Abstract
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.
Highlights
The formation and evolution of the Tasmanian and Drake Passage-Scotia Sea gateways allowed for the establishment and history of the Antarctic Circumpolar Current (ACC)
Reflector-b represents a regional stratigraphic change previously related to strong incursions of the Weddell Sea Deep Water (WSDW) into the Scotia Sea and the South Pacific Deep Water (SPDW) flowing through the Drake Passage (Martos et al, 2013; Pérez et al, 2017)
The large-scale variability of the Antarctic ice sheets appears to be closely linked to the increasing formation of Weddell Sea Deep Water and the broad dynamics of the Antarctic Circumpolar Current
Summary
The formation and evolution of the Tasmanian and Drake Passage-Scotia Sea gateways allowed for the establishment and history of the Antarctic Circumpolar Current (ACC). The regional events represented by the stratigraphic discontinuities have been assumed to be time-synchronous across the southern Scotia Sea basins (e.g., Maldonado et al, 2006; Pérez et al, 2019) Their estimated ages were necessarily based on assumptions of constant sedimentation rates over an underlying igneous crust, the age of which was assessed by spreading magnetic anomaly models (e.g., Eagles et al, 2006; Galindo-Zaldívar et al, 2006; Maldonado et al, 2006, 2014). According to the new core-log-seismic correlation presented in this work, the major changes in the sedimentary stacking pattern of the southern Scotia Sea occurred after major variations in the prevailing regional oceanic circulation regime related to the late Miocene-Pleistocene climatic trends and Antarctic ice sheets dynamics
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