Climatically controlled sedimentation dynamics and export productivity at IODP Site U1537 in the Scotia Sea (Southern Ocean) over the past four glacial cycles

点击翻译按钮获取中文摘要

The Scotia Sea in the Southern Ocean (SO) today is a hydrodynamically important area where Antarctic Bottom Water (AABW) that is previously formed within the Weddell Sea is vigorously mixing into the Antarctic Circumpolar Current. Furthermore, the Scotia Sea is the area where most icebergs that are shedding off marine-based portions of the Antarctic Ice Sheet are drifting out of the Weddell Sea within the so-called “Iceberg Alley”. During past glacial cycles, the position, dimensions and volume transport of the ACC and AABW were substantially different from the modern configuration. This IODP research proposal, aimed to be realised in the framework of a PhD studentship, seeks to identify the continental source areas of sediments deposited at IODP Site 1537 (59°6.65′S, 40°54.37′W, in 3713 m water depth) that was drilled during Expedition 382 during early 2019. Using the detrital neodymium and lead isotope composition of the bulk and fine (<5 µm) grain size fraction, we will identify continental source areas of terrigenous sediments deposited over the past 450 kyr, hence covering four 100-kyr glacial cycles and five glacial terminations at near-millennial resolution. During key intervals these records will be corroborated by additional argon isotopic analyses on the same sediments. Source areas are expected to be mostly positioned within or close to the Weddell Sea and include older cratonic East Antarctic sequences, as well as relatively young continental crust that is supplied as glacially weathered sediment from the Antarctic Peninsula, Pacific sections of West Antarctica, or dust from Patagonia. We will further generate uranium/thorium isotopic data on bulk sediments to assess sedimentation dynamics (focusing versus winnowing) and assess bottom water oxygen starvation as a function of elevated export productivity in the region.Overturning dynamics in the Antarctic zone of the SO were likely much reduced due to a northward shift of the oceanic fronts as well as extended sea ice cover during the past glacial climates. As a consequence, less sediment from more remote locations such as East Antarctica should have been transported to the core site, while regional export productivity was also reduced given extended sea ice and lowered Scotia Sea surface water nutrient concentrations due to reduced glacial upwelling. We hypothesize that sediment provenance, sedimentation dynamics, as well as surface ocean export productivity in the Scotia Sea are strongly linked on millennial timescales. Our aim is to provide a new perspective on the degree of connectivity between, and underlying controls of, the position of SO fronts, the status of Weddell Sea Deep Water export, and bottom water oxygen starvation as a function of elevated surface ocean productivity.