The dynamic controls on carbonate mineral saturation states and ocean acidification in a glacially dominated estuary

Recently, a number of studies have shown that the intrusion of anthropogenic carbon dioxide (CO2) into the ocean has created an acidification effect leading to the reduction in carbonate mineral saturation states (Ω). However, the uptake of atmospheric CO2 is not the only climate-induced phenomenon that leads to a reduction of Ω in marine environments. Over the past ∼250 years, Glacier Bay, AK (GLBA) has experienced rapid deglaciation leading to an increase in the amount of freshwater entering the marine ecosystem. This excess freshwater discharge is low in total alkalinity and reduces the buffering capacity of surface waters and enhances the vulnerability of the estuary to further reductions in pH. The corresponding reduction in Ω may cause these waters to become corrosive to shell-building organisms. To better understand these processes, we collected monthly samples within GLBA that show the variability in Ω throughout the water column. Low Ω values were well correlated with the timing of maximum glacial discharge events and most prominent within the two regions where tidewater glacial discharge was highest. The saturation state with respect to aragonite reached a minimum of 0.40 at the surface during the summer of 2011 before rebounding to a maximum value of 3.26 in the spring of 2012. Aragonite was undersaturated at the surface throughout the entire bay during fall months (Sept. and Oct.). Here, we present results from a year-long study designed to constrain the effects of glacial freshwater discharge on the marine carbonate system and discern the primary controls on Ω in this pristine estuarine environment.1