02690nas a2200301   4500000000100000008004100001653001500042653002500057653002400082653001400106653002400120100001600144700002900160700001700189700001900206700002000225700001800245700001900263700001900282700001800301700002200319245012900341856005400470300002200524490000800546520182000554022001402374       2014                            d10a14C dating10agrounding zone wedge10aice sheet modelling10aice shelf10aPine Island Glacier1 aJames Smith1 aClaus-Dieter Hillenbrand1 aGerhard Kuhn1 aJohann Phillip1 aAlastair Graham1 aRobert Larter1 aWerner Ehrmann1 aSteven Moreton1 aSteffen Wiers1 aThomas Frederichs00aNew constraints on the timing of West Antarctic Ice Sheet retreat in the eastern Amundsen Sea since the Last Glacial Maximum  uhttp://dx.doi.org/10.1016/j.gloplacha.2014.07.015  a224\textendash2370 v1223 a<p>Glaciers flowing into the Amundsen Sea Embayment (ASE) account for \&gt;\&nbsp;35\% of the total discharge of the West Antarctic Ice Sheet (WAIS) and have thinned and retreated dramatically over the past two decades. Here we present detailed marine geological data and an extensive new radiocarbon dataset from the eastern ASE in order to constrain the retreat of the WAIS since the Last Glacial Maximum (LGM) and assess the significance of these recent changes. Our dating approach, relying mainly on the acid insoluble organic (AIO) fraction, utilises multi-proxy analyses of the sediments to characterise their lithofacies and determine the horizon in each core that would yield the most reliable age for deglaciation. In total, we dated 69 samples and show that deglaciation of the outer shelf was underway before 20,600 calibrated years before present (cal\&nbsp;yr\&nbsp;BP), reaching the mid-shelf by 13,575\&nbsp;cal\&nbsp;yr\&nbsp;BP and the inner shelf to within ca. 150\&nbsp;km of the present grounding line by 10,615\&nbsp;cal\&nbsp;yr\&nbsp;BP. The timing of retreat is broadly consistent with previously published radiocarbon dates on biogenic carbonate from the eastern ASE as well as AIO <sup>14</sup>C ages from the western ASE and provides new constraints for ice sheet models. The overall retreat trajectory \textendash slow on the outer shelf, more rapid from the middle to inner shelf \textendash clearly highlights the importance of reverse bedslopes in controlling phases of accelerated groundling line retreat. Despite revealing these broad scale trends, the current dataset does not capture detailed changes in ice flow, such as stillstands during grounding line retreat (i.e., deposition of grounding zone wedges) and possible readvances as depicted in the geomorphological record.</p>  a0921-8181