Export stoichiometry and contribution of copepod faecal pellets to vertical flux of particulate organic carbon, nitrogen and phosphorus

Abstract

Sinking of particles is a key mechanism in the transport of organic matter from the ocean’s productive surface layer to the deep sea and sediments, but also constitutes a loss of carbon and growth-limiting nutrients to the pelagic food web. Knowledge on export of particulate phosphorus is limited, particularly in high-latitude regions, in spite of its role as a co-limiting factor in many marine systems. We therefore investigated suspended concentrations and vertical export (by means of sediment traps) of particulate organic carbon (POC), nitrogen (PON) and total particulate phosphorus (TPP) at 3 contrasting sites in the Fram Strait and Barents Sea opening and quantified the contribution of zooplankton faecal pellets to POC, PON and TPP export. The TPP fluxes are the first to be reported from this region and probably the first from the entire Arctic Ocean. The suspended and exported C:N ratios were close to the Redfield ratio and did not differ significantly from each other (mean atomic ratios of 6.1 and 6.3, respectively). The mean C:P of suspended particles (91) was below Redfield, whereas the exported mean (117) exceeded Redfield, indicating more efficient retention of phosphorus than of nitrogen in the water column. Copepod faecal pellets had low C:P ratios and contributed a higher proportion to phosphorus export (mean of 17%) than to carbon and nitrogen export (10%). Faecal pellets may therefore be an important loss factor for phosphorus from the water column compared to slower-sinking material, which is retained more efficiently.