1 2 Sources of mercury to San Francisco Bay surface sediment as revealed by mercury stable isotopes 3 4 Gretchen E. Gehrke1,* 5 Joel D. Blum1 6 Mark Marvin-DiPasquale2 7 8 1Department of Geological Sciences, University of Michigan 9 1100 North University Ave., Ann Arbor, MI 48109, USA 10 2US Geological Survey 11 345 Middlefield Rd., Menlo Park, CA 94025, USA 12 13 *Corresponding author: telephone: 734-763-9368; fax: 734-763-4690 14 email:
[email protected] 15 16 17 Submitted to Geochimica et Cosmochimica Acta: 25 May 2010 18 1 19 ABSTRACT 20 Mercury (Hg) concentrations and isotopic compositions were examined in shallow-water surface 21 sediment (0-2 cm) from San Francisco (SF) Bay to determine the extent to which historic Hg mining 22 contributes to current Hg contamination in SF Bay, and to assess the use of Hg isotopes to trace sources 23 of contamination in estuaries. Inter-tidal and wetland sediment had total Hg (HgT) concentrations 24 ranging from 161 to 1529 ng/g with no simple gradients of spatial variation. In contrast, inter-tidal and 25 wetland sediment displayed a geographic gradient of δ202Hg values, ranging from -0.30‰ in the 26 southern-most part of SF Bay (draining the New Almaden Hg District) to -0.99‰ in the northern-most 27 part of SF Bay near the Sacramento-San Joaquin River Delta. Similar to SF Bay inter-tidal sediment, 28 surface sediment from the Alviso Slough channel draining into South SF Bay had a δ202Hg value of - 29 0.29‰, while surface sediment from the Cosumnes River and Sacramento-San Joaquin River Delta 30 draining into north SF Bay had lower average δ202Hg values of -0.90‰ and -0.75‰, respectively.