TOO CUNNIING TO BE UNDERSTOOD*:
LATE HOLOCENE CENTRAL CALIFORNIA
CLIMATE RECORDS FROM SAN FRANCISCO
BAY MARSH SEDIMENTS
Scott W. Starratt
USGS, Menlo Park
sstarrat@usgs.gov
*with apologies to
William Shakespeare
CONCLUSION
„
Climate records can be obtained from
marsh ecosystems using diatoms, BUT
...
‹ Detailed knowledge of the modern
ecological controls is necessary
‹ High diversity requires detailed
taxonomic analysis
ENVIRONMENTAL PARAMETERS
IN SAN FRANCISCO BAY
„
Well understood
‹ Salinity
‹ Temperature
‹ pH
„
Poorly understood
‹ Major nutrients
(N, P, Si)
‹
Minor nutrients
(Fe, Cu, Mg, etc.)
Turbidity
‹ Sediment type
‹ Exposure
‹ Oxygen levels
‹
PRE-HISTORIC CLIMATE RECORDS:
LOCAL
„
„
Pollen
Isotopes
‹
‹
‹
„
Oxygen
Carbon
Strontium
Sediment analysis
PRE-HISTORIC CLIMATE RECORDS:
REGIONAL
„
Tree-ring
‹
‹
„
Conifers
Oaks
Lake levels
‹
‹
‹
‹
‹
Mono Lake, California
Owens Lake, California
Pyramid Lake, Nevada
Walker Lake, Nevada
Lake Tahoe, California-Nevada
WHY DIATOMS?
„
„
„
„
„
Live anywhere there is sufficient light and water
Not susceptible to solution in the low pH
environments typical of marshes
High diversity (more than 600 species and varieties in
San Francisco Bay)
Ecological specificity
Problems
‹
‹
‹
Transportation
Bioturbation
High diversity and ecological specificity
WHY MARSHES?
„
„
„
„
Stability of environment for long-term studies
Less susceptible to physical and biological
reworking
Accessibility
Problems
‹ Regional comparability
THE STUDY SITES:
PRESENT
Located between normal
marine and freshwater
environment
Some of the last
remaining areas of
original tidal marsh
40% of the precipitation
that falls in California and
90% of the freshwater
entering San Francisco
Bay flows through the
Sacramento-San Joaquin
River Delta
THE STUDY SITES: PAST
• Rush
Ranch
• Benicia State Park
CLIMATE CONTROLS
CLIMATE CONTROLS
CLIMATE
CONTROLS
WATER FLOW
Factor analysis is used to
determine diatom distribution
ABUNDANCE OF FRESHWATER TAXA
Climate-related intervals
Strontium Isotope-Derived Salinity
Record
Pyramid Lake Record
CONCLUSIONS AND FUTURE
RESEARCH
„
„
„
Preliminary results indicate that diatoms can be used
to study high-resolution climate signals in estuarine
environments
Salinity is not the only variable that controls the
temporal and spatial distribution of diatom species
Regional correlations can be made, but only with
sufficient understanding of the physical, chemical,
and biological parameters controlling the composition
of the diatom floras at each site
Coming in 2007 to the Geological Society of
America Annual Meeting
DIATOMS:
From Pond Scum to Carbon
Sink
Paleontological Society Short
Course
Saturday October 27, 2007
Denver, Colorado