An area of significant and ongoing effort is the measurement of
gas exchange at the air-sea interface. Building on surrogates of
heat, moisture and momentum fluxes, researchers have begun to
establish connections between ocean production and consumption of
climatologically sensitive gases, such as carbon dioxide and
sulfates, aerosol production and the development of marine clouds
[ Watson et al., 1990, 1992]. It is estimated that the
oceans are absorbing between 18 and 40% of anthropogenic CO
emissions, while the oceanic source of N
O to the atmosphere
is approximately equal to the current rate of increase of
atmospheric N
O [ Watson et al., 1992]. Air-sea gas
exchange is a complex process that involves all of the processes
discussed above to determine the transfer velocity of a
particular trace gas and, in addition, information about chemical
reactions within the atmosphere and ocean. Erickson
[1993], in a study of the transfer velocity of CO
,
demonstrated the dependence of the trace gas exchange on the
thermal stability at the air-sea interface. He included this
effect in an extension of the model proposed by Monahan and
Spillane [1984] that considers the relationship between the
surface resistance for the transfer of trace gases across the
air-sea interface and the oceanic whitecap coverage. This work
also highlights the uncertainties in the bulk parameterization of
the drag coefficient that is of concern to all air-sea exchange
mechanisms. Hicks [1989] has assessed trace gas flux
measurement techniques. Direct measurement of the CO
flux is
difficult because of the high signal-to-noise ration inherent in
the method. Smith et al. [1991] have reported flux
estimates based on a very sensitive CO
sensor that appears to
have overcome some of the earlier problems. They observed both
upward and downward fluxes of CO
in response to daily variations
in CO
in the coastal surface seawater where there are changes
in the salinity of the surface water due to freshwater runoff.
Transfer velocity estimates are an order of magnitude larger than
open ocean measurements using radon.
Recent advances in chemical flux measurement using conditional
sampling techniques that combine the measurement of the vertical
velocity and the mean concentration of the trace gas may reduce
much of the uncertainty in atmospheric measurements of tracer
fluxes across the air-sea interface [ Businer and Delany,
1990; Businger and Oncley, 1990].
Hau