Horizontal diffusion and new production in the Sargasso Sea


  • Gary L. Hitchcock,

  • Donald B. Olson,

  • George A. Knauer,

  • Alexander A. P. Pszenny,

  • James N. Galloway


Estimates of vertical particulate carbon flux and inorganic nitrogen input from rain events were evaluated in relation to horizontal diffusion during a short-term (4 days) study in the Sargasso Sea. Productivity (∼300 mg C m−2 d−1) and particulate organic C flux (l-ratio of 0.17) from sediment trap arrays were similar to those recently documented in this region. The drifters traversed the periphery of a small anticyclonic eddy, and an estimate of horizontal diffusivity (∼3 to 10 × 104 cm2 s−1) was derived from relative drifter separation. The corresponding length scale (a few kilometers) and time scale (a day) is related to the effective collection area from which drifting sediment traps can sample the surrounding environment. Measurements of inorganic nitrogen from two rain events were similar to those in a more extensive series of observations from Bermuda. The summer Bermuda data are used to evaluate the inorganic nitrogen input to the oligotrophic surface waters with respect to phytoplankton uptake rates and horizontal diffusion. For small, convective rain events, diffusion may be as important as phyloplankton uptake in reducing nitrogen concentrations to ambient nanomolar levels.