Observations of steady and seasonal salt, heat, and mass transport through a tidal channel

Abstract

One‐year time series of current speed, water temperature, and salinity from a tidal channel in the Exuma Cays, Bahamas, are used to investigate the annual mean and time‐varying transport of salt, heat, and mass. Time series of salinity, heat content, density, and volume transport are decomposed into annual mean, low‐frequency (days to seasons), and high‐frequency (tide dominated) components, and perturbation analysis is used to quantify transport. When perturbation products are averaged over the entire year, steady transport dominates the averages of the time‐varying terms. Harmonic analysis reveals distinct seasonal variability. Seasonal cycles in salt, heat, and mass transport arise from forcing over seasonal timescales and from tidal exchanges in the presence of seasonally varying hydrographic gradients between Exuma Sound and Great Bahama Bank. Maximum seasonal import and export values are small relative to the steady transport. Wind forcing plays a central role, acting both directly and indirectly to produce about half of the annual mean volume transport and most of the seasonal variability about the mean.