Vliv pouštního prachu z Afriky na Ameriku
A team of scientists from the U.S. Geological Survey (USGS) is tracking and collecting samples from a large African dust cloud that originated in the Sahara Desert and is moving over parts of Florida and the Caribbean. The dust cloud is the largest the team has seen since they began studying these events in 1997. The size of this event is likely related to a significant drought in West Africa last year. Millions of tons of dust are transported across the Atlantic Ocean annually. Although the transport of African dust has occurred over geologic time, the quantities have increased and the composition has changed over the last 40 years. The research is part of an ongoing investigation identifying the chemical contaminants and microorganisms traveling with the dust and their effects on ecosystem and human health. The USGS is investigating the link between African dust and declines on coral reefs throughout the Caribbean region and the relation between dust episodes and asthma attacks. Dust clouds may also play an important role in suppressing hurricane development.Introduction - The Dust Hypothesis Why have coral reefs that are bathed in clear oceanic waters throughout much of the Caribbean suffered algal infestation, coral diseases, and near extinction of herbivorous sea urchins almost simultaneously during the 1970s, 1980s, and early 1990s? The best known factors detrimental to coral reefs include sewage, run-off from land, dredging, UV light, etc. These factors do not apply for many affected reefs where human population is low. Is there an alternative way to spread nutrients and diseases? Increasing aridity and desertification in northern Africa began in the mid-1960s, was exacerbated in the 1970s and 1980s, and then began to decline in the 1990s. Is it circumstance that coral reef declines occurred during the same period as desertification? Various peaks in the dust record, at Barbados and elsewhere in the western Atlantic (Prospero and Nees, 1986), coincide with benchmark events on reefs throughout the Caribbean (courtesy of Prospero, 1997) with known coral reef perturbations.HypothesisThe hypothesis proposed here is that many coral reef events, algal infestation, white band and black band disease, sea fan disease, sea urchin die-off and possibly mass coral bleaching are somehow related to dust from north Africa. Mortality Events see the events that have affected Caribbean coralsSignificant Mortality Events That Saharan dust is deposited in the western Atlantic is demonstrated by the following:The record from Barbados and elsewhere Red iron-and clay-rich soils on carbonate islands throughout the Caribbean that are known to be of Saharan dust origin (Muhs et al., 1990) The Amazon rain forest in South America derives essential nutrients (mainly phosphate) from Saharan dust (Swap et al., 1992). The mechanisms by which dust may affect reefs include direct fertilization of benthic algae by iron or other nutrients interacting with NH4 and NO2 NO3-rich submarine ground water, and by broadcasting of bacterial, viral and fungal spores. Example: The fungus affecting sea fans throughout the Caribbean has been identified as a land-based Aspergillus sp. a fungus that does not reproduce in sea water (Smith et al., 1996).ConclusionDust may be a viable explanation for the plight of coral reefs throughout the Caribbean. The hypothesis is in need of verification.ZDROJ: USGS
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