Gulf Stream temperature, salinity and transport during the last millennium
Citable URI
https://hdl.handle.net/1912/1774Location
Straits of FloridaDOI
10.1575/1912/1774Abstract
Benthic and planktonic foraminiferal δ18O (δ18Oc) from a suite of well-dated, high-resolution
cores spanning the depth and width of the Straits of Florida reveal significant
changes in Gulf Stream cross-current density gradient during the last millennium. These
data imply that Gulf Stream transport during the Little Ice Age (LIA: 1200-1850 A.D.)
was 2-3 Sv lower 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 pattern of
flow anomalies with depth suggests reduced LIA transport was due to weaker subtropical
gyre wind stress curl.
The oxygen isotopic composition of Florida Current surface water (δ18O w) 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
smface waters are influenced by the North Atlantic subtropical gyre, δ18Ow increased by
0.3% during the last 200 years. Although a portion (~0.1%) of this shift may be an
artifact of anthropogenically-driven changes in surface water ΣCO2, the remaining δl8Ow
signal implies a 0.4 to 1 psu increase in salinity after 200 yr BP. The simplest
explanation of the δ18Ow data is southward migration of the Atlantic Hadley circulation
during the LIA. Scaling of the δ18Ow records to salinity using the modern low-latitude
δ18Ow-S slope produces an unrealistic reversal in the salinity gradient between the two
sites. Only if C180 w is scaled to salinity using a high-latitude δ18Ow-S slope can the
records be reconciled. Changes in atmospheric 14C paralleled shifts in Dry Tortugas
δ18Ow , suggesting that variable solar irradiance paced centennial-scale Hadley cell
migration and changes in Florida Current salinity during the last millennium.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February, 2006
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Suggested Citation
Thesis: Lund, David C., "Gulf Stream temperature, salinity and transport during the last millennium", 2006-02, DOI:10.1575/1912/1774, https://hdl.handle.net/1912/1774Related items
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