29 
Much shorter fluctuations are also evident in the North Atlantic responses. Ruddiman and 
McIntyre (1981) documented a cooling lasting less than 1000 years that returned the eastern and 
central parts of the high-latitude North Atlantic from full-interglacial SST values to a full-glacial 
condition roughly 10,500 years ago (Fig. 2). This kind of surface-ocean response is also likely 
to have had a significant impact on the formation of North Atlantic deep water, and it may be 
more relevant to future changes on a short-term basis. 
One critical uncertainty in assessing past changes in deep-water formation is the lack of 
knowledge about past sea-ice limits. Sea ice is generally reconstructed from negative evidence, 
such as extreme suppression of productivity of shelled planktonic organisms. Research into 
more definitive methods of estimating past sea-ice limits is recommended. 
DEGLACIAL POLAR FRONT MOVEMENTS 
Fig. 2. Map of deglacial retreat and readvances of the North Atlantic polar front (from 
Ruddiman and McIntyre, 1981). Positions shown were occupied during the major part of the 
intervals indicated, but transitions between positions were not necessarily instantaneous. 
