Image of the Day: The Great Blue Hole

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The Great Blue Hole, a World Heritage site,  is a large underwater sinkhole off the coast of Belize. Jacques Cousteau took the Calypso and his one-man submarines into the hole in 1972 to examine stalactites suspended from overhanging walls. The Great Blue Hole is surrounded by shallow water of Lighthouse Reef Atoll, a nearly perfect circle in the middle of a shallow reef. 

In 1997, geologist Robert F. Dill and divers from the Cambrian Foundation, an organization of mixed-gas divers, visited the Great Blue Hole to collect stalactites for isotopic dating and sea-level studies. Two divers descended 407 ft and obtained two short push cores. Preliminary analyses of the short cores showed fluctuating pollen, spores, mercury, and arsenic levels. Arsenic ranges between 15 and 21 ppm.. The storm layers are light-colored, beautifully laminated, and are distinct from the darker organic and clay-rich sediments representing slow deposition. These sediments provide a long-term record of climate, mercury, arsenic, and African dust flux.

The Belize Great Blue Hole is located far from industrial sources of aerosols but is well within the area affected by silica- and clay-bearing African soil dust. African dust is deposited in the Caribbean mainly between June and October. The hole thus serves as a giant sediment trap where the overall sedimentation rate is slow and layering is preserved due to anoxic conditions. 

http://soundwaves.usgs.gov/2001/06/

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