Researchers have known for years about Heinrich Events, periods of extreme cold in the North Atlantic. They occurred during the last ice age when immense icebergs broke loose from glaciers, and as they melted, deposited debris on the sea floor. (Credit: Osccarr/Flickr)

What massive icebergs tell us about Earth’s chilly past

During the last ice age, giant icebergs broke off from glaciers and surged into the North Atlantic. Called Heinrich events, these surges were previously thought to have weakened the global ocean conveyor belt and sent Earth’s climate into a deep freeze.

A new study suggests that these events may have been caused by changes in atmospheric circulation patterns.

To make the discovery, researchers studied the chemistry of shells produced by benthic foraminifera, single-celled organisms that live near the sea floor.

The organisms were collected from sediment cores recovered from the margins of the Florida Straits. By studying their oxygen isotope composition, researchers were able to reconstruct past changes in the Florida Current Transport, which is directly related to the strength of the global conveyor belt circulation.

Researchers have known for years about Heinrich events, periods of extreme cold in the North Atlantic named for the geologist who first discovered them, Hartmut Heinrich. Six of these events have been identified, and they are known as H1 through H6.

The last ice age

“While there is evidence that the last Heinrich event that occurred around 17,000 years ago was indeed caused by a dramatic reduction in the ocean’s conveyor belt circulation, our new reconstruction of ocean circulation patterns during some earlier Heinrich events, that occurred during the last ice age between 20,000 and 30,000 years ago, did not reveal significant changes in ocean circulation,” says Matthew Schmidt, associate professor of oceanography at Texas A&M University.

“Nevertheless, these Heinrich events were experienced worldwide, so they must have been transmitted via the atmosphere.”

The study “has important implications for our understanding of the mechanisms of abrupt climate change in the past,” Schmidt says. “The more we know about how climate changed in the past, the better prepared we will be for predicting future climate variability.”

Ping Chang, professor of oceanography and atmospheric science and director of the Texas Center for Climate Studies, and researchers from Georgia Institute of Technology, Princeton University, the Woods Hole Oceanographic Institution, the University of Cambridge, and the University of Bremen contributed to the study, which was published in the journal Nature Geoscience.

Source: Texas A&M University

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