The Dust Hypothesis: Why Caribbean coral reefs have suffered during the 1970's through the early 1990's

Precht, Bill Bprecht at
Mon Dec 23 11:01:05 EST 2002

Dear Coral List:

For those following the "dust" for the past few years I thought you might
find these tidbits of interest.

Have a great holiday!
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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?


   Online mini-movie

      Watch USGS scientists Ginger Garrison, Gene Shinn, Chuck Holmes, and
      Dale Griffin in "The Effects of Globally Transported African and
      Asian Dust on Coral Reef and Human Health"

   National Public Radio interview

      Project scientists Gene Shinn and Ginger Garrison were interviewed
      along with geologist/novelist Sarah Andrews on National Public Radio
      station KQED in San Francisco on the popular morning talk show
      "Forum" on January 15, 2002. Listen to the interview.


Mercury From China Rains Down on California

   Environmental News Service (ENS)

   December 20, 2002

SANTA CRUZ, California, - Industrial emissions in Asia are a major source
of mercury in rainwater that falls along the California coast, a new study

The mercury in rainwater is not in itself a health threat, but mercury
pollution is a problem in San Francisco Bay and other California waters
because the toxic element builds up in the food chain. State regulatory
agencies are looking for ways to reduce the amount of mercury entering the
state's waters from various sources.

It is not just the mercury itself but a whole cocktail of atmospheric
pollutants that contribute to the deposition of mercury in rainfall.
Elemental mercury behaves as a gas in the atmosphere and is not washed out
in rain until it has been oxidized into a charged ionic form that can be
captured by water droplets.

Ozone, a major component of urban and industrial smog, plays a key role in
this oxidation process, said Douglas Steding, lead author of a paper
published Thursday in the online edition of the "Journal of Geophysical
Research - Atmospheres." The report by Steding and other researchers from
the University of California, Santa Cruz (UCSC) will appear in a later
print edition of the journal.

"There is a relatively large reservoir of mercury in the atmosphere, and
it's the rate of oxidation that determines how much of it gets deposited in
rainfall," Steding said.

Mercury is a trace contaminant of most coal, and emissions from coal
burning power plants are a major source of mercury pollution in many parts
of the world. In the Pacific Basin, the main source of atmospheric mercury
is coal combustion in China.

China relies on coal as a fuel and accounts for about 10 percent of the
total global industrial emissions of mercury.

Air pollution in China also generates ozone, which peaks during the winter
due to increased fuel consumption for heating. Air loaded with mercury and
ozone moves off the continent into the Western Pacific, where it is
incorporated into developing storms.

"The mercury we measured in rainwater results from a combination of mercury
emissions and ozone production, as well as meteorological factors - the
storm tracks that transport the pollutants across the Pacific," Steding

Steding collected rainwater samples at two sites in central California: on
the coast at UCSC's Long Marine Laboratory and at Moffett Field near San
Jose, on the inland side of the Santa Cruz Mountains. For each rainfall
event, the researchers used air mass trajectories calculated by a national
climate lab to trace the movement of the storms across the Pacific from

Rainwater collected at the coastal site showed the background
concentrations of mercury in storms as they arrived off the Pacific Ocean.
Those measurements were about three times higher than estimates of the
natural, preindustrial level, Steding said.

Rainwater from the inland site showed mercury concentrations 44 percent
higher than at the coastal site. Steding attributed the difference between
the two sites to ozone in Bay Area smog, rather than local emissions of

"There is a local influence of urban smog on the mercury oxidation rate. We
see a background signal of mercury blowing off the Pacific, then a local
enrichment that's probably due to urban smog," Steding said. "If we want to
reduce mercury deposition, it's not enough to shut down local emissions of
mercury, because other pollutants influence how much of the mercury in the
atmosphere ends up in rainwater."

Steding said people should not worry about health effects from the mercury
in rainwater, because the concentrations are very low. But the deposition
in rain does add mercury to surface waters, where the toxin enters the food
chain and builds up to high levels in certain kinds of fish.

State health officials have issued advisories warning people not to eat
fish from more than a dozen bodies of water in California, including San
Francisco Bay.

  #  #  #


Steding, Douglas J.; Flegal, A. Russell

Mercury concentrations in coastal California precipitation:
Evidence of local and trans-Pacific fluxes of mercury to North America


19 December 2002


Mercury In California Rainwater Traced ...

ScienceDaily News Release

... Steding emphasized that people should not worry about health effects
from the mercury in rainwater, because the concentrations are very low.

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