Stable isotope and salinity systematics in estuarine waters and carbonates - San Francisco Bay

• Published in: Geochimica et cosmochimica acta Vol. 60; no. 3
• Main Authors: Ingram, B.L., Conrad, M.E., Ingle, J.C.
• Format: Journal Article
• Language: English
• Published: United States 31-01-1995
• Subjects: CARBONATES; ENVIRONMENTAL SCIENCES; ESTUARIES; MUSSELS; OXYGEN 18; RUNOFF; SALINITY; SAN FRANCISCO BAY; SEASONAL VARIATIONS; STABLE ISOTOPES; WASTE WATER
• ISSN: 0016-7037; 1872-9533

Salinities, {delta}D and {delta}{sup 18}O values of water samples collected bimonthly from two stations in San Francisco Bay estuary during 1991-1993, and along a salinity transect in March of 1992, indicate a linear mixing relation between the isotopic compositions of the waters and their salinities. The salinities and stable isotope compositions of samples from two locations in San Francisco Bay vary in response to changes in freshwater inflow. The data from these locations indicate simple mixtures of Pacific Ocean water (salinity approximate to 33, {delta}{sup 18}O approximate to 0 to -1 parts per thousand, {delta}D approximate 0 to -10 parts per thousand) and Sacramento-San Joaquin River water (salinity approximate to 0, {delta}{sup 18}O = -10 to -12 parts per thousand, {delta}D = -75 to -85 parts per thousand). Preliminary water balance estimates, using isotopic differences between local and upland runoff, suggest that local runoff (including waste water) comprises less than 20 percent of total freshwater entering the bay. The average {delta}{sup 18}O values of mussel shells (Mytilus edulis) collected live from eight locations in San Francisco Bay primarily reflect the {delta}{sup 18}O of the water in which they grew. Shells subsampled along growth bands show that seasonal shifts in salinity and delta(18)O are recorded in the shells. Therefore, the use of stable isotope measurements should be useful in reconstructing pre-instrumental bay salinity and associated freshwater inflow (both annual average values and seasonal variations) to the San Francisco Bay, as well as potentially other estuarine systems.