Reduction in seasonal pH extremes as a result of increase in net community production in coastal environments

Abstract

We estimated the seasonal extremes in pH and aragonite saturation state (Ωarag) for the Yellow Sea for the past 35years using historical datasets of surface nitrate (N) and bottom dissolved O2 concentration and recent (2015‒2019) carbonate datasets. In this retrospective analysis the rate of surface N increase was assumed to set the post-bloom surface dissolved inorganic C concentration resulted from the complete consumption of increased N by phytoplankton, whereas that of seafloor O2 decrease was assumed to reflect the pre-bloom surface C by bringing C-rich seafloor water to the surface. In the Yellow Sea receiving increasing loads of anthropogenic N, the N-driven net community metabolism led to the concurrent increase in organic matter production at the surface and subsequent remineralization at the seafloor, and eventually lowered seasonal pH amplitude by 0.2 but increased the amplitude of Ωarag by 1.0 over the past 35 years.