Drilling Down on the Language of Ocean Coral

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For assistant professor of environmental science Logan Brenner, working on Expedition 389: Hawaiian Drowned Reefs was a dream opportunity.

The expedition, overseen by the International Ocean Drilling Project (IODP), offered Brenner a chance to work among a group of scientists that spanned nations (including Austria, China, France, Japan, and the U.K.) and disciplines (physicists, geochemists, sedimentologists, paleomagnetists) and to further her own research into the planet’s past. 

Brenner is a paleoclimatologist — a scientist who studies the planet’s prehistoric past to understand the impacts of climate then, now, and into the future — who earned her Ph.D. in earth and environmental science from Columbia University and the Lamont-Doherty Earth Observatory.

The expedition, Brenner explains, 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 the 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.

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. Brenner is on the team of researchers who will begin to examine and discover 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 core in half and extracting a small part or flat slab to study. Brenner will use X-ray imaging, which can reveal subtle differences in density as the coral grows over time. This helps researchers to narrow down which parts of the coral they will analyze using geochemistry.

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“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,” says 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,” says 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.”