Abstract:
Planktonic foraminiferal d18O time series from three well-dated, high
sedimentation rate cores near the Florida Keys (24.4N, 83.3W) exhibit repeated
centennial to millennial-scale oscillations during the late Holocene. Isotopic
shifts of 0.2-0.3% over the past 5200 years represent changes in sea-surface
temperature (SST) of 1.0-1.5C or salinity variability of 1-2 psu. The largest
significant
... isotopic events are centered at approximately 200, 2000, 3200, and
prior to 4000 calendar years BP. High Florida Current d18O during the Little
Ice Age (LIA) correlates with published records of high d18O in the Sargasso
Sea and low SST off the coast of west Africa. An interval of generally low
d18O in the Florida Straits from 1800 to 500 years BP is synchronous with the
Medieval Warm Period off west Africa but leads low d18O in the Sargasso Sea by
several hundred years. Synchronous cooling across the subtropical gyre during
the LIA is difficult to explain using interannual North Atlantic Oscillation
patterns but may be consistent with the simulated effects of reduced solar
irradiance. At frequencies between 1/1000 and 1/300 years during the Late
Holocene, Florida Current d18O is coherent with a published estimate of 14C
production rate. Radiocarbon production seems to lead d18O at these
frequencies, but uncertainty in the phase calculation precludes a clear
lead-lag relationship. At frequencies lower than 1/300 years, Florida Current
d18O is coherent and in phase with atmospheric D14C. The coherence of D14C and
d18O at periods >1000 years implies oceanic circulation may play a role in
modulating atmospheric radiocarbon on millennial timescales. 
