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Systematic Mapping of Bedrock and Habitats along the Florida Reef Tract—Central Key Largo to Halfmoon Shoal (Gulf of Mexico)

USGS Professional Paper 1751

by Barbara H. Lidz, Christopher D. Reich, and Eugene A. Shinn

Introduction: Table of Contents Project Overview Project Objective Geologic Setting Primary Datasets Primary Products - Overview Maps & Evolution Overview: Introduction Depth to Pleistocene Bedrock Surface Reef & Sediment Thickness Benthic Ecosystems & Environments Sedimentary Grains in 1989 Summary Illustration Index Map Evolution Overview Tile-by-Tile Analysis Organization of Report Tiles: 1, 2, 3, 4, 5, 6, 7/8, 9/10, 11 Summary Acknowledg- ments References Disclaimer Related Publications

Tile 7/8 Geography Sector-Specific Studies Natural Stressors: Atmospheric, Terrestrial, and Oceanic Sources Introduction Natural Stressors Atmospheric Sources Terrestrial Sources Oceanic Sources Hurricanes, Storm Surge, and Rising Sea Level Geologic Highlights Margin Evolution Flooding the Florida Shelf Addendum Ephemeral Islands and Lighthouses Oceanic Sources: Over long time scales, the greatest oceanic stressor is the fluctuation in global sea level that accompanies glacial (low) and interglacial (high) periods. Other oceanic stressors include fluctuations in deep-ocean circulation (Lee et al., 2002), upwelling of deep-ocean cells from the Gulf of Mexico and Straits of Florida (Lee et al., 2002), and tidal exchange of shallow, turbid Florida Bay and Biscayne Bay waters with clear oceanic water on the reefs (e.g., Tomascik and Sander, 1985; Smith, 1994, 1998). During upwelling events, cold Gulf Stream waters high in phosphate spill briefly over the coral reefs (Leichter et al., 2003). These processes import turbidity, high salinities, low temperatures, and nutrients that are harmful to coral growth. In the south half of the Florida peninsula, natural direction of flow of both surface and groundwater through porous limestone is to the south, toward the offshore reefs (e.g., Douglas, 1947; Porter and Porter, 2002; Reich et al., 2002; Fig. 25A, 25B). Nutrients and chemical pollutants from the Mississippi River watershed and west coast Florida rivers and farmlands reach the reefs via the Gulf Loop Current and Florida Current (e.g., Day et al., 1995; Lee et al., 2002). These current-related events can also change the normal oceanic salinity over the reefs and can increase turbidity. Deep-ocean currents also link waters along the reef tract to those flowing from the north coast of Cuba and the Caribbean (e.g., Lidz and McNeill, 1998; Lee et al., 2002). The world oceans have absorbed carbon dioxide released by human activity in the last century. The process has removed it from the atmosphere, but at a cost to coral reefs and other marine life. Increasing oceanic concentration of atmospheric carbon dioxide reduces calcium-carbonate saturation in surface waters by reducing the pH of ocean water (Kleypas et al., 1999; Downs et al., 2002; Caldeira and Wickett, 2003; Langdon et al., 2003; Marubini et al., 2003, among many others). The lower pH of ocean water means that those organisms that secrete calcium carbonate will do so at much slower rates, affecting the growth and health of their calcium-carbonate skeletons. A lower pH also acidifies the water, making the water more corrosive to existing shells and skeletons of calcium carbonate. Doubling of atmospheric carbon-dioxide concentration over pre-industrial concentration in the 21st century is predicted to reduce carbonate production in tropical shallow-marine environments by as much as 80% (Hallock, 2005). continue to: Hurricanes, Storm Surge, and Rising Sea Level

Coastal & Marine Geology Program > Center for Coastal & Watershed Studies > Professional Paper 1751