Ocean-estuary exchange variability in a large tropical estuary

Abstract

Ocean-estuary exchange variability was studied from 2008 to 2014 at a low latitude coastal plain estuary, Todos os Santos Bay, Brazil, near 13°S. Wind data from Climate Forecast System Reanalysis (CFSR) were used to complement the results of a high-resolution regional ocean model, ROMS. Volume exchange occurred under two distinct circulation patterns, namely Circ+ and Circ−, that matched the down-estuary (spring/summer) and up-estuary (autumn/winter) wind regimes respectively. Circ+ promoted water-column stratification, while Circ− lasted longer, induced more volume exchange, and reversed the estuarine circulation. In addition, a clockwise lateral circulation (looking into the estuary) occurred during Circ+, whereas a counterclockwise lateral circulation was observed during Circ−. Connectivity was observed between Jaguaripe River and Todos os Santos Bay entrance. Increases in Jaguaripe River discharge, in conjunction with up-estuary winds, promoted a northward advection of the river plume toward the main entrance of the estuary, creating a lateral density gradient over Todos os Santos Bay' western shoal. Our results demonstrate that findings about estuarine circulation at higher latitudes are applicable to low latitude estuaries when dynamical depth and/or basin's width indicate that Earth's rotation is relevant.