| Summary: | This project applies Globorotalia truncatulinoides coiling ratios as a proxy for changes in upper ocean hydrography and gyre circulation in the northeastern region of the North Atlantic subtropical gyre over the past 140 thousand years, covering both glacial and interglacial intervals. We used sediment cores from Integrated Ocean Drilling Program Site U1313 to assess the changes in coiling variety. In the modern ocean, this gyre region displays a deep permanent thermocline, favoring the left coiling (sinistral) form. At Site U1313 there are variations in percent sinistral during the warm interglacial interval Marine Isotope Stage 5 (MIS 5) with an increase in the dextral form during the colder substages MIS 5a and c. Previously published sites underneath the western boundary current (Site KNR140-37 PC) and in the center of the gyre (Integrated Ocean Drilling Program Site 1063) show that the percent sinistral stays high throughout interglacial intervals, including MIS 5, and the right coiling (dextral) form dominates during glacial periods. This study’s results are different than previously published data, as there are exceptions to the glacial versus interglacial trend during MIS 5, which suggests a change in gyre circulation and intensity not previously reconstructed. Further comparison to the previously published sites and analysis of additional subpolar sites will help interpret the hydrographic changes occurring in the North Atlantic subtropical gyre. Katharina Billups Marine Science
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