After three years of cold conditions, warm water has returned to Ilulissat Icefjord, home to Jakobshavn Isbrae-Greenland's largest outlet glacier. Jakobshavn has slowed and thickened since 2016, when waters near the glacier cooled from 3 °C to 1.5 °C. Fjord temperatures remained cold through at least the end of 2019, but in March 2020, temperatures in the fjord warmed to 2.8 °C. As a result of the warming, we forecast that Jakobshavn Isbrae will accelerate and resume thinning during the 2020 melt season. The fjord's profound in uence on glacier behavior, and the connectivity between fjord conditions and regional ocean climate imply a degree of predictability that we aim to test with this forecast. Given the global importance of sea-level rise, we must advance our ability to forecast such rapidly changing systems, and this work represents an important rst step in glacier forecasting.

Considerable uncertainty surrounds the extent and timing of the advance and retreat of the Greenland Ice Sheet (GIS) on the continental shelf bordering Baffi n Bay during the last glacial cycle. Here we use marine geophysical and geological data to show that fast-fl owing ice sheet outlets, including the ancestral Jakobshavn Isbrae, expanded several hundred kilometers to the shelf edge during the last glaciation ca. 20 ka. Retreat of these outlets was asynchronous. Initial retreat from the shelf edge was underway by 14,880 calibrated (cal) yr B.P. in Uummannaq trough. Radiocarbon dates from the adjacent Disko trough and adjoining trough-mouth fan imply later deglaciation of Jakobshavn Isbrae, and, signifi cantly, an extensive readvance and rapid retreat of this outlet during the Younger Dryas stadial (YD). This is notable because it is the fi rst evidence of a major advance of the GIS during the YD on the West Greenland shelf, although the short duration suggests that it may have been out of phase with YD temperatures.

Citation for published item:heldonD gF nd tenningsD eF nd endrewsD tFF nd ¡ y gofighD gF nd rognD uF nd howdeswellD tFeF nd eidenkrntzD wFEF @PHITA 9se strem retret following the vqw nd onset of the west qreenlnd urrent in ummnnq roughD west qreenlndF9D uternry siene reviewsFD IRU F ppF PUERTF Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. The deglacial history and oceanography of Uummannaq Trough, central West Greenland 24 continental shelf, was investigated using foraminiferal, sedimentological, and bathymetric 25 records together with a radiocarbon chronology, providing a timeline for the retreat of glacial 26 ice after the Last Glacial Maximum (LGM). To map ice stream retreat, data were collected from 27 cores from the outer (JR175-VC45 and JR175-VC43) and inner (JR175-VC42) Uummannaq 28 Trough. A large ice stream, fed by confluent glaciers draining the interior of the Greenland Ice 29Sheet, extended across the outer shelf during the LGM and was retreating by 15.0 cal kyr BP. 30Foraminiferal data indicate that the 'warm' West Greenland Current (WGC) was established 31 prior to 14.0 cal kyr BP, which is the hitherto earliest record of Atlantic Water found on the 32 West Greenland shelf. For each of the cores, foraminifera indicate that ice sheet retreat was 33 followed quickly by incursion of the WGC, suggesting that the warm water may have 34 enhanced ice retreat. Prior to the Younger Dryas cold event, the existing radiocarbon 35 chronology indicates that the ice sheet retreated to the mid-shelf, where it subsequently 36 stabilised and formed a large grounding-zone wedge (GZW). After the Younger Dryas, around 37 11.5 cal kyr BP, the ice retreated rapidly from the GZW and into the fjords.

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