The spectacular termination that marked the end of the last major ice age represents the largest and most rapid natural climate change in Earth's recent history. Identifying the conditions and processes that led to this termination requires detailed chronologies of sensitive paleoclimate proxies that monitor the last glacial/interglacial transition across the globe. This grant will develop such a chronology in the middle latitudes of the Southern Hemisphere for the reduction of ice volume in the Southern Alps of New Zealand from the last glacial maximum to today?s conditions. Our chronology will be based on newly developed state-of- the-art 10Be surface-exposure dating of glacial landforms produced during this reduction. This grant will determine if the Antarctic deglacial signal extents to middle latitudes of the Southern Hemisphere, thus setting up a test of a recent hypothesis that the Principal Investigator published in Science. The hypothesis posits that large Northern Hemisphere ice sheets, triggered by rising summer sunshine, produced a self-sustaining flood of icebergs and melt water into the North Atlantic, leading to cold northern stadial conditions that altered the global meridional temperature gradients which in turn regulated the major global zonal wind systems. A poleward shift and/or intensification of the Southern Hemisphere westerlies warms the Southern Hemisphere from middle latitudes to Antarctica and purges enough CO2 to the atmosphere by Southern Ocean upwelling to maintain interglacial conditions worldwide. Because New Zealand glaciers lie in middle latitudes near the outer boundary of the Southern Ocean, this hypothesis predicts that their volume loss should correlate with the Antarctic warming pulse and should be in antiphase with the northern stadial triggered by freshwater influx into the North Atlantic. This research will date ice recession in New Zealand?s Southern Alps and thus test this prediction.
Present-day global warming is front-page news. But scientists still do not fully understand the underlying mechanisms that caused the great global warming that ended the last ice age and produced the interglacial conditions of the last 11,700 years, during which human civilization and population has developed. The team has developed a hypothesis of how this great warming was achieved. The grant will produce knowledge of the timing of Southern Hemisphere events to test the hypothesis. This test involves recognition of changes in wind belts and ocean circulation that accompany a shift in the temperature gradient between hemispheres. A shift in the interhemispheric temperature gradient is also expected shortly, as rising atmospheric CO2 is predicted to warm the Southern less than the Northern Hemisphere. Thus, by studying the past great warming, we may be able to anticipate how such changes may occur during the ongoing global warming.
