Field measurements by eddy correlation indicate an average CO2 uptake of 1.9 g C m(-2) d(-1) by the intertidal Wadden Sea estuary in spring 2008. The flux did not show a dependency on the tide and fluxes during high and low tide were comparable. We hypothesize that biological production in the water column and in microbial mats that cover sediments lead to an undersaturation of CO2 that is strong enough to support the observed fluxes. The total carbon uptake by this intertidal estuary from day of the year 101-168 is estimated to be -1.7 Tg C. Extrapolation of this flux over three months in spring suggests that the uptake of CO2 by this estuary over this period is comparable to 24% of the yearly carbon flux over the North Sea and the European estuaries. Citation: Zemmelink, H. J., H. A. Slagter, C. van Slooten, J. Snoek, B. Heusinkveld, J. Elbers, N. J. Bink, W. Klaassen, C. J. M. Philippart, and H. J. W. de Baar (2009), Primary production and eddy correlation measurements of CO2 exchange over an intertidal estuary, Geophys. Res. Lett., 36, L19606, doi: 10.1029/2009GL039285.
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