Seasonal phototransformation of dissolved organic matter to ammonium, dissolved inorganic carbon, and labile substrates supporting bacterial biomass across the Baltic Sea

摘要: [1] We studied the photochemical transformation of dissolved organic matter (DOM) to inorganic carbon (DIC), ammonium (NH4+), and labile substrates supporting bacterial biomass along a salinity gradient throughout Baltic Sea during summer, autumn, spring. The photoproduced DIC, NH4+, DOM were related number photons absorbed irradiations biologically recalcitrant determine apparent quantum yields. yields for photoproduction DIC NH4+ lacked seasonal variation, but behaved differently gradient; decreased, while photoammonification increased with increasing salinity. yield was highest in summer unaffected by annual rate over entire ranged from 0.038 0.049 Tg N, equivalent 13%–23% atmospheric deposition N. phototransformation (DOC), including direct photomineralization indirect mineralization (total 2.71–3.94 C), exceeded river loading photoreactive DOC, assuming that half total DOC input is photoreactive. As terrestrial Sea, major sink such coastal systems.