HR: 11:05h
AN: OS32A-04 INVITED     [Abstracts]
TI: The Nitrogen Isotope Dynamics of the Cariaco Basin
AU: * Sigman, D M
EM: sigman@princeton.edu
AF: Department of Geosciences, Princeton University, Guyot Hall, Princeton, NJ 08544 United States
AU: Thunell, R C
EM: thunell@geol.sc.edu
AF: Department of Geological Sciences, University of South Carolina, Columbia, SC 29208 United States
AU: Muller-Karger, F
EM: carib@seas.marine.usf.edu
AF: College of Marine Science, University of South Florida, 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, Isla de Margarita, 001 Venezuela
AU: Varela, R
EM: rvarela@edimar.org
AF: Fundacion La Salle de Ciencias Naturales, Estacion de Investigaciones Marinas de Margarita, Isla de Margarita, 001 Venezuela
AB: We describe the controls on the N-15/N-14 of water column nitrate and ammonium in the Cariaco Basin and their implications for sinking and sedimentary N. Water column denitrification occurring in the basin has only a very small isotopic imprint on nitrate in the basin because nitrate consumption is nearly complete in the actively denitrifying water near the oxic/anoxic interface (275 m). Being free of a large denitrification signal, the delta-N-15 of shallow thermocline nitrate is 3.5 permil, significantly lower than the mean deep ocean nitrate delta-N-15 of 5 permil. This may be due to the nitrification of newly fixed N, whether it occurs within the basin or in open Atlantic waters that flow into the Cariaco over the sill. The N-15/N-14 of the sinking flux in the deepest trap (1250 m) is similar to that of thermocline nitrate, as expected given the complete consumption of nitrate in the surface layer. Moreover, the N-15/N-14 of the seafloor sediment is similar to that of the sinking flux, as is common in environments of high export production, low bottom water oxygen, and good organic matter preservation. Thus, surface sediment in the modern Cariaco Basin records the N-15/N-14 of the thermocline nitrate, which, in turn, may record the input of newly fixed N to the upper ocean, be it local or more regional in origin. We consider briefly whether these isotopic relationships may have changed in the past and how such changes would affect the downcore record of sediment N-15/N-14 in the Cariaco Basin.
DE: 4243 Marginal and semienclosed seas
DE: 4267 Paleoceanography
DE: 1040 Isotopic composition/chemistry
DE: 1050 Marine geochemistry (4835, 4850)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting