Scientists have peered into one of the least-explored swaths of ocean on Earth, a vast region located off the coast of West Antarctica. It is locked beneath a crust of ice larger than Spain and more than 1,000 feet thick, making its waters perpetually dark—and extremely difficult for humans to access. Now, a team of researchers has bored a hole through the ice and sampled the ocean beneath it. Their work could shed light on a poorly understood, but ominous episode in Antarctica’s recent past.

A team of scientists from New Zealand began this two-month expedition in November. A ski-mounted Twin Otter aircraft ferried them 220 miles from the nearest base, landing near the middle of the Ross Ice Shelf—the massive