Vizcaino, Maoli N.2020-01-082020-01-082019http://udspace.udel.edu/handle/19716/24924This study used downcore Globorotalia truncatulinoides coiling ratios to investigate changes in the upper water column structure of the North Atlantic subtropical gyre’s western boundary from 621-300 Ka (Marine Isotope Stages 15-9). One of the largest deglaciations of the Late Pleistocene, the Mid-Brunhes Event (~430 Ka), occurred in this time interval, prompting this study on the stability of the Gulf Stream during the intense climate perturbation. The depth of the permanent thermocline influences downcore coiling ratios of G. truncatulinoides morphotypes in ocean sediments; when the permanent thermocline is deep sinistral (left-coiling) G. truncatulinoides dominate, and in a shallow permanent thermocline dextral (rightcoiling) G. truncatulinoides dominate. As sediment samples for this study come from Ocean Drilling Program (ODP) sites that lie below the Gulf Stream, G. truncatulinoides coiling ratios from these sites are expected to reflect changes in the Gulf Stream over time. MIS 11, the first interglacial after the MBE, has been hypothesized to be an analogue for modern day climate change because it has similar orbital parameters as today and consequently similar insolation levels. To test the stability of the Gulf Stream over this time interval, 760 samples from ODP Site 1056, Site 1058 and Site 1059 were studied at ~1000 year time-steps, resulting in a high resolution record of G. truncatulinoides coiling ratios. Data were compared to background climate fluctuations over time through published δ18O records of the Late Pleistocene. Results showed percent sinistral, or left-coiling, G. truncatulinoides abundances occurring more frequently than glacial/interglacial cycles seen within the δ18O record. This indicates the presence of millennial scale variations within the data, and thus millennial-scale instabilities in the hydrography at the study sites. These instabilities did not appear to be affected by the MBE despite the severity of the deglaciation, suggesting that the MBE was not a global event. Instead, the data from this study supports previous studies’ hypotheses suggesting precessional forcing as a mechanism behind millennial-scale patterns seen in G. truncatulinoides populations in younger MISs (Billups et al. 2016). This study also revealed a change in sinistral peak characteristics during interglacial MISs when combined with the younger G. truncatulinoides coiling ratio record by Billups et al. (2016) (300-0 Ka). Sinistral G. truncatulinoides populations were low during interglacial maxima until the MIS 6/5 transition (130 Ka), after which sinistral G. truncatulinoides dominated in interglacial intervals. More data with greater spatial coverage would be needed to assess whether the MBE had effects on other parts of the North Atlantic subtropical gyre.Thesis11353196722019-08-07en