Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA
- Univ. of California, Berkeley, CA (United States). Dept. of Geology
- Australian National Univ., Canberra (Australia). Dept. of Geology
- Univ. of Wollongong, New South Wales (Australia). School of Geoscience
- Lawrence Berkeley National Lab., CA (United States). Center for Isotope Geochemistry
- Univ. of California, Berkeley, CA (United States). Dept. of Geography
Stable isotope ({sup 18}O/{sup 16}O and {sup 13}C/{sup 12}C) and minor-element compositions (Sr/Ca and Mg/Ca ratios) of ostracodes and gastropods separated from marsh sediments from San Francisco Bay, Northern California, were used to reconstruct paleoenvironmental changes in Petaluma March over the past 700 yr. The value of {delta}{sup 18}O in the marsh carbonates reflects changes in freshwater inflow, evaporation, and temperature. Mg/Ca and Sr/Ca in ostracode calcite reflect changes in both freshwater inflow and temperature, although primarily reflect temperature changes in the salinity range of about 10--35{per_thousand}. Ostracode {delta}{sup 18}O values show a gradual increase by 5{per_thousand} between 500 yr BP and the present, probably reflecting rising sea level and increased evaporation in the marsh. Superimposed on this trend are higher frequency Mg/Ca and {delta}{sup 18}O variations (3--4{per_thousand}), probably reflecting changes in freshwater inflow and evaporation. A period of low Mg/Ca occurred between about 100--300 cal yr BP, suggesting wetter and cooler conditions during the Little Ice Age. Higher Mg/Ca ratios occurred 600--700 cal yr BP, indicating drier and warmer conditions during the end of the Medieval Warm Period. Both ostracode and gastropod {delta}{sup 13}C values decrease up-core, reflecting decomposition of marsh vegetation, which changes from C{sub 4} ({delta}{sup 13}C {approximately} {minus}12{per_thousand}) to CAM ({delta}{sup 13}C = {minus}26{per_thousand})-type vegetation over time.
- OSTI ID:
- 338611
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 62, Issue 19-20; Other Information: PBD: Oct 1998
- Country of Publication:
- United States
- Language:
- English
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