Tropical North Atlantic Hydrologic Cycle Variability in the Florida Straits During the Last Ice Age

Abstract

Abrupt, millennial-scale climate oscillations, known as Dansgaard-Oeschger (D-O) cycles, characterized the climate system during the last ice age. Proxy evidence suggests these climate oscillations resulted in global-scale reorganizations in the hydrological cycle. For this study, Mg/Ca-paleothermometry and stable isotope measurements were combined on the planktonic foraminifera Globigerinoides ruber (white variety) from Florida Straits 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 delta18OSW (a proxy for upper water column salinity) during Marine Isotope Stages 2 and 3 from 20-35.45 ka BP. As additional proxies for upper water column salinity change, Ba/Ca ratios in G. ruber were also measured to determine the relative contribution of local riverine input on the delta18OSW record and a faunal abundance count record of the planktonic foraminifera N. dutertrei abundance was developed. These results show that rapid upper water column salinity changes occurred across D-O events in the Florida Straits, coeval with climate change in the high-latitude North Atlantic. Furthermore, the G. ruber Ba/Ca record suggests that riverine-derived meltwater from the Gulf of Mexico did not significantly impact surface salinity in the Florida current, calling into question the role of Mississippi River discharge on Atlantic Meridional Overturning Circulation (AMOC) during MIS 2 and 3. Instead, the most likely cause of MIS 2 and 3 salinity changes in the Florida Straits were variations in the strength and position of the Intertropical Convergence Zone. Finally, the timing of surface salinity change was compared with the benthic delta18OC record from the same core. A recent study showed that benthic delta18OC changes on the Florida Margin can be combined with contemporaneous records from the Bahamas Margin to reconstruct Florida Current transport related to AMOC variability. These results show that atmospheric circulation changes lead AMOC changes on the transition out of cold stadial events, suggesting the trigger for these abrupt climate events may reside in the tropics rather than in the high-latitude North Atlantic as previously thought.