Agassiz, A., 1894. A reconnaissance of the Bahamas and of the elevated reefs of Cuba. Bulletin of the Museum of Comparative
Zoology, 26, 1–203.
Agassiz, A., 1899. The islands and coral reefs of Fiji. Bulletin of the
Museum of Comparative Zoology, 33, 1–167.
Agassiz, A., 1900. Explorations of the “Albatross” in the Pacific.
Nature 62, 307–311.
Agassiz, A., 1903a. The coral reefs of the tropical Pacific. Memoirs
Museum of Comparative Zoology, 28, 1–410.
Agassiz, A., 1903b. The coral reefs of the Maldives. Memoirs
Museum Comparative Zoology, 29, 1–168.
Agassiz, A., 1903c. On the formation of barrier reefs and of different types of atolls. Proceedings of the Royal Society London,
71, 412–414.
Darwin, C. R., 1842. The Structure and Distribution of Coral Reefs.
London: Smith Elder, 214 p.
Dobbs, D., 2005. Reef Madness: Charles Darwin, Alexander Agassiz, and the meaning of coral. New York: Pantheon Books, 306 p.
Murray, J., 1889. Structure, origin, and distribution of coral reefs
and islands. Nature, 39, 424–428.
Cross-references
Darwin, Charles (1809–1882)
Gardiner, John Stanley (1872–1946)
Reef Classification by Fairbridge (1950)
Reef Classification by Hopley (1982)
Reef Classification by Maxwell (1968)
Subsidence Hypothesis of Reef Development
AIRBORNE DUST IMPACTS
Eugene A. Shinn
1
, Barbara H. Lidz
2
1
University of South Florida, St. Petersburg, FL, USA
2
U.S. Geological Survey, St. Petersburg, FL, USA
Definition
As in the Dust Bowl of the Midwestern United States in the
1930s, arid-soil conditions exist in other countries today.
Periodically, ground-level winds associated with highenergy fronts, pick up the soils along with whatever chemical or pollutant may be associated with the source soil and
lift them into the troposphere. Wind systems such as the
trade winds transport the dust clouds with their exotic
components around the globe. Impacts of these airborne
dusts are just now being recognized. Many of the non-soil
substances such as pesticides are known to be toxic to
human health, marine life, and coral reef ecosystems.
Background
Soil dust (generally less than 10 µm in diameter) containing viable microbes, toxic minerals, radiogenic elements, feces, and modern pesticides may negatively
impact corals and coral reef-associated organisms as
well as human health and terrestrial ecosystems. Marine
impacts from this noxious mix are likely to be most pronounced in pristine clear-water areas, where corals have
not previously adapted to stressors such as nutrients, pollution, and sedimentation.
In recent years beginning in 1973, the changing climate
and desertification of the North African Sahel region
resulted in increased quantities and ongoing transport of
soil dust to the Americas (Prospero and Nees, 1986).
Shinn et al. (2000) summarized the relation between
annual variations in dust flux and coral demise. Iron, the
most consistent elemental component of soil dust, after silica, has been shown to stimulate red-tide outbreaks in the
Gulf of Mexico (Walsh et al., 2006). Red-tide outbreaks
can have devastating effects on coral reefs.
The quantity of soil dust leaving Africa each year
has been estimated to be as high as 1 billion tons
(D’Almeida, 1986). Hundreds of millions of tons reach
Caribbean reefs and the Amazon rainforest annually
(Prospero et al., 1996).
Processes
African dust periodically impacts the entire East Coast
of the US and occasionally exceeds Environmental Protection Agency atmospheric-particulate standards in
Miami, Florida (Prospero, 1999). African dust has been
transported as far west as Carlsbad, New Mexico (Perry
et al., 1990). During Northern Hemisphere winters,
African dust storms shift southward with the Intertropical
Convergence Zone (ITCZ) and are known to be a major
supplier of nutrients to the Amazon Basin (Swap et al.,
1992).
During Northern Hemisphere summers, the ITCZ shifts
northward, creating conditions conducive to dust storms
and subsequent transport of dust and adhering contaminants across the Atlantic Ocean. The same weather conditions are responsible for creation of Atlantic hurricane
formation, especially the so-called Cape Verde storms that
originate late in the season.
African dust storms initiate when strong winds lift soil
from dried lakebeds, especially in the Bodele Depression,
located in Chad in central Africa (Koren et al., 2006).
Once airborne, the dust is carried by trade winds in the troposphere (below 3,000 m) in what meteorologists call the
Saharan air layer. Dust clouds leaving northwest Africa
typically reach the Americas in 5–7 days. Recent and
ongoing studies indicate African dust storms retard or prevent hurricane formation by suppressing raindrop formation and precipitation, while at the same time shading
sunlight and cooling sea-surface waters. Dust storms also
create hazy days and beautiful sunsets.
Dust-borne winds occur at irregular intervals. Peak formation and transport are associated with positive phases of
the North Atlantic Oscillation (NAO). The NAO is the difference between pressure at the Azores High (sometimes
called the Bermuda High) and the Icelandic Low. The
NAO is dependent on the route and intensity of the trade
winds. During positive NAOs, this persistent barometric
high drifts eastward, closer to Africa where it alters meteorological conditions and suppresses rainfall. Positive
phases of the NAO thus induce droughts. The NAO is
also linked, and influenced, by the much larger El Niño
16
AIRBORNE DUST IMPACTS
Zoology, 26, 1–203.
