Ice Age Terminations

Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric CO2 and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing CO2 and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and CO2. The “sawtooth ” character of late Quater-nary ice-age cycles, with gradual buildupand rapid collapse of ice sheets, has been known since Emiliani’s pioneering oxygen iso-tope (d18O) measurements on marine sediments (1). Explanations of the rapid collapses, dubbed “terminations ” (2), have long been sought. The ice-age cycles have been linked to changes i