Trends of Anthropogenic Dissolved Inorganic Carbon in the Northwest Atlantic Ocean Estimated Using a State Space Model

Abstract

A key element for climate change projection and for carbon emission policy is how effective the ocean is, and will be, in mitigating the effects of anthropogenic CO 2 emissions. The northwest Atlantic is one of the largest oceanic carbon sinks on an areal basis, taking in and storing large amounts of anthropogenic CO 2 (Khatiwala et al., 2013). There are several chemical, physical and biological factors that influence how much CO 2 the ocean takes up throughout the year. In the winter, cold winds cool the surface waters, increasing the solubility of CO 2 (Emerson & Hedges, 2008), which enhances dissolved inorganic carbon (DIC) concentrations in the surface layers as a result of air-sea gas exchange. Temperature also influences the physical uptake processes of the area, as cooling reduces stratification and facilitates the transport of DIC rich waters from the surface to the deeper waters. The shoaling of the mixed layer in the summer traps DIC rich waters in the subsurface ocean where it is no longer in contact with the atmosphere. While respiration will release CO 2 into the surface waters, phytoplankton will use CO 2 for photosynthesis. Strong, seasonal biological production also promotes seasonal uptake of CO 2 from the atmosphere, which is transported deeper via the biological carbon and mixed-layer pumps (Lacour et al., 2019).