Preprints
https://doi.org/10.5194/egusphere-2023-3056
https://doi.org/10.5194/egusphere-2023-3056
02 Jan 2024
 | 02 Jan 2024

High frequency, continuous measurements reveal strong diel and seasonal cycling of pCO2 and CO2 flux in a mesohaline reach of the Chesapeake Bay

A. Whitman Miller, Jim R. Muirhead, Amanda C. Reynolds, Mark S. Minton, and Karl J. Klug

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.

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A. Whitman Miller, Jim R. Muirhead, Amanda C. Reynolds, Mark S. Minton, and Karl J. Klug

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  • RC1: 'Comment on egusphere-2023-3056', Anonymous Referee #1, 20 Feb 2024
  • RC2: 'Comment on egusphere-2023-3056', Anonymous Referee #2, 20 Mar 2024
A. Whitman Miller, Jim R. Muirhead, Amanda C. Reynolds, Mark S. Minton, and Karl J. Klug
A. Whitman Miller, Jim R. Muirhead, Amanda C. Reynolds, Mark S. Minton, and Karl J. Klug

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Short summary
CO2 in mesohaline waters of Chesapeake Bay is seasonally predictable, driven by biological production/consumption. Seasonal CO2 content/air-water flux is related to water temperature, but significant day/night cycling occur in warm months. These mesohaline waters are a net CO2 sink in cold months, and a highly variable, but net CO2 source to the atmosphere in warm months. This is opposite of CO2's temperature-dependent solubility in water. This reach of the Bay is carbon neutral across 3 years.