Dissertation Abstract

The oceanic uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere has caused perturbations to marine biogeochemistry in recent years, including decreasing ocean pH and carbonate mineral saturation states (Ω). Collectively termed “Ocean Acidification (OA), these conditions hinder the growth of biogenic calcium carbonate shells and effectively reduce suitable habitat for some marine calcifiers. Of particular concern is that these changes may impact the economic viability of some ecosystems. Given that the Bering Sea is one of the World’s most productive marine ecosystems and supports both large commercial fishing industries and many subsistence communities, it is integral to understand the susceptibility of this system to OA.

Here, new observations of seasonal variations in the organic and inorganic carbon systems are used to identify new mechanisms leading to CO₂ accumulation and subregional enhancement of vulnerability to OA processes. Net heterotrophic processes and low bottom water Ω were observed near the coast, resulting from the focused deposition of both marine and terrestrial organic matter and its subsequent respiration. Naturally weak circulation processes over the northern shelf also favors CO₂ accumulation in bottom waters. In combination with natural respiration processes, anthropogenic CO₂ was shown to cause very low Ω and seasonal dissolution of carbonate minerals in this area. Sea ice cover was found to inhibit the flux of CO₂ from the surface ocean to the atmosphere, raising the inventory of CO₂ in the water column over the northern shelf.

Low-Ω conditions and areas of carbonate mineral dissolution will continue to expand as anthropogenic CO₂ accumulates in shelf waters in the coming decades, further reducing viable habitat for key calcifiers. Model projections of future surface water conditions indicate that average Ω over the Bering Sea shelf will drop below the observed natural variability near 2100, with average conditions favoring carbonate mineral dissolution (Ω<1) in surface waters by 2150. Between now and the end of the century, episodic events will cause regions of the Bering Sea to be undersaturated in Ω, which could have significant and cascading impacts throughout the Pacific-Arctic Region.