| Summary: | The coastal ocean, the interface between the land and sea is a key environment for the biogeochemical cycling of carbon, yet these heterogeneous environments are historically under sampled. It is now becoming apparent that anthropogenic CO 2 induced ocean acidification is an open ocean syndrome and that ocean acidification in the coastal environments is far more complex. In the coastal ocean several processes will drive CO 2 trends, such as seawater temperature, biological processes, residence time and air to sea gas exchange. We investigate the distribution and fate of inorganic carbon in a tropical coastal environment, influenced by riverine discharge and local marine habitats – coral reefs, seagrass beds and mangroves. The Belize River, which drains the largest catchment in Belize, discharges just north of Belize City and is a source of high pCO 2 (>2000 µatm) water to the coastal environment. We investigate the process that occur once this low pH (<7.6) water enters the coastal ocean and whether this low pH water, which is corrosive to corals (Ω arag <1), reaches the barrier reef. Using a combination of sensor measurements and discrete samples, we found no evidence that river water reaches the barrier reef, located ~20km offshore. This was due to a number of processes occurring in the coastal ocean, including outgassing of CO 2 to the atmosphere and high rates of photosynthesis taking place, likely from benthic seagrass beds.
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