Late Pleistocene sea surface warming as a trigger for catastrophic ice sheet wasting in the North Pacific Ocean

A new, high-resolution planktonic foraminiferal Mg/Ca-based temperature record offshore of Vancouver Island, BC captures the interplay between SSTs and ocean-ice sheet dynamics during the deglacial. The SST record of thermocline dwelling N. pachyderma shows variability through the Last Glacial Maximum and the deglacial, with two distinct warming steps of 2.5 and 3.5°C respectively at 17.2-16.5 and 15.3-14.7 ka from ~3 to 9°C. The SST record of surface dwelling G. bulloides remains a relatively constant 5-6°C during the late glacial, warming to 9°C at the Bølling-Ållerød, close to the average modern winter SSTs in the northern NE Pacific. Throughout the interval of the maximum Cordilleran Ice Sheet extent (~20-17 ka), SSTs were sufficiently warm (5-6°C) to induce significant melt at the ice terminus. Moreover, SST warming of ~3°C coincide with the presence of ice rafted debris at MD02-2496, indicating that ocean thermal forcing played an important role in Cordilleran Ice Sheet retreat. We hypothesize that submarine melting was the dominant mode of ice removal resulting from both subglacial meltwater discharge and warm SSTs during early deglaciation of the CIS, promoting iceberg calving events and rapid evacuation of straits and fjords of the BC region.