| The role of the dominant zooplankton, calanoid copepods, in Arctic marine carbon and nitrogen cycles was investigated in the Northeast Water Polynya off the coast of Greenland during the summer of 1992 and 1993. This high-latitude system was characterized by relatively high molar carbon:nitrogen (C:N) ratios for dissolved and particulate pools in the euphotic zone relative to Redfield stoichiometry. Elevated C:N ratios (8.9) of particulate organic matter were interpreted to be a response by phytoplankton to nutrient limitation in open water regions, particularly in larger cells, and C:N ratios (9.6) of female copepods were even higher due to lipid storage. Moreover, C:N ratios (33.2) for copepod fecal pellets were higher than reported for other systems, presumably from the combined effect of copepods ingesting food with a relatively low nitrogen content and assimilating nitrogen more efficiently than carbon. Average daily egestion in female Calanus hyperboreus was equivalent to 8% of body carbon and 2% of body nitrogen, whereas carbon dioxide respiration and ammonium excretion were approximately in balance (1% of body carbon and nitrogen). Regression analyses indicate that a large proportion (50-80%) of the variability in these rates was explained by carbon and nitrogen concentrations in food. In addition, estimates of community rates suggest that copepods, on average, consumed a considerable amount of the primary production (45%) and egested fecal matter equivalent to 20% of the carbon and 12% of the nitrogen particulate flux sinking from the upper 50 m of the water column, but excreted {dollar}<{dollar}10% of the ammonium utilized by phytoplankton in the surface layer. Furthermore, mass-balance calculations indicate that female copepods recycled ingested carbon to biomass, egested fecal matter, and excreted dissolved organic carbon in approximately equal proportions, while ingested nitrogen primarily was excreted as dissolved organic nitrogen. Hence, copepods formed carbon-rich particulate matter, but resupplied dissolved pools at relatively low C:N ratios. Because C:N ratios of particulate and dissolved pools and their associated fluxes were higher than Redfield proportions, it was concluded that the use of the Redfield ratio underestimated carbon export by 25% and therefore may be unsuitable for Arctic systems. |
