Saharan Dust: Transport and Adverse Biological Effects in the Caribbean

1
Saharan Dust Transport and Adverse Biological
Effects in the Caribbean

• Karen Edwards
• Marine Sciences Interdisciplinary Seminar
• November 14, 2001

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Outline

• Background Global Dust
• Transport of Saharan dust
• Source
• Transport/ deposition
• Patterns/controls of transport
• Adverse biological effects
• Caribbean sea fan disease
• Red tides in the Gulf of Mexico
• Conclusions
• Climate change
• Human health

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Some Relative Sizes

• Human Hair 100 microns
• Sand 63 microns and larger
• Dust 63 microns and smaller
• Fungal Spores 1 5 microns
• Bacteria 0.2 15 microns
• Dust transported over long distances
• diameter lt 10 microns
• Saharan dust 2.5 microns
• From The Secret Life of Dust

4

• 2,350 million US tons of dust put in atmosphere
  each year
• 35 (770 million US tons) from north Africa

Perkins, 2001.
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On a Global Scale, Dust

• Affects radiative properties of the atmosphere,
• Serves as a reactive surface for atmospheric
  gases,
• Adds minerals and nutrients to ocean,
• Affects air quality and visibility and
• Affects human health.

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Atmospheric vs Riverine Inputs to Ocean
Units 109 moles/yr Jickells, 1995.
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Global Distribution of Deserts
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TOMS Satellite Image
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Saharan Dust
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Major African Vegetation Zones
deMenocal, 1993.
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Sources of Fine-grained Dust

• Arid regions
• Ancient sedimentary basins
• Topographical lows
• Sediments from
• wadis,
• lake and playa,
• alluvial fans, and
• alluvial floodplains

?Expect to see highly weathered
particles. Prospero, 1999.
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Size Distribution of Dust Particles

• Function of many factors including
• Physical properties of the soil matrix
• Condition of the surface, and
• Wind field above the surface.
• Prospero, 1999.

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How Is Dust Mobilized?
16-17 September 1994 Karyumpudi et al., 1999
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The Saharan Air Layer
N
S
Karyampudi, 1999.
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The Saharan Air Layer
Latitude 20.5N Karyampudi, 1999.
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The Saharan Air Layer
Longitude 22W Karyampudi, 1999.
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The Saharan Air Layer Dust Mobilization

• Dust plume within easterly wave troughs
• SAL well-mixed, 5-6km deep
• Rise of the SAL bottom/sinking of top
• Mixing with marine layer
• Inversion layer due to temperature differences
• Middle-level jet near southern edge
• Maximum dust concentration in ridge-region to
  north of middle-level jet
• Karyampudi, 1999.

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Transport Across the Atlantic
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Summer vs. Winter Atmospheric Circulation Patterns
deMenocal, 1993.
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Transport Across the Atlantic
Perry et al., 1997.
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Saharan Dust over the Caribbean
http//eol.jsc.nasa.gov/debrief/STS065/STS065-75-4
7.htm
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• The wind had been for twenty-four hours
  previously E.N.E., and hence, from the position
  of the ship, the dust probably came from the
  coast of Africa. The atmosphere was so hazy that
  the visible horizon was only one mile distant.
• Charles Darwin, 1845

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Average Barbados Dust Concentration
http//coastal.er.usgs.gov/african_dust/barbados.h
tml
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Increase in Dust Transport
Prospero Nees, 1986.
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Saharan Dust and the NAO
1986, Low-NAO index (0.28) 1989, High-NAO index
(4.73)
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NAO Control of Dust Export
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Summary Saharan Dust Transport

• Topographical lows produce heavily weathered
  particles
• Easterly waves in the summer pick up dust
• Saharan Air Layer carries dust
• ITCZ controls the latitude of transport
• Correlated to rain fall deficits controlled by
  the NAO

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Biological Effects
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Biological Effects of Saharan Dust

• A significant source of primary nutrients to the
  ocean.
• Experiments have shown ocean basins may be Fe
  limited ? input of iron stimulates primary
  production.
• Adverse effects
• Aspergillosis of sea fans (gorgonian corals)
• Red tides in the Gulf of Mexico

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Sea Fan Disease

• In 1983 and again in the mid-1990s a
  Caribbean-wide epizootic pathogen affecting the
  sea fans Gorgonia ventalina and G. flabellum was
  reported.

http//earthobservatory.nasa.gov/Study/Dust/
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Sea Fan Disease
Nagelkerken et al., 1997.
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Sea Fan Disease
Nagelkerken et al., 1997.
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Sea Fan Disease

• The pathogenic agent soil fungus Aspergillus
  sydowii.
• Does not reproduce in seawater.

Shinn et al., 2000., Weir et al., in press.
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Microbial data of air samples collected on St.
John, USVI

• July 23 Dust
• 12 isolates 4 plant pathogens
• July 26 Dust
• 35 isolates 7 plant pathogens

Griffen et al., 2001.
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Microbial data of air samples collected on St.
John, USVI
Griffen et al., 2001.
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Microbial Data of Air Samples

• Cultivatable organisms
• 0.23/liter cultivatable microbes in dust season.
• 0.01/liter cultivatable microbes in non-dust
  season.
• Organisms from dust caused disease in healthy sea
  fans.
• Griffen et al, 2001, Weir et al, in press.

