Seasonal and Spatial Variability in Surface pCO2 and Air-water CO2 Flux in the Chesapeake Bay

Baoshan Chen1, Wei-Jun Cai2, Jean Brodeur1, Najid Hussain2, Jeremy M Testa3, Wenfei Ni4 and Qian Li1, (1)University of Delaware, School of Marine Science and Policy, Newark, DE, United States, (2)University of Delaware, School of Marine Science and Policy, Newark, United States, (3)University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, MD, United States, (4)University of Maryland Center for Environmental Science, Cambridge, MD, United States
Abstract:
Interactions between riverine inputs, internal cycling, and oceanic exchange result in dynamic variations in the surface water partial pressure of carbon dioxide (pCO2) in estuaries. Here, we report the first bay-wide, annual-scale observations of surface pCO2 and air-water CO2 flux along the main stem of Chesapeake Bay, revealing large annual variations in pCO2 (43–3408 µatm) and a spatial-dependence of pCO2 on internal and external drivers. The low salinity upper bay was a net source of CO2 to the atmosphere supported by inputs of CO2-rich Susquehanna River water and the respiration of allochthonous organic matter, but this region was also characterized by low pCO2 during spring and fall phytoplankton blooms. pCO2 decreased downstream due to CO2 ventilation supported by long water residence times, stratification, mixing with low pCO2 water masses, and carbon removal by biological uptake. The net effect of biogeochemical modification downstream led to pCO2 nearly in equilibrium with the atmosphere in waters of salinity 12, but the mesohaline and polyhaline middle and lower bay were net CO2 sinks (-5.15 and -5.70 mmol m-2 d-1), respectively. Although the main stem bay oscillated between a weak sink and source of CO2 (-2.7 x 109 to 0.4 x 109 mol C y-1) during the dry hydrologic year 2016, our calculations suggest that the CO2 flux could be up to (-10 to -14) x 109 mol C y-1 during a wet year. In contrast to many other estuaries worldwide, Chesapeake Bay and other large estuaries could be absorbing CO2 from the atmosphere.