Orbital and millennial-scale upper ocean dynamics in the Pacific Southern Ocean since the Mid-Pleistocene Transition

The Southern Ocean plays a critical role in the Earth system, both for the uptake of anthropogenic carbon and for the exchange of heat and nutrients between high and low latitudes. This is particularly valid for the Subantarctic Southern Ocean where atmosphere-ocean-cryosphere interactions and teleconnections between high and low latitudes play an important role in past and future climate change providing the major link between Antarctica and the low latitudes. In general, atmosphere-ocean interactions within the Southern Ocean are believed to control sea ice cover, upper ocean stratification, biological nutrient utilization, and exposure rates of CO₂-enriched deep water. Thus, they have been considered to play a key role in explaining the variability in atmospheric CO₂ concentrations, which are controlled by biogeochemical and physical processes.

Beyond information from continental margin records, little is known on millennial-scale variability in the pelagic Southern Ocean. High resolution sediment archives reaching back various glacial/interglacial cycles have not been explored so far. This includes the time span beyond the reach of the presently available ice-cores and will likely be critical for evaluating the extended time-interval of the ongoing European Beyond EPICA – oldest ice (BE-OI) ice core drilling initiative. Our project focuses on high resolution paleoceanographic reconstructions (biomarker-based sea surface temperatures, biogenic opal, Antarctic Circumpolar Current strength, ice-rafted detritus) of upper ocean dynamics at Expedition 383 IODP Site 1539 in the subantarctic South Pacific in vicinity of the modern Subantarctic Front (SAF). This location is characterized by unusually high sedimentation-rates (~10-50 cm/kyr), mainly because Site U1539 is reached by the northerly extended opal belt during glacials with high diatom ooze deposition. This unique setting provides a high-resolution pelagic sediment archive in an area with strong oceanographic gradients (close to the SAF with strong dynamics of SST, ACC strength, and the influence of the opal belt).

We expect that high resolution records from IODP Expedition 383 Site U1539 could substantially enhance our understanding of sub-orbital climate variations and potential tipping points in the Southern Ocean and their link to the marine carbon cycle and Antarctic ice-sheet stability.