A graveyard is located off the coast of the Galápagos Islands, nearly a kilometer below the surface. There is no marking on it. It doesn’t receive any visitors. However, for years, scientists have been extracting skeletons from those icy, dark waters, and the tale those skeletons tell is probably more concerning than it is.
There, a community of deep-sea stony corals coexisted peacefully for over 117,000 years. They made it through the previous Ice Age. The subsequent warming did not harm them. They endured climatic fluctuations that altered continents and coastlines. Then, about 5,000 years ago, they just vanished. Not in tiny quantities. Not having any trouble. Absent. The fossil record is silent for over a millennium before, in an almost equally bizarre turn of events, they resurface.
The most likely explanation to date has been provided by a group of researchers at the University of Bristol, and it’s not what most people would anticipate. The results, which were published in PNAS, link the disappearance to a prolonged La Niña phase rather than the El Niño events that are usually held responsible for surface coral stress. Stronger ocean circulation drove deep, nutrient-rich water upward during that extended La Niña period, which may seem beneficial until you consider the impact on oxygen levels at depth. In a sense, the corals choked.
The methodology is a little crazy, so it’s worth stopping. The team used uranium-thorium dating to reconstruct a record that goes back farther than most human history can comprehend after gathering over 900 dead stony corals from depths of up to 1,000 meters. That’s how you create a timeline that lengthy, one piece at a time, when practically nothing about the work is simple.
The assumption that the outcome challenges is what makes it unsettling. In some areas of marine science, there has been a quiet belief that the deep ocean is at least insulated, if not safe. Reefs in the tropics bleach. Temperatures at the surface rise. The upper layers are stirred by storms. However, things were meant to be more stable down there in the darkness and cold. This research makes it more difficult to defend that notion. The corals were not protected from this upheaval by whatever had protected them from previous ones.
The lead author of the study, Joseph Stewart, expressed caution, pointing out that even minute changes in global climate patterns can cause massive ecosystem collapse far below the surface. The implication is unrestrained, but the language is. Many things that live in the deep are more exposed than we previously believed if a stable, ancient community of corals can be taken offline for a millennium due to changes in ocean circulation.
It’s strange to build a warning around corals. They resemble rocks. In actuality, they are animals that have unintentionally created reefs over centuries, supporting entire worlds of fish and invertebrates in areas that have never seen sunlight. As this story develops, it’s difficult to avoid feeling a little uneasy about how easily we’d missed them. They don’t look good in photos. Unlike tropical reefs, they are not featured in nature documentaries. Most people will never come across one. And yet here they are, more accurately capturing the mood swings of the climate than nearly anything on land.
It took centuries to recover. That’s the part that stays. Ecosystems may reappear, but they will do so on very different timescales than those on which humans live. Although there is a sense that the warning is coming a little later than would have been helpful, co-author Laura Robinson pointed out that understanding how long these systems take to recover will be crucial for conservation. What occurs above the deep ocean is inextricably linked to it. It was never the case. It wasn’t until someone went down and retrieved the bones that we could see the evidence.
