High frequency, continuous measurements reveal strong diel and seasonal cycling of pCO2 and CO2 flux in a mesohaline reach of the Chesapeake Bay
Abstract. We estimated hourly air-water gas transfer velocities (k600) for carbon dioxide in the Rhode River, a mesohaline subestuary of the Chesapeake Bay. Gas transfer velocities were calculated from estuary-specific parameterizations developed explicitly for shallow, microtidal estuaries in the Mid-Atlantic region of the United States, using standardized wind speed measurements. Combining the gas transfer velocity with continuous measurements of pCO2 in the water and in the overlying atmosphere, we determined the direction and magnitude of CO2 flux at hourly intervals across a 3-year record (01 July 2018 to 01 July 2021). Continuous year-round measurements enabled us to document strong seasonal cycling whereby the Rhode River is net autotrophic during cold-water months (Dec–May), and largely net heterotrophic in warm-water months (Jun–Nov). Although there is inter-annual variability in CO2 flux in the Rhode River, the annual mean condition is near carbon neutral. Measurement at high temporal resolution across multiple years revealed that CO2 flux can reverse during a single 24-hour period. pCO2 and CO2 flux are mediated by temperature effects on biological activity and are inverse to temperature-dependent physical solubility of CO2 in water. Biological/biogeochemical carbon fixation and mineralization are rapid and extensive, so sufficient sampling frequency is crucial to capture unbiased extremes and central tendencies of these estuarine ecosystems.
Status: open (until 22 Mar 2024)
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