Horizontal Exchange on Central Georges Bank

Publisher Website
Google Scholar
Abstract
An axisymmetric model of the evolution of temperature over central Georges Bank in spring, summer, and early fall is used to estimate bounds on the horizontal dispersion coefficient, KH, consistent with the observed development of a "hot spot" in this region. We find that KH is in the range of 150–380 m2∙s−1, in agreement with estimates based on drogue dispersion (EG&G 1979). The effect of such a dispersion rate on passive scalars is considered for a variety of initial distributions. Although, in the absence of air–sea transfer, any initial salinity difference across the central portion of the Bank would be essentially eliminated in a few weeks, local precipitation appears to be sufficient to maintain the observed distribution. Our results indicate that maintenance of primary production at 2 g C∙m−2∙d−1 over the central portion of the Bank requires that greater than 50% of the nitrogen demand be supplied by local regeneration, assuming the Redfield ratio to be appropriate. Because exchange with off-the-Bank waters is slowest for the very center of the Bank, the supply of new nitrogen to this area should be particularly low. On the other hand, fish larvae in this area may benefit from a relatively long residence time.Key words: horizontal exchange, Georges Bank, heat budget, nitrogen budget, residence time