Warming Arctic Ocean driving intense carbon emissions, finds NASA study

Thawing permafrost and carbon-rich runoff from Canada’s 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 – more than three times what New York City emits annually.

Scientists have for decades studied how carbon cycles between the open ocean and atmosphere, a process called air-sea CO2 flux. However, the observational record is sparse along the coastal fringes of the Arctic, where the terrain, sea ice, and long polar nights can make long-term monitoring and experiments challenging.

“With our model, we are trying to explore the real contribution of the coastal peripheries and rivers to the Arctic carbon cycle,” said lead author Clément Bertin, a scientist at Littoral Environnement et Sociétés in France.

Such insights are critical because about half of the area of the Arctic Ocean is composed of coastal waters, where land meets sea in a complex embrace. And while the study focused on a particular corner of the Arctic Ocean, it can help tell a larger story of environmental change unfolding in the region.

The study was conducted 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. The model assimilates nearly all available ocean observations collected for more than two decades by sea- and satellite-based instruments (sea level observations from the Jason-series altimeters, for example, and ocean-bottom pressure from the GRACE and GRACE Follow-On missions).

Scientists used the model to simulate the discharge of fresh water and the elements and compounds it carries – including carbon, nitrogen, and silica – across nearly 20 years (from 2000 to 2019).

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.

The researchers, from France, the U.S., and Canada, found that the river discharge was triggering such intense outgassing in the southeastern Beaufort Sea that it tipped the carbon balance, leading to a net CO2 release of 0.13 million metric tons per year – roughly equivalent to the annual emissions from 28,000 gasoline-powered cars. The release of CO2 into the atmosphere varied between seasons, being more pronounced in warmer months, when river discharge was high and there was less sea ice to cover and trap the gas.

Since the 1970s, the Arctic has warmed at least three times faster than anywhere else on Earth, transforming its waters and ecosystems, the scientists said. Some of these changes promote more CO2 outgassing in the region, while others lead to more CO2 being absorbed.

Scientists are tracking changes in the Arctic and beyond because ocean waters remain a critical buffer against a changing climate, sequestering as much as 48 percent of the carbon produced by burning fossil fuels.

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