Non-Redfield carbon and nitrogen cycling in the Arctic: Effects of ecosystem structure and dynamics

The C:N ratio is a critical parameter used in both global ocean carbon mode ls and field studies to understand carbon and nutrient cycling as well as t o estimate exported carbon from the euphotic zone. The so-called Redfield r atio (C:N = 6.6 by atoms) [Redfield et nl., 1963] is widely used for such c alculations. Here we present data from the NE Greenland continental shelf t hat show that most of the C:N ratios for particulate (autotrophic and heter otrophic) and dissolved pools and rates of transformation among them exceed Redfield proportions from June to August, owing to species composition, si ze, and biological interactions. The ecosystem components that likely compr ised sinking particles and had relatively high C:N ratios (geometric means) included (1) the particulate organic matter (C:N = 8.9) dominated by nutri ent-deficient diatoms, resulting from low initial nitrate concentrations (a pproximately 4 mu M) in Arctic surface waters, (2) the dominant zooplankton , herbivorous capepods (C:N = 9.6), having lipid storage typical of Arctic copepods; and(3) copepod fecal pellets (C:N = 33.2). Relatively high dissol ved organic carbon concentrations (median 105 mu M) were approximately 25 t o 45 mu M higher than reported for other systems and may be broadly charact eristic of Arctic waters. A carbon-rich dissolved organic carbon pool also was generated during summer. Since the magnitude of carbon and nitrogen unc oupling in the surface mixed layer appeared to be greater than in other reg ions and occurred throughout the productive season, the C:N ratio of partic ulate organic matter may be a better conversion factor than the Redfield ra tio to estimate carbon export far broad application in northern high-latitu de systems.