Coastal Ocean Acidification

As a result of increasing atmospheric carbon dioxide (CO₂) loading into the ocean, the pH of the upper ocean has been decreasing, leading to ocean acidity at an unprecedented rate. Numerous observations have reported that these changes can directly impact the ocean ecosystem and, thus, the health and sustainability of living marine resources. The U.S. northeast coastal ocean is identified as a region that could be significantly influenced by coastal acidification. The Northeast Regional Association of Coastal and Ocean Observing Systems (NERACOOS) has established the Northeast Coastal Acidification Network (NECAN) to serve as a conduit to the regional collaborative research and monitoring of environmental change due to acidification. NECAN’s recent publication has provided a comprehensive synthesis report for the current condition of coastal acidification in the U.S. northeast coastal ocean, physical/biochemical controllers, and impacts on marine calcifiers, crustaceans, and lower trophic food web planktons. The degree of coastal acidification (lowering pH) can be measured by 1) the CO₂ content in the water from the air-sea flux and respiration process; 2) Ω – the degree of saturation of calcium carbonate mineral calcite relative to the mineral aragonite; and 3) the buffering capacity – a measurer of the seawater’s capacity to resist the adding of carbonic acid. The enhanced acidification condition in the region changes with short-term variability caused mainly by the seasonality of lower trophic level biological respiration, precipitation minus evaporation, and changes in coastal river discharge, and long-term variability due to climate change-induced interannual-decadal fluctuation of atmospheric CO₂ loading and the inflow of the cool and less salty water from the upstream.

The variability is manifested through the fully nonlinear interaction of physical, biological, and chemical processes. We develop a full three-dimensional, prognostic acidification model by coupling the US Northeast Coastal Forecast Model System (NECOFS) with the European Regional Seas Ecosystem Model (ERSEM), naming it “the US Northeast Biogeochemistry Ecosystem Model (NeBEM).” NeBEM was designed to understand the complex coastal acidification process in the northeastern coastal region and provide stakeholders with a scientific and visual tool to assess and predict the acidification condition in the region. NeBEM was validated by 1-D (vertical) and 3-D experiments in Massachusetts Bay (Lu et al., 2022a, b) and the 3-D experiments over the US Northeast.