Determining paleoceanographic circulations, with emphasis on the Last Glacial Maximum

The inference, from radiocarbon and other data, that the North Atlantic Ocean circulation during the Last Glacial Maximum was reduced, is examined. Because glacial periods are thought to be windier than non-glacial ones, a reduced circulation is difficult to rationalize. A first step is to note that the circulation of mass is unlikely to correspond simply to the circulation of heat or freshwater (salt). By merely permitting an enhanced input of southern hemisphere water into the North Atlantic, one can accommodate significantly increased radiocarbon ages. Such an input is equally interpretable as owing to an increased mass circulation, rather than a decreased one. Inferred estimates from paleo-shear estimates in the Florida Current are re-interpreted as producing an indeterminate net flow there. Determination of the paleocirculation rates is not simpler than the problem in the modern ocean: it is fully three-dimensional and requires an adequate data base to determine the mass flux rates. r 2002 Elsevier Science Ltd. All rights reserved.