ice cap close to sea level on the Taitao Peninsula. The age of this ice cap is unclear but it may represent evidence of glacier growth during the Antarctic Cold Reversal and/or Younger Dryas Chronozone. Maximum glacier positions are difficult to determine along much of the western side of the Andes south of 42 degrees S because of the limited land there, and it is assumed that most of these glaciers had marine termini. In the south-east of the mapped area, in the Fuegan Andes (Cordillera Darwin), the landform record provides evidence of ice-sheet initiation. By adding published dates for glacier advances from the literature we present maps of pre-Last Glacial Maximum (LGM) glacier extent, LGM extent and the positions of other large mapped moraines younger than LGM in age. A number of large moraines occur within the known LGM limits. The age of these moraines is unknown but, since many of them lie well outside the established maximum Neoglacial positions, the possibility that they reflect a return to glacial climates during the Younger Dryas Chronozone or Antarctic Cold Reversal cannot be discounted.
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9.
  • Harrison, Stephan, et al. (författare)
  • Early and mid-Holocene age for the Tempanos moraines, Laguna San Rafael, Patagonian Chile
  • 2012
  • Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 31, s. 82-92
  • Tidskriftsartikel (refereegranskat)abstract
    • 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.
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10.
  • Harrison, Stephan, et al. (författare)
  • Glaciar Leon, Chilean Patagonia: late-Holocene chronology and geomorphology
  • 2008
  • Ingår i: Holocene. - : SAGE Publications. - 0959-6836. ; 18:4, s. 643-652
  • Tidskriftsartikel (refereegranskat)abstract
    • Glaciar Leon is a temperate, grounded outlet of the eastern North Patagonian Icefield (NPI). It terminates at an active calving margin in Lago Leones, a 10 km long proglacial lake. We take a multidisciplinary approach to its description and use ASTER imagery and clast sedimentology to describe the geomorphology of the glacier and its associated moraines. We date periods of glacier retreat over the last 2500 years using a combination of lichenometric, dendrochronological, cosmogenic and optically stimulated luminescence techniques and show that the glacier receded from a large terminal moraine complex some 2500 years ago and underwent further significant recession from nineteenth-century moraine limits. The moraine dates indicate varying retreat rates, in conjunction with significant downwasting. The bathymetry of Lago Leones is characterized by distinct ridges interpreted as moraine ridges that dissect the lake into several basins, with water depths reaching 360 m. The fluctuations of Glaciar Leon appear to have been controlled by the interplay between climatic forcing and calving dynamics.
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