Ocean alkalinity enhancement in an estuary

A high-resolution numerical ocean model is used to assess ocean alkalinity enhancement (OAE) in the San Francisco Bay (SFB) estuary. A novel tracer-based approach is introduced to simulate alkalinity release and the subsequent CO 2 ingassing. The model is run for 6 days and accurately reproduces observational data of currents, density, and tides. Estuarine dynamics induce mixing, advect buoyant water out of the Bay, and transport the added alkalinity from deep in the estuary to the surface of the open ocean. Over 80% of the tracer remains in the upper 15 m throughout the simulation. The estimated air-sea equilibration rate of the added alkalinity is approximately 2% per day. Alkalinity exported to the open ocean plays a disproportionately large role in increasing the CO 2 ingassing rate compared to that in the estuary. This rate is relatively fast compared to open-ocean OAE studies due to the San Francisco Bay buoyant plume, which confines the released alkalinity to the surface mixed layer. While estuaries offer many benefits for OAE releases, further studies are needed to quantify their biogeochemical and ecosystem impacts.