Last Glacial Cycle and Deglaciation

At the last glacial maximum (LGM, ~21ka), ice-sheet expansion in Antarctica was responsible for around 15 m of global sea level fall, with growth most likely taking place over continental shelves exposed as a result of sea level fall from the development of Northern Hemisphere ice sheets (Siegert, 2001).

There are currently three different ideas about the onset of deglaciation: (1) changes in the water balance of the North Atlantic, the source region for much of the global thermohaline circulation, serve to propagate the deglacial signal worldwide; (2) changes in the Southern Ocean, as recorded in some ice cores, lead deglaciation as seen in Greenland ice; and (3) synchronicity in the timing of high-latitude climate change in both hemispheres, and some tropical records, suggest that tropical forcing is a key initiator of deglaciation. It may seem surprising that this controversy has not already been settled. The most important confound for establishing synchronicity, or its absence, among the available palaeoclimate records revolves around chronology development. It is notoriously difficult to date LGM ice layers and sediments to an accuracy of better than 1-2 thousand years. It is also difficult to separate local climate or geomorphic signals from large transformations that are regionally or globally important. What is needed to resolve the deglacial synchronicity issue are better records from rapidly deposited deglacial sequences across a range of longitudes and latitudes in the Southern Ocean that use sedimentary or glacial outlet indicators to directly track regional climate systems. Currently there are too few precisely dated records of the LGM from the Southern Ocean. Chapter 12 brings together several geological datasets relevant to the LGM in an attempt to constrain the ice volume at this important time of climate change.

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