HR: 13:40h
AN: PP13B-01 INVITED     [Abstracts]
TI: The role of changing seasonality in North Atlantic abrupt climate changes
AU: * Alley, R B
EM: rba6@psu.edu
AF: Department of Geosciences, Pennsylvania State University, Deike Building, University Park, PA 16802 United States
AU: Denton, G H
AF: Climate Change Institute, University of Maine, 5790 Bryand Global Sciences Center, Rm 303, Orono, ME 04469 United States
AU: Comer, G C
AF: GCI, 20875 Crossroads Circle Suite 100, Waukesha, WI 53186 United States
AU: Broecker, W S
AF: Geochemistry, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9 W PO Box 1000, Palisades, NY 10964 United States
AB: Cooling around the North Atlantic associated with ice-age millennial oscillations was primarily a wintertime phenomenon, enforced and amplified by sea-ice formation. As summarized by Denton et al. (submitted, QSR), Greenland ice-core indicators of mean-annual temperature change show the Younger Dryas much colder than the Little Ice Age and almost as cold as the glacial maximum, whereas indicators primarily of summer temperature in Greenland and NW Europe, such as moraine positions, indicate a Younger Dryas much warmer than glacial maximum and not much colder than the Little Ice Age. A large, Antarctic-like seasonal cycle in Younger Dryas sea ice explains these observations, and is consistent with a wide range of data and models. The "conveyor" circulation is important not just for heat transport to the North Atlantic but also for salt transport that maintains high surface density and allows wintertime deep mixing to suppress sea-ice formation. The abrupt-climate-change "switch" for the ice-age events may be as simple as whether North Atlantic water sinks before it freezes, or freezes before it sinks.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
DE: 1827 Glaciology (1863)
DE: 1600 GLOBAL CHANGE (New category)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting