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Methods for Estimating Air-Sea Fluxes of CO2 Using High-Frequency Measurements
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)
Department of Environmental Science, Aarhus University, Denmark.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (awep)
2012 (English)In: Boundary-layer Meteorology, ISSN 0006-8314, E-ISSN 1573-1472, Vol. 144, no 3, 379-400 p.Article in journal (Refereed) Published
Abstract [en]

The most direct method for flux estimation uses eddy covariance, which is also the most commonly used method for land-based measurements of surface fluxes. Moving platforms are frequently used to make measurements over the sea, in which case motion can disturb the measurements. An alternative method for flux estimation should be considered if the effects of platform motion cannot be properly corrected for. Three methods for estimating CO2 fluxes are studied here: the eddy-covariance, the inertial-dissipation, and the cospectral-peak methods. High-frequency measurements made at the land-based Ostergarnsholm marine station in the Baltic Sea and measurements made from a ship during the Galathea 3 expedition are used. The Kolmogorov constant for CO2, used in the inertial-dissipation method, is estimated to be 0.68 and is determined using direct flux measurements made at the Ostergarnsholm site. The cospectral-peak method, originally developed for neutral stratification, is modified to be applicable in all stratifications. With these modifications, the CO2 fluxes estimated using the three methods agree well. Using data from the Ostergarnsholm site, the mean absolute error between the eddy-covariance and inertial-dissipation methods is 0.25 mu mol m(-2) s(-1). The corresponding mean absolute error between the eddy-covariance and cospectral-peak methods is 0.26 mu mol m(-2) s(-1), while between the inertial-dissipation and cospectral-peak methods it is 0.14 mu mol m(-2) s(-1).

Place, publisher, year, edition, pages
2012. Vol. 144, no 3, 379-400 p.
Keyword [en]
Baltic Sea measurements, CO2 fluxes, Cospectral-peak technique, Eddy covariance, Galathea 3 expedition, Inertial-dissipation technique
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
URN: urn:nbn:se:uu:diva-174821DOI: 10.1007/s10546-012-9730-9ISI: 000308316700004OAI: oai:DiVA.org:uu-174821DiVA: diva2:529008
Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Air-Sea Fluxes of CO2: Analysis Methods and Impact on Carbon Budget
Open this publication in new window or tab >>Air-Sea Fluxes of CO2: Analysis Methods and Impact on Carbon Budget
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Carbon dioxide (CO2) is an important greenhouse gas, and the atmospheric concentration of CO2 has increased by more than 100 ppm since prior to the industrial revolution.  The global oceans are considered an important sink of atmospheric CO2, since approximately one third of the anthropogenic emissions are absorbed by the oceans. To be able to model the global carbon cycle and the future climate, it is important to have knowledge of the processes controlling the air-sea exchange of CO2. In this thesis, measurements as well as a model is used in order to increase the knowledge of the exchange processes.

The air-sea flux of CO2 is estimated from high frequency measurements using three methods; one empirical method, and two methods with a solid theoretical foundation. The methods are modified to be applicable for various atmospheric stratifications, and the agreement between methods is good in average.

A new parameterization of the transfer velocity (the rate of transfer across the air-sea interface), is implemented in a Baltic Sea model. The new parameterization includes also the mechanism of water-side convection. The impact of including the new parameterization is relatively small due to feedback processes in the model. The new parameterization is however more representative for flux calculations using in-situ measurement or remote sensing products. When removing the feedback to the model, the monthly average flux increases by up to 20% in some months, compared to when water-side convection is not included.

The Baltic Sea carbon budget was estimated using the Baltic Sea model, and the Baltic Sea was found to be a net sink of CO2. This is consistent with some previous studies, while contradictory to others. The dissimilarity between studies indicates the difficulty in estimating the carbon budget mainly due to variations of the CO2 uptake/release in time and space. Local variations not captured by the model, such as coastal upwelling, give uncertainties to the model. Coastal upwelling can alter the uptake/release of CO2 in a region by up to 250%. If upwelling would be included in the model, the Baltic Sea might be considered a smaller sink of CO2.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 47 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1020
Keyword
air-sea exchange, carbon dioxide, Baltic Sea, eddy-covariance method, inertial dissipation method, cospectral-peak method, Baltic Sea measurements, CO2 fluxes, Galathea 3 expedition, Baltic Sea modeling, water-side convection, coastal upwelling, carbon budget
National Category
Meteorology and Atmospheric Sciences
Research subject
Meteorology
Identifiers
urn:nbn:se:uu:diva-194960 (URN)978-91-554-8599-3 (ISBN)
Public defence
2013-04-05, Hambergsalen, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2013-03-14 Created: 2013-02-20 Last updated: 2013-04-02Bibliographically approved

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Norman, MariaRutgersson, AnnaSahlée, Erik

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