HR: 14:30h
AN: OS52H-03    [PDF]
TI: Vertical fluxes of nitrate and silicate at the New England shelf-break front: Implications for distributions of diatom productivity
AU: * Covert, P
EM: pcovert@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University 104 Ocean Admin. Bldg., Corvallis, OR 97331 United States
AU: Hales, B
EM: bhales@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University 104 Ocean Admin. Bldg., Corvallis, OR 97331 United States
AU: Hebert, D
EM: hebert@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882-1197 United States
AU: Houghton, R
EM: houghton@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AB: Using the Lamont Pumping Seasoar coupled with a fast-response continuous nutrient analysis system we have measured nitrate (NO$_{3}$$^{-}$) and silicate (Si(OH)$_{4}$) concentrations at high spatial resolutions in the New England shelf break front region during the NESPEX program in August of 2002. Shoreward of the front, the nutricline was at approximately 25 m, while seaward of the front the nutricline was at approximately 40 m. Vertical fluxes of NO$_{3}$$^{-}$, calculated using concentration gradients derived from our high-resolution data combined with a constant vertical eddy diffusivity based on a dye-tracer release (k$_{z}$; see Houghton abstract, this session), were ~0.01 æmol m$^{-2}$ s$^{-1}$ and appear to be similar both seaward and shoreward of the front. This NO$_{3}$$^{-}$ flux has the potential to support new production rates of approximately 0.2 mmol C m$^{-2}$ h$^{-1}$. These fluxes will be compared with fluxes calculated using vertical eddy diffusivities estimated with microstructure temperature measurements and models based on Richardson number. Vertical fluxes of nitrate and silicate are approximately equal shoreward of the front; seaward of the front, nitrate fluxes exceed silicate fluxes by a factor of two. This difference implies a shift in the phytoplankton community species assemblage from one that has significant reliance on Si(OH)$_{4}$ uptake-e.g. diatoms-onshore, to one with less reliance on Si(OH)$_{4}$ offshore. This implication is supported by onshore-offshore differences in the ratio of in situ-measured optical backscatter to chlorophyll fluorescence, as well apparent onshore-offshore differences in biogenic consumption of alkalinity (see Bandstra et al abstract, this session).
DE: 4219 Continental shelf processes
DE: 4568 Turbulence, diffusion, and mixing processes
DE: 4845 Nutrients and nutrient cycling
SC: Ocean Sciences [OS]
MN: 2004 Ocean Sciences Meeting