The timing of the last deglaciation in North Atlantic climate records

To determine the mechanisms governing the last deglaciation and the sequenc e of events that lead to deglaciation, it is important to obtain a temporal framework that applies to both continental and marine climate records. Rad iocarbon dating has been widely used to derive calendar dates for marine se diments, but it rests on the assumption that the 'apparent age' of surface water (the age of surface water relative to the atmosphere) has remained co nstant over time(1,2). Here we present new evidence for variation in the ap parent age of surface water (or reservoir age) in the North Atlantic ocean north of 40 degrees N over the past 20,000 years. In two cores we found app arent surface-water ages to be larger than those of today by 1,230 +/- 600 and 1,940 +/- 750 years at the end of the Heinrich 1 surge event (15,000 ye ars BP) and by 820 +/- 430 to 1,010 +/- 340 years at the end of the Younger Dryas cold episode. During the warm Bolling-Allerod period, between these two periods of large reservoir ages, apparent surface-water ages were compa rable to present values. Our results allow us to reconcile the chronologies from ice cores and the North Atlantic marine records over the entire degla ciation period. Moreover, the data imply that marine carbon dates from the North Atlantic north of 40 degrees N will need to be corrected for these hi ghly variable effects.