Other
Scientific paper
Jun 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51.1345b&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 51, Issue 6, pp.1345-1363
Other
20
Scientific paper
Benthic fluxes in two southern California borderland basins have been estimated by modeling water column property gradients, by modeling pore water gradients and by measuring changes in concentration in a benthic chamber. Results have been used to compare the different methods, to establish budgets for biogenic silica and carbon and to estimate rate constants for models of CaCO 3 dissolution. In San Pedro Basin, a low oxygen, high sedimentation rate area, fluxes of radon-222 (86 ± 8 atoms m -2 s -1 ), SiO 2 (0.7 ± 0.1 mmol m -2 d -1 ), alkalinity (1.7 ± 0.3 meq m -2 d -1 ), TCO 2 (1.9 ± 0.3 mmol m -2 d -1 ) and nitrate (-0.8 ± 0.1 mmol m -2 d -1 ) measured in a benthic chamber agree within the measurement uncertainty with fluxes estimated from modeling profiles of nutrients and radon obtained in the water column. The diffusive fluxes of radon, SiO 2 and TCO 2 determined from modeling the sediment and pore water also agree with the other approaches. Approximately 33 ± 13% of the organic carbon and 37 ± 47% of the CaCO 3 arriving at the sea floor are recycled. In San Nicolas Basin, which has larger oxygen concentrations and lower sedimentation rates than San Pedro, the fluxes of radon (490 ± 16 atoms m -2 s -1 ), SiO 2 (0.7 ± 0.1 mmol m -2 d -1 ), alkalinity (1.7 ± 0.3 meq m -2 d -1 ), TCO 2 (1.7 ± 0.2 mmol m -2 d -1 ), oxygen (-0.7 ± 0.1 mmol m -2 d -1 ) and nitrate (-0.4 ± 0.1 mmol m -2 d -1 ) determined from chamber measurements agree with the water column estimates given the uncertainty of the measurements and model estimates. Diffusion from the sediments matches the lander-measured SiO 2 and PO 4 3- (0.017 ± 0.002 mmol m -2 d -1 ) fluxes, but is not sufficient to supply the radon or TCO 2 fluxes observed with the lander. In San Nicolas Basin 38 ± 9% of the organic carbon and 43 ± 22% of the CaCO 3 are recycled. Approximately 90% of the biogenic silica arriving at the sea floor in each basin is recycled. The rates of CaCO 3 dissolution determined from chamber flux measurements and material balances for protons and electrons are compared to those predicted by previously published models of CaCO 3 dissolution and this comparison indicates that in situ rates are comparable to those observed in laboratory studies of bulk sediments, but orders of magnitude less than those observed in experiments done with suspended sediments.
Berelson William M.
Hammond Douglas E.
Johnson Kenneth S.
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