Carbon sinks marine organic matter

Sea water contains a much lower concentration of dissolved organic matter than river water. More than half of this dissolved organic load is of a humic nature. These dissolved organic acids tend to flocculate as the salinity increases (10). Hair and Bassett (11) have observed an increase in the particulate humic acid load of an estuary as one approaches the sea. Although no studies of the distribution of humic materials throughout an estuarine system have been performed, it would appear that estuaries and their sediments in particular, act as a major sink for the dissolved and particulate humic materials. Nissenbaum and Kaplan (12) have observed that terrestrial humic materials are not deposited at great distances from shore in the marine system. A study of the flux of particulate carbon through the Chesapeake Bay comes to a similar conclusion (13). 

Figure 12 DOM cycling in the ocean. DOM is initially produced as a by-product of marine production in the mixed layer. Carbon stable isotope data suggests that some fraction of this organic matter becomes incorporated into the longer-term reservoir of rather refractory DOM to be subducted into the deep ocean. Newly produced DOM may also assemble into particles to enter the POM cycle. POM is oxidized, or transported into the deep ocean on large, rapidly sinking particles where biological activity may cause further oxidation, or drive re-dissolution to HMW DOM.

Inspection of the global carbon cycle provides a useful backdrop for considering the natural fate of wood. Terrestrial ecosystems accumulate an extremely small fraction of the organic matter photosynthesized within them. Almost all (>99%) of the organic material produced on land is remineralized back to carbon dioxide and water within an average half-life of 10-100 years 11). The small fraction that escapes is exported by rivers to lakes and coastal marine zones, where a portion of the plant debris becomes waterlogged, sinks, and is incorporated in bottom deposits (12). 

---