Dissolved Organic Matter

At approximately 662 gigatons of carbon (GtC), Dissolved Organic Matter (DOM) far outnumbers Particulate Organic Matter, which includes organisms and marine snow, and constitutes more than 99% of organic carbon in the ocean's water column (1). Yet, most DOM released by phytoplankton, the primary source of DOM, is quickly degraded by heterotrophs within hours to days (2). As a result, the majority of DOM (~630 GtC) that is found in the ocean has a lifetime (determined via 14C-carbon dating) of over 16,000 years (2). DOM is operationally classified into the following groups based on their lifetime (2):

• labile DOM (removal within hours to days)
• semi-labile DOM (removal within weeks to months)
• semi-refractory DOM (removal over years to decades)
• refractory DOM (removal over centuries to millenia)

References

1. Hansell, D.A., C.A. Carlson, D.J. Repeta, and R. Schlitzer. 2009. Dissolved organic matter in the ocean: A controversy stimulates new insights. Oceanography 22(4):202–211, https://doi.org/10.5670/oceanog.2009.109
2. Dittmar, T., Lennartz, S.T., Buck-Wiese, H. et al. Enigmatic persistence of dissolved organic matter in the ocean. Nat Rev Earth Environ 2, 570–583 (2021). https://doi.org/10.1038/s43017-021-00183-7