Pleistocene Glacial Cycles Intervals of Extreme Warmth and Cold

Studies of Antarctic ice cores show that Pleistocene climate variability in the different sectors of the southern high latitudes (detailed in Chapter 11) has occurred out of phase. This raises questions about the response of the southern high latitudes to external climate drivers, such as orbital insolation, solar variability and internal amplifiers such as thermohaline circulation and carbon cycle changes that operate at both Croll-Milankovitch and millennial-decadal time scales. These questions highlight a need for appropriate time series of climate variability from all sectors of the Southern Ocean. Recovery of sediment sequences with expanded Pleistocene sections, such as those from beneath the McMurdo Ice Shelf as undertaken by the ANDRILL programme (see www.andrill.org), permits the study of the structure and timing of glacial and interglacial cycles in the Southern Ocean at millennial time scales that extend well beyond the last four major climate cycles. In addition, several groups organised under the International Marine Global Change Study (IMAGES) programme have proposed to collect long piston cores for Pleistocene research from several sectors of the Southern Ocean. With new high-resolution Pleistocene time series from both the Antarctic margin and offshore sites, we can begin to determine if the abrupt climate changes that have been documented from the Atlantic and Indian sectors, and in polar ice cores, have also occurred in the Pacific basin. During the last decade, many palaeoceanographic studies focused on millennial climate variability (e.g. on the Dansgaard-Oeschger (DO) events). They show that ocean thermohaline circulation is capable of becoming unstable in response to climate change and modifications to the cryosphere. The existing palaeoceanographic record documents mainly the North Atlantic Ocean, and modelling experiments have mostly explored the variability of North Atlantic Deep Water formation forced by fresh water flux from ice surge events. However, Southern Ocean sea ice may be important during glacial periods, and the glacial 'on/off modes of global circulation could also be linked to deep-water formation in the Southern Ocean.

0 0

Post a comment