In this 2017 satellite image, sediment from Canada's Mackenzie River flows in milky eddies into the Beaufort Sea. Scientists are studying how river flow drives carbon dioxide emissions in this part of the Arctic Ocean. Photo credit: NASA Earth Observatory image by Jesse Allen using USGS Landsat data
Runoff from one of North America's largest rivers is causing powerful carbon dioxide emissions into the Arctic Ocean.
When it comes to influencing climate change, the world's smallest ocean is of great importance. 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 causing part of the Arctic Ocean to release more carbon dioxide (CO2) than it absorbs.
The Impact of the Mackenzie River on Carbon Emissions
The study, published earlier this year in the journal Geophysical Research Letters, examines how scientists use cutting-edge computer models to study rivers like 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 experienced significantly higher temperatures in all seasons in recent years, resulting in 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-kilometer journey that begins near Alberta. Along the way, the river acts as a conveyor belt for mineral nutrients as well as organic and inorganic substances. These materials flow into the Beaufort Sea as a soup of dissolved carbon and sediment. Some carbon is ultimately released into the atmosphere or outgassed through natural processes.
Like a conveyor belt of carbon, the Mackenzie River, seen here from NASA's Terra satellite in 2007, drains an area of nearly 700,000 square miles (1.8 million square kilometers) as it travels north to the Arctic Ocean. Some of the carbon comes from thawing permafrost and peat bogs. Image credit: NASA/GSFC/METI/ERSDAC/JAROS and ASTER science team USA/Japan
Scientists consider the southeastern Beaufort Sea to be a low-to-moderate CO2 sink, meaning it absorbs more greenhouse gases than it releases. However, there is great uncertainty due to a lack of data from the remote region.
Advanced modeling techniques and results
To fill this gap, the study team adapted a global biogeochemical ocean model called ECCO-Darwin, developed at NASA's Jet Propulsion Laboratory (JPL) in Southern California and the Massachusetts Institute of Technology (MIT) in Cambridge. The model integrates almost all available ocean observations collected over more than two decades from sea-based and satellite-based instruments (e.g. sea level observations from Jason series altimeters and seafloor pressure from the GRACE and GRACE Follow-On missions). ).
Scientists used the model to simulate the release of freshwater and the elements and compounds it contains – including carbon, nitrogen and silica – over a period of almost 20 years (from 2000 to 2019).
The French, American and Canadian researchers found that the river's flow in the southeastern Beaufort Sea led to degassing so severe that the carbon balance was thrown into disarray, resulting in a net CO2 release of 0.13 million tons per year , which is about the equivalent of 0.13 million tons per year. to the annual emissions of 28,000 gasoline cars. The release of CO2 into the atmosphere varied seasonally and was 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 been studying the carbon cycle between the ocean and atmosphere for decades, a process called air-sea CO2 flux. However, observational records are rare on the coastal edges of the Arctic, where terrain, sea ice and long polar nights can complicate long-term monitoring and experiments.
“With our model we try 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.
This knowledge is essential because about half of the Arctic Ocean's surface consists of coastal waters, where land and sea meet in a complex embrace. And although the study focused on a specific part of the Arctic Ocean, it can help tell a broader story of environmental change in the region.
Scientists say the Arctic has warmed at least three times faster than anywhere else on Earth since the 1970s, changing its waters and ecosystems. Some of these changes promote increased CO2 outgassing in the region, others lead to increased CO2 uptake.
For example, as Arctic regions thaw and snow and ice melt more rapidly, rivers flow faster and release more organic matter from permafrost and peat bogs into the ocean. On the other hand, microscopic phytoplankton floating near the ocean's surface are increasingly taking advantage of shrinking sea ice to thrive in the new open water and sunlight. These plant-like marine organisms trap and absorb atmospheric CO2 during photosynthesis. The ECCO-Darwin model is used to study these blooms and the connections between ice and life in the Arctic.
Scientists are tracking these big and seemingly small changes in the Arctic and beyond as our ocean waters continue to be an important buffer against climate change, sequestering up to 48% of the carbon produced by burning fossil fuels.