OCEAN CIRCULATION AND ATMOSPHERIC CO2 CHANGES: COUPLED USE OF MODELS AND PALEOCEANOGRAPHIC DATA

We have perturbed a simple model of oceanic circulation in a series of sensitivity tests to determine how circulation changes associated with the last glacial maximum could affect observable or potentially observable paleoceanographic parameters. Ultimately, we want to use such paleoceanographic data to construct models of glacial ocean circulation. We have found that the different circulation patterns that we imposed in our sensitivity tests have dramatically different responses for the distribution of PO4, O-2, and partial derivative C-13 contents of the oceans. They also produce different levels of low-latitude productivity. By comparing the coupled responses of several of these paleoceanographic prameters to the responses from the sensitivity tests it is possible to constrain the possible glacial circulation scenarios to a relatively small number. We give, as one example, a case where intermediate turnover is significantly higher than the present and deep ocean turnover has dropped. In addition, exchange of waters between the intermediate- and high-latitude surface ocean is much lower. The result of this scenario is an atmosphere with 60 ppm lower atmospheric CO2, low latitudes with about 40% higher productivity, and a change in the planktic/benthc partial derivative C-13 contrast of about 0.3 parts per thousand. When we compare our model to other independent paleoceanographic data, we find that the major point of disagreement is in the distribution of surface water partial derivative C-13 in the Antarctic region. We believe that somewhat more complex box models which take open system effects into account will resolve this discrepancy.