Freshwater forcing from the Greenland Ice Sheet during the Younger Dryas: evidence from southeastern Greenland shelf cores

Abstract

We present evidence for freshwater forcing from the Greenland Ice Sheet during the last deglaciation, explore its potential involvement in the Younger Dryas cooling, and investigate the role of Atlantic Intermediate Water in the retreat of the Greenland Ice Sheet. Paleoceanographic conditions and ice-sheet retreat history are interpreted from IRD, stable isotopes and foraminiferal assemblages in sediment cores retrieved along the length of the Kangerlussuaq Trough, a cross-shelf trough on the southeast Greenland shelf. The Vedde Ash (11,980±cal. yr BP), which is a marker bed within the Younger Dryas, and the Saksunarvatn tephra (10,180±cal. yr BP) an early Holocene marker horizon, have been located in these cores. The tephra markers and calibrated 14C dates on foraminifers and molluscs provide the basis for the age models in the cores. The stable isotope records indicate a 0.5 ‰ depletion of the 18O between 13.4 and 12.8 cal ka BP. A pronounced light isotope event, exceeding 1.5 ‰ on the inner shelf and 0.8 ‰ on the outer shelf, occurs at the beginning of the Younger Dryas Cold period (12.8 cal. ka BP) and ends by 12 cal ka BP, immediately before deposition of the Vedde Ash. The light isotope spikes are interpreted as glacial meltwater spikes associated with retreat of the adjacent Greenland Ice Sheet. Associated with the light isotope events are episodic high percentages of the Atlantic Intermediate Water benthic foraminiferal species, Cassidulina neoteretis, which continue from the Bølling/Allerød into the Younger Dryas. High percentages of this species suggest that Atlantic Intermediate Water entered the Kangerlussuaq Trough during the Allerød and the Younger Dryas via the Irminger Current, as it does today. We conclude that advection of Atlantic Intermediate Water into the Kangerlussuaq Trough, south of the Denmark Strait, promoted melting and retreat of the marine portions of the Greenland Ice Sheet, explaining the observed glacial meltwater spikes.