The Hidden Language of Ocean Coral

Logan Brenner, a scientist at Columbia’s Lamont-Doherty Earth Observatory, is part of an international collaboration to drill into the ocean’s past.

Marie DeNoia Aronsohn
May 30, 2024
Headshot of paleoclimatologist Logan Brenner

For Logan Brenner, an adjunct associate research scientist at Columbia University’s Lamont-Doherty Earth Observatory, joining the International Ocean Drilling Project’s (IODP) Expedition 389: Hawaiian Drowned Reefs was a dream opportunity. 

The project offered Brenner a chance to work among a group of scientists spanning nations, including Austria, China, France, Germany, Japan, Spain, and the U.K., and disciplines—physicists, geochemists, sedimentologists, paleomagnetists—and to further her own research into the planet’s past. 

Brenner, an assistant professor of environmental science at Barnard College, is a paleoclimatologist—a scientist who studies the planet’s prehistoric past to understand the impacts of climate then, now and into the future. She earned her Ph.D. in Earth and Environmental Science from Lamont where she studied coral geochemistry. 

“I first heard about this opportunity when I was still a grad student studying with Brad Linsley at Lamont. I was so super excited to be a part of it,” said Brenner. The expedition involved sending a small crew out to sea for two months this past fall, to gather samples from 12 fossil coral reefs drowned by rising sea levels and exposure to the ever-growing volcanic archipelago of Hawaii. According to IODP, this area of the deep ocean contains unique reefs that hold important information about past climates and how coral reefs responded to changing conditions. Scientists can reconstruct sea-level change during important time periods in Earth’s climate history by studying coral samples.

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Coral cores collected by Brad Linsley and his research team in Panama. The cores are split in half and analyzed to reconstruct the history of coral bleaching and hydrologic changes in the region back to the mid-1800s. (Photo: Brad Linsley)

Brenner, who was expecting her second child in April, did not go out to sea but joined the onshore members of the mission in Bremen, Germany, in February. There, the team identified the coral samples and began deciding which ones to analyze. This research, which is ongoing, will hopefully shed light on the hidden past of the corals to help explain what the planet was like as many as 500,000 years ago.

The process of examining corals begins by cutting the cylindrical coral core in half and extracting a small part or flat slab to analyze. Brenner will use X-ray imaging, which can reveal subtle differences in density as the coral grows over time. This kind of imaging helps researchers to narrow down which parts of the coral they will analyze using geochemistry.

“As the corals grow, they have a calcium carbonate skeleton, and this skeleton often reflects the composition of the water that it’s growing in,” said Brenner. “It’s taking in different metals, different isotopes, and different nutrients, depending on the water that’s flowing around it, and the composition of the waters, or the way in which coral actually calcifies, can be influenced by climate. So essentially, [we] have within the skeleton a record of environmental change as it’s growing over time.”

The world’s oceans absorb huge amounts of carbon dioxide (CO2), which has helped to slow global warming. However, escalating climate change is warming the oceans and changing their chemistry, which has damaged coral reefs.

“Reefs are constantly facing vulnerability now, so it’s important to understand the conditions in which they were able to grow—or not grow—in the past,” said Brenner. “Maybe there was this sudden rise in sea level. How did the reef react in the past? How did it recover? Did it recover? So that could potentially inform the situation we could be facing today.”

The team will take several months to complete its analysis. Brenner, who deeply loves water, is eager to discover ways to protect the world’s oceans.

“I get a different feeling when I’m standing by the ocean than when I’m standing in a forest,” said Brenner. “It’s the vastness and mystery of it all and the power of water.”