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Abstract: Did Dust Do It?

SHINN, E. A., USGS Center for Coastal Geology, St. Petersburg, Florida


Shelf areas occupied by Holocene coral reefs throughout the Caribbean and Florida were flooded by post-glacial sea-level rise beginning around 6,000 ka. The rate of rise was ~1 m/1000 yr. During the past 6,000 years of flooding, reef corals that grow slowly, Montastraea annularis (~7 mm/yr=7 m/1000 yrs) and Porities porities (14 mm/yr=14 m/1000 yrs) could have grown upward 42 and 84 m, respectively. In addition, corals with higher growth rates, Acroporids (~10 cm/yr=100 m/1000 yr), considered to be important reef framework builders, could have grown 600 m vertically. Other contributing reef species with intermediate growth rates also have large growth potential. Considering all species, coral reef growth should have easily kept pace with rising sea level during the past 6,000 years. However, less than 5% of Caribbean coral reefs have actually kept pace with post- glacial sea-level rise, and areas of exposed Pleistocene limestone are not uncommon on Caribbean reefs. What events or combination of events prevented coral reefs from keeping pace with rising sea level during the past 6,000 years?

It is speculated that African aerosols, (estimated I billion tons/year), have impacted reefs throughout the Quaternary. Close agreement between peak dust-fall years at a Barbados collection site and significant outbreaks of macroalgae, coral diseases, and die-offs of reef-building organisms suggest a causal relation. It is hypothesized that nutrients, including iron, and possible pathogens such as fungal spores, and bacteria embedded in African dust, combined with hurricanes and cold-water events, have periodically devastated corals and prevented Caribbean reefs from keeping pace with rising sea level during the past 6,000 years.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah