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A Correction for the Thermal Mass-Induced Errors of CTD Tags Mounted on Marine Mammals
Stockholm University, Faculty of Science, Department of Meteorology . University of Gothenburg, Sweden.ORCID iD: 0000-0003-1124-4564
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Number of Authors: 62018 (English)In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 35, no 6, p. 1237-1252Article in journal (Refereed) Published
Abstract [en]

The effect of thermal mass on the salinity estimate from conductivity-temperature-depth (CTD) tags sensor mounted on marine mammals is documented, and a correction scheme is proposed to mitigate its impact. The algorithm developed here allows for a direct correction of the salinity data, rather than a correction of the sample's conductivity and temperature. The amplitude of the thermal mass-induced error on salinity and its correction are evaluated via comparison between data from CTD tags and from Sea-Bird Scientific CTD used as a reference. Thermal mass error on salinity appears to be generally O(10(-2)) g kg(-1), it may reach O(10(-1)) g kg(-1), and it tends to increase together with the magnitude of the cumulated temperature gradient (T-HP) within the water column. The correction we propose yields an error decrease of up to similar to 60% if correction coefficients specific to a certain tag or environment are calculated, and up to 50% if a default value for the coefficients is provided. The correction with the default coefficients was also evaluated using over 22 000 in situ dive data from five tags deployed in the Southern Ocean and is found to yield significant and systematic improvements on the salinity data, including for profiles whose T-HP was weak and the error small. The correction proposed here yields substantial improvements in the density estimates, although a thermal mass-induced error in temperature measurements exists for very large T-HP and has yet to be corrected.

Place, publisher, year, edition, pages
2018. Vol. 35, no 6, p. 1237-1252
Keywords [en]
Data processing, In situ oceanic observations, Instrumentation, sensors, Profilers, oceanic
National Category
Environmental Engineering Earth and Related Environmental Sciences
Research subject
Atmospheric Sciences and Oceanography
Identifiers
URN: urn:nbn:se:su:diva-159163DOI: 10.1175/JTECH-D-17-0141.1ISI: 000438020400005OAI: oai:DiVA.org:su-159163DiVA, id: diva2:1241807
Available from: 2018-08-24 Created: 2018-08-24 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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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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