Sediment from Canada’s Mackenzie River empties into the Beaufort Sea in milky swirls in this 2017 satellite image. Scientists are studying how river discharge drives carbon dioxide emissions in this part of the Arctic Ocean. Credit: NASA Earth Observatory / Jesse Allen (using Landsat data from USGS)
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When it comes to influencing climate change, the world's smallest ocean punches above its weight. It's been estimated that the cold waters of the Arctic absorb as much as 180 million metric tons of carbon per year—more than three times what New York City emits annually—making it one of Earth's critical carbon sinks. But recent findings show that thawing permafrost and carbon-rich runoff from Canada's Mackenzie River trigger part of the Arctic Ocean to release more carbon dioxide (CO2) than it absorbs.

The study, published earlier this year in Geophysical Research Letters , explores how scientists are using state-of-the-art computer modeling to study rivers such as the Mackenzie, which flows into a region 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 recent years across all seasons, leading to more melting and thawing of waterways and landscapes.

In this marshy corner of Canada's Northwest Territories, the continent's second largest river system ends a thousand-mile journey that begins near Alberta. Along the way, the river acts as a conveyor belt for mineral nutrients as well as organic and inorganic matter. That material drains into the Beaufort Sea as a soup of dissolved carbon and sediment. Some of the carbon is eventually released, or outgassed, into the atmosphere by natural processes.

Scientists have thought of the southeastern Beaufort Sea as a weak-to-moderate CO2 sink, meaning it absorbs more of the greenhouse gas than it releases. But there has been great uncertainty due to a lack of data from the remote region.

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