Forms of Organic Matter in Seawater

To this point, organic matter in the ocean has been treated primarily as RKR average plankton . We 

Depth (m) Dissolved (10 tonnes C) Approximate concentration ( gC/L) Particulate (10 tonnes C) Approximate concentration (MgC/L) Living fraction (10 tonnes C) Approximate % of particulate 

Although somewhat arbitrary, the 0.45-/rm cutoff between dissolved and particulate organic matter is for the most part convenient. For example, particles above about 1.0 m are observable with a microscope and tend to settle in seawater. Particles less than 1.0 m are submicroscopic and generally sink very slowly and disperse as a result of Brownian motion. In addihon, particles less than 0.45 //m fall below the range of most living organisms (except for some viruses and small bacteria). 

Essentially, all the dissolved organic matter in seawater can be assumed to be non-living. However, particulate organic matter can be either living or dead, with the latter often referenced to as detritus . 

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