Warming Arctic waters are emitting carbon: NASA study

WASHINGTON: Once known to be Earth's critical carbon sinks, an increasingly warming Arctic Ocean is driving intense carbon dioxide (CO2) emissions, according to a study by NASA.

It’s been estimated that the cold waters of the Arctic absorb as much as 180 million metric tonnes of carbon per year – more than three times what New York City emits annually.

But, the study showed that thawing permafrost and carbon-rich runoff from Canada’s Mackenzie River trigger part of the Arctic Ocean to release more CO2 than it absorbs.

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 Clement Bertin, a scientist at Littoral Environnement et Societes 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.

Using a global ocean biogeochemical model called ECCO-Darwin, which was developed at NASA’s Jet Propulsion Laboratory in Southern California and the Massachusetts Institute of Technology in Cambridge, the study explored the Mackenzie rivers, 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. The 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).

The researchers, from France, the US 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 tonnes 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.