HR: 17:45h
AN: PP44A-08    [Abstracts]
TI: Florida Current Temperature and Salinity Variability during the Last Millennium
AU: * Lund, D C
EM: dlund@whoi.edu
AF: Woods Hole Oceanographic Institution, Mail Stop 24, Woods Hole, MA 02543 United States
AU: Curry, W B
EM: wcurry@whoi.edu
AF: Woods Hole Oceanographic Institution, Mail Stop 24, Woods Hole, MA 02543 United States
AB: Planktonic foraminiferal time series from four well-dated, high sedimentation rate cores exhibit significant changes in Florida Current $\delta^{18}$O, SST, and $\delta^{18}$O$_{w}$ during the past 1000 years. On the Florida Margin (24.4 $\deg$N, 83.3 $\deg$W), {\it G. ruber} $\delta^{18}$O in two cores increased by 0.1-0.2 $\permil$ from 500 to 200 yr BP. During the same time interval, Mg/Ca-derived SSTs warmed by 0.5-1.0 $\deg$C. These shifts in $\delta^{18}$O and temperature require an increase in $\delta^{18}$O$_{w}$ of 0.2-0.4 $\permil$, equivalent to a salinity increase of 1-2 psu. From 200 yr BP to present, $\delta^{18}$O$_{w}$ values decreased by 0.1-0.2 $\permil$. On the other side of the Florida Current (FC), two cores from the Great Bahama Bank (24.6 $\deg$N, 79.3 $\deg$W) also support a ~1-2 psu increase in salinity, but the shift occurs about 200 years later. {\it G. ruber} $\delta^{18}$O at the Great Bahama Bank sites changed little from 1000 to 300 yr BP, but from 300 yr BP to present, it increased by 0.2-0.3 $\permil$. SSTs during the last 300 years increased by 0.5-1.0 $\deg$C, indicating that $\delta^{18}$O$_{w}$ increased by 0.3-0.4 $\permil$ since 300 yr BP. In the earlier portion of the record, $\delta^{18}$O$_{w}$ variability is on the order of 0.1 $\permil$. Mg/Ca analyses from the Great Bahama Bank indicate that coretop SSTs are similar to those at 1000 yr BP (the so-called Medieval Warm Period). SSTs were 0.5-1.0 $\deg$C cooler during the Little Ice Age (~750 to 200 yr BP). Although small, these changes in SST are consistent in magnitude and timing in two separate time series. The Florida Current SST variability is similar to that estimated for the Sargasso Sea (Keigwin, 1996), although the Sargasso Sea reconstruction implies higher SSTs than modern during the Medieval Warm Period. Changes in Florida Current salinity result from evaporation-precipitation variability in the central and western tropical Atlantic, the source region for much of the FC surface water (Schmitz and Richardson, 1991). Evidence of centennial-scale hydrologic variability from the Cariaco Basin (Haug {\it et al.}, 2001; Black {\it et al.}, 2004) and the Yucatan Peninsula (Hodell {\it et al.}, 2001; 2002) implies the Inter-Tropical Convergence Zone (ITCZ) shifted southward during the Little Ice Age. If the ITCZ migrated south during the LIA, it may have led to increased salinity in the tropical Atlantic, Caribbean, and the FC. While modern observational records indicate the salinity of the Florida Margin sites follows that of the Caribbean and tropical Atlantic, the Great Bahama Bank is more influenced by the relatively salty North Atlantic subtropical gyre (Levitus, 1994). The time lag in the $\delta^{18}$O$_{w}$ records from the Florida Margin and Great Bahama Bank indicates that salinity first increased in the tropical Atlantic, followed by a similar magnitude increase about 200 years later in the North Atlantic subtropical gyre.
DE: 4215 Climate and interannual variability (3309)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting