Water exchange across the Strait of Hormuz. Effects of tides and rivers runoff

Abstract

The Persian Gulf exchanges water with the Arabian Sea by means of an inverse-estuary circulation. Fresher surface waters are imported while heavier, saltier waters are exported near the bottom. This mechanism compensates for the loss of freshwater by excess evaporation, maintaining the Gulf’s environmental conditions. To assess the effects of climate change and local anthropogenic stressors, the salt budget driven only by natural mechanisms must be well understood. A previous study with the Hybrid Coordinate Ocean Model (HYCOM), showed that the salt, or equivalent-freshwater, exchange through the Strait of Hormuz is composed of overturning and horizontal components, both well correlated with the basin-averaged net evaporation in the Gulf. Tidal forcing and river runoff inside the Gulf were not considered. Here we report results of experiments with a newer, higher-resolution implementation of HYCOM, forced with the same atmospheric products but including the tidal forcing and riverine inflow in the Gulf’s basin. We found that the mean exchange across a vertical section in the Strait of Hormuz is significantly sensitive to the addition of rivers and tides. In the numerical simulations, river runoff inside the Gulf tends to increase the freshwater exchange while the tides lead to appreciable reduction in the net transport.