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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

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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