The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Aqua satellite captured this true-color image of a large open water lead traversing the ice of the northern Arctic Ocean on May 13, 2013. Located north of Canada, the long, wide crack extends hundreds of kilometers across the ice to end north of the Arctic Circle.
Although the Arctic’s ice cap often appears as a solid sheet of stationary ice, it is actually made up of many smaller pieces. Through the winter, the ice is in constant motion as the pieces shift, crack and grind against each other as they are buffeted by winds and pushed by currents. Strong motion of wind and water often results in cracks (leads) appearing between pieces of ice.
Although the appearance of leads in the winter or spring is common, the frigid temperatures and shifting ice will usually cause a lead to narrow and close in short order. As temperatures rise, and the summer melt season begins, many leads remain open. By summer’s peak, hundreds of thousands of square miles of Arctic sea will have melted, only to refreeze again in the winter. While the summer melt is extensive, ice covers much of the Arctic Ocean year-round. But the extent of the summer sea ice – as well as the maximum extent of winter sea ice – has been diminishing.
According to an article published by the National Oceanic and Atmospheric Administration (NOAA) in April, 2013 “for scientists studying summer sea ice in the Arctic, it’s not a question of ‘if’ there will be nearly ice-free summers, but ‘when’”. Current best estimates, based on several models, predict that nearly ice-free summers are likely by 2050 – and possibly within the next ten to twenty years.