Nitrogen-carbon ratios, marine organic

Figure 1 Typical carbon and nitrogen stable isotope ratios of collagen extracted from various species. In this example the terrestrial animals consume only C3 plants (herbivores and omnivores) or animals that consume only C3 plants (carnivores and omnivores). The marine organisms are distinguished from the terrestrial organisms through the value, which is less depleted in The value indicates the trophic level of an organism in the food web.

Of the organic carbon entering the ocean, about 35% accumulated in marine sediments as organic carbon with a molar C/N/P ratio of about 250/20/1 (Mackenzie, 1981) the rest was respired and oxidized to CO2 and evaded the ocean. The nitrogen and phosphorus riverine fluxes of 1 and 0.045 x 1012 moles y1, respectively, represented the nutrient fluxes necessary to support the organic matter accumulation of 11.7 x 1012 moles C y1. 

The carbon isotope ratios of marine and freshwater organisms are more variable, depending on local ecological circumstances, and often overlap with those of terrestrial plants and their consumers. These foods typically have much higher nitrogen isotope values, however, and their high protein content will contribute much more carbon to bone collagen than will plants foods which are only 10-20% protein. 

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