Paleoclimatic and paleoceanographic studies of estuarine and marine sediments using strontium isotopes
Strontium isotopic ratio ([sup 87]Sr/[sup 86]Sr) measurements in fossil carbonates and phosphates are used to evaluate paleoceanographic and paleoclimatic environments in Quaternary, Pliocene-Pleistocene, and mid-Cretaceous estuarine and marine sediments. The use of [sup 87]Sr/[sup 86]Sr measurements as an estuarine paleosalinity and paleoclimatic indicator is developed and applied to San Francisco Bay. [sup 87]Sr/[sup 86]Sr measurements of foraminifer and molluscan fossils contained in estuarine sediments of late Pleistocene (ca 115 to 125 ka) and late Holocene (4.5 ka) age show cyclic variations indicating that salinity fluctuated with periods of several hundred years, probably reflecting wet-dry cycles associated with fluctuations in solar irradiance caused by sunspot cycles. The average salinity in San Pablo and Richardson bays was significantly lower (by 6 to 8%) over much of the past 4.5 ka than at present, reflecting a combination of decreased freshwater inflow at present associated with water diversion and wetter climatic conditions prior to 2000 years ago. Salinity data are converted to river discharge using salinity-delta flow relations derived from historical records for San Francisco Bay. The data indicate that annual freshwater inflow was at least twice the modern pre-diversion average between 2.5 and 3.0 Ka; this time period is also identified as one of wetter climatic conditions by lake level and treeline records from the Sierra Nevada. Strontium isotopic measurements of marine carbonate and fish teeth to middle Cretaceous age are used to increase the resolution of the existing seawater Sr isotope versus time curve and to assess models for global oceanic anoxic events. The new data using fish teeth show less scatter and variability than previous data. Negative excursions in the [sup 87]Sr/[sup 86]Sr ratio of 7-14 parts in 10[sup [minus]5] during Aptian anoxic events suggest a link between increased submarine volcanism and oceanic anoxia.
- Research Organization:
- Stanford Univ., CA (United States)
- OSTI ID:
- 5297124
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SAN FRANCISCO BAY
PALEOCLIMATOLOGY
SEDIMENTS
STRONTIUM ISOTOPES
ISOTOPE RATIO
CRETACEOUS PERIOD
PLEISTOCENE EPOCH
PLIOCENE EPOCH
QUATERNARY PERIOD
STRONTIUM 86
STRONTIUM 87
ALKALINE EARTH ISOTOPES
BETA DECAY RADIOISOTOPES
CENOZOIC ERA
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC AGES
HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
ISOMERIC TRANSITION ISOTOPES
ISOTOPES
MESOZOIC ERA
NUCLEI
PACIFIC OCEAN
PALEONTOLOGY
RADIOISOTOPES
SEAS
STABLE ISOTOPES
SURFACE WATERS
TERTIARY PERIOD
540311* - Environment
Aquatic- Basic Studies- Radiometric Techniques- (1990-)
540110