Anthropogenic nitrogen-induced changes in seasonal carbonate dynamics in a productive coastal environment

Abstract

We estimated the seasonal extremes in pH and the aragonite saturation state (Ωarag) for the Yellow Sea over the past 30 years using recent (2015‒2018) carbonate datasets, along with historical datasets of surface N and bottom water dissolved O2 concentrations. The rate of increase in surface N was assumed to set the post-bloom surface dissolved inorganic C concentration resulting from the complete utilization of N by phytoplankton, while the decrease in bottom water O2 was assumed to reflect the pre-bloom surface C, as a consequence of C-rich bottom water (resulting from the transport of greater amounts of organic matter from the surface) being brought to the surface. With the increasing loads of anthropogenic N, the net community metabolism (an increase in organic matter production at the surface and subsequent remineralization at the seafloor) has lowered the seasonal amplitude of pH by 0.14, but increased the amplitude of Ωarag by 0.8.