Millennial Scale Changes in Antarctic Climate

The climate of the last glacial period is strongly dominated by the occurrence of rapid millennial-scale climate changes known as D-O events (e.g. North Greenland Ice Core Project Members, 2004). These occur in Greenland as rapid (occurring in <40 years) warmings by more than 10°C (Huber et al.. 2006). Counterparts to them are clearly seen in numerous other NH records. What concerns us here is what was happening in Antarctica in relation to those events, and what it tells us about the causes.

The longest D-O events have very clear counterparts, initially labelled as 'A-events' in Antarctic climate records. Using the high time-resolution available from the Byrd ice core, Blunier and Brook (2001) showed that while Greenland was cold before a D-O warming, Antarctica experienced a steady warming (by up to ~3°C). As soon as Greenland temperature jumped, Antarctic temperature started to cool again. It was suggested that this was the pattern expected from simple models involving changes in ocean heat transport (Stocker and Johnsen, 2003), with Antarctica and the Southern Ocean able to accumulate heat when ocean heat transport to the north was weak.

Further support for this model has come from the finding (using the EPICA cores at both Dome C and Dronning Maud Land (Kohnen station)) that there is a subdued southern counterpart to every D-O event (EPICA

Community Members, 2006). It has not yet been possible to show whether the timing of the weaker, shorter events is consistent with the model. However, central Antarctic climate of the last glacial appears to have been dominated by slow warmings and coolings of between 0.5 and 3°C that are most likely associated with changes in meridional ocean heat transport, and thus with rapid warmings in the north. The southern warm events have been named as 'Antarctic Isotopic Maxima (AIM)' (Blunier and Brook, 2001), with the A-events representing the largest AIM. Very similar temperature variability was found in the Dome C record for previous glacial periods as for the most recent one, strongly suggesting that the same mode of millennial variability held sway for the last 800kyr (Jouzel et al., 2007).

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