In Panama, some 10 meters below the surface of the ocean, divers float in a cloud of white dust. The sound of a giant hydraulic drill cuts through the muffled underwater soundscape. The crackle of snapping shrimp can barely be heard. This is part of the job description for scientists who study coral cores: long, cylindrical samples taken vertically from coral colonies. These cores, when studied in a lab, can contain lifetimes of data.

Coral cores, like tree rings, ice cores, and sediment cores, can yield invaluable data about earth’s atmospheric and climatic past. Braddock Linsley, a lead researcher at Columbia University’s Lamont-Doherty Earth Observatory, has been working with coral records for over 30 years. Recently, in a once-forgotten core collected in Panama and pushed to the back of a shelf, he’s found something surprising.

At the Lamont-Doherty campus, located just north of New York City on the cliffs of the Palisades, this coral core is part of Linsley’s personal collection, something many coral researchers hold. Studying these cores allows them to look back on century-scale data sets. This way, they can determine the chemical composition of the environment well before human instrumentation was available. Each “layer” of new coral growth represents a year in the coral’s, and thus earth’s, past, something scientists can decipher through close examination of the sample.

Coral core collections often stay in the hands of the researchers that work with them. However, there are a few publicly accessible collections. A large repository of cores is housed in St. Petersburg, Florida, in a facility owned by the United States Geological Survey. The Australian Institute of Marine Science hosts the largest collection of coral cores in the world. Lamont-Doherty’s coral collection is nascent, receiving funding for the first time only about 10 years ago. Linsley’s own collection is also housed here. His oldest core is from 1521.

The coral cores live in a room fondly known as The Crypt. The Crypt is a part of Columbia's larger core repository, made up of sediment cores from the bottom of the ocean as well as from lakes and rivers. Over 20,000 sediment cores, categorized in floor-to-ceiling shelves, line every available inch of wall space in the basement-level repository.

Each core is preserved in a half-pipe-shaped, 8-foot long metal container. When asked why the precise 8-foot measurement, Nichole Anest, curator of the facility, laughed. When the repository opened in 1949, this was the standard size for readily available rain gutters used for homes, she explained. They happened to be the perfect vessel for housing delicate sediment samples from the deep ocean.

At the Australian Institute of Marine Science (AIMS), Neal Cantin uses his cores to look at coral bleaching. “Depending on the severity of the heat stress and depending on the severity of the bleaching response that that colony experienced, you'll see three or four different signals of a bleaching event in the banding pattern that we see in the skeleton,” Cantin said. Coral cores, run through an X-ray or CT scanner, reveal dark-to-light oscillating bands. Similar to rings on a tree, each of these bands indicates a year in the coral colony’s life. Lauren Toth, a researcher at the United States Geological Survey’s coral facility, says their oldest records date back 100,000 years. They use their data alongside tree and ice cores to piece together a fuller picture of the past.

What makes corals unique from these other paleoclimate records, however, is twofold. One, they’re indicative of the climate underwater, whereas tree and ice cores can only yield information about the atmosphere above surface level. Marine sediment cores from the bottom of the ocean also do this, but represent a very different depth and light environment, so valuable data can be gleaned from both. Two, they contain information about the shallow tropics, where ice and tree cores aren’t found. Because tropical trees don’t experience dramatic seasonal temperature shifts, their rings don’t yield as descriptive data as their more poleward counterparts.

The foundations for Linsley’s work at Lamont-Doherty were laid about 40 years ago, when he first collected a sample from a large coral in Panama. Collected in 1984, the colony is over 300 years old. It was the very first coral he ever worked on. The bottom of the cylindrical core, almost 21 feet in length, dates back to 1716.

Cantin remembers a tropical coring trip of his own years ago through his work with AIMS. He remembers the reef being vibrant and busy. When the coral coring device began drilling, marine life scattered at the sound. However, various animals returned. “Some get pretty curious,” he said. “Little rockfish want to see what’s going on.”

Five years ago, Logan Brenner, one of Linsley’s PhD students, was analyzing data from the core. But to the pair, the data didn’t make sense. So Brenner refiled the core. Years later, Linsley happened upon the data and realized he’d given his student the wrong age model, something that would skew the data if incorrect. It was as if someone with 2020 vision had put on the glasses of a nearly blind person.

To decipher all the potential information held in these cores, scientists have to study, millimeter by millimeter, the dust from a section of the coral core in a series of machines. Each millimeter, visible now only as a pinch of dust at the bottom of a test tube, is carefully labeled and placed on the shelves of Linsley’s lab. It wasn’t always this neat. “I’m not a very organized guy,” he said.

Recently, he decided to recalculate the data. “All of a sudden, it looked just like river discharge,” he said. The corals had taken up barium, a heavy metal similar to calcium, from surrounding seawater. This had, in turn, come from local river discharge and mangroves. Barium in the coral skeletons can serve as a geochemical tracer of regional hydrology, something scientists can measure and glean information from.

In this case, the operation of the Panama Canal relies on rainfall in the previous year. Discharge from rivers and mangroves in Panama is directly related to rainfall—and that meant the corals were recording the region’s precipitation patterns. This could have predictive implications which may assist the Panama Canal Authority in managing canal operations. This waterfall of natural phenomena has the potential to help scientists guess how corals may react to future climate changes.

The paper that Linsley is writing about his findings isn’t out yet, so the final figures could not be included in this piece. What they look like, however, is three near-perfectly matching and synchronous curves. They show that Linsley’s down core, or near-monthly, coral barium concentrations are highly correlated with Panama precipitation. If these things do line up, it means that the geochemistry of corals in Panama provide an accurate picture of timing and amplitude of droughts and flooding back to 1716 CE. Further, that scientists may be able to use these results to better understand the evolving relationship between El Niño and La Niña events and rainfall in Panama over the last three centuries.

Linsley points out a break in the core he’s working on. The chalky, porous sample has a weathered, brown band. This is where the coral bleached, presumably due to extreme heat, but was able to survive and continue its growth for many years, as can be seen through the many further feet of coral core in the cardboard box he’s just pulled down off a shelf. The box was heavy, and dust settled on the linoleum floor while he unwrapped the core.

Linsley spoke about what it was like years ago, before the technological advances they rely on today. “We did it by hand in the lab, loud music blaring and flipping valves and transferring the gas by hand. So it was very slow. And now the computers are running it. You can set up a run and go home and come back in the morning and, if everything worked right, you get your data,” he said.

Studying corals and the climate can be heavy work. “I haven’t been everywhere, but I’ve seen a lot of devastated reefs,” Linsley said. As reefs deteriorate across the planet, this work becomes ever more important. Cantin echoed the statement: “The frequency of stress through the system is getting worse and [is] definitely concerning.”

Lauren Toth of USGS, also deeply engaged in coral ecology, feels worried but hopeful. She understands the potential held in these ancient cylindrical samples. The information that can be gathered from the cores, she says, is limited only by the technology we have to decipher it.