Monterey Bay Aquarium Research Institute
Marine Botany

Diatoms Geology and Paleontology

  • The earliest diatom fossils come from 100 million years ago. During all this time, as diatoms died, their heavy shells sank to the bottom of the sea. Because they are hard and chemically stable in seawater, the shells are preserved. As millennia go by, more shells form thicker and thicker deposits of diatomaceous earth or diatomaceous oozes over large expanses of the sea floor. Since the deposits are stable and immobile, we can use what we know about modern diatoms and diatom assemblages to learn about the ancient earth.

  • Temperature: different diatom species prefer different temperatures. By comparing the number of cold-water and warm-water species found in a fossil assemblage, we can estimate the temperature of the water they live in. Temperature preferences for unknown fossil species can be determined by their statistical association with other, known species. The results agree with other methods, such as a similar method using foraminiferan data, oxygen isotope data that reflects the size of polar ice caps, and accumulation of biologically generated calcium carbonate from corals and mollusk shells.
  • Water Circulation: the abundance and size of diatoms give an indication of how well the water is mixed. Further, the diversity of an assemblage may reflect lateral water movements. This kind of data shows increased upwelling, or bottom-water mixing, and greater ocean circulation during glacial periods, when sea level dropped.

    Diatoms have been used similarly in historic times to chart ocean currents and track the long-term motion of Antarctic Bottom Water.

    • Shorelines: some diatoms living in brackish water have little tolerance for salinity changes and other chemicals in the water. Their habitat is a narrow band offshore or in estuaries with preferred features. Shoreline changes can alter the composition of the water and shift the boundaries of these sensitive communities.
    • Similar techniques can be used to estimate paleosalinity, paloedepth, and nutrient concentrations in different areas of the globe during different geologic ages.

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Anatomy and Morphology

copyright John Becker 1996.

Last updated: Feb. 05, 2009