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In 1999, the U.S. Geological Survey (USGS) donated the central exhibit for the dedication of Windley Key Fossil Reef Geological State Park and its Alison Fahrer Environmental Education Center. Yet another exhibit was added early this year. The park and environmental-education center are located in an old quarry on Windley Key, FL, within the Key Largo Limestone, a fossil coral reef of Pleistocene age.
The new exhibit showcases a modern coral sample collected more than 25 years ago that has yielded copious information about historical climatic events.
Working out of the USGS Fisher Island Field Station in Miami Beach in 1975, Harold Hudson (now chief restoration officer with the National Oceanic and Atmospheric Administration [NOAA]'s Florida Keys National Marine Sanctuary, Key Largo) and Bob Halley (now a geologist at the USGS St. Petersburg Science Center [CCWS] in St. Petersburg, FL) cored one of the largest and oldest living head corals in the Florida Keys, recovering a core 4 inches in diameter and 10 feet long. The core was slabbed, and X-ray photographs were prepared. Harold measured and counted the annual growth bands in the X-radiographs and determined that the coral had begun growing on Pleistocene limestone the same year that the pilgrims landed at Plymouth Rock, and so we dubbed the core the "Bicentennial Core." The photographs and core data were used in several presentations, and the core and another taken from the same coral in 1978 became the basis of a Ph.D. dissertation by Ellen Druffel.
Formerly with the Woods Hole Oceanographic Institution, Ellen, who is now a professor at the University of California, Irvine, performed year-by-year 14C analyses on the core to look for variations related to climate change and seawater circulation over the past 200 years. Among her observations, later published in Science, were that the 14C data clearly reflected the period of atmospheric nuclear testing, and she could see lowered water temperature associated with the later part of the Little Ice Age. Various stress bands are visible in the X-radiograph, including one that correlates with an 1895 cold front that killed orange groves in central Florida. Another stress band was formed during an unusually cold front in the winter of 1969-70; that cold spell killed numerous 100-plus-year-old nearshore corals. The Bicentennial Core also contains a wide stress band that formed in many corals between 1941 and 1942. We assumed for many years that this band was yet another sign of a cold winter because of its similarity to the one that formed in 1969-70. Recent studies since the late 1980s, however, have shown that water temperatures high enough to cause bleaching in corals (expulsion of symbiotic algae) can also produce stress bands. With this new information, one wonders whether bleaching due to high temperatures could have caused the 1941- 42 stress band.
Harold and the curators of Windley Key Fossil Reef State Park's environmental-education center recently prepared two displays of the Bicentennial Core. The actual core with notations and associated photographs rests alongside the coral reef geologic exhibit prepared 5 years ago by the CCWS. The other display is the X-radiograph of the core mounted vertically, with notations of historical events that occurred during the coral's lifetime. The new exhibit credits the USGS and is seen by approximately 14,000 people each year.
In addition to Florida Keys tourists, college geology and biology students and numerous high-school groups visit the quarry and environmental-education center several times each week. College geology departments across the United States send groups on field trips to the Keys to study modern carbonate processes. The National Film Board of Canada is planning a series on the geology of barrier islands that will include the USGS exhibits as a way to show the geologic development of the Florida Keys.
in this issue: Microbial Life in Antarctic Lakes
Coral Reef Exhibit
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