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Red Tides Florida Red Tide Bloom of Gymnodinium
breve
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Saharan Dust and Florida Red Tides

• Walsh and Steidinger propose a causal chain of
  events to permit landfall of large red tides on
  west Florida beaches
• Summer Saharan dust events
• Sufficient rainfall
• Dissolution of aeolian iron
• Seed stocks of both T. erythraeum and G. breve
• Release of DON to all dinoflagellate competitors
• Selective grazing stress on other dinoflagellates
  as well as diatoms, and
• Onshore flows to complete landfall.

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1. Dust Concentration at Miami
Lenes et al., 2001.
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2. Miami Rainfall
Lenes et al., 2001.
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3. Atmospheric vs Riverine Fe Input
Duce and Tindale, 1991.
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3. Fe(II) vs. Fe(III)
Duce and Tindale, 1991.
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3. Photoreduction of Fe(III)

• At a pH of 2.5-5 the following reaction may
  produce Fe(II)
• Fe(OH)(H2O)52 H2O hvgtFe(H2O6)2(OH)aq
• Duce and Tindale, 1991.

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4. ECOHAB Cruise Track
Lenes et al., 2001.
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4. Cruise Results
Large red tide of gt 5 x 106 cells/L in October
1999 Lenes et al., 2001.
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5. Bloom Dynamics

• July 1999 total dissolved iron 16 nmol/kg
• Trichodesmium surface stock of 20 colonies/L.
• DON reached 15-20µM
• This organic nitrogen could have supported the
  red tide of gt20µg chl/L of the toxic
  dinoflagellate, Gymnodinium breve, found on the
  West Florida Coast during October 1999.
• Lenes et al., 2001.

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Iron Limitation of Trichodesmium

• Molar particulate N/Fe ratios
• 465 for Trichodesmium
• 5,000 for nitrate-using diatoms
• 16,000 for smaller ammonium-using
  dinoflagellates
• Trichodesmium severe Fe limitation
• kFe of 1.0 nmol Fe/kg
• background levels lt0.1 nmol Fe/kg
• Walsh and Steidinger, 2001.

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Time Series of Tricho. and G. breve
Walsh and Steidinger, 2001.
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Saharan Dust and Florida Red Tides

• Walsh and Steidinger propose a causal chain of
  events to permit landfall of large red tides on
  west Florida beaches
• Summer Saharan dust events
• Sufficient rainfall
• Dissolution of aeolian iron
• Seed stocks of both T. erythraeum and G. breve
• Release of DON to all dinoflagellate competitors
• Selective grazing stress on other dinoflagellates
  as well as diatoms, and
• Onshore flows to complete landfall.

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Conclusions
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Conclusions

• Transport of dust well-established
• Controlled by NAO
• Increased Desertification
• Adverse Biological Effects
• Pathogens in the dust
• Aspergillus in sea fans
• White plague bacteria
• Iron in the dust
• Red Tides in the Gulf of Mexico
• More work needs to be done

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Climate Effects

• Saharan dust cools climate warming estimates.
• Dust clouds - suppress rainfall making dry
  conditions even drier.
• www.gsfc.nasa.gov/gsfc/earth/

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Effects on Human Health

• 1997 EPA PM 2.5 standard
• NIH identifies airborne dust as the primary
  source of allergic stress worldwide
• 17-fold increase Barbados asthma 1973-1996
• Griffen et al., 2001.

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Thanks
Eugene Shinn, and Garriett Smith for sending
papers. Marc Alperin, John Bane, Conrad Neumann,
Hans Paerl, Cisco Werner Alfredo
Arechavaleta, Sarah Carr, Melanie Meaux, Melissa
Southwell
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References
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The Loop Current
http//www.rsmas.miami.edu/ryan/oc/atlantic/loop-
current.html
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Processes to Create Fine-grained Dust

• Precipitation in the highlands weathers rocks and
  soils.
• Fine particles are carried downstream to the
  basin and deposited in river channels and wadis.
• In the dry season, the deposits become exposed,
  dry out, crack and flake.
• When wind velocity increases, the disrupted soil
  surface is easily deflated, and clouds of
  fine-grained dust are carried away.
• ?Expect to see highly weathered particles.
• Prospero, 1999.

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Diadema 1983 Die-off

• In January 1983 there was a mass mortality of
  Diadema on the Caribbean coast of Panama
• By September 1983 this mortality had extended to
  many other areas of the Caribbean.
• Population densities of Diadema were reduced to
• 1.1- 5.8 of their previous levels in Panama,
• 1 in Jamaica and
• 0.6 in Curaçao.

Lessios, 1984. http//coastal.er.usgs.gov/afric
an_dust/diadema.html
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Diadema Mass Mortality

• Initial outbreaks of Diadema mortality followed
  Caribbean surface water circulation.
• September 1983, die-offs occurred at Barbados,
  upstream from any affected areas.

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Caribbean Transport

• A dust-born pathogen
• Impact Panama in January and
• By summer affect the entire Caribbean.
• Provide a source of the pathogen to Barbados and
  other isolated regions.

Shinn et al., 2000 Roberts, 1997.
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Theories

• Sedimentation, runoff from land, sewage,
  pollution, ship groundings, temperature, etc.
• New hypothesis Saharan dust is a contributor to
  coral reef decline. (Shinn, 2000).

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Barbados Mineral Dust Annual Average and
Benchmark Caribbean Events
http//coastal.er.usgs.gov/african_dust/barbados.h
tml
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The ITCZ
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Australian, Gobi and Saharan Dusts

• Australia
• particle size modes 8 12 µm
• highly aggregated soil
• large quantities of clay pellets
• The Gobi
• Stony desert
• Main dust source in China is the Tarim basin
• Saharan
• mode at 2-3µm
• Prospero, 1999.