Biologic and geologic responses to physical processes: examples from modern reef systems of the Caribbean-Atlantic region

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Coral reefs and associated depositional environments of the Caribbean-Atlantic region have characteristics that reflect control by physical processes, both oceanic and atmospheric. Wave direction and wave power help determine sites for productive reef development and shape reef morphology as well as community structure. Spur and groove orientations reflect changes in direction of waves as they refract across a reef-dominated shelf. Abrupt topography of reef-dominated shelf margins interacts with tidally modulated flows to create an energetic and productive deep reef environment which is buffered from the modifying effects of forceful wave action. Shallow wave-reef interactions involve dissipative effects of wave breaking, turbulence, and friction, resulting in measured wave energy transformations ranging from 72 to 97% depending on reef configuration and water depth. Dissipative processes produce strong reef-normal surge currents that transport sediment lagoonward, drive backreef lagoon circulation, and influence fluid flow and diagenesis within the reef. The intensity of these processes is modulated at the tidal frequency. Other long period waves (infragravity) are important agents of mass transport of water and fine sediment. Low speed, long duration currents forced by long waves are potentially important for transporting larvae as well as fine sediment out of a given reef-lagoon system. Ocean-scale currents impinging on steep island and continental margin topography may cause reef-limiting upwelling and nutrient loading. The Caribbean Current upwells on the Nicaragua shelf and carbonate platforms of the Nicaraguan Rise. High trophic resources favor algal rather than coral communities and large (20-30 m relief) Halimeda biotherms occupy niches normally reserved for coral reefs. Thermodynamic air-sea interactions (heat, moisture and momentum flux) regulate the physical properties of reef lagoon and bank top waters. In extra-tropical reef settings (e.g. Bermuda, Florida, Bahamas and Arabian Gulf) cold air outbreaks cause precipitous drops in bank water temperatures and significant increases in bank water salinity and suspended sediment load. Water temperatures are routinely forced below the limit for survival of reef corals and many species of calcareous green algae. Associated increases in the density of shallow waters produce a disequilibrium with surface waters of the adjacent ocean favoring shelf transport to deep water sites of reef development and beyond. © 1992.

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Continental Shelf Research

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