In September, a group of scientists led by Jørgen Berge of the Arctic University of Norway uncovered a startling amount of action beneath the surface of the dark waters of the Arctic Ocean. Even during winter—a season without sunshine or warmth—plankton, crustaceans, and fish were going about their lives in the area studied.

Now, a new study by some of the same researchers reveals that during long winters in the Arctic Circle, marine creatures are able to navigate by moonlight. In a study in the journal Current Biology, they report that zooplankton migrate by the light of the Moon rather than the Sun during the winter, moving from the surface of the ocean to depths of about 165 feet in conjunction with the full Moon.

The researchers examined more marine environments in a follow-up to their first study, finding that even at different depths and environments—under layers of ice, on the open sea, and more—marine life follows the same pattern in the winter. Instead of migrating according to 24-hour days, based on the movements of the Earth around the Sun, zooplankton shifted to a 24.8-hour lunar day, moving up and down throughout the water column when the Moon rose above the horizon.

The way that plankton move through the ocean influences the carbon cycle, because plankton absorb carbon dioxide during photosynthesis, moving it into deeper waters as the plankton migrate and are eaten at different levels of the water column. Some of that carbon sinks to the bottom of the ocean as plankton die, and is stored there for centuries. Thus, this new knowledge of what plankton do during the winter might impact climate models.