In January 2012 Jorgen Berge and two colleagues were tooling around Kongsfjorden, on the coast of Svalbard, in a small rubber boat with an outboard motor. The fjord, a stopover site on a two-week-long sea-ice research cruise, provided a rare opportunity to look for marine life in shallow, open waters in the high north during the dead of winter. It was the middle of the night, but the hour didn’t really matter: In the Arctic at that time of year, darkness coats everything, day and night. As does a bitter cold, so the three Norwegian scientists had donned heavily insulated, traffic-cone-orange suits accented with reflective strips—helpful should anyone tumble into the icy water and require rescue. As the team motored along, an eerie glow began to surround them. Berge, mesmerized, leaned over the gunwale for a closer look. “There was this fantastic spectacle of blue-green light in the water,” he says via video chat on Skype. Berge, an amiable marine biologist whose face is...