Antarctic Circumpolar Current dynamics, and terrigenous sediment provenance variations in the Drake Passage during the last 140,000 years

• Main Author: Wu, Shuzhuang
• Other Authors: Lamy, Frank, Tiedemann, Ralf, Kuhn, Gerhard
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2020
• Subjects: paleoceanography; paleoclimate; Antarctic Circumpolar Current; Drake Passage; multi-proxy; grain-size; geochemistry; 550; 550 Earth sciences and geology; ddc:550; Antarctic; Antarctic Peninsula; Pacific; Patagonia; The Antarctic; Antarc*
• Online Access: https://media.suub.uni-bremen.de/handle/elib/4448; https://doi.org/10.26092/elib/245; https://nbn-resolving.org/urn:nbn:de:gbv:46-elib44489

The Antarctic Circumpolar Current (ACC) is the largest ocean current system on Earth. Through promoting deep water upwelling and new water masses formation, the ACC plays a crucial role on global ocean circulation and climate changes. The Drake Passage is the narrowest constriction for the ACC and exerts a strong control on the physical, chemical, and biological exchange between the Pacific and Atlantic Ocean. Resolving changes in the ACC through this specific channel is, therefore, important for elevating our knowledge of the Southern Ocean’s role in global ocean circulation and climate variability. However, previous studies showed a significant disagreement of the ACC flow speed changes and its potential impacts on ocean circulation and climate variability remain elusive. In Wu et al., (2019), we identified southern Patagonia and the Antarctic Peninsula as the main sources for terrigenous sediments in the modern Drake Passage region, based on a comprehensive set of surface sediment samples. We found the variability of the ACC shows a clear bottom current speed pattern in the Drake Passage responding to the dynamics of ocean fronts, in agreement with modern observation. Understanding present-day sediment provenance and transport processes is crucial for studies about the dynamics of ocean circulation, as well as for paleoclimate reconstructions in the Drake Passage. Further, we reconstruct changes in the ACC strength in the central Drake Passage over the past 140,000 years. We found substantial reductions in ACC bottom flow speeds during the glacial periods and increased bottom currents during interglacials. The amplitude was larger during Termination II compared to Termination I. Superimposed on these long-term changes, we found strong millennial-scale fluctuations in ACC intensity, increasing in amplitude toward the Last Glacial Maximum (LGM). We hypothesize that the central ACC reacts highly sensitive to the Southern Hemisphere millennial-scale climate oscillations, likely related to westerly’s wind stress, ...