02 December 2005

Tahiti coral drilling program yields exciting results

Forty-two days of drilling in three different parts of Tahiti's coral reef ended this week with scientists from nine nations "all excited and confident that the scientific objectives of the mission have been met," one of them wrote in a logbook.

The 28 scientists left the drilling vessel DP Hunter in the Port of Papeete on Nov. 16 to return to their home institutions before the next stage of the Integrated Ocean Drilling Program's Tahiti Sea Level Expedition. That will occur in mid-February when they join their onshore colleagues in Bremen, Germany, to further analyze the fossil coral core material collected from the Tahiti drilling.

"There is still a very big job ahead in Bremen and beyond, but with the incredible material we have collected over the last 42 days we should all get ready for some very exciting science with far reaching implications for understanding global sea-level and climate change and reef evolution," said Jody Webster, one of the participating scientists.

Her comment was part of her last logbook entry she has shared with visitors to the expedition's Internet website since the Oct. 8 start of coral drilling into the coral reef surrounding the island of Tahiti. Ms. Webster is a coral specialist with the James Cook University in Australia. The expedition's co-chief scientists are Gilbert Camoin of the CEREGE Institute in France and Yasufumi Iryu of Tohoku University in Japan. Other scientists are from New Caledonia, the U.S.A., Germany, the United Kingdom, Scotland, The Netherlands and Switzerland.

Most of the coral drilling took place off Maraa, a point separating Tahiti's west and south coasts. As work finished there, Ms. Webster reported, "We are now confident that we have recovered a good portion of the post-glacial (<23,000 years old) reef sequence at Maraa."

For two days, the expedition "drilled two 40-meter (131 ft.) deep holes very close to the steep shelf edge in water depths of around 80 meters" (262 ft.), modifying "our drilling technique" so that "we are now drilling with steel splits (or two half tubes) inside the core barrel rather than a complete plastic liner tube. This has greatly improved core recovery, preservation and also reduced the drilling time," Ms. Webster wrote in her logbook.

On Nov. 7, "the Seacore drillers recovered a beautiful (and continuous) three meter (9.8 ft.) section of fossil reef material." Recovery was 100% "and a sight to behold", she wrote.

The expedition is hoping Tahiti's coral will provide records of changes in sea surface temperature and information on climatic anomalies including the El Nino/Southern Oscillation events during the last ice age.

The coral drilling began off Maraa, moved to the coral reef off Tahiti's northeast coast opposite Papenoo and Tiarei, returned to Maraa and then went to the reef off Tahiti's northwest coast opposite the Commune of Faa'a, which is next to the capital of Papeete.

Drilling off the Tahiti-Faa'a International Airport started in about 60 meters (197 ft.) of water with the scientists drilling to about 80 meters (262 ft.) of fossil reef material.

During the early stages of drilling, Ms. Webster reported the recovery of core samples of rock and sediment that "are incredibly diverse, from in-place domed and robust branching coral frameworks to thick sequences of dark, well laminated sediments between and surrounding the corals. Fascinating stuff," she wrote.

When the drilling moved to the second site opposite Papenoo and Tiarei, the scientists recovered "excellent fossil coral reef material from the very earliest part of the sea-level rise following the end of the last ice age", Ms. Webster wrote in her logbook.

The drilling returned to the reef area off Maraa in early November. After drilling three holes deep into the coral, the recovered material was "fascinating with branching coral frameworks set in thick sequences of microbially derived laminated grey sediments.

"The geomicrobiologists were also jumping for joy as they identified a strange purple biofilm (or mucus) associated with tiny minerals in a cavity. Microscope work today confirmed the presence of lots of microbes," Ms. Webster wrote in her Nov. 3 logbook entry.

Tahiti was chosen for the coral drilling "because the island is located in a tectonically stable region", according to the IODP scientists. "Consequently, changes in sea level here can be related solely to global effects. Because the corals off Tahiti have strict ecological requirements and are extremely sensitive to environmental changes, both natural and human-induced, they are accurate, sensitive recorders of past sea level and climatic change."

The Tahiti Sea Level Expedition hopes the drilling will enable scientists to learn more about the timing and course of past global sea level changes to better understand present and future sea level rise due to global greenhouse conditions.

Source: pidp.eastwestcenter.org


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