| Abstract: A simple model of silicon cycling has been embedded
in a coarse-resolution ocean general circulation model. The modeled distribution
of silicate was extremely sensitive to the parameterization of the effects
of mesoscale eddies, and was somewhat sensitive to the distribution of
dissolution within the water column. The modeled export flux of biogenic
silica varied by a factor of 2 with respect to both the range of dissolution
and eddy parameterizations. The best results were found when eddies were
parameterized as mixing along isopycnals while simulataneously driving
an advective flux so as to homogenize the depth of isopycnal surfaces (the
so-called Gent-McWilliams parameterization). The Gent-McWilliams scheme
produced the most realistic stratification field in the Southern Ocean,
reducing vertical exchange and hence export fluxes of biogenic silica.
This scheme did not solve the model's tendency to underpredict the formation
of the North Atlantic Deep Water and to overpredict the importance of Antarctic
source waters in the abyss, especially in the Atlantic. When used with
a temperature-dependent dissolution scheme, this model predicted a global
production of 89 Tmol yr SUP -1 with about 40% occurring in both the Southern
Ocean and the tropics. In both the North Pacific and Southern Oceans, local
silicate maxima are maintained by near-surface inflow of silicate with
outflow of depth. The modeled production of biogenic silica showed little
sensitivity to polar freshening when the Gent-McWilliams parameterization
was used. The results emphasize the impact of including both the diffusive
and advective effects of eddies, as in the Gent-McWilliams parameterization.
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