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Seasonal Meandering of the Polar Front Upstream of the Kerguelen Plateau
Stockholm University, Faculty of Science, Department of Meteorology .ORCID iD: 0000-0002-0531-3810
Stockholm University, Faculty of Science, Department of Meteorology . University of Gothenburg, Sweden.ORCID iD: 0000-0003-1124-4564
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2018 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 45, no 18, p. 9774-9781Article in journal (Refereed) Published
Abstract [en]

The location of the Antarctic Polar Front (PF) is mapped in the Southern Indian Ocean bydecomposing the shape of temperature and salinity profiles into vertical modes using a functional PrincipalComponent Analysis. We define the PF as the northernmost minimum of temperature at the subsurface andrepresent it as a linear combination of the first three modes. This method is applied on an ocean reanalysisdata set and on in situ observations, revealing a seasonal variability of the PF latitudinal position that ismost pronounced between the Conrad Rise and the Kerguelen Plateau. This shift coincides with variationsin the transport across the Northern Kerguelen Plateau. We suggest that seasonal changes of the upperstratification may drive the observed variability of the PF, with potentially large implications for thepathways and residence time of water masses over the plateau and the phytoplankton bloom extendingsoutheast of the Kerguelen Islands.

Place, publisher, year, edition, pages
2018. Vol. 45, no 18, p. 9774-9781
Keywords [en]
functional principal component analysis, antarctic polar front, southern indian ocean, kerguelen
National Category
Oceanography, Hydrology and Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-160774DOI: 10.1029/2018GL079614ISI: 000447761300049OAI: oai:DiVA.org:su-160774DiVA, id: diva2:1253261
Available from: 2018-10-04 Created: 2018-10-04 Last updated: 2020-01-23Bibliographically approved
In thesis
1. Unraveling the thermohaline structure of the Southern Ocean using functional data analysis
Open this publication in new window or tab >>Unraveling the thermohaline structure of the Southern Ocean using functional data analysis
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Southern Ocean connects the Indian, Pacific and Atlantic Oceans and provides a direct pathway to exchange mass, heat and salt across the Global Ocean, therefore playing an important role in the global climate system. Due to the complexity of its structure and the general inadequacy of its sampling, both in time and space, it remains a challenge to describe and visualize the three dimensional pattern of its circulation and the associated tracer distribution (temperature, salinity, oxygen or nutrients). This thesis contributes to the understanding of the thermohaline structure of the ocean and especially of the remote Southern Ocean by introducing a novel decomposition method, the Functional Principal Component Analysis applied on vertical profiles of temperature and salinity. To this end, we first normalize hydrographic profiles by using a functional spline representation. Then the statistical method of dimension reduction and feature extraction reveals the main spatial patterns of the temperature and salinity variations. The first two vertical modes contribute to 90% of the combined variance and are related to very robust structures of the Global Ocean. The first mode is mainly controlled by temperature and the second by salinity. In the Southern Ocean, the vertical modes present circumpolar patterns that can be closely related to the stratification regimes that define the circumpolar fronts. Notably the Polar Front is located at the natural boundary between the region controlled by the first (thermal) mode to the north and the second (haline) mode to the south. A mapping of the fundamental zonation is provided with an estimate of the width of the water mass boundaries. As a validation of this method, the Antarctic Polar Front is investigated further in the Indian sector using the same statistical framework. We show that the Polar Front latitudinal position varies seasonally upstream of the Kerguelen Plateau. This meandering is confirmed by hydrographic data gathered by elephant seals equipped with miniaturized sensors. The proposed statistical method provides an objective way to define water mass boundaries and their spatial variability. It offers a useful framework for representing the density structure of the ocean in a reduced-dimension space while maximizing the variance explained. The functional approach also provides a robust way to validate model outputs against observations from any platforms.

Place, publisher, year, edition, pages
Stockholm: Department of Meteorology, Stockholm University, 2018. p. 42
Keywords
Southern Ocean, Front, Water mass, Antarctic Polar Front, Descriptive Physical Oceanography, Functional Principal Component Analysis, Elephant Seal, Biologging
National Category
Oceanography, Hydrology and Water Resources
Research subject
Atmospheric Sciences and Oceanography
Identifiers
urn:nbn:se:su:diva-161034 (URN)978-91-7797-496-3 (ISBN)978-91-7797-497-0 (ISBN)
Public defence
2018-11-30, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 14:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

Available from: 2018-11-07 Created: 2018-10-15 Last updated: 2018-11-06Bibliographically approved

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