Dr. Pieter Tans, CMDL
Objective:
Directly measure the air-sea flux of CO2 and relate it to
environmental forcing.
Description:
Current large uncertainties in the air-sea flux of CO2 prevent
us from verifying the partitioning of fossil fuel CO2
between the ocean and the terrestrial biosphere. This limits our ability
to realistically model future atmospheric CO2 levels. By
measuring the flux using direct flux measurements such as the relaxed
eddy accumulation, eddy correlation and gradient methods we can establish
robust relationships between environmental forcing and gas exchange on
short time scales.
Method:
Most flux calculations rely on empirical relationships of gas transfer
with wind speed which have a significant uncertainty
associated with them (Figure 1) Techniques are
now in
hand to improve our estimates of air-sea fluxes. We propose to measure
air-sea fluxes directly on 1/2 hour time scale in the air boundary layer
by three independent direct air side measurements; to parameterize
this flux (and gas transfer velocity) with environmental forcing
functions; and to compare the results with measurement of gas
transfer velocities from gas mass balances in the ocean. The latter
verification is essential to validate the relaxed eddy
accumulation method for measurement of CO2
fluxes over the ocean.
Accomplishment: A proposal to perform this work in the
North Atlantic in June 1996 has been funded. A dozen different research
groups will participate in the cruise
(GAS EX-98)
Key reference:
MacIntyre, S., R. Wanninkhof, and J.P. Chanton, Chapter 3, Trace gas
exchange across the air-water interface in freshwater and
coastal marine environments, in Methods in Ecology- Biogenic Trace Gases:
Measuring Emissions from Soil and Water, edited by P.A.
Matson, and R.C. Harriss, pp. 52-97, Blackwell Science, Cambridge, Mass,
1995.
Wanninkhof, R., Relationship between gas exchange and wind speed over
the ocean., J. Geophys. Res., 97, pp. 7373-7381, 1992.
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