June-July
2007
Christmas in August
Researchers prepare for field project
in remote tropical Pacific
About two dozen researchers from EOL are gearing up for
a trip to Christmas Island, a coral atoll near the equator
roughly 1,300 miles (2,100 kilometers) south of Hawaii. The
island’s remote marine environment will serve as an
outdoor laboratory for the team to study the chemistry and
physics of sulfur in the atmosphere.
Dubbed PASE, the Pacific Atmospheric Sulfur Experiment
runs August 2–September 10. The research team will
make airborne observations from the C-130 during flights
undertaken about every other day.
“In order to understand the whole global atmosphere,
we have to break it down into manageable chunks by going
out and studying one phenomenon,” explains Chris Cantrell,
one of NCAR’s co-investigators for PASE. “In
this case, we’re looking at what happens to sulfur
compounds that come out of the ocean and turn into gas species
and aerosols.”
Christmas Island, where PASE takes
place, is part of Kiribati, a Pacific island nation
that consists of 33 atolls straddling the equator
and the International Date Line. (Image courtesy
CIA World Factbook.) |
At the center of PASE is dimethyl sulfide (DMS), a sulfurous
gas produced naturally by phytoplankton (microscopic algae
in the ocean) that, along with salt, gives the sea its
distinctive smell. Scientists estimate that marine DMS
produces about 50% of the natural sulfur in Earth’s
atmosphere.
When DMS is released from seawater into the air, it is
oxidized to form sulfuric acid, which in turn can
generate sulfate aerosols. The aerosols have the direct
effect of reflecting sunlight back to space, cooling the
atmosphere. They also have an indirect effect on Earth’s
climate by functioning as cloud condensation nuclei, attracting
molecules of water that condense around them and form clouds.
Clouds have a major impact on Earth’s temperature
and climate.
“The more we study aerosols, the more we keep finding
out,” Chris says. “We’ve been interested
in sulfate aerosols for a long time, so it’s an opportunity
for us to get some more data.”
Because Christmas Island is situated in the trade winds
(the prevailing wind pattern in the tropics), cloud-free
periods are common during August and September. During
the campaign’s first phase, researchers will study
the chemistry and physics of gases and aerosols in a cloud-free
environment. During the second phase, they’ll try
to develop a better understanding of how aerosols form
in the outflow of marine cumulus clouds.
Christmas Island is an ideal setting for PASE because
the island is far from anthropogenic (human-produced) sources
of atmospheric sulfur, such as industry, that may taint
measurements. In addition, the surrounding ocean waters
produce consistently high levels of DMS.
It’s not an easy place to run a field campaign,
though. Everything on the island is imported, including
food, drinking water, and other necessities. No international
carriers provide service to the island via air or sea,
and there is only one major road. A C-17 military aircraft
will transport all supplies for PASE to Christmas Island,
including a satellite dish. The researchers will stay at
a hotel that has pre-ordered food supplies from Hawaii.
“Christmas Island is part of a developing country,
so things like Internet communications are just beginning
to show up,” says Vidal Salazar (EOL), logistics
coordinator for PASE. “It’s nothing like Bora
Bora or Tahiti.”
On the Web
More
about PASE
Where
in the world is Christmas Island? |
There
are actually two Christmas islands. One is a territory
of Australia located in the Indian Ocean about 1,600
mi (2,600
Christmas Island is the
largest coral atoll in the world, measuring
248 square miles (642 square kilometers)
including a large infilled lagoon. (Image
courtesy NASA Earth Observatory.) |
km) northwest of Perth and 300 mi (480 km) south
of Jakarta, Indonesia.
The other, where PASE takes place, is part of
Kiribati, an island nation that consists of 33
far-flung atolls straddling the equator and the
International Date Line. The islands extend about
2,400 mi (3,900 km) from west to east and about
1,300 mi (2,100 km) from north to south. Their
combined land area is roughly 310 square mi (810
square km). Christmas Island occupies 248 of those
square miles, giving it the largest land area of
any atoll in the world.
Kiribati, pronounced kee-ree-bus, is a local
variant of the word Gilbert. The Gilbert Islands
became part of Kiribati when the nation gained
independence from Britain in 1979. Kiribati’s
unusual spelling is accounted for by the fact that
the written Kiribati language lacks the letter “s” and
represents that sound with “ti” instead.
Christmas Island, known in the local language
as Kiritimati (kee-rees-mass) Island, was named
by Captain James Cook, who on December 24, 1777,
became its European discoverer. During World War
II, the island was a staging area for the Pacific
theater, and in 1957 Britain exploded its first
hydrogen bomb there. Today, the island has a population
of about 5,000. Most government services are located
in London, on the northern end of the island. The
island is an important seabird nesting site that
attracts an estimated six million birds each year. |
In this issue...
Christmas
in August
Nuts
about science
NCAR
welcomes new researchers
SOARS
protégés in the thick of another summer
Just
before Sunrise....
Strong
winds damage hangar roof at Jeffco
Short
Takes
Bill
Randel to lead ESSL/ACD
Just One Look
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