Strontium Isotopic Composition of Estuarine Sediments as Paleosalinity-Paleoclimate Indicator

The strontium isotopic composition of biogenic precipitates that occur in estuarine sediments can be used as proxy indicator of paleosalinity and for assessing precipitation and river discharge rates over thousands of years. In the San Francisco Bay estuary, river water with low $^{87}$Sr/$^{86}$Sr...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 1992-01, Vol.255 (5040), p.68-72
Main Authors: Ingram, B. L., Sloan, D.
Format: Article
Language:English
Subjects:
540310 - Environment, Aquatic- Basic Studies- (1990-)
580000 - Geosciences
ALKALINE EARTH ISOTOPES
ANIMALS
BETA DECAY RADIOISOTOPES
Brackish
CHEMICAL ANALYSIS
Climate
Composition
ELECTRON CAPTURE RADIOISOTOPES
ENVIRONMENTAL SCIENCES
ESTUARIES
Estuarine sediments
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FORAMINIFERA
Fresh water
Freshwater
GEOSCIENCES
HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
INVERTEBRATES
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
MICROORGANISMS
Mud
MULTI-ELEMENT ANALYSIS
NUCLEI
PACIFIC OCEAN
PALEOCLIMATOLOGY
PALEONTOLOGY
PROTOZOA
Proxy reporting
RADIOISOTOPES
River deltas
River water
RIVERS
SALINITY
SAN FRANCISCO BAY
SARCODINA
Scientific Concepts
Sea level
Sea water
SEAS
SEDIMENTS
STABLE ISOTOPES
STREAMS
Strontium
STRONTIUM 86
STRONTIUM 87
STRONTIUM ISOTOPES
Surface water
SURFACE WATERS
Water
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Description
Summary:The strontium isotopic composition of biogenic precipitates that occur in estuarine sediments can be used as proxy indicator of paleosalinity and for assessing precipitation and river discharge rates over thousands of years. In the San Francisco Bay estuary, river water with low $^{87}$Sr/$^{86}$Sr ratio (average, 0.7065) and low Sr concentration (0.13 parts per million) mixes with seawater with a higher $^{87}$Sr/$^{86}$Sr ratio (0.7092) and Sr concentration (7.9 parts per million). The predicted mixing relation between salinity and Sr isotopic composition is confirmed by measurements of modern estuarine surface waters. A paleosalinity record obtained from foraminifera for the ancestral San Francisco Bay during oxygen isotope substage 5e of the last interglacial reflects a global rise and fall of sea level, and short time-scale variations related to fluctuations in discharge rates of the Sacramento and San Joaquin rivers.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.255.5040.68