Cave Records Hint at How the Dominoes Fell in Early Abrupt Climate Changes

Georgia Institute of Technology Assistant Professor Kim Cobb and graduate student Jud Partin are investigating the mechanisms that drove the abrupt climate change events that occurred on Earth thousands of years ago by analyzing mineral deposit stalagmites taken from caves in the tropical Pacific island of Borneo.

Stalagmites are pillar-like rock formations that grow from the floor of caves over time as rain water that is mixed with calcium carbonate and other elements seeps through the ground and drips onto the cave floor. The calcium carbonate and other elements accumulate and harden into layers that create a column of rock.

The customary means of analyzing Earth's ancient climatic history is to drill for ice core samples from the Arctic and Greenland, at the North Pole, or from Antarctica, at the South Pole. Such ice core samples have shown that while past abrupt climate change has affected the Earth globally, there is a difference in the patterns of events recorded in the ice in the Northern and Southern samples. This means that the Northern Hemisphere and Southern Hemisphere each have their own distinctive patterns of abrupt climate change.

Cobb and Partin theorize that the tropical Pacific waters may provide the mechanistic link between the two systems: the missing link that either drives or synthesizes the distinct patterns of the Northern and Southern Hemispheres.

The results of Cobb's and Partin's study suggest that the tropical Pacific had an active role in some of the abrupt climate change events of Earth's past and that the tropical Pacific may even have played a leading role in some of the changes.

Cobb's and Partin's research team collected stalagmites from the Gunung Buda cave system in Borneo taking three separate stalagmites from two separate caves--previous cave studies have used only one stalagmite from a single cave. This allowed for the creation of a near-continuous record of Earth's climate from 25,000 years ago to the present. By using more than one stalagmite from more than one cave, Cobb and Partin were able to compare and isolate shared climate-related signals.

After cutting open each stalagmite (rock), the researchers took 1,300 measurements of the rock's chemical content. This was used to determine the relative moisture of the climate at various periods of history, which are recorded in the stalagmite from the oldest and most ancient layers at the bottom to the present, and newest, at the top. Radioactive decay analysis of the elements uranium and thorium permitted the rocks to be dated. Measuring the ratio of oxygen isotopes determined the amount of precipitation at given times.

In this way, they were able to produce a high-resolution and continuous record of the climate for the equatorial rainforest in Borneo. Partin said: "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."

Cobbs said: "Our records contain signatures of both Northern and Southern Hemisphere climate influences as the Earth emerged from the last ice age, which makes sense given its equatorial location...[the Pacific] reflects the complexity of mechanisms linking high and low latitude climate."

For instance, the research results suggest that the tropical Pacific began drying out about 20,000 years ago. This drying trend may have pre-conditioned the North Atlantic to experience an abrupt climate change event known as the Heinrich 1 event that occurred there about 16,500 years ago.

Cobb concludes by saying: "As more [cave] studies are done...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."

"Cave records provide clues to climate change," Georgia Institute of Technology.