The evolution of subantarctic fronts, deep ocean ventilation and flow vigour at the Agulhas Plateau: surface-deep coupling across climate transitions of the past 3 Ma

• Main Authors: Starr, Aidan, Hall, Ian R., Barker, Stephen, Van Der Lubber, Jeroen, Hemming, Sidney R., Jiménez-Espejo, Francisco J., Lathika, Nambiyathodi
• Format: Conference Object
• Language: unknown
• Published: European Geosciences Union 2020
• Subjects: Antarctic; Southern Ocean; Antarc*; North Atlantic Deep Water; North Atlantic
• Online Access: http://hdl.handle.net/10261/237709; https://doi.org/10.5194/egusphere-egu2020-10495

EGU General Assembly 2020, Online 4–8 May 2020 [EN] The geometry of large-scale deep ocean circulation is closely linked to processes occurring in the Southern Ocean (SO). The SO is the ‘window’ through which much of the world’s ocean interior interacts with the atmosphere, and understanding the complex relationships coupling SO dynamics to deep circulation can provide valuable insights into biogeochemical and physical processes important to global climate. Of particular interest is how these processes interacted with, and behaved under different climate states, such as the glacial-interglacial cycles of the Pleistocene (0-2.8 Ma), and the intensification of Northern Hemisphere glaciation during the transition from the warm Mid-Pliocene (3.3-3.1 Ma) to the early Pleistocene. Here, we utilise new composite sediment core records (41oS, 25oE, 2700-2900 m water depth) to reconstruct deep chemical and physical ventilation at the Agulhas Plateau, as well as the competing presence of warm Subtropical waters vs cold Subantarctic waters in the surface, over the past ~3 Ma. We present records of the ‘sortable silt’ flow speed proxy, the stable isotope (δ18O, δ13C) composition of benthic foraminifera, bulk sediment element concentrations, and the accumulation of ice-rafted debris (IRD). The sortable silt proxy demonstrates that deep physical ventilation is largely decoupled from deep chemical ventilation as indicated by benthic δ13C, with higher flow speeds coincident with more depleted δ13C. Furthermore, deep ventilation is related to changes in the terrigenous sediment composition: deep flow speeds and δ13C vary concurrently with bulk sediment geochemistry (K/Al, Ti). At the Agulhas Plateau, we interpret deep chemical ventilation and near-bottom flow speeds to reflect changes in the advection of northern-sourced deep waters (e.g. North Atlantic Deep Water and its glacial equivalent) and meridional variability in the location of the deep-reaching Antarctic Circumpolar Current (ACC) and its associated fronts. The ...