- APPLICATION TO EARTH SCIENCES RESEARCH
Because of their rapid evolution during the Cenozoic, particularly during time of climate change,
diatoms are extremely useful in providing a chronology for marine stratigraphic sections. Major advances have
been made as a result of the Ocean Drilling Program (ODP) and its predecessor, the Deep Sea Drilling Project (DSDP).
Diatom biostratigraphy is particularly useful in high-latitude environments, where due to the dissolution of
calcareous microfossils, diatoms may be the only biostratigraphic marker preserved in the sediments.
Many of chronologies developed at deep ocean sites (DSDP and ODP) can be utilized in onshore sequences such at the
Monterey Group in California.
Coastal and estuarine studies
Diatoms have been used to evaluate the impact of man on the nearshore environment.
Recent studies in Chesapeake Bay have documented changes in the ecosystem as a result of clearing land for
agricultural purposes and the overuse of inorganic fertilizers. In San Francisco Bay, diatoms have been used to
identify natural variations in precipitation over the past 3,000 years, as well as for studying the impact of
reducing freshwater flow into the bay as a result of increased damming of rivers for agricultural and municipal uses.
The sensitivity of diatoms to changes in temperature, salinity, and nutrients makes them ideal
indicators of past ocean history. They can be used to analyze the effect of large-scale changes in global temperature
such as took place in the mid-Pliocene and during interglacial intervals in the Pleistocene; the tectonically driven
opening and closing of major marine pathways such as the Isthmus of Panama; or short-term events such as El Niņo.
Due to the relative small size (even the Great Lakes) of the basins, lake systems are subject to
substantial variations in temperature, conductivity, and nutrient load. Diatoms are excellent proxies for all these
parameters. In the upper Midwest, the shifting of air masses resulting from the melting of continental glaciers and
middle Holocene aridity have been documented. The impact of the pioneers transforming the forests of the upper
Midwest to agricultural land can be seen through changes (which reflect nutrient load) in the diatom flora of small
lakes. In eastern California, the rise and fall of pluvial lakes over 800,000 years has been tracked.
Along the Oregon and Washington coasts, magnitude 9 or greater seismic events have left their
marks in the diatom record. An instantaneous influx of shallow marine diatoms into a shallow freshwater pond may
suggest the rapid subsidence of the area as a result of an earthquake.
The sensitivity of diatoms to environmental change makes them useful indicators of such
man-made problems as acid rain. The pH tolerance of particular taxa can be used to document both the damage to
the ecosystem and its subsequent recovery.
One of the most interesting applications of diatoms occurred during World War II. Diatoms were used to
determine the launch point for the balloons used by the Japanese to bomb the Pacific Northwest. Sediments from
ballast were used to pinpoint the beach from which the balloons were launched. Diatom assemblages are also unique
enough that they can be used to trace the movement of stolen property (based on the diatoms that accumulate on the
surface over time), including vertebrate fossils (based on the composition of the matrix in which the fossils were found).
CURRENT USGS PROJECTS USING DIATOMS
Western Lakes Project
Work in Owens Lake is unraveling the rate and timing of glacial-interglacial cycles in the
Diatoms used in conjunction with other microfossils to document increased global warming during the
Warm Climate Intervals
High-resolution studies of diatom floras are being used to document rapid (decadal to century)
fluctuations in climate along the California coast.
Diatom studies in coastal ponds and marshes have helped to refine our knowledge of the interval
between large seismic events along this subduction zone.
National Cooperative Geologic Mapping Program
Diatoms provide stratigraphic control for several mapping along the
West Coast, particularly in rocks of Cretaceous, Eocene, Miocene, and Pliocene age.
USGS Energy Program
Diatoms can be used for both stratigraphic control and assessing the productivity of the
environment in which sediment were deposited.
LINKS TO OTHER INFORMATION
The Diatom Collection of the California Academy of Sciences
Diatom Home Page
Diatom Paleolimnology Data Cooperative NOAA Paleoclimatology Program
Great Lakes Diatoms
Introduction to the Bacillariophyta
Patrick Center for Environmental Research at The Academy of Natural Sciences