HR: 0830h
AN: OS31C-0223    [PDF]
TI: Silica cycling in mobile mud deposits of coastal French Guiana
AU: * Panzeca, C
EM: cpanzeca@ic.sunysb.edu
AF: Stony Brook University, Marine Science Research Center, Stony Brook, NY 11794-5000 United States
AB: Coastal French Guiana lies within the Amazon - Guianas mobile mud belt and is characterized by intensely reworked migrating mud waves. Diatoms are the primary source of autochthonous organic matter in these deposits and are rapidly remineralized under suboxic diagenetic conditions. The siliceous diatom frustules are subject to dissolution and recycling, burial, or diagenetic alteration. Pore water profiles demonstrate that mudwave deposits are undersaturated with respect to biogenic silica, reaching values ranging from 200-600 $\mu$M at depth. Overall, dissolved Al varies inversely with dissolved Si between sampling sites but inverse relations are not discernable within individual cores. Dissolved K is often depleted with depth. Analyses indicate that frustules may be stored as whole or partially dissolved diatoms, metal-oxide coated frustules, authigenic clay-coated frustules, or completely altered particles. Operational leaches of sediment indicate that the commonly used (1% Na$_{2}$CO$_{3}$) alkaline procedure underestimates biogenic silica content in these sediments, presumably by failing to react with metal-oxide coated frustules and alteration products. A combined mild acid (0.1 N HCl) / mild alkaline (1% Na$_ {2}$CO$_{3}$) leach procedure, used previously in the Amazon delta, was presumed to more accurately quantify reactive Si. Total reactive Si and K extracted from mudwave sediments lies on the regional trend for the Amazon delta (K/Si = 0.19 mol/mol), implying similar authigenic minerals. SEM observations of experimentally incubated diatoms demonstrated the potential for rapid alteration of diatoms into authigenic clays in the mudwave deposits.
DE: 3022 Marine sediments--processes and transport
DE: 4805 Biogeochemical cycles (1615)
DE: 4825 Geochemistry
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting