Effect of winter wind variability on plankton transport over Georges Bank

Abstract

A detailed physical model of Georges Bank, including M 2 tidal rectification, realistic topography, Mellor-Yamada 2.5 mixed-layer dynamics, and time-varying wind forcing, was used to simulate plankton transport. Wind records from January 1 through March 4 of each year from 1968 through 1993 were selected to force the model. For each year, two model runs were made, one time-variant and the other using the mean wind stress for the entire period. Simulations using no wind and a 26-year climatological mean (1968–1998) also were conducted. Differences in net transport and 2-month mean currents between the vector-averaged and time-varying runs for a given year were slight. Plankton distribution in time-varying winds moved in response to transient wind events, but distributions at the end of the 60-day simulation period were remarkably similar to those from model runs using vector-averages of the same winds. Interannual differences were significant; depending on the direction of the mean wind stress, tracers were transported to several different regions on and off the bank. The use of wind-stress averages over a 2-month period is supported for models addressing transport on that time scale. Interannual variability in winter wind stress may play a major role in determining transport and subsequent recruitment of plankton on the bank.