Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmpp22b..07k&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #PP22B-07
Other
1620 Climate Dynamics (3309), 4267 Paleoceanography
Scientific paper
Sediments in Emerald Basin, on the continental shelf off Halifax, N.S., accumulate at a rate of about 30 cm/thousand years. This rate is great enough to record century to millennial scale changes in the surface and deep (~230m) waters in the basin. In 1998 we cored Emerald Basin, and other locations in the nearby slope water system, in order to develop an ocean-climate history of the region using paleoceanographic techniques. The core top has a modern 14C age, and other 14C dates indicate approximately linear sedimentation rates to 1600 calendar years B.P. Today the continental shelf off Nova Scotia is bathed by a mixture of coastal and slope waters. This mixture varies on interannual to interdecadal timescales. For example, the work of Petrie and Drinkwater and others of the Bedford Institute clearly shows that during the very strong minimum phase of the North Atlantic Oscillation during the 1960s, the Labrador Current was colder and fresher than today and intruded into Emerald Basin. Sea surface temperatures (SST) decreased by 1-2 degrees on an annual average basis, and bottom water temperatures dropped by about 4 degrees. We applied 5 proxies for seawater temperature changes to the sediments of Emerald Basin. Surface water temperature changes are reflected in the percent abundance of the polar planktonic foraminifer N. pachyderma (s.), in the oxygen isotope ratio (d18-O) of the shells of this species, and in the unsaturation ratio of alkenones produced by phytoplankton. Bottom water temperature changes are recorded by the d18-O of benthic forams, and by the Mg/Ca in their shells. All five of these proxies indicate the ocean warmed suddenly sometime in the past 150 years or so. The exact date is uncertain because 14C dating is inaccurate in recent centuries, but we believe this abrupt warming probably correlates with the ice melt layer evidence for warming in the ice caps of the Canadian Archipelago. This region is known to be one of the main source regions for the Labrador Current. Before this recent warming, SST was continually lower by 1-2 degrees, and bottom water was colder by about 6 degrees. These results suggest that there was no Medieval Warm Period off Nova Scotia. Because there is no evidence of Medieval warming in the Canadian archipelago, it seems likely that coastal waters from Baffin Bay to at least as far south as Nova Scotia were continually cold for ~1500 of the past 1600 years. The present hydrography on the Scotian Shelf may be strongly influenced by anthropogenic effects.
Keigwin Lloyd D.
Rosenthal Yair
Sachs Jeffrey
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