A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum

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 20ka, 15ka, 10ka and 5ka, 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 priorit. © 2014 The Authors

Map of the eastern Amundsen Sea Embayment, West Antarctica.

<p>The location of the study area is indicated by large black box in the upper right corner. The general bathymetry is based on IBCSO v. 1 data [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.ref027" target="_blank">27</a>]. Continuous orange line indicates the LGM grounding line position (25 ka BP; [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.ref023" target="_blank">23</a>])–dashed sections mark uncertain positions. Continuous green line indicates the LGM grounding line position based on this study—dashed green line marks yet uncertain sections. Locations of grounding-zone wedges (GZW) derived from Graham et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.ref008" target="_blank">8</a>] (GZWs 1 & 2), and Klages et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.ref013" target="_blank">13</a>] (GZWa). Thick black lines mark the axes of paleo-ice stream troughs. Locations of sediment cores described in detail for this study are indicated by red-circled black dots (cores VC453, PS69/256-1, and PS69/300-1 [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.ref011" target="_blank">11</a>] are indicated by red-circled white dots). Lines x-x’ and y-y’ in inset mark the location of PARASOUND profiles in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.g004" target="_blank">Fig 4</a>. The simplified display of mega-scale glacial lineations (MSGLs), linear scours (LS), and the grounding-zone wedge ‘a’ (GZWa) in the white box in inset is based on glacial landform information presented in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.g003" target="_blank">Fig 3</a>, and from recent reconstructions by Klages et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.ref013" target="_blank">13</a>]. Small black box indicates the location of MSGLs shown in the inset in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.g003" target="_blank">Fig 3</a>. WAIS––West Antarctic Ice Sheet; PIT(W, E)––Pine Island-Thwaites Trough (West, East); AT––Abbot Trough; BI––Burke Island; TI––Thurston Island; AIS––Abbot Ice Shelf; KP––King Peninsula; CIS––Cosgrove Ice Shelf; CP––Canisteo Peninsula; PIG––Pine Island Glacier; TG––Thwaites Glacier; mbsl––meters below sea level.</p

Accelerator mass spectrometry radiocarbon ages.

<p>Included information: Core number, publication code, sampling depth, dated material [pF = planktic foraminifera; bF = benthic foraminifera], radiocarbon age [yrs BP], standard deviation [±1σ], marine reservoir effect [MRE], calibrated years [yrs] before the present [BP].</p

Detailed multibeam swath bathymetry.

<p>Data shows the location of grounding-zone wedge ‘a’ (‘GZWa’) and glacial landforms emerging NNE from it within the deep (~800 meters below sea level) outer portion of Abbot Trough. Sediment core locations are indicated by black dots, sediment echography profiles in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.g004" target="_blank">Fig 4</a> are marked by lines x-x’ and y-y’. Inset shows MSGLs located in small black box in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181593#pone.0181593.g002" target="_blank">Fig 2</a>. Grid cell size 30 m, grid illuminated from NW.</p

Sediment echography profiles and data logs for sediment cores PS75/190–3 and PS75/192-1.

<p>The cores were recovered from the upper parts of an acoustically stratified unit that overlies an acoustically transparent unit. Core data include lithology (lithological key is given above respective subbottom profiles), grain-size distribution (gravel/sand/mud), magnetic susceptibility, water content, shear strength, p-wave velocity (Vp), organic carbon content (C_org), relative palaeointensity (RPI_ARM(14-50mT)) in standardized form (only for PS75/190-3 –M.L.E. = ‘Mono Lake Excursion’; L.E. = ‘Laschamp Excursion’), facies (described in text), and calibrated (cal.) accelerator mass spectrometry radiocarbon ages of mixed benthic/planktic calcareous foraminifera in kiloyears before present (ka BP). The age models for the cores are displayed in boxes ‘Age- depth plot’ (red crosses refer to ages obtained from gravity cores PS75/190-3 & PS75/192-1; blue crosses: PS75/192-3; age uncertainties are indicated by black bars; dates with asterisk indicate duplicate dates for samples PS75/190-3 200 centimeter below seafloor (cmbsf) and PS75/192-1 214 cmbsf; stratigraphic locations of M.L.E. and L.E. are indicated by green dots).</p