Climate state dependent sedimentation dynamics in the southern Scotia Sea during the last four glacial cycles

The Southern Ocean (SO) is of major importance in shaping climate transitions due to its substantial potential in storing carbon in the deep ocean and its release to the atmosphere most dominantly during glacial terminations. Through wind driven upwelling of deep waters and high latitude deep water formation, the SO acts as a gateway between the surface ocean and its interior. With the Antarctic Circumpolar Current (ACC), the world’s largest current system, the SO connects all three major basins of the global ocean and therefore integrates and responds to climate signals across the globe. Additionally, the SO exerts a major influence on the Antarctic Ice Sheet and partly controls its mass balance.

The evolution of deep-water formation and export, as well as its interplay with the ACC and the Antarctic Ice Sheet are important factors that are still poorly constrained. We present a largely isotope geochemical based high-resolution multi-proxy reconstruction of IODP Site U1537 to examine these interplays in the southern Scotia Sea. The Scotia Sea is a key area in the SO, where newly formed well ventilated Weddell Sea Deep Water (WSDW) is admixed into and entrained underneath the ACC.

Sedimentation in this area is mainly modulated by the strong ocean currents, as seen by extremely high sediment focusing throughout. Detrital neodymium (Nd) as well as authigenic and detrital lead (Pb) isotope compositions in Southern Ocean sediments provide insights into sediment sources, which can be clearly identified due to the distinct crustal ages of East and West Antarctica and its surrounding areas. Sediments at Site U1537 are dominantly sourced from the Antarctic Peninsula and the Weddell Sea region. The sediment provenance investigations are additionally complemented by K’-Ar analyses on the <63 µm fractions of the sediment samples, providing average age information. All of our obtained isotopic records reveal substantial variations during glacial-interglacial transitions.

Site U1537 provides evidence for low bottom water oxygenation (derived from authigenic uranium) and likely no WSDW export into the Scotia Sea during the Last Glacial Maximum. The data further suggests early deglacial pulses of WSDW export. We advocate that these pulses might be a considerable contributor to the reestablishment of interglacial-type deep ocean ventilation and AMOC conditions. A substantial increase in current-shelf interaction along the Antarctic margin in the Pacific sector is seen during MIS5e. Taken together, our multi-proxy approach highlights the complex sedimentation regime in the Scotia Sea and provides new paleoceanographic insights towards the circulation and frontal dynamics as a function of climatic boundary conditions at submillennial-scale resolution.