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Science & Technology

September 1, 2008
Volume 86, Number 35
pp. 57-60

Geotraces Gets Going

Largest ever ocean chemistry study will span about 20 years

Rachel Petkewich

NEARLY THREE-QUARTERS of the globe is covered by oceans that humans know very little about. To tease apart the chemistry of these vast waters, marine geochemists and chemical oceanographers typically have gone to sea and collected data to profile individual trace elements and isotopes such as iron (see page 62), zinc, or lead.

But these isolated studies make figuring out the interrelated chemical nature of the oceans nearly impossible. Fueled by concerns about how climate change could affect ocean chemistry and armed with several technological advances for conducting oceanographic research, scientists from around the world now hope to address those issues with a concerted project of unprecedented scope called Geotraces.

Gregory A. Cutter
Bottled Seawater Specially designed carousels of 12-L bottles will collect water samples.

The largest research program ever focused on the chemistry of the oceans, Geotraces aims to understand how the broad array of trace elements and isotopes in the ocean behave and how their behavior ultimately affects the global carbon cycle and climate, says chemical oceanographer Robert F. Anderson of the Lamont-Doherty Earth Observatory at Columbia University. He is cochairing the Geotraces' Scientific Steering Committee with geochemist Gideon M. Henderson of Oxford University.

Perhaps the most pressing reason to do this study now, according to participant scientists, relates to understanding climate change. Chemical oceanographers need to characterize distributions of trace elements and isotopes in the ocean and establish a baseline for future comparison before human activities elicit further changes.

Trace elements including aluminum, manganese, cadmium, and neodymium, or stable isotopes such as 15N and 13C give unique information about the continental sources of these elements. Radioisotopes such as 230Th and 231Pa provide information about the fates of trace elements, such as the rates at which they absorb onto various kinds of organic and inorganic oceanic particles.

"By studying a suite of elements together, we can learn a lot more about the whole ensemble than we can by studying one element alone," Anderson says. He adds that "the community realized a few years ago that to make a big advance in understanding how these elements and isotopes operate in the ocean, we all need to work together." The project involves chemical oceanographers, marine geochemists, paleoceanographers, radiochemists, and trace-metal chemists, as well as researchers studying contaminants and modeling.

PLANNING FOR GEOTRACES began in 2001 and is expected to take about a decade, and research and data-collecting expeditions will take another decade, commencing within the next year, Anderson says. The initial components of a science plan were put in place at a meeting of about 85 scientists from 15 countries in Toulouse, France, in 2003. To date, scientists from 30 countries have participated in planning. Anderson explains that the entire project will be funded by individual governments and likely will include research ships from a dozen countries.

All of that makes it hard to put a price tag on this kind of a project, Anderson explains. But he estimates that a total of about $200 million will be needed to support the scientists' research needs.

"Preliminary results from the Antarctic cruises already show exciting findings."

That may not sound like much compared with other ocean studies or, say, putting a satellite into orbit, but keep in mind that the figure doesn't include ship costs. Each government usually keeps separate accounting for ship costs, which run about $40,000 per day for expeditions that can last for months. For example, chemical oceanographers generally do not include ship costs when writing a proposal for research funding to the National Science Foundation because NSF has a separate ship budget.

Though Geotraces may be the largest global chemical oceanography study, it is certainly not the first. Global-scale investigation of trace elements and isotopes has evolved significantly since the 1970s' pioneering Geochemical Ocean Sections Study (GEOSECS). Thanks to recent advances in "clean," contaminant-free sampling protocols and the development of sensitive analytical techniques such as multiple-collector plasma source mass spectrometry, oceanographers can now measure a wider range of metal elements and isotopes more precisely, accurately, and faster than before.

In addition, researchers now know how to use elemental and isotopic information to reconstruct the history of the ocean, which, combined with powerful new modeling capabilities, is important for predicting the ocean's future behavior.

To make the most of the upcoming data collection expeditions, researchers involved with Geotraces are doing several different types of work. Some scientists are securing funding or consulting with modelers. Many researchers include modeling in their projects almost as an afterthought, but the researchers with Geotraces are involving modelers even before setting off on an expedition, says Edward R. Urban, executive director of the Scientific Committee on Oceanic Research, a nongovernmental organization that coordinates international ocean studies. This forethought, the researchers say, should help make sure that the data they collect will be of the type and form that are useful for modelers.

Much of the current work that scientists are doing for Geotraces is centered around testing specially designed water sampling equipment and making sure systems to deposit, archive, and access data are in place and comply with the laws of the participating countries.

In June and July, a group of Geotraces researchers conducted a five-week "intercalibration cruise" in the Atlantic Ocean near Bermuda to make sure all of the participants in the expeditions are on the same page in terms of sampling equipment and analytical analyses, says Gregory A. Cutter, a chemical oceanographer at Old Dominion University in Norfolk, Va., and chair of the Geotraces Intercalibration Committee.

Geotraces is not requiring that scientists use any one specific analytical method. In a research program that is going to last a decade, it is unwise to dictate a method that might limit participation or stifle innovation in analysis, Cutter says. So on the Bermuda trip, the researchers tested different samplers and hauled up 30,000 L of water from different locations and depths in the ocean. These samples have been shipped to researchers who plan to participate in the future trace element and isotope data collection expeditions so they can all verify their analytical equipment and methods now. The second intercalibration cruise is planned for next year in the Pacific Ocean off California, and related intercalibration exercises will continue on all Geotraces research expeditions, Cutter adds.

Gregory A. Cutter
Keep It Clean To keep samples free of trace-metal contamination, researchers prepare water samples for storage in a plastic clean room built inside a 20-foot cargo container on the deck of a research ship.

All of the data from Geotraces have to go somewhere accessible to researchers involved now and in future generations. Although individual countries will likely keep data repositories, a central Web-based database will be housed at the British Oceanographic Data Centre in Liverpool, England. The database will corral chemical measurements and metadata such as methodologies, says Christopher Measures, a chemical oceanographer at the University of Hawaii, Manoa, who cochairs the Geotraces Data Management Committee with Reiner Schlitzer of the Alfred Wegener Institute in Bremerhaven, Germany. Measures adds that checking the quality of the data will be important so theories about the composition and chemistry of the oceans are not developed from bad data.

EARLIER THIS YEAR, Geotraces researchers collected the project's first data???from the Antarctic???aboard vessels operated by Germany, France, and Australia; these expeditions were affiliated with another international research program. Anderson says the scientists collecting data plan to report those first results from Geotraces at the American Society for Limnology & Oceanography meeting in Nice, France, in January.

Planning for expeditions dedicated to Geotraces is well along, Anderson says. Canada has funding for an expedition to the Arctic Ocean in 2009. Japan's cruise to the Indian Ocean scheduled for 2009 was delayed to 2010 due to unexpected increases in fuel prices. The U.S. expects to set sail in the Atlantic in 2010 and the Pacific in 2012. A U.K. cruise to the South Atlantic is funded but not scheduled yet. Germany, the Netherlands, and China have proposals in to their respective governments.

"By no means will we wait until the end of Geotraces to start publishing," Anderson adds. "Preliminary results from the Antarctic cruises already show exciting findings, such as never-seen-before large emissions of iron associated with hydrothermal vents at midocean ridges."

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