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This study uses a neural network model trained with in situ data, combined with satellite data and hydrodynamic model products, to compute the daily estuarine export of dissolved organic carbon (DOC) at the mouths of Chesapeake Bay (CB) and Delaware Bay (DB) from 2007 to 2011. Both bays show large flux variability with highest fluxes in spring and lowest in fall as well as interannual flux variability (0.18 and 0.27 Tg C/year in 2008 and 2010 for CB; 0.04 and 0.09 Tg C/year in 2008 and 2011 for DB). Based on previous estimates of total organic carbon (TOCexp) exported by all Mid-Atlantic Bight estuaries (1.2 Tg C/year), the DOC export (CB+DB) of 0.3 Tg C/year estimated here corresponds to 25% of the TOCexp. Spatial and temporal covariations of velocity and DOC concentration provide contributions to the flux, with larger spatial influence. Differences in the discharge of fresh water into the bays (74 billion m(3)/year for CB and 21 billion m(3)/year for DB) and their geomorphologies are major drivers of the differences in DOC fluxes for these two systems. Terrestrial DOC inputs are similar to the export of DOC at the bay mouths at annual and longer time scales but diverge significantly at shorter time scales (days to months). Future efforts will expand to the Mid-Atlantic Bight and Gulf of Maine, and its major rivers and estuaries, in combination with coupled terrestrial-estuarine-ocean biogeochemical models that include effects of climate change, such as warming and CO2 increase.

Plain Language Summary This study combines satellite data, field work observations, and statistical and numerical models to investigate the seasonal and interannual variability of dissolved organic carbon (DOC) export from two major East Coast estuaries, Chesapeake, and Delaware Bays. DOC is a food supplement, supporting growth of microorganisms and plays an important role in the global carbon cycle through the microbial loop, a marine pathway which incorporates DOC into the food chain. Using this novel methodology, we were able to better quantify the combined contribution of these estuaries to the East Coast carbon budget and contrast estuarine properties affecting the DOC export, such as riverine inputs, time scales of variability, and geomorphology. The combined DOC contribution of these two estuaries represents 25% of the total organic carbon exported by all Mid-Atlantic Bight (the coastal region running from Massachusetts to North Carolina) estuaries, and 27% of the total atmospheric carbon dioxide uptake in the Mid-Atlantic Bight.