NOAA/WDS Paleoclimatology - Florida Straits 35 - 20 KYrBP Mg/Ca SST and d18Osw Reconstructions

STUDY NOTES: Planktonic foraminiferal Mg/Ca and abundance data plus reconstructed SST and d18O-seawater from a Florida Straits sediment core covering the Last Glacial Maximum and Marine Isotope Stage 3 (35 - 20 KYrBP).
ABSTRACT SUPPLIED BY ORIGINATOR: Abrupt, millennial-scale climate oscillations, known as Dansgaard-Oeschger (D-O) cycles, characterized the climate system of the last glacial period. Although proxy evidence shows that D-O cycles resulted in large-scale changes in atmospheric circulation patterns around the planet, an understanding of how Atlantic Meridional Overturning Circulation (AMOC) varied across these events remains unclear. Here, we take advantage of the fact that both tropical atmospheric circulation changes corresponding to north-south shifts in the Intertropical Convergence Zone (ITCZ) and large-scale changes in ocean circulation associated with AMOC variability can be reconstructed in the same sediment core from the Florida Straits to examine the relationship between atmospheric and ocean circulation changes across D-O events. To reconstruct surface water conditions, Mg/Ca-paleothermometry and stable isotope measurements were combined on the planktonic foraminifera Globigerinoides ruber (white variety) from sediment core KNR166-2 JPC26 (24 19.61'N, 83 15.14'W; 546 m depth) to reconstruct a high-resolution record of sea surface temperature and d18OSEAWATER (a proxy for upper mixed layer salinity) during Marine Isotope Stages (MIS) 2 and 3 from 20 - 35 ka BP. As an additional proxy for upper water column salinity change, we also generate a faunal abundance record of the salinity-sensitive planktonic foraminifera Neogloboquadrina dutertrei. Our results suggest that rapid reductions in sea surface salinity occurred at the onset of D-O interstadials, while stadials are characterized by increased surface salinities. The most likely cause of these salinity changes was variation in the strength and position of the ITCZ across D-O events. Finally, we examine the relationship between millennial-scale atmospheric circulation changes recorded in the planktonic records and ocean circulation changes inferred from the benthic d18O record from our core. Our results provide some of the first evidence that AMOC strength did vary across at least one of the millennial-scale D-O cycles of MIS 3.