Preprints
https://doi.org/10.5194/cp-2022-7
https://doi.org/10.5194/cp-2022-7
 
24 Feb 2022
24 Feb 2022
Status: a revised version of this preprint was accepted for the journal CP and is expected to appear here in due course.

The sensitivity of the Eocene-Oligocene Southern Ocean to strength and position of wind stress

Qianjiang Xing1,2, Dave Munday3, Andreas Klocker2,4,5, Isabel Sauermilch2,6, and Joanne M. Whittaker2 Qianjiang Xing et al.
  • 1CSIRO‐UTAS Quantitative Marine Sciences PhD Program, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
  • 2Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Australia
  • 3British Antarctic Survey, Cambridge, United Kingdom
  • 4Australian Research Council Centre of Excellence for Climate Extremes, University of Tasmania, Hobart, Australia
  • 5Department of Geosciences, University of Oslo, Oslo, Norway
  • 6Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands

Abstract. The early Cenozoic opening of the Tasmanian Gateway (TG) and Drake Passage (DP), alongside the synergistic action of the westerly winds, led to a Southern Ocean transition from large, subpolar gyres to the onset of the Antarctic Circumpolar Current (ACC). However, the impact of changing latitudinal position and strength of the wind stress in altering the early Southern Ocean circulation have been poorly addressed. Here, we use an eddy-permitting ocean model (0.25°) with realistic Late Eocene paleo-bathymetry to investigate the sensitivity of the Southern Ocean to paleo-latitudinal migrations (relative to the gateways) and strengthening of the wind stress. We find that southward wind stress shifts of 5 or 10°, with a shallow TG (300 m), lead to dominance of subtropical waters in the high latitudes and further warming of the Antarctic coast (increase by 2 °C). Southward migrations of wind stress with a deep TG (1500 m) cause the shrinking of the subpolar gyres and cooling of the surface waters in the Southern Ocean (decrease by 3–4 °C). With a 1500 m deep TG, and maximum westerly winds aligning with both the TG and DP, we observe a proto-ACC with a transport of ~47.9 Sv. This impedes the meridional transport of warm subtropical waters to Antarctic coast, thus laying a foundation for thermal isolation of the Antarctic. Intriguingly, proto-ACC flow through the TG is much more sensitive to strengthened wind stress compared to the DP. We suggest that topographic form stress can balance surface wind stress at depth to support the proto-ACC while the sensitivity of the transport is likely associated with the momentum budget between wind stress and near-surface topographic form stress driven by the subtropical gyres. In summary, this study proposes that the thermal isolation of Antarctica is a consequence of a combination of gateway deepening and the alignment of maximum wind stress with both gateways.

Qianjiang Xing et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-7', Michiel Baatsen, 06 May 2022
    • AC1: 'Reply on RC1', Qianjiang Xing, 06 Aug 2022
  • RC2: 'Comment on cp-2022-7', Anonymous Referee #2, 07 Jul 2022
    • AC2: 'Reply on RC2', Qianjiang Xing, 06 Aug 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on cp-2022-7', Michiel Baatsen, 06 May 2022
    • AC1: 'Reply on RC1', Qianjiang Xing, 06 Aug 2022
  • RC2: 'Comment on cp-2022-7', Anonymous Referee #2, 07 Jul 2022
    • AC2: 'Reply on RC2', Qianjiang Xing, 06 Aug 2022

Qianjiang Xing et al.

Qianjiang Xing et al.

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Short summary
A high resolution ocean model and realistic paleobathymetry are applied to obtain accurate simulation results. We firstly propose that the alignment of the maximum wind stress with deep TG and DP is a trigger of proto-Antarctic Circumpolar Current (proto-ACC) and thermal isolation of the Antarctic. We use zonal momentum budget analysis to explore the nature of the proto-ACC and the sensitivity of its transport through gateways to doubled wind stress.