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Direct determination of the air-sea transfer velocity of co2 during asgamage

J.C.M. Jacobs, W. Kohsiek and W.A. Oost

In the year 1996 the experimental phase of the Air Sea GAs exchange in the framework of the Marine Aerosol and Gas Exchange program (ASGAMAGE) of the International Global Atmospheric Chemistry project (IGAC) was carried out. This report mainly focuses on the efforts of the Royal Netherlands Meteorological Institute (KNMI) to determine the air-sea transfer velocity of CO2, kw. The measurements reported on here were performed at
"Meetpost Noordwijk" (MP), a research platform some 9 km off the Dutch coast in the North Sea (52° 16° N, 04° 18'E). During two intensive observation periods, in May and October, respectively, CO2 fluxes were determined by means of the eddy correlation technique. Special care was taken in the data treatment to avoid the effect of cross-talk on the CO2 fluxes. The air-sea CO2 concentration difference was measured simultaneously.
Occasionally, mostly during slack tide, the vertical CO2 concentration profile within the water was determined. On these occasions no significant gradients of CO2 concentration in the water column between 0.5 and 15 m below mean sea level were found. The combination of flux data and air-sea concentration difference allowed us to compute km for CO2 directly.
Results from the two observation periods, one with downward CO2 fluxes (May) and one with upward CO2 fluxes (October), are consistent. A relation with the wind speed adjusted to a height of 10 m and neutral stratification, UNro, was determined for the pooled data from the two experimental phases. The relation recommended here reads: k. = 0.53 U cm/h with Un,10 in m s-1. Relations with other geophysical parameters could so far not be found from the present data set.

Bibliografische gegevens

J.C.M. Jacobs, W. Kohsiek and W.A. Oost. Direct determination of the air-sea transfer velocity of co2 during asgamage
KNMI number: WR-97-06, Year: 1997, Pages: 35

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