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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 Atmospheric Sources: Atmospheric stressors in the Florida-Caribbean region include the influx of African dust (Figs. 5, 98A, 98B). African dust has long been known to impact the Caribbean (e.g., Darwin, 1845; D'Almeida, 1986; Prospero and Nees, 1986; Muhs et al., 1990; Perry et al., 1997; Prospero, 1999) and can be observed as red (iron) layers within calcrete (Fig. 93B). Prevailing winds bring African dust to the Florida Keys primarily from June through October (Table 8). African Dust Websites in Fall 2004 ftp://jwocky.gsfc.nasa.gov/pub/eptoms/images/display_aero/y2000/ http://www.nrlmry.navy.mil/aerosol/Case_studies/19990203_sahara/19990203_sahara.html http://www.osei.noaa.gov/Events/Dust http://www.sptimes.com/News/090500/Worldandnation/What_s_in_the_wind.shtml http://coastal.er.usgs.gov/african_dust/satellite.html http://seawifs.gsfc.nasa.gov/cgibrs/level3.pl?DAY===tclr Table 8. Increasing awareness of the effects of African dust on environment and human health has led to development of websites on African dust. Figure 98. (A) Photo taken on 15 September 2000 during period of normal visibility in the U.S. Virgin Islands. View is northward to Jost van Dyke, British Virgin Islands. The nearest islands are approximately 1 km distant. (B) Photo of same view taken on 28 June 2000 shows visibility when African dust enters the region. Photos are courtesy of Virginia H. Garrison. [larger version] The impacts of dust import, some well established and some hypothesized, are numerous. Bahamian Indians made crude pottery from clays that are not native to carbonate settings. Recent studies have linked African dust with red tides (Walsh and Steidinger, 2001) and seafan and coral diseases (Figs. 3, 4, 5; Hayes et al., 1997; Shinn, 1997; Shinn et al., 2000; Weir et al., 2000; Garrison et al., 2003). Shinn et al. (2001) and Griffin et al. (2001, 2002) have suggested that microbes transported by dust may have contributed to the 1983 Caribbean-wide demise of the black spiny sea urchin Diadema antillarum (Fig. 4B) and may pose a threat to human health as well. Lessios et al. (1984) documented the extent of the urchin's demise. African dust transports more than sediment particles. Herbicides, pesticides, bacteria, viruses, fungi, nutrients, heavy metals, polyaromatic hydrocarbons, carcinogens (radioactive isotopes), and even live locusts have been carried in dust clouds to the Florida-Caribbean region (e.g., Ritchie and Pedgley, 1989; Muhs et al., 1990). Atmospheric dust is well known for producing spectacular tropical sunsets (Fig. 99). Figure 99. Typical sunset in the Florida Keys, caused by sunlight reflecting off atmospheric dust. [larger version] Ozone depletion and global warming are among atmospheric factors thought to be triggering mass coral-bleaching events (e.g., Glynn, 1984; Ogden and Wicklund, 1988; Fig. 4E, 4F). Extreme air and water temperatures stress the coastal marine system (e.g., Buddemeier and Smith, 1988; Hallock, 1988; Fanning, 1989; Hanson and Maul, 1993; McPherson and Halley, 1996; Abramovitz and Dunn, 1998; Albritton et al., 2001). Very high or very low water temperatures can cause bleaching (Fig. 4E, 4F) and can be lethal to corals (e.g., Roberts et al., 1982; Hoegh-Guldberg, 1999). Corals under temperature stress lose the ability to synthesize protective sunscreens and become more sensitive to UV rays in sunlight (e.g., Randel et al., 1995; Shick et al., 1996; Anderson et al., 2001; Fitt et al., 2001; Rowan, 2004, among others). Such photo-oxidative stress also reduces fitness, rendering reef-building organisms more susceptible to emerging diseases. Recovery from bleaching events is dependent on many factors. Recovery requires settlement of imported planktonic (free-swimming) coral larvae and a hard substrate (bottom) suitable for larval attachment (Shinn, 1976). Resettlement is affected by the effects of currents, distance from larval sources, predators, water quality, and competition, mostly with algae, for substrate. Unusually severe winter cold fronts impacted coral communities keys-wide in 1970 (Hudson et al., 1976) and again in 1977 (Porter et al., 1982; Roberts et al., 1982) when it snowed in Miami. Reefs opposite major tidal passes in the middle Keys and in exposed locations in the lower Keys were particularly vulnerable. Both events killed not only the more temperature-sensitive branching corals (Acropora spp.), but also the much hardier head corals including Montastrea annularis as far inshore as at Hen and Chickens patch reef (Figs. 42B, 45A, 45B; Hudson et al., 1976; Hudson, 1981). On the shallow shelf, storm winds churn fine-grained silts and lime mud in Florida and Biscayne Bays and in Hawk Channel into the water column, increasing turbidity (e.g., Fig. 74A). Commonly, water in Hawk Channel is so cloudy that the channel bottom cannot be seen from above (Fig. 48B). continue to: Terrestrial Sources

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