Therefore, the C/N ratio serves as a tool for understanding the sources of sedimentary organic matter, which can lead to information about the ecology, climate, and ocean circulation at different times in Earth's history.
[1][4] The lack of cellulose, which has a chemical formula of (C6H10O5)n, and greater amount of proteins in algae versus vascular plants causes this significant difference in the C/N ratio.
[7] However, for more practical applications, desired C/N ratios can be achieved by blending commonly used substrates of known C/N content, which are readily available and easy to use.
An important process called sediment diagenesis accounts for the other 9% of organic carbon that sank to the deep ocean floor, but was not permanently buried, that is 9% of the total organic carbon produced is degraded in the deep ocean.
An exponential increase in C/N ratios is observed with increasing water depth—with C/N ratios reaching ten at intermediate water depths of about 1000 meters and up to 15 in the deep ocean (deeper than about 2500 meters) [citation needed].
[6] Post-depositional diagenesis occurs in organic-carbon-poor marine sediments where bacteria can oxidize organic matter in aerobic conditions as an energy source.
[11] The same principle described above explains the preferential degradation of nitrogen-rich organic matter within the sediments, as they are more labile and in higher demand.
This principle has been utilized in paleoceanographic studies to identify core sites that have not experienced much microbial activity or contamination by terrestrial sources with much higher C/N ratios.
This has been proposed to explain lower-than-expected C/N signatures of organic carbon in sediments undergoing post-depositional diagenesis.
[1][13] Though wood from living trees around lakes have consistently higher C/N ratios than wood buried in sediment, the change in elemental composition is not large enough to remove the vascular versus non-vascular plant signals due to the refractory nature of terrestrial organic matter.
[13] Using the C/N ratio in conjunction with other sediment observations, such as physical variations, D/H isotopic analyses of fatty acids and alkanes, and δ13C analyses on similar biomarkers can lead to further regional climate interpretations that describe the more significant phenomena at play.
Any excess C will cause the N originally in the soil to be consumed, competing with the plant for nutrients (immobilization) – at least temporarily until the microbes die.