Browsing by Author "Leventer, A"
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- ItemA community-based geological reconstruction of Antarctic ice sheet deglaciation since the last glacial maximum(Elsevier, 2014-09-15) Bentley, MJ; O'Cofaigh, C; Anderson, JB; Conway, H; Davies, B; Graham, AGC; Hillenbrand, CD; Hodgson, DA; Jamieson, SSR; Larter, RD; Mackintosh, AN; Smith, JA; Verleyen, E; Ackert, RP; Bart, PJ; Berg, S; Brunstein, D; Canals, M; Colhoun, EA; Crosta, X; Dickens, WA; Domack, E; Dowdeswell, JA; Dunbar, R; Ehrmann, W; Evans, J; Favier, V; Fink, D; Fogwill, CJ; Glasser, NF; Gohl, K; Golledge, NR; Goodwin, I; Gore, DB; Greenwood, SL; Hall, BL; Hall, K; Hedding, DW; Hein, AS; Hocking, EP; Jakobsson, M; Johnson, JS; Jomelli, V; Jones, RS; Klages, JP; Kristoffersen, Y; Kuhn, G; Leventer, A; Licht, K; Lilly, K; Lindow, J; Livingstone, SJ; Massé, G; McGlone, MS; McKay, RM; Melles, M; Miura, H; Mulvaney, R; Nel, W; Nitsche, FO; O'Brien, PE; Post, AL; Roberts, SJ; Saunders, KM; Selkirk, PM; Simms, AR; Spiegel, C; Stolldorf, TD; Sugden, DE; van der Putten, N; van Ommen, TD; Verfaillie, D; Vyverman, W; Wagner, B; White, DA; Witus, AE; Zwartz, DA 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 1a. 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. © 2014 The Authors. CC BY license
- ItemEast Antarctic ice sheet retreat as a response to meltwater pulse 1A(Scientific Committee on Antarctic Research, 2008-07) Mackintosh, A; Domack, E; Leventer, A; White, DA; Fink, D; Gore, DB; Dunbar, RWe develop an empirical model of East Antarctic Ice Sheet (EAIS) retreat during the last termination in Mac.Robertson Land. Exposure dating, marine cores and swath bathymetry indicate retreat from the continental shelf and ice sheet drawdown in coastal mountains began ~13 ka. Calving re-entrant bays formed during initial retreat and persisted for 100's years in Iceberg Alley and 10's years at Neilson Basin. Exposure dates in Framnes Mountains within the same drainage basin as Iceberg Alley indicate ~350 m of ice thinning was complete by ~7 ka. EAIS retreat at many sites on the Antarctic perimeter (including these three) immediately post-dated Meltwater Pulse 1A (MWP1A). Rather than being a source of MWP1A, our data support a hypothesis that rapid eustatic sea level rise during this time unhinged the ice-sheet margin from its stability point at the shelf edge. Thereafter, the rate of EAIS retreat depended on trough geometry, akin to the present-day response of fiord glaciers, until retreat ceased when sea level stabilised. Our findings reinforce a concern that marine-based portions of Antarctic Ice Sheets are vulnerable to collapse if sea level rise approaches the rates (~4m/century) achieved during MWP1A, as a consequence of melting ice in Greenland and elsewhere.
- ItemLast major retreat of Antarctic ice sheets forced by sea level rise and ocean warming(University of Auckland, 2009-07-01) Mackintosh, AN; Domack, E; Golledge, NR; Dunbar, R; Leventer, A; White, D; Fink, D; Gore, DB; Lavoie, CThe retreat of Antarctic ice sheets during the transition from the last glacial period to the Holocene provides the most recent example of ice sheet response to major climate forcing and thus allows rates of ice sheet decay and coupling to sea level rise to be quantified. We observe through a combination of land- and marine-based geochronology and ice sheet modelling, a highly-resolved temporal record of deglaciation of the East Antarctic Ice Sheet across the Mac.Robertson Land shelf. Our reconstruction demonstrates that deglaciation of deep-shelf troughs and lowering of the ice sheet surface occurred in two phases, from 14 - 12 and 12 - 7 ka before present (BP). Our consideration of possible mechanisms for the observed retreat of the marine ice margin of Mac.Robertson Land favours rapid rates of eustatic sea level rise associated with Meltwater Pulse 1a (MWP-1a) at ~14 ka BP and warming of the marginal oceans and atmosphere to nearmodern levels ~2 ka later. In support of this interpretation is the comparison of our land-marine sequence to other well-constrained marine deglacial events from both West and East Antarctica, including the Ross and Weddell Sea embayments. Our results show that periods of rapid sea level rise can initiate instability in Antarctica’s ice masses, including the margins of East Antarctica, and indicate that a combination of sea level rise and oceanic warming is a powerful driver of ice retreat.
