Glacial Atlantic Ocean Circulation: What do we really know?
September 10, 2009
Clark 507, 12:15 p.m.
National Center for Atmospheric Research, Boulder, CO
The Last Glacial Maximum (LGM) d13C data show large differences from
present-day data, and imply a much stronger Atlantic vertical nutrient
gradient during the LGM. The observation of an apparent divide between
low-nutrient waters above about 2km depth and high-nutrient waters below
2km depth, has led to the idea that the oceanic mass flux must exhibit a
similar structure in the LGM. Rather than invoking a fundamentally
different flow, it is shown that most of the LGM Atlantic data can
alternatively be explained under a present-day oceanic circulation
regime, by just changing the d13C of waters in the surface-ocean.
Another tracer that has been widely used to infer past changes in oceanic circulation is the sedimentary Pa/Th ratio. Recent reconstructions of past changes in the Atlantic Meridional Overturning Circulation (AMOC) based on Pa/Th, and the difficulties inherent in such a reconstruction, are discussed.
The talk ends with some recent model results indicating a new mechanism by which the AMOC may play a role in regulating northern hemisphere climate.