Modeling the Response of Tropical North Atlantic Subsurface Temperatures to Atlantic Meridional Overturning Circulation Variability under Last Glacial Maximum Boundary Conditions

Prior studies have drawn attention to the asymmetric response of tropical North Atlantic surface and subsurface temperatures to Atlantic meridional overturning circulation (AMOC) changes. During periods weakened AMOC the entire surface of the tropical North Atlantic region experiences atmospheric-induced cooling, while the subsurface experiences an even larger warming due to rapid reorganizations of ocean circulation patterns (Zhang, 2007; Chang et al., 2008; Chiang et al., 2008; Wan et al., 2009). The subsurface ocean response to a slowdown of AMOC appears to be due to an opening of the equatorward pathway of the North Atlantic subtropical cell, allowing warm salinity maximum waters of the subtropical gyre to enter the equatorial zone along the western boundary (Chang et al., 2008). While this may serve as an important oceanic teleconnection mechanism linking abrupt climate changes in the high-latitude North Atlantic to the tropics, the applicability of this teleconnection mechanism to past abrupt climate events remains uncertain, as most water hosing experiments simulating AMOC reductions are conducted under modern climate boundary conditions. In this study, we investigate how past climate boundary conditions can affect the response of tropical North Atlantic surface and subsurface temperatures to AMOC changes through model analyses using a high-resolution version of the NCAR Community Climate System Model (CCSM3) under realistic Last Glacial Maximum (LGM) forcing boundary conditions. Preliminary results indicate that the overall response of surface and subsurface tropical North Atlantic temperatures to AMOC variability remains similar to that of modern climate hosing experiments, suggesting the teleconnection mechanism operated under LGM boundary conditions. Results from this study may also have significant implications for the abrupt reduction in West African Monsoon precipitation during periods of reduced AMOC.