New Method of Studying Ancient Fossils Points to Carbon Dioxide As a Driver of Global Warming

A team of American and Canadian scientists has devised a new way to study Earth's past climate by analyzing the chemical composition of ancient marine fossils. The first published tests with the method further support the view that atmospheric CO2 has contributed to dramatic climate variations in the past, and strengthen projections that human CO2 emissions could cause global warming.

In the current issue of the journal Nature, geologists and environmental scientists from the California Institute of Technology, the University of Ottawa, the Memorial University of Newfoundland, Brock University, and the Waquoit Bay National Estuarine Research Reserve report the results of a new method for determining the growth temperatures of carbonate fossils such as shells and corals. This method looks at the percentage of rare isotopes of oxygen and carbon that bond with each other rather than being randomly distributed through their mineral lattices.

Because these bonds between oxygen-18 and carbon-13 form in greater abundance at low temperatures and lesser abundance at higher temperatures, a precise measurement of their concentration in a carbonate fossil can quantify the temperature of seawater in which the organisms lived. By comparing this record of temperature change with previous estimates of past atmospheric CO2 concentrations, the study demonstrates a strong coupling of atmospheric temperatures and carbon dioxide concentrations across one of Earth's major environmental shifts.

According to Rosemarie Came, a postdoctoral scholar in geochemistry at Caltech and lead author of the article, only about 60 parts per million of the carbonate molecular groups that make up the mineral structures of carbonate fossils are a combination of both oxygen-18 and carbon-13, but the amount varies predictably with temperature. Therefore, knowing the age of the sample and how much of these exotic carbonate groups are present allows one to create a record of the planet's temperature through time.

"This clumped-isotope method has an advantage over previous approaches because we're looking at the distribution of rare isotopes inside a single shell or coral," Came says. "All the information needed to study the surface temperature at the time the animal lived is stored in the fossil itself."

In this way, the method contrasts with previous approaches that require knowledge of the chemistry of seawater in the distant past--something that is poorly known.

The study contrasts the growth temperatures of fossils from two times in the distant geological past. The Silurian period, approximately 400 million years ago, is thought to have been a time of highly elevated atmospheric CO2 (more than 10 times the modern concentration), and was found by the researchers to be a time of exceptionally warm shallow-ocean temperatures--nearly 35 degrees C. In contrast, the Carboniferous period, roughly 300 million years ago, appears to have been characterized by far lower levels of atmospheric carbon dioxide (similar to modern values) and had shallow marine temperatures similar to or slightly cooler than today-about 25 degrees C. Thus, the draw-down of atmospheric CO2 coincided with strong global cooling.

"This is a huge change in temperature," says John Eiler, a professor of geochemistry at Caltech and a coauthor of the study. "It shows that carbon dioxide really has been a powerful driver of climate change in Earth's past."

The title of the Nature paper is "Coupling of surface temperatures and atmospheric CO2 concentrations during the Paleozoic era." The other authors are Jan Veizer of the University of Ottawa, Karem Azmy of Memorial University of Newfoundland, Uwe Brand of Brock University, and Christopher R. Weidman of the Waquoit National Estuarine Research Reserve, Massachusetts.

Source: Caltech

Related stories:

Tropical quartet: 4 storms with more to come
(AP) -- The tropics seem to be going crazy what with the remnants of Gustav, the new threat from Hanna, a strengthening Ike and newcomer Josephine. Get used to it.
Climate change target may lead to 'dangerously misguided' policies
The pledge from G8 countries to cut global emissions by 50 per cent by 2050, in an effort to cut global warming to 2ºC, could lead to ‘dangerously misguided’ climate change adaptation policies, according to new research from The University of Manchester.
Phoenix Mission Conducting Extended Activities on Mars
NASA's Phoenix Mars Lander, having completed its 90-day primary mission, is continuing its science collection activities. Science and engineering teams are looking forward to at least another month of Martian exploration.
Chemist Discovers the Elusive Chemical Middleman That Removes Acid Rain
(PhysOrg.com) -- Researchers have discovered the middleman in the complex chemical reaction that is essential to the atmosphere's ability to break down pollutants, especially the compounds that cause acid rain. The study improves the basic understanding of the chemical removal of acid rain and will allow scientists to better model how pollutants are removed from the atmosphere and to predict potential environmental conditions.
2007 Hurricane Forecasts Took Blow from Winds and Saharan Dry, Dusty Air
(PhysOrg.com) -- A new analysis of environmental conditions over the Atlantic Ocean shows that hot, dry air associated with dust outbreaks from the Sahara desert was a likely contributor to the quieter-than-expected 2007 hurricane season.
Strange molecule in the sky cleans acid rain, scientists discover
Researchers have discovered an unusual molecule that is essential to the atmosphere's ability to break down pollutants, especially the compounds that cause acid rain. It's the unusual chemistry facilitated by this molecule, however, that will attract the most attention from scientists.
Antarctic climate: Short-term spikes, long-term warming linked to tropical Pacific
Dramatic year-to-year temperature swings and a century-long warming trend across West Antarctica are linked to conditions in the tropical Pacific Ocean, according to a new analysis of ice cores conducted by scientists at the National Center for Atmospheric Research (NCAR) and the University of Washington (UW). The findings show the connection of the world's coldest continent to global warming, as well as to periodic events such as El Niño.
Study Links Warming of Indian Ocean to Decreased Rainfall in Africa
(PhysOrg.com) -- A study led by a team of geographers from the University of California, Santa Barbara, suggests that warming of the Indian Ocean –– a direct result of climate change –– is to blame for a steep decline in rainfall over the eastern seaboard of Africa, which has serious implications for the region's food security.

News discussion:

General Science news