Temperature dynamics in a small Pacific Northwest estuary and its sloughs

Water temperature is an important physical characteristic for estuarine ecology and biogeochemistry. Temperature is mainly controlled by the mixing of river and ocean water in addition to surface heat flux. Despite the importance of temperature in estuaries, few studies have explored its dynamics, especially at tidal to seasonal timescales. Here we investigate temperature variability in the Yaquina Bay estuary, a small, partially- to well-mixed estuary in the Pacific Northwest. We find that the river, ocean, and atmosphere drive temperature variability in the estuary on low-frequency (seasonal and subseasonal) and high-frequency (diurnal and semidiurnal) timescales. The seasonal cycle is the largest component of temperature variability. Subseasonal variability depends strongly on river and ocean temperatures, surface heat flux, and residence time, which varies in response to river discharge and tidal amplitude. High-frequency variability depends strongly on the along-channel temperature gradient, with diurnal variability arising from a combination of tidal advection and local surface heating that varies with tidal-solar phasing. Heat exchange with intertidal sediments complicates temperature dynamics near mudflats. In summer, temperature contributes significantly to the along-channel density gradient. These results highlight the sensitivity of estuarine temperature to changing climate conditions and the importance of considering temperature in the management of estuaries for species of ecological, cultural, and economic concern.