Borneo caves provide clues to climate change over last 25,000 years

Washington, Sept 27 : A study of caves of the tropical Pacific island of Borneo has helped scientists understand how the Earth’s climate suddenly changed several times over the last 25,000 years.

Georgia Tech Asst. Prof. Kim Cobb and graduate student Jud Partin analyzed stalagmites, pillar-like rock formations that stem from the ground in caves, to produce a high-resolution and continuous record of the climate over the equatorial rainforest.

Stalagmites are formed as rainwater, mixed with calcium carbonate and other elements, makes its way through the ground and onto the cave floor. As this solution drips over time, it hardens in layers, creating a column of rock.

The team collected stalagmites from the Gunung Buda cave system in Borneo in 2003, 2005 and 2006.

Analysis of three stalagmites from two separate caves allowed the pair to create a near-continuous record of the climate from 25,000 years ago to the present.

While this study is not the first to use stalagmites to examine climate over this time period, it is the first to do so in the tropical Pacific. Typically, in these types of studies, only one stalagmite is analyzed, but Partin and Cobb compared their three stalagmite records to isolate shared climate-related signals.

“These stalagmites are, in essence, tropical ice cores forming over thousands of years. Each layer of the rock contains important chemical traces that help us determine what was going on in the climate thousands of years ago, much like the ice cores drilled from Greenland or Antarctica,” said Partin.

The scientists cut open each stalagmite and took 1,300 measurements of their chemical content to determine the relative moisture of the climate at various periods in history starting from the oldest layers at the bottom to the present at the top.

They dated the rocks by analyzing the radioactive decay of uranium and thorium, and determined the amount of precipitation at given times by measuring the ratio of oxygen isotopes.

The records revealed “signatures of both Northern and Southern Hemisphere climate influences as the Earth emerged from the last ice age, which, according to Prof. Cobb made sense given its equatorial location.

For example, Partin and Cobb's records showed that the tropical Pacific began drying about 20,000 years ago and that this trend might have pre-conditioned the North Atlantic for an abrupt climate change event that occurred about 16,500 years ago, known as the Heinrich 1 event.

“Tropical Pacific climate was not a simple linear combination of high-latitude climate events. It reflects the complexity of mechanisms linking high and low latitude climate,” said Prof. Cobb.

“Currently our knowledge of how these dramatic climate changes occurred comes from just a few sites. As more studies are done from caves around the world, hopefully we'll be able to piece together a more complete picture of these changes. Understanding how the dominoes fell is very important to our understanding of our current warming trend,” he said.

The findings appear in the Sept 27 issue of the journal Nature. (With inputs from ANI)

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