S70 The effects of the 8.2 ka event on the ITCZ of the Tropical Atlantic

Sunday, 23 January 2011
Matthew A. Burger, Ohio University, Athens, OH; and A. Wagner, C. Morrill, and B. L. Otto-Bliesner

The 8.2 ka event, which occurred 8200 years before present, was a period of abrupt cooling that is recorded in multiple proxy records across the Northern Hemisphere. It is hypothesized that the 8.2 ka event was caused by the release of fresh water from the proglacial Lake Agassiz into the Labrador Sea and North Atlantic Ocean. According to this hypothesis, fresh water flowed into the main region of North Atlantic Deepwater formation. Density differences between the fresh and saline waters caused the Atlantic Meridional Overturning Circulation (AMOC) to slow down, resulting in cooler surface temperatures over Greenland and Europe.

While much of the proxy evidence for the 8.2 ka event is from the region surrounding the North Atlantic basin, recent studies suggest impacts from the event extended beyond this region. We will consider the effects of the 8.2 ka event on the Intertropical Convergence Zone (ITCZ) using model simulations and published proxy records from lake and ocean sediment cores and speleothems. Two model simulations were completed, in which fresh water was added in two different regions, with one simulation showing a cooling in the high-latitude North Atlantic and a reduction in the AMOC comparable to proxy records and the other only minimal responses. Both 8.2 ka climate model simulations largely agree with the proxy data in terms of showing a southward shift of the ITCZ, however, diverging the most as the distance from the equator increases. These results indicate that a reduction in the AMOC and subsequent cooling of high-latitude North Atlantic surface temperatures are not the direct cause of a southward shift in the ITCZ during the 8.2 ka event.

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