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

Antarctic glacial history and sea-level change - Leg 178 samples Antarctic Peninsula margin sediments

The Antarctic Ice Sheet is a key feature of the global climate engine today, and has been so for most of its 35 Myr or longer history. It influences global circulation (mainly through bottom water production), eustatic sea-level change, biological production and albedo. And yet the details of that history are poorly known, despite two decades of measurement and interpretation of lowlatitude ice-volume proxies. The most effective of those proxy measurements, oxygen isotopes and sea-level change, are ambiguous, and disagree. Recently, a way out of this impasse has emerged, that is technically difficult but much more direct. It involves sampling and dating sediments transported beneath the grounded ice sheet and deposited seaward of the grounding line around the Antarctic margin. We now appreciate that the ice sheet “drains” mainly by rapid flow in ice streams that slide on a shearing bed of diamict. Over the life of the ice sheet, those glacially-transported sediments have formed progradational wedges on the outer continental shelf. They, and their derived sediments redeposited in drifts on the upper continental rise, should therefore contain a record of ice sheet advance to the continental shelf edge. The prograded wedge is essentially unsorted making it difficult to recover, and the topsets are prone to subsequent erosion. The drifts have formed by more continuous deposition of sorted silty clays that are easier to recover but less direct, needing clues from the wedge to aid interpretation. The two depositional environments are complementary. Additional useful features of the Antarctic margin are the deep basins eroded on the inner continental shelf during glacial maxima, which preserve an expanded Holocene record of climate change

Latitudinal variance in the drivers and pacing of warmth during mid‐Pleistocene MIS 31 in the Antarctic Zone of the Southern Ocean

Early Pleistocene Marine Isotope Stage (MIS)-31 (1.081 to 1.062 Ma) is a unique interval of extreme global warming, including evidence of a West Antarctic Ice Sheet (WAIS) collapse. Here we present a new 1000-year resolution, spanning 1.110-1.030 Ma, diatom-based reconstruction of primary productivity, relative sea surface temperature changes, sea-ice proximity/open ocean conditions and diatom species absolute abundances during MIS-31, from the Scotia Sea (59° S) using deep-sea sediments collected during International Ocean Discovery Program (IODP) Expedition 382. The lower Jaramillo magnetic reversal (base of C1r.1n, 1.071 Ma) provides a robust and independent time-stratigraphic marker to correlate records from other drill cores in the Antarctic Zone of the Southern Ocean (AZSO). An increase in open ocean species Fragilariopsis kerguelensis in early MIS-31 at 53° S (Ocean Drilling Program Site 1094) correlates with increased obliquity forcing, whereas at 59° S (IODP Site U1537; this study) three progressively increasing, successive peaks in the relative abundance of F. kerguelensis correlate with Southern Hemisphere-phased precession pacing. These observations reveal a complex pattern of ocean temperature change and sustained sea surface temperature increase lasting longer than a precession cycle within the Atlantic sector of the AZSO. Timing of an inferred WAIS collapse is consistent with delayed warmth (possibly driven by sea-ice dynamics) in the southern AZSO, supporting models that indicate WAIS sensitivity to local sub-ice shelf melting. Anthropogenically enhanced impingement of relatively warm water beneath the ice shelves today highlights the importance of understanding dynamic responses of the WAIS during MIS-31, a warmer than Holocene interglacial

High-resolution paleomagnetic records from Laguna Potrok Aike (Patagonia, Argentina) for the last 16,000 years

Holocene and Late-glacial records documenting variations in direction and intensity of the geomagnetic field during the last 16,000 cal. BP are presented for Southern Patagonia. This continuous high-resolution terrestrial record from Laguna Potrok Aike (51°58`S, 70°23`W) was recovered within the SALSA (South Argentinean Lake Sediment Archives and modeling) project. Mineral magnetic measurements indicate that pseudo single-domain magnetite is the major carrier of the remanence allowing the reliable definition of stable natural remanent magnetization inclinations and declinations from alternating field demagnetization and principal component analysis. Paleomagnetic secular variation records reveal many of the familiar features of declination and inclination that have previously been recorded in other records from South Argentina but conspicuous centennial-scale differences are also observed. The results illustrate the potential of PSV records for dating sedimentary sequences in southern South America