Did shifting winds drive shallow ventilation of the Southwest Pacific Ocean across the last glacial termination?
Monday, 15 December 2014
At the end of the last ice age, a rapid increase in atmospheric CO2 concentration coincided with changes in seawater δ13C suggesting that invigorated ventilation of the deep ocean released CO2 to the atmosphere. We present here high-resolution, benthic foraminiferal δ13C and δ18O records from a 4-core depth transect in the Southwest Pacific Ocean that document shallow stratification and poor ventilation below ~660 m in the last glacial period. Starting at 17 ka, rapid convergence of shallow and intermediate-depth (660-2050 m) δ13C suggests thickening and increased ventilation of intermediate water, which was interrupted by restratification starting during the Antarctic Cold Reversal (ACR; 14.5-12.8 ka). δ18O and δ13C from two planktonic foraminiferal species, G.bulloides and G. inflata, growing at different depths, suggest changes in thermocline depth and a switch in source location of mixed layer and shallow subsurface waters from proximal Southern Ocean and more distal equatorial sources which was coeval with changes in intermediate water ventilation. The close coincidence of these changes with early Southern Hemisphere warming and wind-driven upwelling in the Southern Ocean suggests that latitudinal shifts in the southern Westerly wind belt affected intermediate water formation and initiated CO2 release from the ocean early in the termination.