UC San Diego

The pH of the world’s surface oceans is decreasing from increased uptake of anthropogenic CO2. In addition to increasing anthropogenic CO2, the coastal ocean pH and carbon balance is affected by many other processes affecting input, uptake and release of carbon in this region. The lateral flux of estuarine carbon to the coastal ocean has recently been recognized as a significant contributor to coastal carbon fluxes, making it important to understand how these fluxes affect this environment in the context of ocean acidification (OA). In the present study, I measured the flux of dissolved inorganic carbon (DIC) and total organic carbon (TOC) from a small saltmarsh in Southern California, the San Dieguito Lagoon (SDL), to the adjacent coastal ocean over diel and seasonal timescales. The combined net flux of DIC and TOC (F¬DIC+TOC) to the ocean ranged from 3.0x103 to 42.1x103mol C h-1 over the course of this study. On an annual timescale the net, export of DIC and TOC totaled 0.060x109 mol C yr-1. A rain and flooding event (36 mm rain in three days) significantly increased FDIC+TOC (40x103to 90x103mol C h-1), resulting in nearly a doubling of the annual flux. The findings highlight the importance of assessing coastal carbon fluxes on different timescales and under varying environmental conditions. Elevated levels of total alkalinity (TA) and pH were observed at the mouth of the estuary relative to the coastal ocean, suggesting that the SDL potentially could partly buffer against local acidification of coastal surface waters in this area.