Gulf Stream Temperature, Salinity and Transport During the Last Millenium

David Lund, Ph.D., 2006
William Curry, Advisor

Benthic and planktonic foraminiferal d18O (d18Oc) from a suite of well-dated, high-resolution cores spanning the depth and width of the Straits of Florida indicate Gulf Stream vertical current shear was anomalously low during the Little Ice Age (LIA: 1200-1850 A.D.). Assuming a constant level of no motion, the foraminfieral data imply transport was 2-3 Sv lower during the LIA than today. The timing of reduced flow is consistent with cold conditions in Northern Hemisphere paleoclimate archives, implicating Gulf Stream heat transport in centennial-scale climate variability of the last 1,000 years.

The oxygen isotopic composition of Florida Current surface water (d18Ow) near Dry Tortugas increased 0.4‰ during the course of the Little Ice Age (LIA: ~1200-1850 A.D.), equivalent to a salinity increase of 0.8-1.5 psu. On the Great Bahama Bank, where surface waters are influenced by the North Atlantic subtropical gyre, d18Ow increased by 0.3‰ during the last 200 years, a 0.4 to 1 psu increase in salinity. The simplest explanation of the d18Ow data is southward migration of the Atlantic Hadley circulation during the LIA. Changes in atmospheric 14C paralleled shifts in Dry Tortugas d18Ow, suggesting that variable solar irradiance paced centennial-scale Hadley cell migration and changes in Florida Current salinity.