The vertical nitrogen flux caused by zooplankton diel vertical migration

Three species of vertically migrating copepods (Pleuromamma pisekii, P. gracilis and P. abdominalis) were collected at dawn and at dusk from the upper 200 m in the North Atlantic (36.5°N, 19.2°W) between 11 and 18 July 1996. For all 3 species, the nitrogen content of individuals caught at dawn was significantly greater than for individuals caught at dusk. Theoretical considerations suggest that this dawn-dusk difference in nitrogen content represents material that is exported from the surface each day (the so called active N-flux). The rate of this active N-flux was 0.46 μg N ind. -1 d -1 for P. pisekii, 0.34 μg N ind. -1 d -1 for P. gracilis and 5.17 μg N ind. -1 d -1 for P. abdominalis.