Biologically Mediated Seasonality of Aragonite Saturation States in Jinhae Bay, Korea

Abstract

Aragonite saturation states (Omega(arag)) were estimated for the surface and bottom waters of Jinhae Bay over four seasons to assess the major controlling factors. The surface and bottom waters of Jinhae Bay were highly supersaturated with respect to aragonite in spring, autumn, and winter. In summer, however, most of the bottom waters were undersaturated, even though the surface waters were supersaturated. This can be explained by the phytoplankton-carbonate saturation state interaction; high primary production increases Omega(arag) in surface waters, whereas vertical export and the subsequent remineralization of organic matter decreases Omega(arag) in subsurface waters. A strong linear correlation between the Omega(arag) values and dissolved oxygen concentrations supported the idea that biological activity is a major factor controlling Omega(arag) in Jinhae Bay. The ocean acidification induced by the invasion of anthropogenic CO2 also considerably affected the aragonite saturation state in all seasons, particularly in winter, when the Omega(arag) values have been reduced by 32-35% in the surface waters and 33-37% in the bottom waters since the preindustrial era. In Jinhae Bay, the undersaturation with respect to aragonite in summer can have large impacts on the calcifying benthic organisms; mussel calcification may no longer occur, and the oyster calcification rate is probably reduced by 50%. In addition, the pH and Omega(arag) decreases associated with the anthropogenic CO2 increase may reduce the calcification rates of oyster and mussel in all seasons, particularly in winter.