Evolution of the northeast Labrador Sea during the last interglaciation

Abstract

Boreal summer insolation during the last interglaciation (LIG) generally warmed the subpolar to polar Northern Hemisphere more than during the early Holocene, yet regional climate variations between the two periods remain. We investigate northeast Labrador Sea subsurface temperature and hydrography across terminations (T) I and II and during the LIG to assess the impact of two different magnitudes of boreal summer insolation increase on the northeast Labrador Sea. We use Mg/Ca ratios in Neogloboquadrina pachyderma (sinistral) as a proxy of calcification temperature to document changes in subsurface temperatures over Eirik Drift. Our corresponding record of δ18O of seawater documents changes in water mass salinity. Mg/Ca calcification temperatures peak early in the Holocene coincident with peak boreal summer insolation. In contrast, LIG temperatures are relatively constant through the interglaciation, and are no warmer than peak Holocene temperatures. During the first half of the LIG, δ18O of seawater remains depleted, likely from southern Greenland Ice Sheet retreat and enhanced Arctic freshwater and sea‐ice export to the Labrador Sea. The consequent stratification of the Labrador Sea and attendant suppressed convection explains delayed deep‐ocean ventilation and a cooler subsurface in the northeast Labrador Sea during the LIG.