HR: 1340h
AN: OS33A-0575    [Abstracts]
TI: Seasonal to interannual depth-dependent changes in phosphorus flux in Cariaco Basin, Venezuela
AU: * Benitez-Nelson, C R
EM: cbnelson@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences, Columbia, SC 29208 United States
AU: O'Neill, L
EM: lauren.oneill@msci.sc.edu
AF: University of South Carolina, Department of Geological Sciences, Columbia, SC 29208 United States
AU: Thunell, R
EM: Thunell@geol.sc.edu
AF: University of South Carolina, Department of Geological Sciences, Columbia, SC 29208 United States
AB: One of the major removal pathways of phosphorus (P) from the water column is through the formation, sinking, and burial of particles formed during marine biological production. Yet the flux of P containing particles to the seafloor remains one of the least studied components of the P cycle. In this study, particulate inorganic P (PIP) and particulate organic P (POP) fluxes were measured in a series of samples collected from sediment traps ranging in depth from 275 to 1255 m from November 1995 - November 2002 in Cariaco Basin, Venezuela. PIP concentrations averaged 40- 60 % (depending on depth) of the total particulate P (TPP) measured in the traps. PIP fluxes decreased by 75 % between the surface and deep waters, from a median of 28.6 to 6.3 \mu mol m$^{-2}$ d$^{-1}$, whereas POP fluxes decreased by only 50 %, from 17.2 to 8.5 \mu mol m$^{-2}$ d$^{-1}$. TPP, PIP and POP all vary seasonally and higher fluxes follow higher production during the upwelling season from late January to April. The relationship between particulate organic C (POC) and POP is relatively constant (POC:POP = 283) throughout the entire water column over the entire period (r$^{2}$ = 0.58). However, there is a much tighter relationship between POP and POC in upwelling (January through April, r$^{2}$ = 0.85) versus non upwelling (May through December, r$^{2}$ = 0.40) seasons. Furthermore, upwelling, and hence higher production appears to be associated with higher POC:POP ratios (327 versus 258 in non upwelling periods). Higher than Redfield POC:POP ratios may indicate that preferential release of P containing organic matter is occurring, but if true, it is restricted to the upper 250 m of the water column above the shallowest sediment trap. An alternative explanation may be that the composition of plankton in the Cariaco Basin does not conform to the Redfield-ratio. Plankton tow samples collected over the upper 200 m with a $>$ 200 um mesh had POC:POP ratios of 294 +/- 38. However, there is no other evidence that the euphotic zone of Cariaco Basin is dominated by unique flora. The lower POC:POP ratios associated with non upwelling, low production events imply either 1) a different consortium of species is dominant during these periods, and/or 2) that a large portion of the POP pool is derived from other, nonbiologically derived particles.
DE: 4807 Chemical speciation and complexation
DE: 4825 Geochemistry
DE: 4845 Nutrients and nutrient cycling
DE: 4800 OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting