Time-Transgressive Deglacial Retreat of Polar Waters from the North Atlantic

Abstract

A 9300 yr-old zone of disseminated volcanic ash in North Atlantic sediments between 45° N and 65° N provides a time-synchronous reference layer against which we have compared the stratigraphic level of deglacial warming of ocean surface waters. In the Atlantic north of 45° N the most prominent feature of this warming is the replacement of low-carbonate glacial marine sediment containing only a single species of polar Foraminifera by calcareous oozes containing a diverse temperate fauna and flora. The local terminations of glacial conditions marked by this change are not synchronous at these latitudes, but range from 13,500 yr B.P. or older in the southeast near Great Britain to 6,500 yr B.P. or younger in the northwest near Greenland. Regionally, these local warmings trace the progressive westward and northward retreat of polar water from the North Atlantic. Since the withdrawal of polar water from the North Atlantic coincides with the northward shrinkage of temperate-latitude continental ice sheets, it is the best oceanic analog to continental deglaciation. Faunal, floral, lithologic, and isotopic parameters showing evidence for a sudden deglacial warming may not be time-synchronous; those parameters are subject to a range of environmental controls and may thus respond differently to the causal mechanism for global warming.