The spinning heart of the Arctic
North of Alaska and Canada, a vast, clockwise-spinning ocean current called the Beaufort Gyre dictates the life and death of Arctic sea ice. For millennia, this 600-mile-wide gyre acted as a nursery for the Arctic's oldest and thickest ice. Sea ice would get caught in the current and circulate for years, growing thicker and more resilient. This multi-year ice, which once covered most of the region, formed a bright, reflective shield over the ocean.
The gyre also functions as the Arctic Ocean's largest freshwater reservoir. Driven by persistent anticyclonic winds, its circulation corrals enormous quantities of freshwater from river runoff, precipitation, and melting glaciers. Since the 1990s, the volume of freshwater stored in the gyre has increased dramatically. By 2018, it had accumulated an extra 6,400 cubic kilometers of fresh water, a 40% increase compared to the 1970s climatology. The total freshwater volume now exceeds 8,000 cubic kilometers, nearly double the volume of Lake Michigan. This freshwater layer is significant because it floats above the warmer, saltier Atlantic water below, insulating the sea ice from the heat.
A feedback loop in overdrive
The system is changing rapidly. The decades-long decline of summer sea ice has left the ocean surface exposed to the wind for longer periods. This increased wind action spins the gyre faster, trapping more freshwater and preventing its slow, natural release into the Atlantic. The Arctic's blanket of sea ice has lost about two-thirds of its thickness since 1958, and today, 70% of the ice cover is thin seasonal ice that melts each summer.
This sets up a powerful positive feedback loop known as the ice-albedo feedback. Older, thicker ice is highly reflective. When it melts and is replaced by dark ocean water, the surface absorbs significantly more solar radiation. This absorbed heat warms the water, which in turn melts more ice, exposing more dark water. The process reinforces itself, accelerating the warming. The annual average loss of multi-year ice in the Beaufort Sea quadrupled between the 1997-2001 period and the 2017-2021 period. In 2018 alone, the region lost 385,000 square kilometers of multi-year ice.
Scientists also observe a phenomenon called "Atlantification," where warmer, saltier water from the Atlantic pushes farther into the Arctic, weakening the cold freshwater layer from below. To monitor these shifts, researchers rely on an array of moored instruments and drifting profilers from the Beaufort Gyre Observing System (BGOS), which has been collecting data on water temperature, salinity, and ice draft since 2003.