Aquatic Sciences Meeting, Albuquerque 2001

SS19 Revisiting Redfield: C:N:P Stoichiometry in Aquatic Ecosystems (Disciplinary Connections)

Date: Tuesday, February 13, 2001, Time: 10:00:00 AM

Location: Acoma/Zuni/Tesuque

Fennel, K, , COAS OSU, Corvallis, USA, kfennel@oce.orst.edu

Spitz, Y, H, COAS OSU, Corvallis, USA, spitz@oce.orst.edu

Letelier, R, M, COAS OSU, Corvallis, USA, letelier@oce.orst.edu

Abbott, M, R, COAS OSU, Corvallis, USA, mabbott@oce.orst.edu

Karl, D, M, SOEST, Univ. of Hawaii, Honolulu, USA, dkarl@soest.hawaii.edu

A DETERMINISTIC MODEL FOR N2-FIXATION AT STATION ALOHA IN THE SUBTROPICAL NORTH PACIFIC OCEAN

In the subtropical North Pacific Gyre dramatic variations of elemental stoichiometries from the mean Redfield ratios have been observed in connection with blooms of N2-fixing microorganisms. The input of new nitrogen to the pelagic community by N2-fixation significantly affects new and export production and drives oscillations in the relative importance of nitrogen versus phosphorus control. Despite its relevance for biogeochemical cycling, variations in elemental stoichiometries are not accounted for in current biogeochemical models, which generally assume a tight coupling of elemental cycles by fixed elemental ratios. We present a 1D physical/biological model that resolves the uncoupled cycling of nitrogen and phosphorus and allows shifts in nitrogen versus phosphorus control. N2-fixation by Trichodesmium is explicitly included employing a mechanistic parameterization of the physiological response of Trichodesmium to its physical environment. Typical N:P ratios are assigned to the modeled functional groups allowing variations in the N:P stoichiometries of inorganic and organic matter pools. A simulation at stn. ALOHA in the subtropical North Pacific Ocean captures essential features of the biological system including the vertical structure and seasonal course of chlorophyll, the seasonal cycle and interannual differences in diazotrophic biomass, the mean vertical particle flux and a shift in the relative importance of nitrogen versus phosphorus limitation.

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Aquatic Sciences Meeting, Albuquerque 2001

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