Subtropical W-Atlantic subsurface warming during deglacial times of reduced Atlantic Meridional Overturning Circulation

The Atlantic Meridional Overturning Circulation (AMOC) is intimately linked to abrupt North Atlantic climate change and is a key player for the transport of tropical heat to high northern latitudes. A deglacially reduced AMOC resulted in surface cooling in wide areas of the tropical North Atlantic, while the subsurface ocean experienced regional warming by several degrees due to the reorganization of ocean circulation at intermediate depths (Schmidt et al., 2012). The S-Caribbean (Tobago Basin) is crucial in this respect as several modelling studies predicted substantial subsurface warming during periods of reduced AMOC (Schmidt et al., 2012).We here reconstruct surface and subsurface temperature and salinity changes during the past 30 kyr, based on stable isotope (δ13C, δ18O) and elemental (Mg/Ca) ratios of planktonic surface dwelling (G. ruber) and deep dwelling foraminiferal species, (G. truncatulinoides). The studied sediment core is influenced by cooler and fresher tropical waters during modern circulation conditions. During deglacial times of AMOC slowdowns subsurface waters warmed and became more saline, as the weakened thermohaline circulation allowed Subtropical Gyre waters to enter the tropical W-Atlantic (Chang et al. 2008). Our high resolution data further imply that the inflow of Subtropical Gyre waters into the tropical Atlantic led to the abrupt increase of subsurface temperatures by ~6°C. Such subsurface warming is much higher than the 2.5°C warming proposed by modeling studies. Furthermore, subsurface salinity rose simultaneously with temperatures, pointing to the replacement of cooler/fresher tropical waters by warmer/saltier Subtropical Gyre waters