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The control of the Southern Hemisphere Westerlies on the position of the Subtropical Front
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences.ORCID iD: 0000-0003-0008-1886
2013 (English)In: Journal of Geophysical Research - Oceans and Atmospheres, ISSN 0148-022A, Vol. 118, no 10, 5669-5675 p.Article in journal (Refereed) Published
Abstract [en]

In recent years the latitudinal position of the Subtropical Front (STF) has emerged as a key parameter in the global climate. A poleward positioned front is thought to allow a greater salt flux from the Indian to the Atlantic Ocean and so drive a stronger Atlantic Meridional Overturning Circulation. Here the common view that the STF aligns with the zero wind stress curl (WSC) is challenged. Based on the STF climatologies of Orsi et al. (1995), Belkin and Gordon (1996), Graham and De Boer (2013), and on satellite scatterometry winds, we find that the zero WSC contour lies on average ∼10°, ∼8°, and ∼5° poleward of the front for the three climatologies, respectively. The circulation in the region between the Subtropical Gyres and the zero WSC contour is not forced by the WSC but rather by the strong bottom pressure torque that is a result of the interaction of the Antarctic Circumpolar Current with the ocean floor topography. The actual control of the position of the STF is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front. For the Agulhas Leakage problem, the southern boundary of the so-called Super Gyre may be the most relevant property but this cannot easily be identified in observations.

Place, publisher, year, edition, pages
2013. Vol. 118, no 10, 5669-5675 p.
Keyword [en]
Subtropical Front, wind stress curl, Southern Ocean, satellite data, fronts, Dynamical Subtropical Front
National Category
Oceanography, Hydrology, Water Resources
Research subject
Marine Geology
URN: urn:nbn:se:su:diva-97489DOI: 10.1002/jgrc.20407ISI: 000327380100057OAI: diva2:678428

AuthorCount: 4;

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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