A coupled model simulation of ocean thermohaline properties of the Last Glacial Maximum

Abstract

The imposition of glacial boundary conditions leads to heat loss to the atmosphere from the deep ocean through enhanced vertical mixing and active turbulent heat fluxes. At a near-equilibrium LGM state, the deepwater temperature becomes close to the freezing point, a result supported by several recent proxy estimates. The LGM boundary conditions also result in a marked modification in the sea surface salinity. Sea surface salinity is decreased in the northern hemisphere, largely due to freshening of the northern North Atlantic, and is increased over the Southern Ocean in part due to an increase in sea ice formation and a drier climate in the southern high latitudes. In conclusion, deep ocean conditions simulated by the coupled model are in reasonable qualitative agreement with observational proxy evidence. The coupled model results largely illustrate mechanisms responsible for the LGM deep ocean change. In particular, the redistribution of surface freshwater budget leads to a weaker and shallower North Atlantic overturning circulation and rather different deep ocean thermohaline properties during the LGM.