Sea ice and the ocean mixed layer over the Antarctic continental shelf

• Main Author: Petty, AA
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UCL (University College London) 2014
• Subjects: Antarctic; Southern Ocean; The Antarctic; Weddell; Antarc*; Sea ice
• Online Access: https://discovery.ucl.ac.uk/id/eprint/1417883/1/1051535_Alek%20Petty_%20THESIS_PETTY.pdf; https://discovery.ucl.ac.uk/id/eprint/1417883/

In this thesis, a modelling approach is taken to investigate the sea ice and ocean mixed layer over the Antarctic continental shelf. A primary motivation is to understand why the Amundsen and Bellingshausen (AB) shelf seas are flooded by Circumpolar Deep Water that is several degrees Celsius warmer than the cold shelf waters prevalent in the Weddell and Ross (WR) seas. An idealised sea ice-mixed layer model is used to investigate this apparent bimodal distribution. The formation of shelf waters (fully mixed water column) is shown to be driven primarily by the ‘cold’ WR atmospheric forcing, independent of the ocean profile, suggesting that the regional difference in atmospheric forcing alone is sufficient and perhaps necessary to account for the bimodal distribution in shelf sea temperature. Coupling the mixed layer model to the sea ice model CICE extends the study to the entire Southern Ocean, and provides a more accurate representation of the sea ice and the processes controlling mixed layer deepening within the shelf seas. The model captures well the expected sea ice thickness distribution, and produces deep (>500 m) mixed layers in the WR shelf seas each winter. Shallower wintertime mixed layers are produced in the AB seas. Deconstructing the surface mechanical power input to the mixed layer, shows that the salt flux from sea ice growth/melt dominates the evolution of the mixed layer in all four shelf seas. An analysis of the sea ice mass balance demonstrates the contrasting mean annual ice growth, melt and export within each of the four shelf seas. The CICE-mixed layer model is also used to investigate recent and future trends in the sea ice and mixed layer. The recent ERA-Interim forced simulation compares well with the observed regional trends in ice concentration, but shows mainly insignificant trends in the sea ice, the surface inputs of salt and heat, and the mixed layer depth over the shelf seas. The future HadGEM2-ES forced simulation shows, in-contrast, significant declines in the sea ice, the ...