As Arctic warms, its waters emit carbon: study

When it comes to influencing climate change, the world’s smallest ocean looms large. Cold Arctic waters are estimated to absorb up to 180 million tons of carbon per year, more than three times what New York City emits each year, making it one of the world’s largest carbon sinks. the most critical on the planet. But recent findings show that thawing permafrost and carbon-rich runoff from Canada’s Mackenzie River are prompting part of the Arctic Ocean to release more carbon dioxide (CO₂) that it does not absorb.

The study, published earlier this year in Geophysical research letters , explores how scientists use cutting-edge computer modeling to study rivers such as the Mackenzie, which flows into a region of the Arctic Ocean called the Beaufort Sea. Like many regions of the Arctic, the Mackenzie River and its delta have faced significantly higher temperatures in recent years across all seasons, leading to increased melting and thawing of waterways and landscapes.

In this swampy corner of Canada’s Northwest Territories, the continent’s second-largest river system completes 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 materials. These materials flow into the Beaufort Sea as a soup of dissolved carbon and sediment. Some carbon is ultimately released or outgassed into the atmosphere through natural processes.

Scientists consider the southeastern Beaufort Sea to be low to moderate CO.₂ sink, which means it absorbs more greenhouse gases than it releases. But great uncertainty reigns due to the lack of data on this remote region.

To fill this gap, the study team adapted a global ocean biogeochemical model called ECCO-Darwin, developed at NASA’s Jet Propulsion Laboratory in Southern California and the Massachusetts Institute of Technology in Cambridge. The model assimilates almost all available ocean observations collected over more than two decades by sea-based and satellite instruments (sea level observations from Jason series altimeters, for example, and ocean floor pressure from missions GRACE and GRACE Follow-On). ).

Scientists used the model to simulate the release of fresh water and the elements and compounds it carries, including carbon, nitrogen and silica, over almost 20 years (from 2000 to 2019).

The researchers, from France, the United States and Canada, discovered that the river’s flow triggered such intense degassing in the southeastern Beaufort Sea that it tipped the carbon balance, leading to a net release of CO.₂ releasing 0.13 million metric tons per year, roughly equivalent to the annual emissions of 28,000 gasoline-powered cars. The release of CO₂ in the atmosphere varied seasonally, being more pronounced in warmer months, when river flows were high and there was less sea ice to cover and trap the gas.

Ground zero for climate change

Scientists have studied the carbon cycle between the ocean and atmosphere for decades, a process called air-sea CO.₂ flow. However, observational records are rare along the coastal fringes of the Arctic, where terrain, sea ice, and long polar nights can make long-term monitoring and experiments difficult.

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

Such knowledge is essential because about half of the Arctic Ocean’s surface area is made up of coastal waters, where land meets the sea in a complex embrace. And while the study focused on a particular part of the Arctic Ocean, it can help tell a broader story of the environmental changes taking place in the region.

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

For example, as Arctic lands thaw and snow and ice melt more, rivers flow faster and release more organic matter from permafrost and peatlands into the ocean. On the other hand, microscopic phytoplankton floating near the ocean surface are increasingly taking advantage of shrinking sea ice to flourish in the new open water and sunlight. These plant-like marine organisms capture and absorb atmospheric CO₂ during photosynthesis. The ECCO-Darwin model is used to study these blooms and the links between ice and life in the Arctic.

Scientists are tracking these large and seemingly small changes in the Arctic and beyond as our ocean waters remain a critical buffer against climate change, sequestering up to 48% of the carbon produced by burning fossil fuels.