Seasonality of dimethylated sulfur compounds cycling in north China marginal seas

Dimethylated sulfur compounds play an important role in global sulfur cycle. We investigated the seasonality of dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO), dimethylsulfide (DMS) and associated processes in two north China marginal seas during 2014 and 2016. High concentrations of DMS, DMSP and DMSO occurred in summer/spring, while the lowest were observed in winter. This clear seasonality was primarily driven by biomass abundance and phytoplankton communities, reflected in chlorophyll a concentrations and the composition/ratios of diatoms and dinoflagellates. The spring maximum was attributed to the annual occurrence of algal bloom. The sea-to-air fluxes of DMS also varied largely between seasons, with an average of 8.84, 11.87, 10.50 and 2.14 μmol m^-2 day^-1 in spring, summer, autumn and winter, respectively. Given the seasonal uncertainty of sea-to-air flux, the seasonality or situations where specific blooms occur regularly should be considered for accurate estimation of annual global DMS emission.