Downward export of respiratory carbon and dissolved inorganic nitrogen by diel-migrant mesozooplankton at the JGOFS Bermuda time-series station

Published calculations suggest that downward fluxes of respiratory carbon (RC) and dissolved inorganic nitrogen (DIN) associated with diel-migrant zooplankton are significant forms of export production. In this study, we examined variability in downward fluxes of RC and DIN due to diel-migrant mesozooplankton (200–2000 μm) on seven occasions between 25 March and 8 April 1990 at the JGOFS (Joint Global Ocean Flux Study) station off Bermuda. Downward fluxes due to migrators crossing 150 m ranged from 6 to 41 mgC m−2 day−1 (RC) and 2 to 5 mgN m−2 day−1 (DIN). In comparison to gravitational fluxes of POC and PON measured with particle traps at 150m during the same period, mesozooplankton RC flux was 18–70% of POCflux and mesozooplankton DIN flux was 17–82% of PON flux. If the RC and DIN fluxes due to migrators are considered in calculations of export production, the percentage of the production exported below 150 m over the study period would increase by an average of 25% for carbon and 21% for nitrogen. These results support the contention that metabolic activities of diel-migrant zooplankton should be included in calculations of export of carbon and nitrogen out of the mixed layer.