Tropical Influence on High Latitude Climate Change During the Last Deglaciation

Ice core data and marine records suggest an inter-hemispheric out of phase relationship during D/O events during the last glacial period, and during the last deglaciation. Here we present multi-proxy results from sediment cores from the Nordic Seas and the North Atlantic that can be directly compared with ice core records and Sea Surface Temperature (SST) records from the tropics. We are now able to document at decadal resolution that every cold reversal in the Greenland Ice cores has an imprint of strong meltwater input to the North Atlantic/Nordic Seas. These gave a strong feedback on the climate by several times reducing the potential of deep water convection in the North Atlantic. A similar scenario as described for the H1, and the following rapid warming, can be shown for the Younger Dryas period. Paleo-records from high northern latitudes also clearly indicate that the warming following the last glacial maximum took place simultaneously with the warming in the Southern Hemisphere at about 19kyr (cal.yrs), as a respond to the same forcings, i.e. increased insolation and increased release of CO2 to the atmosphere. At 18kyr the northward heat transport was disrupted during Heinrich event 1 in the North Atlantic as a result of the incipient warming that triggered melting of surrounding continental ice sheets, which led to melt water run off and near to a collapse of the Thermohaline Circulation (THC). The strongly reduced convection in the north lasted for about 2-3kyr yrs and led to a cooling in the North Atlantic region. Simultaneously, heat was building up in the tropics as less heat was distributed northward. As soon as the THC recovered in the North Atlantic, the heat that was built up in the tropics during H1, could be advected northward, leading to a series of rapid warmings in a flickering fashion in the North Atlantic region. Simultaneously with the warming at high latitudes, the tropics and the Southern Hemisphere experienced a cooling (Antarctic Cold Reversal-ACR) due to the heat gained in the Southern Hemisphere during the H1 is distributed northward. All known forcing mechanisms should at this point drive the climate globally into an interglacial mode. However, several times the climate at high northern latitude is punctuated by several cold periods, like the Younger Dryas cold period.