Ziel
To understand the global carbon balance we need to know what processes regulate the exchange of gases like carbondioxide between the various reservoirs; the exchange hetween the atmosphere and the ocean is one of the largest in this respect. Studies to quantify the air-sea exchange of CO2 as well as other important biogeochemical gases like nitrogen compounds, methane and sulphur compounds, have been successful only to a certain extent: the difference between the results of a number of generally accepted methods to determine the transfer velocity for CO2 can be a factor 2 or more, depending on the circumstances. Measurements of the CO2 transport with the so-called eddy correlation technique even gave values for the transfer velocity up to two orders of magnitude larger than those from other methods.
In the 1993 ASGASEX (for Air Sea GAS EXchange) experiment at Meetpost Noordwijk (MPN), a research platform off the Dutch coast, indications were found that the discrepancy between the eddy correlation data and those from other methods may be explained by so far unsuspected vertical gradients in the CO2 concentration in the first few meters of the water column. If these gradients exist, not only the controversy between the methods can be laid to rest and the advantages of the different methods can finally be combined, but also a new and fundamental insight is gained in the process of air-sea gas exchange. With this in mind we ask support for another experiment, ASGAMAGE, to take place during 2 periods of 5 weeks in the spring and fall of 1996 at and around MPN.
The objectives are
-To find relationships between the transport coefficients for the gas fluxes and any relevant geophysical parameters. To this end we will simultaneously measure gas fluxes, using different methods, a large number of oceanic (waves, whitecaps, bubbles, currents, temperatures, salinity) and atmospheric (wind, temperature, humidity, fluxes of momentum, heat and moisture, aero.sol) parameters and gas concentrations (C02, N20, CH4 and DMS) in air and water. -To intercompare different methods and systems to measure the transfer velocity of trace gase.s over the sea. The transfer velocity will be measured with the dual-tracer technique, with 2-4 independent eddy correlation systems and an eddy accumulation system.
-To find out whether and, if at all, under what conditions there can be a significant vertical C02 gradient in the upper meters of the water column; this will be done by measuring the C02 content (pC02) of the sea water at two depths, at least one of which will be variable.
-To test new methods and new equipment to measure air-sea fluxes of CO2, N20, CH4 and DMS, among them a system to perform eddy-correlation meusurements from a moving platform, fast re.sponding sensors for N20 and DMS and an eddy-accumulation sy.stem.
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3730 AE De Bilt
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