Agassiz, A., 1899. The islands and coral reefs of Fiji. Bulletin of the
Museum of Comparative Zoology, 33, 1–167.
Agassiz, A., 1900. Explorations of the “Albatross” in the Pacific.
Nature 62, 307–311.
Agassiz, A., 1903a. The coral reefs of the tropical Pacific. Memoirs
Museum of Comparative Zoology, 28, 1–410.
Agassiz, A., 1903b. The coral reefs of the Maldives. Memoirs
Museum Comparative Zoology, 29, 1–168.
Agassiz, A., 1903c. On the formation of barrier reefs and of different types of atolls. Proceedings of the Royal Society London,
71, 412–414.
Darwin, C. R., 1842. The Structure and Distribution of Coral Reefs.
London: Smith Elder, 214 p.
Dobbs, D., 2005. Reef Madness: Charles Darwin, Alexander Agassiz, and the meaning of coral. New York: Pantheon Books, 306 p.
Murray, J., 1889. Structure, origin, and distribution of coral reefs
and islands. Nature, 39, 424–428.
Cross-references
Darwin, Charles (1809–1882)
Gardiner, John Stanley (1872–1946)
Reef Classification by Fairbridge (1950)
Reef Classification by Hopley (1982)
Reef Classification by Maxwell (1968)
Subsidence Hypothesis of Reef Development
AIRBORNE DUST IMPACTS
Eugene A. Shinn
1
, Barbara H. Lidz
2
1
University of South Florida, St. Petersburg, FL, USA
2
U.S. Geological Survey, St. Petersburg, FL, USA
Definition
As in the Dust Bowl of the Midwestern United States in the
1930s, arid-soil conditions exist in other countries today.
Periodically, ground-level winds associated with highenergy fronts, pick up the soils along with whatever chemical or pollutant may be associated with the source soil and
lift them into the troposphere. Wind systems such as the
trade winds transport the dust clouds with their exotic
components around the globe. Impacts of these airborne
dusts are just now being recognized. Many of the non-soil
substances such as pesticides are known to be toxic to
human health, marine life, and coral reef ecosystems.
Background
Soil dust (generally less than 10 µm in diameter) containing viable microbes, toxic minerals, radiogenic elements, feces, and modern pesticides may negatively
impact corals and coral reef-associated organisms as
well as human health and terrestrial ecosystems. Marine
impacts from this noxious mix are likely to be most pronounced in pristine clear-water areas, where corals have
not previously adapted to stressors such as nutrients, pollution, and sedimentation.
In recent years beginning in 1973, the changing climate
and desertification of the North African Sahel region
resulted in increased quantities and ongoing transport of
soil dust to the Americas (Prospero and Nees, 1986).
Shinn et al. (2000) summarized the relation between
annual variations in dust flux and coral demise. Iron, the
most consistent elemental component of soil dust, after silica, has been shown to stimulate red-tide outbreaks in the
Gulf of Mexico (Walsh et al., 2006). Red-tide outbreaks
can have devastating effects on coral reefs.
The quantity of soil dust leaving Africa each year
has been estimated to be as high as 1 billion tons
(D’Almeida, 1986). Hundreds of millions of tons reach
Caribbean reefs and the Amazon rainforest annually
(Prospero et al., 1996).
Processes
African dust periodically impacts the entire East Coast
of the US and occasionally exceeds Environmental Protection Agency atmospheric-particulate standards in
Miami, Florida (Prospero, 1999). African dust has been
transported as far west as Carlsbad, New Mexico (Perry
et al., 1990). During Northern Hemisphere winters,
African dust storms shift southward with the Intertropical
Convergence Zone (ITCZ) and are known to be a major
supplier of nutrients to the Amazon Basin (Swap et al.,
1992).
During Northern Hemisphere summers, the ITCZ shifts
northward, creating conditions conducive to dust storms
and subsequent transport of dust and adhering contaminants across the Atlantic Ocean. The same weather conditions are responsible for creation of Atlantic hurricane
formation, especially the so-called Cape Verde storms that
originate late in the season.
African dust storms initiate when strong winds lift soil
from dried lakebeds, especially in the Bodele Depression,
located in Chad in central Africa (Koren et al., 2006).
Once airborne, the dust is carried by trade winds in the troposphere (below 3,000 m) in what meteorologists call the
Saharan air layer. Dust clouds leaving northwest Africa
typically reach the Americas in 5–7 days. Recent and
ongoing studies indicate African dust storms retard or prevent hurricane formation by suppressing raindrop formation and precipitation, while at the same time shading
sunlight and cooling sea-surface waters. Dust storms also
create hazy days and beautiful sunsets.
Dust-borne winds occur at irregular intervals. Peak formation and transport are associated with positive phases of
the North Atlantic Oscillation (NAO). The NAO is the difference between pressure at the Azores High (sometimes
called the Bermuda High) and the Icelandic Low. The
NAO is dependent on the route and intensity of the trade
winds. During positive NAOs, this persistent barometric
high drifts eastward, closer to Africa where it alters meteorological conditions and suppresses rainfall. Positive
phases of the NAO thus induce droughts. The NAO is
also linked, and influenced, by the much larger El Niño
16
AIRBORNE DUST IMPACTS