Emissions of biogenic sulfur compounds and their regulation by nutrients during an Ulva prolifera bloom in the Yellow Sea

Highlights: • High concentrations of biogenic sulfur were observed during an Ulva prolifera bloom. • Peak values of biogenic sulfur concentrations appeared at the late-bloom stage. • Sea-to-air flux of DMS was about five times higher than that of the non-bloom region. • Biogenic sulfur was released by the U. prolifera and promoted by added nutrients. Three cruises were conducted during an Ulva prolifera bloom in 2018 off the Qingdao coast to observe early-, late-, and after-bloom characteristics. Spatio-temporal changes in dimethylsulfide (DMS), dimethylsulphoniopropionate (DMSP), and acrylic acid (AA) and their relationships with environmental parameters were examined. Mesocosm experiments tested the effect of nutrient on the release of biogenic sulfur compounds during the decline period. Biogenic sulfur concentrations contrasted with those in non-bloom regions and reached their highest values during the late-bloom period. The average sea-to-air DMS flux was about 5 times higher than those of non-bloom regions. The mean concentrations of DMS and DMSP in the enclosures were 3–5 times those of in-situ seawater. Biogenic sulfur release was promoted by the addition of high concentrations of nutrients as U. prolifera was declining. The contribution of the U. prolifera bloom to atmospheric DMS was estimated to be 125 kg S d⁻¹.