Dissolved sulfide distributions in the water column and sediment pore waters of the Santa Barbara Basin

Geochimica et Cosmochimica Acta
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Abstract

Dissolved sulfide concentrations in the water column and in sediment pore waters were measured by square-wave voltammetry (nanomolar detection limit) during three cruises to the Santa Barbara Basin in February 1995, November–December 1995, and April 1997. In the water column, sulfide concentrations measured outside the basin averaged 3 ± 1 nM (n= 28) in the 0 to 600 m depth range. Inside the basin, dissolved sulfides increased to reach values of up to 15 nM at depths >400 m. A suite of box cores and multicores collected at four sites along the northeastern flank of the basin showed considerable range in surficial (<0.5 cm) pore-water sulfide concentrations: <0.008, 0.01, 0.02, to as much as 0.4 μM at the 340, 430, 550, and 590 m sites, respectively. At a core depth of 10 cm, however, pore–water sulfides exhibited an even wider range: 0.005, 0.05, 0.1, and 100 μM at the same sites, respectively. The sulfide flux into the deep basin, estimated from water-column profiles during three cruises, suggests a fairly consistent input of 100–300 nmole m−2 h−1. In contrast, sulfide fluxes estimated from pore-water sulfide gradients at the sediment water interface were much more variable (−4 to 13,000 nmole m−2 h−1). Dissolved silicate profiles show clear indications of irrigation at shallow sites (340 and 430 m) in comparison to deeper basin sites (550 and 590 m) with low (<10 μM) bottom-water dissolved-oxygen concentrations. Pore-water profiles indicate ammonia generation at all sites, but particularly at the deep-basin 590 m site with concentrations increasing with sediment depth to >400 μM at 10 cm. Decreases in water-column nitrate below the sill depth indicate nitrate consumption (−55 to −137 μmole m−2 h−1) similar to nearby Santa Monica Basin. Peaks in pore-water iron concentrations were generally observed between 2 and 5 cm depth with shallowest peaks at the 590 m site. These observations, including observations of the benthic microfauna, suggest that the extent to which the sulfide flux, sustained by elevated pore-water concentrations, reaches the water column may be modulated by the abundance of sulfide-oxidizing bacteria in addition to iron redox and precipitation reactions.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Dissolved sulfide distributions in the water column and sediment pore waters of the Santa Barbara Basin
Series title Geochimica et Cosmochimica Acta
DOI 10.1016/S0016-7037(99)00084-8
Volume 63
Issue 15
Year Published 1999
Language English
Publisher Elsevier
Contributing office(s) Toxic Substances Hydrology Program
Description 11 p.
First page 2199
Last page 2209