Buoyancy flux, turbulence, and the gas transfer coefficient in a stratified lake

Gas fluxes from lakes and other stratified water bodies, computed using conservative values of the gas transfer coefficient k 600 , have been shown to be a significant component of the carbon cycle. We present a mechanistic analysis of the dominant physical processes modifying k 600 in a stratified lake and resulting new models of k 600 whose use will enable improved computation of carbon fluxes. Using eddy covariance results, we demonstrate that i) higher values of k 600 occur during low to moderate winds with surface cooling than with surface heating; ii) under overnight low wind conditions k 600 depends on buoyancy flux β rather than wind speed; iii) the meteorological conditions at the time of measurement and the inertia within the lake determine k 600 ; and iv) eddy covariance estimates of k 600 compare well with predictions of k 600 using a surface renewal model based on wind speed and β .