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Josefa Verdugo is a Chilean marine biogeochemist based in Bremerhaven, Germany, who drills cores from drifting sea ice to trace the pathways of methane—a potent greenhouse gas—between water, ice, and the atmosphere. She has participated in three research expeditions in the Arctic Ocean.

The first time I went to the Arctic Ocean, I felt so privileged to see it with my own eyes, to walk on the ice knowing that beneath me was 4,000 meters of seawater.

The water, ice, and parts of the seabed contain methane—the third most abundant greenhouse gas in the atmosphere. Sea ice is not really taken into consideration when accounting for how methane moves around the Arctic Ocean, but my research shows that it has an important role.

Sediments on the seafloor of the Siberian shelf, off eastern Russia, release methane, and when seawater freezes, the gas becomes trapped in tiny bubbles in the ice, or remains dissolved in pockets of brine that can form between the layers of ice. Pushed by currents and wind, the sea ice then drifts across the Arctic Ocean carrying this supply of methane to areas that might not have other sources. In 2017, I sampled a floe north of Svalbard, Norway, that had traveled thousands of kilometers. When the ice starts to melt, methane dissolved in brine is released into the seawater and can eventually diffuse into the atmosphere.

It’s shocking to see how much ice is melting in the Arctic each summer. Without sea ice acting as a barrier between the ocean and the air, more methane from the seafloor in shallow coastal areas can enter the atmosphere, causing more warming—and more melting.

On each expedition, my colleagues and I travel to a drifting floe by icebreaker, then reach our sample sites on foot, using sledges to carry our instruments. Sometimes the conditions are very tough: storms, extremely cold temperatures, complete darkness.

When we are working on the ice, safety is the most important consideration. Each person has a buddy, and we repeatedly check each other’s face for frostbite. We also have polar bear guards. If they see a bear around, we leave the equipment and rush back to the vessel.

On my first expedition, we finished cutting through the ice, and one of the other scientists told me, “Put your face on the hole. See it and smell it and feel it.” It was so fresh, and I could taste the salty brine squeezing out of the ice.

Once we remove the core—which can be three meters long—we have to work fast to collect basic measurements. I drill small holes along the core and insert a thermometer to measure the temperature before it changes. I have to remove my big mittens to manipulate the equipment; underneath them I wear thin nitrile gloves so I don’t contaminate the sample. But it’s difficult to work with freezing hands.

To measure methane, we take a second ice core, put it immediately in a tight plastic sleeve to prevent gases from escaping, and quickly bring it on board. In the ship’s cold room, at -20 °C, I cut the core into 10-centimeter pieces with a saw; then I let the ice melt in vacuum-sealed bags and measure the dissolved methane. I compare how the concentration varies between different types and ages of sea ice. Some multilayered floes contain brine pockets of methane-eating microbes, so have lower methane concentrations than other samples.

All of the time I spend on the ice is special, but during my last expedition, we went walking in the dark. There was a tremendous orange moon and a sky full of stars. There was no sound—only the drifting snow and the wind and our steps. I had to take a moment to realize where I was because it looked like a totally different planet. It was magic.