The role of Southern Ocean fronts in the global climate system

• Main Author: Graham, Robert M.
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Stockholms universitet, Institutionen för geologiska vetenskaper 2014
• Subjects: Southern Ocean; fronts; jets; Antarctic Circumpolar Current; wind stress; chlorophyll; iron; Last Glacial Maximum; Climate Research; Klimatforskning; Oceanography; Hydrology and Water Resources; Oceanografi; hydrologi och vattenresurser; Geosciences; Multidisciplinary; Multidisciplinär geovetenskap; Antarctic; Curl; The Antarctic; Antarc*
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-108736

The location of fronts has a direct influence on both the physical and biological processes in the Southern Ocean. However, until recently fronts have been poorly resolved by available data and climate models. In this thesis we utilise a combination of high resolution satellite data, model output and ARGO data to improve our basic understanding of fronts. A method is derived whereby fronts are identified as local maxima in sea surface height gradients. In this way fronts are defined locally as jets, rather than continuous-circumpolar water mass boundaries. A new climatology of Southern Ocean fronts is presented. This climatology reveals a new interpretation of the Subtropical Front. The currents associated with the Subtropical Front correspond to the western boundary current extensions from each basin, and we name these the Dynamical Subtropical Front. Previous studies have instead suggested that the Subtropical Front is a continuous feature across the Southern Ocean associated with the super gyre boundary. A comprehensive assessment of the relationship between front locations and wind stress is conducted. Firstly, the response of fronts to a southward shift in the westerly winds is tested using output from a 100 year climate change simulation on a high resolution coupled model. It is shown that there was no change in the location of fronts within the Antarctic Circumpolar Current as a result of a 1.3° southward shift in the westerly winds. Secondly, it is shown that the climatological position of the Subtropical Front is 5-10° north of the zero wind stress curl line, despite many studies assuming that the location of the Subtropical Front is determined by the zero wind stress curl. Finally, we show that the nutrient supply at ocean fronts is primarily due to horizontal advection and not upwelling. Nutrients from coastal regions are entrained into western boundary currents and advected into the Southern Ocean along the Dynamical Subtropical Front. At the time of the doctoral defense, the following paper was ...