Seasonal trends in surface pCO₂ and air‐sea CO₂ fluxes in Apalachicola Bay, Florida, from VIIRS ocean color

Joshi, I. D., N.D. Ward, E.J. D’Sa, C.L. Osburn, T.S. Bianchi, and D. Oviedo‐Vargas. 2018. Journal of Geophysical Research: Biogeosciences 123:2466–2484.

https://doi.org/10.1029/2018JG004391

Abstract

Estuaries have been recognized as important sources of carbon dioxide (CO₂) to the atmosphere; however, contributions of these systems to regional and global carbon budgets are not well constrained due to limited information on seasonal and spatial variability. In this study, we use satellite remote sensing to obtain seasonal pCO₂ distribution and air‐sea CO₂ fluxes in Apalachicola Bay, a national estuarine research reserve located in the northern Gulf of Mexico that receives seasonally varying dissolved organic matter‐rich waters from the Apalachicola River. A combination of time series (2005–2016) and seasonal field observations (2015–2016) of pH and biophysical variables were used to develop seasonal pH‐pCO₂ relationships for obtaining surface pCO₂estimates and air‐sea CO₂ fluxes from Visible and Infrared Imaging Radiometer Suite (VIIRS) ocean color data. Monthly and seasonal maps of pCO₂ and air‐sea CO₂ fluxes showed a general trend of higher fluxes in winter and summer corresponding to high river flow and warm water temperatures. However, CO₂ fixation via photosynthesis and low water temperatures contributed to lower fluxes to the atmosphere in spring and fall, respectively. Throughout the study period, Apalachicola Bay was a net source of CO₂ with large seasonal and spatial variability and a mean annual CO₂ flux to the atmosphere of 3.4 ± 3.1 mol·m⁻²·year⁻¹ (9.4 ± 8.5 mmol·m⁻²·day⁻¹), consistent with fluxes reported for other estuaries. This study demonstrates the critical role that satellite observations can play to improve the estuarine contributions to the global carbon flux estimates.