First System-Wide Estimates of Air-Sea Exchange of Carbon Dioxide in the Chesapeake Bay

Estuaries are estimated to play a major role in the global carbon cycle by degassing between 0.25 and 0.4 Pg C y^-1, comparable to the uptake of atmospheric CO₂ by continental shelf waters and as much as one quarter of the uptake of atmospheric CO₂ by the open ocean. However, the global estimates of estuarine CO₂ gas exchange are highly uncertain mostly due to limited data availability and extreme heterogeneity of coastal systems. Notably, the air-water CO₂ flux for the largest U.S. estuary, the Chesapeake Bay, is yet unknown. Here we provide first system-level CO₂ gas exchange estimates for the Chesapeake Bay, using data from the Chesapeake Bay Water Quality Monitoring Program (CBWQMP) and other data sources. We focus on the main stem of the Chesapeake Bay; hence, tributaries, such as the tidal portions of the Potomac and James Rivers, are not included in this first estimation of the flux. The preliminary results show the Bay to be a net source of CO₂ to the atmosphere, outgassing on average 0.2 Tg C yr^-1 over the study period, between 1985 and 2013. The spatial and temporal variability of the gas exchange will be discussed.