Depth-dependent elemental compositions of particulate organic matter (POM) in the ocean -: art. no. 1032

[1] For the determination of the elemental composition of particulate organic material (POM) and its impact on the marine carbon cycle, we assembled C: N data for POM from many different sources into a single data collection for joint evaluation. The data set contains 10,200 C: N values, encompassing all major oceans and trophic levels, showing that C: N ratios are highly variable with values below the traditional Redfield ratio ( C: N = 6.6) to values greatly exceeding it. On a global mean, C: N ratios of marine sinking particles from the surface water amount to 7.1 +/- 0.1, and there is a systematic increase of C: N ratios with depth of 0.2 +/- 0.1 units per 1000 m. The discrepancy with results from analyses of dissolved nutrient fields, yielding constant C: N ratios close to the Redfield value, can be explained by the implicit depth averaging caused by depth variations of the surfaces under consideration. Additionally, due to preferential remineralization of nitrogen compared to carbon, the C: N ratio of the dissolving component, which is seen on dissolved nutrient fields, is smaller than the C: N ratio of the remaining particles. For carbon flux estimations, elevated and depth dependent C: N ratios should be implemented in biogeochemical models to correctly represent relative strengths of downward carbon and nitrogen fluxes.