The Cosquer cavern is being eaten away by sea level rise and pollution, and diver-archaeologists are racing the tide.

Henri Cosquer knew the risks of cave diving when he explored a long cavity cut into the limestone cliffs near the city of Marseille, on the Mediterranean coast of southern France. But he dared it, going a little further each trip in the summer of 1985.

“I came up in a pitch-dark cave. You are soaking, you come out of the mud and you slide around… It took me a few trips to go right around it,” he said of that first discovery. “At the start, I saw nothing with my lamp and then I came across a hand print.”

What he’d discovered was stunning. An immense cavern, with a tunnel entrance over 120 feet below the surface, filled with rock art engravings and paintings from a span of over 8000 years from 27000 to 19000 BC.

In 1991, after three other divers died in the tunnel leading to the cave following rumors, Cosquer reported the site to the French government.

When he found it, there were over 600 recognizable images and carvings inside. But in 2011, the sea level inside the cave rose abruptly 5 inches, irreparably and immediately damaging many of the fragile paintings.

There is nothing to be done that will stop sea level changes in the cave, so diver-archaeologists are rushing to record the art and geography of Cosquer Cavern in as much detail as possible. A slightly smaller scale replica of the entire cavern has already been made, but the original may not last out the decade.

No amount of 3D mapping or visual recording can replace what will be lost in that cavern, though, and not only emotionally. There are traces of cloth on the wall, which could tell us what hunter-gatherers wore 20,000 years ago. Soot caught under millennia of calcite deposits could tell us what they burned for fuel. We still don’t know what the purpose of the cave was. While it was in use, that deep-ocean entrance was on dry land, but the long, difficult tunnel was still a long and difficult tunnel.

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