Abstract
Understanding feedbacks between the Greenland Ice Sheet (GrIS) and the Atlantic Meridional Overturning Circulation (AMOC) is crucial for reducing uncertainties over future sea level and ocean circulation change. Reconstructing past GrIS dynamics can extend the observational record and elucidate mechanisms that operate on multi-decadal timescales. We report a highly-constrained last glacial vertical profile of cosmogenic isotope exposure ages from Sermilik Fjord, a marine-terminating ice stream in the southeast sector of the GrIS. Our reconstruction reveals substantial ice-mass loss throughout the Younger Dryas (12.9-11.7 ka), a period of marked atmospheric and sea-surface cooling. Earth-system modelling reveals that southern GrIS marginal melt was likely driven by strengthening of the Irminger Current at depth due to a weakening of the AMOC during the Younger Dryas. This change in North Atlantic circulation appears to have drawn warm subsurface waters to southeast Greenland despite markedly cooler sea surface temperatures, enhancing thermal erosion at the grounding lines of palaeo ice-streams, supporting interpretation of regional marine-sediment cores. Given current rates of GrIS meltwater input into the North Atlantic and the vulnerability of major ice streams to water temperature changes at the grounding line, this mechanism has important implications for future AMOC changes and northern hemisphere heat transport.
Highlights
Contemporary observations of the Greenland Ice Sheet (GrIS) and North Atlantic are too short (
We propose that ice-mass loss from southern Greenland across the YD was driven by entrainment of warm sub-surface water in the cross-shelf troughs, leading to thermal erosion at the grounding line of southern GrIS marine-terminating outlets such as Sermilik and Kangerlussuaq[12], consistent with the hypothesis that ocean circulation was more important than air temperature change in this region during the YD15,17,19
Increased stratification in the northeast Atlantic following the cessation of North Atlantic Deep Water (NADW) formation increased the marine reservoir age in this region[18], and the anomalously low marine reservoir age observed southeast of Greenland throughout the YD16 could be explained by such subsurface current reorganisations, supporting the interpretation of isotopic records from marine sediment cores from the North Atlantic off the SE GrIs19
Summary
Contemporary observations of the GrIS and North Atlantic are too short (
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
