Miocene to present oceanographic variability in the Scotia Sea and Antarctic Ice Sheet dynamics: Insight from revised seismic-stratigraphy following IODP Expedition 382

Scotia Sea and the Drake Passage is key towards understanding the development of modern oceanic circulation patterns and their implications for ice sheet growth and decay. The sedimentary record of the southern Scotia Sea basins documents the regional tectonic, oceanographic and climatic evolution since the Eocene. However, a lack of accurate age estimations has prevented the calibration of the reconstructed history. The upper sedimentary record of the Scotia Sea was scientifically drilled for the first time in 2019 during International Ocean Discovery Program (IODP) Expedition 382, recovering sediments down to ∼643 and 676 m below sea floor in the Dove and Pirie basins respectively. Here, we report newly acquired high resolution physical properties data and the first accurate age constraints for the seismic sequences of the upper sedimentary record of the Scotia Sea to the late Miocene. The drilled record contains four basin-wide reflectors – Reflector-c, -b, -a and -a' previously estimated to be ∼12.6 Ma, ∼6.4 Ma, ∼3.8 Ma and ∼2.6 Ma, respectively. By extrapolating our new Scotia Sea age model to previous morpho-structural and seismic-stratigraphic analyses of the wider region we found, however, that the four discontinuities drilled are much younger than previously thought. Reflector-c actually formed before 8.4 Ma, Reflector-b at ∼4.5/3.7 Ma, Reflector-a at ∼1.7 Ma, and Reflector-a' at ∼0.4 Ma. Our updated age model of these discontinuities has major implications for their correlation with regional tectonic, oceanographic and cryospheric events. According to our results, the outflow of Antarctic Bottom Water to northern latitudes controlled the Antarctic Circumpolar Current flow from late Miocene. Subsequent variability of the Antarctic ice sheets has influenced the oceanic circulation pattern linked to major global climatic changes during early Pliocene, Mid-Pleistocene and the Marine Isotope Stage 11.

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