Analyzing Radiocarbon in Coral, Researchers Look Back On 400 Years of Monsoons

by AMNH on

Research posts

A diver touches the surface of a very large, dome-shaped coral underwater. This Porites coral, which measures more than 16 feet (5 m) in height and 130 feet (40 m) in circumference, is one of the largest found in nature. It was sampled for the 2019 study.
Courtesy of N. Goodkin

In East Asia, summer and winter monsoons can have an outsized impact on local communities.

These seasonal storms can determine how much freshwater is available, whether farmlands flood or wither from drought, the level of air quality, and the potential of wind energy production. But how these major weather systems change over time, and how they interact with other climate factors, is still poorly understood.

Part of the gap in knowledge comes from the fact that standardized records about East Asian monsoons don’t go back farther than the 18th century, and much of the existing material focuses on land observations. But a new study from Museum Curator Nathalie Goodkin and colleagues published this week by the American Geophysical Union analyzes coral to peer back 400 years and evaluate how monsoons in East Asia have varied over time.

Coral like the stony Porites lutea are skeletons built by individual coral polyps over hundreds of years. As they grow, these skeletons carry clues about contemporaneous environmental conditions—such as surface temperature and water mixing—and lock in years of valuable data that scientists can use to reconstruct climate conditions of the past. In the work that Goodkin, an assistant curator in the Department of Earth and Planetary Sciences, and colleagues are conducting in Southeast Asia, corals are analyzed for changes in ocean circulation driven by winds.

"The coral sampled for this study, called To Nhât, or Vietnamese for 'the big one,' is one of the largest corals ever found in nature and has opened up a window that, from an ocean studies perspective, gives us a glimpse farther back in time,"  says Goodkin.

By analyzing radiocarbon content in a 4.6-meter core of coral, Goodkin and team were able to look back about 400 years in history and point to links between East Asian Monsoons and other climate systems, including the Siberian High, a collection of cold dry air at high latitude, and El Nino-Southern Oscillation, a tropical climate system.

They also identified periods where monsoons varied greatly from year to year. Such periods included 1640 to 1660—a time during which the Ming Dynasty was destabilized by drought, floods, famine, and disease before collapsing.