HR: 08:30h
AN: PP41A-03    [PDF]
TI: Expression of Heinrich Events in the Southern Ocean
AU: * Sachs, J P
EM: jsachs@mit.edu
AF: Department of earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology 77 Massachusetts Avenue, Room E34-254, Cambridge, MA 02139 United States
AU: Anderson, R F
EM: boba@ldeo.columbia.edu
AF: Lamont-Doherty earth Observatory of Columbia University, Geochemistry Building P.O. Box 1000, Palisades, NY 10964 United States
AU: Pahnke, K
EM: pahnkek@cf.ac.uk
AF: School of Earth, Ocean and Planetary Sciences, Cardiff University Park Place, Cardiff, CF10 3YE United Kingdom
AU: Zahn, R
EM: rainer@geo.ub.es
AF: Department d'Estratigafia, Paleontologia i Geosciencies Marines, Universitat de Barcelona Campus de Pedralbes, Barcelona, 08028 Spain
AB: Eight massive iceberg discharges to the North Atlantic, Heinrich Events (HEs), occurred between 65,000-10,000 years ago during the last glacial period. Each resulted in extreme freshening and cooling of the North Atlantic and substantial reorganization of the North Atlantic's meridional overturning circulation. Synchronous changes in the chemistry or biology of sediment cores from the Southwest equatorial Atlantic, the Southeast subtropical Atlantic and the Arabian Sea, and in a speleothem from southeastern China argue for a widespread impact of Heinrich Events on climate. Yet most evidence for climate change associated with HEs is from the Northern Hemisphere, clustered in the North Atlantic region. Here we show for the first time that HEs had a profound impact on the Subantarctic Southern Ocean, causing sea surface temperatures (SSTs) to rise and algal productivity to soar in the waters east of New Zealand. Algal productivity increased concurrently in Subantarctic waters southwest of Africa, southeast Atlantic Ocean. Sea surface temperatures in Chatham Rise core MD97-2120 ($45\deg$32' S, $174\deg$56' E, 1210 m) were reconstructed from both alkenone unsaturation ratios and from Mg/Ca ratios in shells of the planktonic foraminifer {\it G. bulloides}. Algal productivity was inferred from the concentration of alkenones in the same core and in core TN057-21-PC2 from the Cape Basin. Elevated thorium-230 normalized fluxes of alkenones and authigenic uranium concentrations in the Cape Basin core are consistent with increased algal productivity during HEs. Our results support the notion of a `bipolar seesaw' in temperature during major alterations of the North Atlantic's meridional overturning circulation. At the same time, the large increases in Subantarctic algal productivity that accompanied those events imply that the meridional overturning circulation of the Southern Ocean changed significantly. We propose several mechanisms by which flooding of the North Atlantic with meltwater during HEs could result in increased SSTs and productivity in the Subantarctic Ocean.
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 4267 Paleoceanography
DE: 4845 Nutrients and nutrient cycling
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting