D-O Variability in Greenland Summit δ18Op Controlled by Southern Extent of Sea Ice in the North Atlantic During the Last Glacial.

Dansgaard-Oeschger (D-O) events are some of the most rapid warming events in the paleoclimate record and represent the transition from a cold Greenland stadial (GS) to a warm Greenland interstadial (GI). Preceding these warming episodes, global oceanic thermohaline circulation was weakened and, in some cases, halted altogether. During these events the sea ice distribution in the North Atlantic is greatly reduced. In Greenland ice cores, D-O events manifest as peaks in the oxygen and hydrogen isotope ratios of ice (δice for short). Recent work has linked sea ice concentration in the North Atlantic to changes in Greenland δice, but this relationship is still poorly understood. In modern studies of Greenland snow, δice is strongly correlated to Greenland temperature. However, the δice-T relationship is complicated in studies of the past because the correlation changes in time. Furthermore, large changes in sea ice extent will reshape Greenland moisture sourcing by reducing oceanic evaporation and re-routing atmospheric circulation. This study constrains the δice-sea ice relationship with sea-ice forcing experiments in a climate model simulation of GIs and GSs. Using the isotope-enabled Community Atmosphere Model (iCAM), two sea ice forcing experiments are carried out: a low sea ice, interstadial climate (LGMGI) and a high sea ice, stadial climate (LGMGS). Water tracers are added to iCAM to detail the relative contribution of moisture source regions to Greenland snowfall. A technique for tag-based decomposition of Greenland precipitation demonstrates how changes in Greenland δice during D-O events can be explained by the dramatic increase of moisture sourcing from the Greenland, Norwegian, and Icelandic (GIN) seas and the north Atlantic during the wintertime. This increase is modulated by the presence of sea ice in the GIN seas + north Atlantic, which acts as a cap on the ocean, preventing evaporation. These results provide context for sea-ice reconstructions of the north Atlantic during D-O events. This work demonstrates that D-O δice signals are highly related to the amount of evaporation occurring in the north Atlantic, regardless of changes in the atmospheric circulation or temperature, although these do change alongside changes in sea ice distribution.