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Using eddy covariance to estimate air-sea gas transfer velocity for oxygen
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (AWEP)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (AWEP)ORCID iD: 0000-0001-7656-1881
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (AWEP)
2016 (English)In: Journal of Marine Systems, ISSN 0924-7963, E-ISSN 1879-1573, Vol. 159, 67-75 p.Article in journal (Refereed) Published
Abstract [en]

Air-sea gas transfer velocity for O2 is calculated using directly measured fluxes with the eddy covariance technique. It is a direct method and is frequently used to determine fluxes of heat, humidity, and CO2, but has not previously been used to estimate transfer velocities for O2, using atmospheric eddy covariance data. The measured O2 fluxes are upward directed, in agreement with the measured air-sea gradient of the O-2 concentration, and opposite to the direction of the simultaneously measured CO2 fluxes. The transfer velocities estimated from measurements are compared with prominent wind speed parameterizations of the transfer velocity for CO2 and O2, previously established from various measurement techniques. Our result indicates stronger wind speed dependence for the transfer velocity of O2 compared to CO2 starting at intermediate wind speeds. This stronger wind speed dependence appears to coincide with the onset of whitecap formation in the flux footprint and the strong curvature of a cubic wind -dependent function for the transfer velocity provides the best fit to the data. Additional data using the measured O2 flux and an indirect method (based on the Photosynthetic Quotient) to estimate oxygen concentration in water, support the stronger wind dependence for the transfer velocity of O2 O-2 to CO2.

Place, publisher, year, edition, pages
2016. Vol. 159, 67-75 p.
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
URN: urn:nbn:se:uu:diva-287887DOI: 10.1016/j.jmarsys.2016.02.008ISI: 000375506200006OAI: oai:DiVA.org:uu-287887DiVA: diva2:923556
Available from: 2016-04-26 Created: 2016-04-26 Last updated: 2017-01-29
In thesis
1. Air-sea exchange of O2 and CO2: Processes controlling the transfer efficiency
Open this publication in new window or tab >>Air-sea exchange of O2 and CO2: Processes controlling the transfer efficiency
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

World oceans cover more than 70% of the earth surface and constitutes a major sink of atmospheric CO2. Two of the most important gases in the marine carbon cycling are O2 and CO2 and hence accurate descriptions of the air-sea gas exchange of these gases are crucial. Still there is a lack of knowledge of the relative importance of processes controlling the efficiency of the air-sea gas transfer. This is especially true for Arctic and high latitude seas were studies on air-sea gas exchange are few. By studying processes causing water-side turbulence, using gases of different solubility and various measurement techniques, more knowledge on the governing processes can be obtained.

Here we present the very first air-sea fluxes of O2 using atmospheric eddy covariance measurements and investigate the dependence between the gas transfer velocity of O2 and turbulence generated by the mean wind. The instrument was found to suffer from the limited precision and time response, causing significant corrections on the O2 flux. After correcting for this, the O2 fluxes displays an anti-correlation with the air-sea fluxes of CO2 in agreement with the measured air-sea gradient of O2. The transfer velocities for O2 indicates a stronger wind dependence than other commonly used parameterizations of the transfer velocity for CO2 and O2, this especially for wind speeds > 5 m s-1 where the typical onset of wave breaking occur.

During two winter months eddy covariance measurements were taken over a high Arctic fjord. The data revealed a significant enhancement of the gas transfer velocity for CO2 from water-side convection, generated by cooling of surface waters. The dependence between water-side convection and gas transfer velocity were found for winds as high as 9 m s-1, but were strongest for wind speeds< 7  m s-1.  The data also showed on enhanced air-sea gas transfer of CO2 when conditions were unstable very close to neutral. This enhanced transfer were associated to increased contribution to the CO2 flux from downdraft of air with higher concentrations of CO2.  The combined effect of water-side convection and turbulence generated by wind results in a very effective transfer, thus the air-sea gas exchange at these latitudes may be significantly underestimated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 42 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1471
Keyword
air-sea flux, oxygen, transfer velocity, water-side convection, Arctic, UVCN
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:uu:diva-314166 (URN)9789155498061 (ISBN)
Public defence
2017-03-17, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2017-02-24 Created: 2017-01-30 Last updated: 2017-02-24Bibliographically approved

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