Thawing permafrost and carbon-rich runoff from Canada\u2019s Mackenzie River is triggering part of the Arctic Ocean to release more carbon dioxide (CO2) than it absorbs, a NASA study has found. The findings indicate a threat to the ocean which is considered once Earth's critical carbon sinks, absorbing as much as 180 million metric tons of carbon per year \u2013 more than three times what New York City emits annually. Scientists have for decades studied how carbon cycles