The oceans hold the largest reservoir of carbon, with a vast amount in an extremely complex mixture of recalcitrant dissolved organic matter (RDOM). Although microbes are known to produce RDOM, little is known about which specific molecules microbes produce. Via ultrahigh-resolution mass spectrometry, we identified RDOM molecules of microbial origin commonly produced in incubation experiments, and found that these formulae were extensively distributed in different oceans. The large scale distribution and accumulation of the microbial-derived RDOM molecules highlights their immediate persistent after microbial reworking. Decoding these long masked microbial RDOM molecules and their chemical characteristics lays a key foundation to comprehend the cycling of RDOM under the changing ocean.

refractory dissolved organic matter; microbial activity; seawater; ultrahigh-resolution mass spectrometry