Chilean margin sediments reveal millennial-scale Patagonian ice sheet fluctuations and Antarctic Circumpolar Current variability over the last 160,000 years

Abstract

Orbital- and millennial-scale changes in Southern Hemisphere climate and oceanographic conditions impact the Chilean offshore margin sedimentary depositional environment. Understanding palaeoenvironmental changes at the Chilean margin can shed light on changes in the western extent of the southern Patagonian Ice Sheet and velocity of the Cape Horn Current. Before now, records of western–southern Patagonian ice sheet were incomplete at a millennial-scale resolution back to MIS 6. Here, we present results from a composite sedimentary record from International Ocean Discovery Program (IODP) Site U1542 recovered from the south Chilean margin off the western Magellan Strait entrance at 53°S. We use sedimentary facies analysis, granulometry, X-ray fluorescence, and isotopic analysis across the uppermost ∼42 m of the stratigraphy to examine the interplay of along-slope oceanic bottom currents and down-slope ice sheet-derived flows at a millennial scale over the past 160 ka. We find the southern Chilean margin to be highly sensitive to terrestrial ice sheet extent, upper continental slope contour current velocity, and millennial-scale Southern Hemisphere climate change. We determine that the extent of the Patagonian Ice Sheet readily fluctuates, advancing to the Chilean continental shelf edge at least 22 times over the last 160,000 years and often retreating into the Chilean fjords. We reconstruct the flow speed of the Cape Horn Current, a northern branch of the Antarctic Circumpolar Current, using sortable silt and find it declines during glacial periods by 51% but rebounds during millennial-scale Antarctic warm periods. The millennial-scale changes observed within the core were likely driven by coupled shifts of the Southern Hemisphere westerly winds and Southern Ocean front migration.