Sensitivity of paleonutrient tracer distributions and deep-sea circulation to glacial boundary conditions

We use a carbon cycle model coupled to an ocean general circulation model to explore the links between sea surface boundary conditions, the deep-sea circulation, and the distribution of paleonutrient tracers (delta(13)C and Cd/Ca) from Last Glacial Maximum (21,000 B.P.) sediments. A glacial flow field with a shallower and 50% reduced North Atlantic overturning circulation generally reproduces the tracer data but cannot explain the strong glacial-interglacial shift in delta(13)C in the Southern Ocean. Sensitivity experiments with changes of +/-1 in salinity in the glacial salinity boundary fields show circulation patterns ranging from even stronger than the present day one to nearly a shutdown of the Atlantic deep-sea circulation. Our model results indicate that the overturning in the North Atlantic is linearly related to the zonal wind forcing in the Southern Ocean but with half of the sensitivity of Toggweiler and Samuels [1993]. Atmospheric pCO(2) appears to be insensitive to changing circulation and sea surface forcing; a tropical cooling of 4 degrees C can only explain 8% of the glacial-interglacial pCO(2) change documented in ice cores.