Geologists Create 5-Million-Year Climate Record

Brown University geologists have created the longest continuous record of ocean surface temperatures, dating back 5 million years. The record shows slow, steady cooling in the eastern equatorial Pacific, a finding that challenges the notion that the Ice Ages alone sparked a global cooling trend. Results are published in Science.

Using chemical clues mined from ocean mud, Brown University researchers have generated the longest continuous record of ocean temperatures on Earth.

The 5-million-year record is a history of temperatures in the eastern equatorial Pacific, or EEP, located off the coast of South America. The area is an anomaly – a huge swath of cool water in the tropics – that plays an important role in global climate. In the EEP, trade winds pull nutrient-rich cold water to the surface, which makes for fertile fisheries off the coasts of Peru, Chile and Ecuador. The interplay of wind and water can also fuel El Niño events, a large-scale warming in the EEP that slows the upwelling of cold water and forces changes in weather, such as droughts or floods, far from the tropical Pacific.

In the EEP, the Brown geology team found that surface temperatures were 27° C 5 million years ago. Surface temperatures are 23° C today. In between, they found a pattern of steady cooling – roughly one degree Celsius every million years.

This finding, published in Science, contradicts the long-standing notion that rapid glacier growth in the high northern latitudes about 3 million years ago alone set off dramatic cooling of the global climate. The finding shows instead that glaciation was part of a long-term cooling trend.

The climate record suggests that ocean regions near Antarctica were the main driver of EEP cooling by continuously pumping cold water into the area. This finding was bolstered by additional evidence that glacial cycles affected the tropical Pacific long before the advent of large ice sheets in the Northern Hemisphere.

“The Southern Hemisphere, not the Northern Hemisphere, more likely had a stronger effect on temperature and productivity in the eastern Pacific,” said Kira Lawrence, a graduate student in the Department of Geological Sciences and the lead author of the Science paper. “We may need to refocus where we look to understand the evolution of climate over the past 5 million years.”

Lawrence, post-doctoral research fellow Zhonghui Liu, and Professor Tim Herbert used sediment cores pulled from hundreds of meters below the surface of the Pacific by a ship operated by the Ocean Drilling Program, an international research organization. Moving down the cores, collecting small samples of gray mud, scientists can go back in time. The end result: Thousands of glass vials filled with climate history.

But how do you extract history from mud? The answer was found in tiny marine fossils.

To date the sediments, the geologists analyzed fossils and traces of oxygen trapped in the shells of microscopic ocean organisms. To get temperatures, the Brown team looked to algae, infinitesimal surface-dwellers that produce fatty compounds called alkenones. Algae crank out two kinds of alkenones depending on the surrounding water temperature. When water is cooler, algae make more of one kind. When water is warmer, they produce more of another. By carefully measuring the amount of these alkenones in each sample, researchers were able to calculate past surface temperatures.

The resulting 5-million-year timeline might have a practical use. Scientists trying to predict future climate change may use the data in computer simulations that model natural climate variability as well as predict the impact of accelerated warming due to greenhouse gas emissions.

Herbert said the work has other implications for understanding climate change.

“Results from the past prove that it is possible for the EEP to exist in a kind of permanent El Niño state, which would have immense climate and biological repercussions if it were to happen again under global warming,” Herbert said. “The geological evidence also suggests that to predict warming in the EEP, the key ocean region to monitor is near Antarctica.”

The National Science Foundation and the Geological Society of America funded the work.

Media Contact

Wendy Lawton EurekAlert!

More Information:

http://www.brown.edu

All latest news from the category: Earth Sciences

Earth Sciences (also referred to as Geosciences), which deals with basic issues surrounding our planet, plays a vital role in the area of energy and raw materials supply.

Earth Sciences comprises subjects such as geology, geography, geological informatics, paleontology, mineralogy, petrography, crystallography, geophysics, geodesy, glaciology, cartography, photogrammetry, meteorology and seismology, early-warning systems, earthquake research and polar research.

Back to home

Comments (0)

Write a comment

Newest articles

Lighting up the future

New multidisciplinary research from the University of St Andrews could lead to more efficient televisions, computer screens and lighting. Researchers at the Organic Semiconductor Centre in the School of Physics and…

Researchers crack sugarcane’s complex genetic code

Sweet success: Scientists created a highly accurate reference genome for one of the most important modern crops and found a rare example of how genes confer disease resistance in plants….

Evolution of the most powerful ocean current on Earth

The Antarctic Circumpolar Current plays an important part in global overturning circulation, the exchange of heat and CO2 between the ocean and atmosphere, and the stability of Antarctica’s ice sheets….

Partners & Sponsors