- ItemRetreat history of the East Antarctic ice sheet since the last glacial maximum(Elsevier, 2014-09-15) Mackintosh, AN; Verleyen, E; O'Brian, PE; White, DA; Jones, RS; McKay, RM; Dunbar, R; Gore, DB; Fink, D; Post, AL; Miura, H; Leventer, A; Goodwin, ID; Hodgson, DA; Lilly, K; Crosta, X; Golledge, NR; Wagner, B; Berg, S; van Ommen, TD; Zwartz, D; Roberts, SJ; Vyverman, W; Massé, GThe East Antarctic Ice Sheet (EAIS) is the largest continental ice mass on Earth, and documenting its evolution since the Last Glacial Maximum (LGM) is important for understanding its present-day and future behaviour. As part of a community effort, we review geological evidence from East Antarctica that constrains the ice sheet history throughout this period (∼30,000 years ago to present). This includes terrestrial cosmogenic nuclide dates from previously glaciated regions, 14C chronologies from glacial and post-glacial deposits onshore and on the continental shelf, and ice sheet thickness changes inferred from ice cores and continental-scale ice sheet models. We also include new 14C dates from the George V Land – Terre Adélie Coast shelf. We show that the EAIS advanced to the continental shelf margin in some parts of East Antarctica, and that the ice sheet characteristically thickened by 300–400 m near the present-day coastline at these sites. This advance was associated with the formation of low-gradient ice streams that grounded at depths of >1 km below sea level on the inner continental shelf. The Lambert/Amery system thickened by a greater amount (800 m) near its present-day grounding zone, but did not advance beyond the inner continental shelf. At other sites in coastal East Antarctica (e.g. Bunger Hills, Larsemann Hills), very little change in the ice sheet margin occurred at the LGM, perhaps because ice streams accommodated any excess ice build up, leaving adjacent, ice-free areas relatively unaffected. Evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the LGM, an observation supported by ice cores, which suggest that interior ice sheet domes were ∼100 m lower than present at this time. Ice sheet recession may have started ∼18,000 years ago in the Lambert/Amery glacial system, and by ∼14,000 years ago in Mac.Robertson Land. These early pulses of deglaciation may have been responses to abrupt sea-level rise events such as Meltwater Pulse 1a, destabilising the margins of the ice sheet. It is unlikely, however, that East Antarctica contributed more than ∼1 m of eustatic sea-level equivalent to post-glacial meltwater pulses. The majority of ice sheet recession occurred after Meltwater Pulse 1a, between ∼12,000 and ∼6000 years ago, during a period when the adjacent ocean warmed significantly. Large tracts of East Antarctica remain poorly studied, and further work is required to develop a robust understanding of the LGM ice sheet expansion, and its subsequent contraction. Further work will also allow the contribution of the EAIS to post-glacial sea-level rise, and present-day estimates of glacio-isostatic adjustment to be refined. © 2014 The Authors. CC-BY Licence.
- ItemRetreat of the East Antarctic ice sheet during the last glacial termination(Nature Publishing Group, 2011-03) Mackintosh, AN; Golledge, NR; Domack, E; Dunbar, R; Leventer, A; White, D; Pollard, D; DeConto, R; Fink, D; Zwartz, D; Gore, DB; Lavoie, CThe retreat of the East Antarctic ice sheet at the end of the last glacial period has been attributed to both sea-level rise and warming of the ocean at the margin of the ice sheet, but it has been challenging to test these hypotheses. Given the lack of constraints on the timing of retreat, it has been difficult to evaluate whether the East Antarctic ice sheet contributed to meltwater pulse 1a, an abrupt sea-level rise of approximately 20 m that occurred about 14,700 years ago. Here we use terrestrial exposure ages and marine sedimentological analyses to show that ice retreat in Mac. Robertson Land, East Antarctica, initiated about 14,000 years ago, became widespread about 12,000 years ago, and was completed by about 7,000 years ago. We use two models of different complexities to assess the forcing of the retreat. Our simulations suggest that, although the initial stage of retreat may have been forced by sea-level rise, the majority of the ice loss resulted from ocean warming at the onset of the Holocene epoch. In light of our age model we conclude that the East Antarctic ice sheet is unlikely to have been the source of meltwater pulse 1a, and, on the basis of our simulations, suggest that Antarctic ice sheets made an insignificant contribution to eustatic sea-level rise at this time. © 2011, Nature Publishing Group.