U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12, 1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigations Report 99-4018B

Redox Gradients in the Vicinity of the Santa Barbara Basin: Application of Techniques Developed within the San Francisco Bay Toxics Study

By James S. Kuwabara, Alexander van Geen, Daniel C. McCorkle, Joan M. Bernhard, Yan Zheng, Brent R. Topping

This paper is available in pdf format: Kuwabara.pdf

ABSTRACT

Methodology for trace sulfide determinations, developed within the San Francisco Bay-Estuary Toxics Study, was applied in an investigation of redox gradients in the suboxic Santa Barbara Basin. Water-column distributions of dissolved oxygen, sulfide and nitrate, and pore-water distributions for dissolved sulfide and iron indicate very different redox conditions between the coring sites within the Santa Barbara Basin and its vicinity, and provide a contrast to the more-oxidizing conditions just north of the basin's sill. For example, pore-water sulfide concentrations exhibited a range of 5 orders of magnitude, indicating a primary sulfide source from the deep basin (that is from depths greater than 500 m). An estimate for sulfide flux out of the basin using water-column data (9 to 138 nmoles-m^-2-h^-1) is consistent with spatial and temporal variability of pore-water gradients near the sediment-water interface (-4 to 13,000 nmoles-m^-2-h^-1). This variability in pore-water gradients affects the authigenesis and mobility of trace elements in the Santa Barbara Basin.