CONSTRAINTS FROM PALEOTRACER DATA ON THE NORTH-ATLANTIC CIRCULATION DURING THE LAST GLACIAL MAXIMUM

We investigate the extent to which the paleotracers, delta(13)C and de lta(18)O, constrain the North Atlantic Ocean general circulation durin g the last glacial maximum (LGM). The distinction is made in this work between the depiction of water mass distributions and the inference o f the oceanic circulation. The delta(13)C data indicate that water mas ses formed in the North Atlantic and in the Southern Ocean were distri buted differently during the LGM, but the extent of the differences ca nnot be quantified because of uncertainties in the end-member composit ion. Reasonable choices of values for the end-members produce volumes of Lower North Atlantic Deep Water (NADW) significantly smaller than i n the modern Atlantic, in agreement with previous studies. To explore the range of circulations consistent with this water mass distribution , a coarse resolution inverse model of the North Atlantic is constrain ed with delta(13)C and delta(18)O paleodata. The model shows that the glacial period tracer distribution is fully consistent with the circul ation rates estimated for the modem ocean. However, the paleodata are also consistent with a circulation rate of one-half the modern flux of NADW, and indeed there are an infinite number of rates of deep water movement that are possible. To remove this ambiguity, the central need is for a data type capable of setting the overall rates of water move ment, i.e., a ''clock'', such as that provided by geostrophy or a well -sampled radioactive tracer.