When it comes to influencing climate change, the world's smallest ocean punches above its weight. The cold waters of the Arctic are estimated to absorb up to 180 million metric tons of carbon per year—more than three times what New York City emits annually—making it one of the Earth's critical carbon sinks. But recent findings show that thawing permafrost and carbon-rich runoff from Canada's Mackenzie River are causing parts of the Arctic Ocean to release more carbon dioxide (CO2) than it absorbs. The study, published earlier this year in the journal Geophysical Research Letters , explores how scientists are using cutting-edge computer modeling to study rivers like the Mackenzie, which flows into an area of the Arctic Ocean called the Beaufort Sea. Like many parts of the Arctic, the Mackenzie River and its delta have faced significantly warmer temperatures in all seasons in recent years, leading to greater melting and thawing of waterways and land.