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The Dynamical Subtropical Front
Stockholm University, Faculty of Science, Department of Geological Sciences.ORCID iD: 0000-0003-0008-1886
Stockholm University, Faculty of Science, Department of Geological Sciences.
2013 (English)In: Journal of Geophysical Research - Oceans and Atmospheres, ISSN 0148-022A, Vol. 118, no 10, 5676-5685 p.Article in journal (Refereed) Published
Abstract [en]

The Southern Ocean Subtropical Front (STF) is thought to play a key role in the global climate system. Theory suggests that the latitude of the STF regulates the volume of saline Agulhas Leakage into the Atlantic Ocean from the Indian. Here we use satellite sea surface temperature (SST) and sea surface height (SSH) data to study the physical characteristics of the STF water mass boundary. We find that the strong currents in this region do not align with the surface water mass boundary. Therefore, we provide a new climatology for these currents which we define as the Dynamical STF (DSTF). The DSTF is the eastward extension of the western boundary current in each basin and is characterized by strong SST and SSH gradients and no seasonal cycle. At the center of each basin it merges with the Sub-Antarctic Front. On the eastern side of basins, the STF surface water mass boundary coincides with a separate region of multiple SST fronts. We call this the Subtropical Frontal Zone (STFZ). The fronts in the STFZ have a large seasonal cycle and no SSH signature. Despite lying close to the same water mass boundary, the DSTF and STFZ are completely unrelated. We therefore suggest the term STF only be used when referring to the surface water mass boundary. When studying the strong currents on the western side of basins the term DSTF is more relevant and, similarly, the term STFZ better describes the region of enhanced SST gradients towards the east.

Place, publisher, year, edition, pages
2013. Vol. 118, no 10, 5676-5685 p.
Keyword [en]
ubtropical front, Agulhas Leakage, Southern Ocean, wind stress curl, sea surface temperature, sea surface height
National Category
Oceanography, Hydrology, Water Resources
Research subject
Marine Geology
URN: urn:nbn:se:su:diva-97487DOI: 10.1002/jgrc.20408ISI: 000327380100058OAI: diva2:678423

AuthorCount: 2;

Available from: 2013-12-12 Created: 2013-12-12 Last updated: 2014-11-03Bibliographically approved
In thesis
1. The role of Southern Ocean fronts in the global climate system
Open this publication in new window or tab >>The role of Southern Ocean fronts in the global climate system
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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. 

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2014. 41 p.
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 355
Southern Ocean, fronts, jets, Antarctic Circumpolar Current, wind stress, chlorophyll, iron, Last Glacial Maximum
National Category
Climate Research Oceanography, Hydrology, Water Resources Geosciences, Multidisciplinary
Research subject
Marine Geology
urn:nbn:se:su:diva-108736 (URN)978-91-7447-991-1 (ISBN)
Public defence
2014-12-05, Ahlmannsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

Available from: 2014-11-13 Created: 2014-11-03 Last updated: 2014-11-04Bibliographically approved

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