Stable isotopes, Sr/Ca, and Mg/Ca in biogenic carbonates from Petaluma Marsh, northern California, USA
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 Marsh 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 BR 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 {approx} -12{per_thousand}) to CAM ({delta}{sup 13}C = -26 {per_thousand})-type vegetation over time.
- Research Organization:
- Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US) (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 833680
- Report Number(s):
- LBNL-43990; GCACAK; TRN: US200430%%1731
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 62, Issue 19-20; Other Information: Journal Publication Date: Oct. 1998; PBD: 19 Oct 2004; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALCITE
CARBONATES
EVAPORATION
HEAT EXCHANGERS
LITTLE ICE AGE
PLANTS
SALINITY
SAN FRANCISCO BAY
SEA LEVEL
SEDIMENTS
STABLE ISOTOPES
ENVIRONMENTAL TEMPERATURE
HORMONAL THERAPY
RECOMBINANT GROWTH HORMONE
GROWTH HORMONE
SOMATOMEDIN C
SOMATOMEDIN B
GROWTH HORMONE RECEPTOR
SOMATOMEDIN BINDING PROTEIN 3