Response of the Southern Ocean circulation to changes in global climate

• Main Author: Morrison, Adele Kim
• Format: Doctoral or Postdoctoral Thesis
• Language: unknown
• Published: 2019
• Subjects: Ocean circulation Computer simulationAntarctic Ocean; Oceanography Antarctic Ocean; Ocean-atmosphere interaction Antarctic Ocean; Climatic changes; Antarctic; Southern Ocean; The Antarctic; Antarctic Ocean; Antarc*
• Online Access: http://hdl.handle.net/1885/155903; https://doi.org/10.25911/5d514d48a4ade; https://openresearch-repository.anu.edu.au/bitstream/1885/155903/5/b35684203-Morrison_A.pdf.jpg

The Southern Ocean circulation plays a central role in the dynamics of past and future global climate change. However, due to a scarcity of observations and the difficulty of accurately modelling the Southern Ocean, we lack a comprehensive understanding of how the circulation responds to change. The energetic eddy field directly impacts the response of the circulation, but the small scale of the eddies has generally been below the resolution of numerical ocean models. This thesis makes use of two high resolution idealised ocean models to investigate the role of eddies in modifying the response of the Southern Ocean circulation to changing wind stress and surface buoyancy forcing. The simulations demonstrate that the eddy field is significant in the dynamical response, but that the impact on different aspects of the circulation is complex and subtle. The Antarctic Circumpolar Current (ACC) transport increases only weakly in response to enhanced Southern Ocean wind stress, due to the enhanced eddy field, which efficiently eliminates momentum input. In contrast, the eddy field only partially compensates wind- driven increases in the upper overturning circulation, resulting in a moderate overturning increase in response to enhanced westerly winds. Southern Ocean heat uptake is also shown to be dependent on changes in the eddy field. Mid-depth warming occurs primarily due to a decrease in the upward eddy heat flux, associated with reduced isopycnal temperature gradients in a warmer climate. However, increased wind stress may reduce the mid-depth heat uptake; a transient cooling trend arises from the wind-driven enhancement of the vertical eddy heat flux. The uncoupled idealised models also permit an in-depth analysis of the response of the Southern Ocean overturning to changes in surface buoyancy forcing. A suite of buoyancy forcing perturbations show that mid-latitude heat and freshwater fluxes may be as significant as wind stress in altering the strength of the upper overturning circulation. Analysis of the ...