Glacial/Interglacial response rate of subpolar North Atlantic waters to climatic change: the record in oceanic sediments

Abstract

Estimated rates of response of northeast Atlantic surface waters to large-scale palaeoclimatic changes have been reconstructed in two forms: (1) as changes through time of estimated temperature at selected points in space, and (2) as movements through space of the polar front during particular intervals in time. Three periods of rapid change between the glacial and interglacial climatic extremes were examined: a short cold episode during isotopic stage 7 (the next-to-last interglaciation); the deglacial warming into the last interglaciation at the isotopic stage 6/5 boundary; and the most recent deglacial warming into the present interglaciation at the isotopic stage 2/1 boundary. Changes in sea-surface temperature of 7-11 °G (estimated from transfer function analysis) are characteristically registered in these cores in a few thousand years. The corresponding temporal rates of cooling or warming recorded usually average 1-5 °C/1000 years (a) for the complete climatic shift. During local passage of the polar front, these rates are even higher. Regional advance and retreat rates of the polar front along a NW/SE axis from Cape Farewell, Greenland, to Spain characteristically range from 200 to 1600 m/a during these intervals. These estimates represent the rates of change presently recorded in the sediments. The actual (faster) rates of oalaeo-oceanographic change in the overlying North Atlantic surface waters will only be determined once the smoothing effects of vertical mixing can be removed.