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The Altamaha River Estuary off the southeastern U.S. is a complex and dynamic system formed by three interconnected sounds: Altamaha, Doboy, and Sapelo. Here, we use a high-resolution ocean model to investigate the controls of salinity and residence time variability in the system. Model simulations of temperature and salinity compared favorably with the continuous measurements from the Georgia Coastal Ecosystems Long Term Ecological Research hydrographic moorings. Our results indicate that variability in the estuary depends on location and scales of interest. On seasonal scales, Altamaha and Doboy Sounds are primarily influenced by fluctuations in river discharge. During peak discharge, salinity and residence times typically decreased in those areas, and the salinity front moved downstream, while the reverse was observed during low discharge conditions. Simulations with idealized forcing also revealed lower Altamaha Sound and Doboy Sound as areas most affected by possible changes in the hydrological cycle, such as droughts. Changes in wind, on the other hand, had minimal effect on salinity and residence time variability in those areas. An opposite response was observed in Sapelo Sound, which was most affected by variations in wind forcing, showing limited response to changes in river discharge. Our results suggest significant spatial differences in the estuarine response to possible changes in forcing and in hydrological conditions.

Agonsi, M., Castelao, R., Sheldon, J.E. and Di Iorio, D. 2026. Physical controls of salinity and residence time variability in the Altamaha River estuary. Estuarine, Coastal and Shelf Science. 338(109910). (DOI: https://doi.org/10.1016/j.ecss.2026.109910)