By Thomas Smith
Medill Reports

Scientists are making discoveries about the Earth’s climate by studying single-celled protists that lived hundreds of thousands of years ago. Shells from foraminifera, a type of protist, have differing chemical compositions that reflect the planet’s climate. Foraminifera still exist in the oceans today, and analyzing the preserved shells lets scientists paint a picture of what the world looked like in the past.

“Because we can observe them in the modern, and what their shell chemistry responds to we can then use their chemistry to look back in time to figure out what was going on,” Minda Monteagudo said.

Monteagudo, an oceanography and climate researcher with Georgia Tech’s department of earth and atmospheric sciences, presented data at the 2020 Comer Climate Conference that examines the ratio of magnesium to calcium in foraminifera shells over the last 150,000 years. Our planet goes through glacial and interglacial cycles over long periods of time, and having a good thermometer for past eras helps experts understand changes in the planet’s climate today.

The ages-old and information-rich foraminifera shells are made primarily of calcium carbonate, a delicate chalk-like substance, which is best preserved in sediment cores found in shallower waters. Monteagudo said her recent research focuses on sediment cores near the Line Islands in the central Pacific Ocean, an understudied area with a rewarding cache of cores.

Principal component analysis, a statistical tool that helps make sense of large sets of numbers, was used to help interpret the data. Monteagudo said her dataset contains multiple variables, and principal component analysis helps sort through the noise and identify patterns.

Data compiled by Monteagudo is publicly available, as is data from numerous scientific researchers. Monteagudo said sharing information is an important resource to understanding climate because research can elucidate different aspects of Earth’s interconnected systems.

“We use the shell chemistry to go back in time,” Monteagudo said. “In my case, I use chemistry that tells us about temperature. And by having records in a whole bunch of different locations, we can try to say something about what the pattern looks like.”

Yuxin Zhou, a graduate student at Columbia University, presented research on the flow of fresh water in the Atlantic Ocean over the last 150,000 years at the climate conference. The research posits that Atlantic freshwater fluxes are largely caused by iceberg breakoffs, which are more likely to occur in shifts between glacial and interglacial states. Zhou said his research uses a new method of analysis which comes with its own uncertainties but reinforces scientific certainty because it confirms previous scientific findings.

“The Comer Conference is such a wonderful opportunity that brings together different projects that maybe work on the same thing from different sides, and we can compare notes,” Zhou said.

Oceans and climate shifts are globally connected, which is part of the reason why it is so important to see the whole
picture of what the Earth looked like millions of years ago. Levels of carbon dioxide correlate with the planet’s temperature and glacial state, so studying the past helps demonstrate the impacts of human-contributed carbon dioxide emissions.

“We’re basically running a giant experiment with the planet,” Monteagudo said, “and so it can help to do the kind of paleo work that we do, to see the climate system and the kind of swings that it had before human interference, to have kind of a background state of what we can expect as normal variability.”

Thomas Smith is a science reporter at Medill. You can follow him on twitter at @TomGoodwinSmith.