The salinity and temperature of the Florida Current are key parameters affecting the transport of heat into the North Atlantic, yet little is known about their variability on centennial timescales. Here we report replicated, high-resolution foraminiferal records of Florida Current surface hydrography for the last millennium from two coring sites, Dry Tortugas and the Great Bahama Bank. 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. 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. Although a portion (~0.1 per mil) of this shift may be an artifact of anthropogenically driven changes in surface water SumCO2, the remaining d18Ow signal implies a 0.4–1 increase in salinity after 200 years B.P. The simplest explanation of the d18Ow data is southward migration of the Atlantic Hadley circulation during the LIA. Scaling of the d18Ow records to salinity using the modern low-latitude d18Ow-S slope produces an unrealistic reversal in the salinity gradient between the two sites. Only if d18Ow is scaled to salinity using a high-latitude d18Ow-S slope can the records be reconciled. Variable atmospheric 14C paralleled Dry Tortugas d18Ow, suggesting that solar irradiance paced centennial-scale migration of the Inter-Tropical Convergence Zone and changes in Florida Current salinity during the last millennium.

Core tops contain more radiocarbon than expected in modern samples, indicating contamination with bomb 14C and post-1950 A.D. deposition ages. We calibrated the down-core raw 14C values to calendar ages using CALIB 4.3 (Stuiver et al.,1998) and a reservoir age of 400 years. Each date is based on G. ruber from the >250 µm size fraction. Average sedimentation rate is 25 cm/kyr and average sampling interval is 20 years for core W167-79GGC. See Lund and Curry (2004) for the W167-79GGC age model.

Supplement to: Lund, David C; Curry, William B (2006): Florida Current surface temperature and salinity variability during the last millennium. Paleoceanography, 21(2), PA2009