Organic Carbon Pathways in the Ocean

To understand the distribution and pathways of organic material in the ocean, the key question is What happens to that 99% of the phytoplankton biomass that is remineralized between photosynthesis and burial  

Sediment trap studies in the open ocean show that the flux of organic carbon at any depth is directly proportional to the rate of primary productivity in the surface water and inversely proportional to the depth of the water column (Suess, 1980 see Section 8.5.1)  

9-16 as a plot of the ratio of carbon flux/primary production vs water depth. As can be seen, about 10% of the primary production falls to a depth of 400 m, whereas only about 1% reaches 5000 m. 

This general relationship has other implications and applications. If depth in Fig. 9-16 can be transformed into time, then the slope of the plot represents a rate constant for in situ organic carbon loss from the sinking particles. Assuming an average settling rate of 100 m/day, the previous equation becomes  

This discussion suggests a rapid and relatively direct transport of organic material vertically through the ocean water column. However, this transport is not efficient and under average ocean conditions (primary productivity = 100 gC/m year and water depth of 4000 m) only 5% of the production can be expected to reach the ocean floor. 

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