INHERENTLY UNSTABLE CLIMATE BEHAVIOR DUE TO WEAK THERMOHALINE OCEAN CIRCULATION

The oceanic thermohaline circulation (THC) carries Light, warm surface water polewards and dense, cold deep water equator-wards, thereby tra nsporting a large amount of heat towards the poles and significantly a ffecting high latitude climate. The THC has been remarkably stable, an d its variability quite low over the Holocene period (the past 10,000 years). The much greater climate instability and high-frequency variab ility recorded in ice(1) and deep-sea(31) cores throughout the precedi ng 150,000 years has been linked to greater THC variability(2,3). Here we argue, using a global coupled ocean-atmosphere-ice general circula tion model with realistic geography, that there is a wide range of wea k mean states of the THC that Cannot be stably sustained by the climat e system. When the model THC is forced into a state in the unstable ra nge, the THC may rapidly strengthen, collapse or display strong oscill ations. The existence of this unstable regime may account for the grea ter variability of the THC and climate before the Holocene period.