HR: 10:20h
AN: OS32A-01    [Abstracts]
TI: Temporal Variability in the Nutrient Chemistry of the Cariaco Basin
AU: * Scranton, M I
EM: mscranton@notes.cc.sunysb.edu
AF: Stony Brook University, Marine Sciences Research Center, Stony Brook, NY 11794-5000 United States
AU: McIntyre, M
EM: mcintyre@seas.marine.usf.edu
AF: University of South Florida, College of Marine Science, St. Petersburg, FL 33701 United States
AU: Taylor, G T
EM: gtaylor@notes.cc.sunysb.edu
AF: Stony Brook University, Marine Sciences Research Center, Stony Brook, NY 11794-5000 United States
AU: Muller-Karger, F
EM: carib@seas.marine.usf.edu
AF: University of South Florida, College of Marine Science, St. Petersburg, FL 33701 United States
AU: Fanning, K
EM: kaf@seas.marine.usf.edu
AF: University of South Florida, College of Marine Science, St. Petersburg, FL 33701 United States
AU: Astor, Y
EM: yastor@edimar.org
AF: Fundacion La Salle de Ciencias Naturales, Estacion de Investigaciones Marinas de Margarita, Apartado 144 Porlamar, Isla Margarita, 6301 Venezuela
AB: Nutrient data have been collected monthly at the CARIACO time series site in the Cariaco Basin since 1995, providing a uniquely detailed picture of the cycling of NO3-, NO2-, NH4+, PO4 and SiO2 in this permanently anoxic system underlying a major coastal upwelling zone. Our data indicate that nutrients for phytoplankton growth are primarily supplied by upwelling of subsurface water on a seasonal basis. In addition coastal runoff seems to supply important amounts of silica and ammonium to surface waters on a few occasions. We saw no indication of local nitrogen fixation in the Cariaco surface waters, as nutrients appear in Redfield ratio amounts at depths (35-55 m) immediately below the euphotic layer throughout the 8.5 year study period. In the suboxic zone, our data are not sufficiently detailed to resolve all important features. However, they do support an important influence of intrusions on the chemistry of the redox gradient. For example, we occasionally, but do not always, observe partial phosphate removal in a zone above the first appearance of sulfide, which is associated with intermittent intrusions of oxygenated water. When there is no evidence of an intrusion, the phosphate removal is not seen. In the suboxic zone, there appear to be thin layers where ammonium and nitrite coexist, potentially permitting anaerobic ammonium oxidation (anammox) to take place. We also observe decreases in alkalinity near the interface which appear to be associated with sulfide oxidation. In the deep waters, concentrations of ammonium, phosphate and silica continue to increase at a rate consistent with prior studies. However rates of sulfide increase are lower than predicted, probably due to microbial and/or chemical sulfide removal associated with recent oxygen intrusions.
DE: 4805 Biogeochemical cycles (1615)
DE: 4845 Nutrients and nutrient cycling
DE: 4219 Continental shelf processes
DE: 4227 Diurnal, seasonal, and annual cycles
DE: 4802 Anoxic environments
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting