On a frigid afternoon in May, I slipped through a crack in the sea ice and dropped into the Arctic Ocean. The icy water hit my face and neoprene-clad head so hard I thought I would vomit. I was diving just south of Lancaster Sound, off the northern tip of Baffin Island in the Canadian Arctic. The water was 29 degrees (-2°C), about as cold as seawater gets before it freezes.
My teeth clenched the regulator as I tried to fight back nausea. Soon my breaths slowed, my head numbed to the shock, and I swam down into the blackness. At one point I looked back up at the ice, expecting it to appear as it most often does this early in the season—blue, featureless, lifeless. But something wasn’t right.
The ice was stained green and brown. It moved. I blinked and checked my depth. I tried to make sure I wasn’t suffering vertigo, which can be deadly to a diver working alone under the three-foot-thick (one meter) roof of ice. Then it hit me: It wasn’t ice at all—I was watching a massive cloud of amphipods, tiny shrimplike crustaceans, as they fed on phytoplankton that grow on the underside of the ice in spring when the sun returns to the Arctic. I was seeing the foundation of the ecosystem, the combination of ice and minute life-forms upon which all the bigger animals—polar bears, whales, birds, and seals—depend.