Nutrients, oxygen and inferred new production in the Northeast Water Polynya 1992

Nutrient and oxygen distributions were measured during a hydrographic survey of the Northeast Water Polynya off the northeast coast of Greenland (77–81°N, 6–17°W) during July–August 1992 and were interpreted in the context of satellite imagery of the region. Satellite imagery revealed a convoluted plume of cold water flowing along isobaths from underneath fast ice in the southwestern portion of the polynya toward the northeast. This plume carried relatively high nutrient and low oxygen inventories. Nitrate to phosphate ratios were low in the polar water, consistent with an ultimate source of this water mass in the Pacific sector of the Arctic Ocean. It is hypothesized that the low N:P Arctic outflow might be the cause of nitrate limitation along the east coast of America as far as Cape Hatteras. Gradients of both nutrients and oxygen inventories in the euphotic zone were observed along and across the axis of mean flow within the polynya and are shown to be due to net production of organic matter. On the basis of these spatial gradients of nitrate and oxygen, an assumed along-axis current velocity of 10 cm s−1, and the observed relationships of biologically removed inorganic carbon with nitrate and oxygen, the net organic matter production was estimated to be 40–60 mmol(C) m−2 d−1. This represents the organic carbon available for export from the polynya euphotic zone. Nutrient-deficient and oxygen-rich waters were observed merging with the southward flowing East Greenland Current, suggestive of possible export, however, the ultimate fate of organic carbon produced within the polynya requires further study

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 models and field studies to understand carbon and nutrient cycling as well as to estimate exported carbon from the euphotic zone. The so-called Redfield ratio (C:N = 6.6 by atoms) [Redfield et al., 1963] is widely used for such calculations. Here we present data from the NE Greenland continental shelf that show that most of the C:N ratios for particulate (autotrophic and heterotrophic) and dissolved pools and rates of transformation among them exceed Redfield proportions from June to August, owing to species composition, size, and biological interactions. The ecosystem components that likely comprised sinking particles and had relatively high C:N ratios (geometric means) included (1) the particulate organic matter (C:N = 8.9) dominated by nutrient-deficient diatoms, resulting from low initial nitrate concentrations (approximately 4 μM) in Arctic surface waters; (2) the dominant zooplankton, herbivorous copepods (C:N = 9.6), having lipid storage typical of Arctic copepods; and (3) copepod fecal pellets (C:N = 33.2). Relatively high dissolved organic carbon concentrations (median 105 μM) were approximately 25 to 45 μM higher than reported for other systems and may be broadly characteristic of Arctic waters. A carbon-rich dissolved organic carbon pool also was generated during summer. Since the magnitude of carbon and nitrogen uncoupling in the surface mixed layer appeared to be greater than in other regions and occurred throughout the productive season, the C:N ratio of particulate organic matter may be a better conversion factor than the Redfield ratio to estimate carbon export for broad application in northern high-latitude systems