The Mackenzie River Basin, one of North America's largest rivers, significantly increases carbon dioxide emissions in the Arctic Ocean and challenges the region and its position as a major carbon sink.
Despite absorbing about 180 million tons of carbon each year, recent studies show that melting permafrost and carbon-rich outflows from the Mackenzie River cause parts of the Arctic Ocean to release more carbon dioxide than it absorbs.
The study, conducted using advanced computer modeling techniques, focuses on the Beaufort Sea, where the Mackenzie River flows into the Arctic Ocean. Rising temperatures in the Arctic region have caused increased melting and thawing of the river and its estuary. Located in Canada and the Northwest Territories, the region is the culmination of the second largest river system in North America, which originates in Alberta and extends for a thousand miles. The Mackenzie River acts as a transporter of mineral nutrients along with organic and inorganic matter to the Beaufort Sea, forming a mixture of dissolved carbon and sediment. Some of this carbon is released naturally into the atmosphere. Although scientists originally considered the southeastern Beaufort Sea to be a weak to moderate sink of carbon dioxide, recent data from the remote region have raised considerable uncertainty.
To address this shortcoming, the research team used ECCO-Darwin, a global ocean biogeochemical model developed by NASA and #039 Jet Propulsion Laboratory and the Massachusetts Institute of Technology. The model incorporates more than two decades of ocean observations collected from marine and satellite-based instruments. By simulating freshwater discharge from 2000 to 2019 and related elements and compounds, including carbon, nitrogen and silica, the researchers found that discharge from the Mackenzie River triggered a strong discharge in the southeastern Beaufort Sea. This upset the carbon balance, resulting in net emissions of 0.13 million tonnes of CO2 per year, equivalent to the annual emissions of 28,000 petrol cars. The release of carbon dioxide into the atmosphere was influenced by seasonal changes, which were stronger in warmer months when river flows were higher and sea ice was less.
The Arctic region has been a source of climate change since the 1970s, warming three times faster than the global average. The study highlights the importance of understanding the influence of coasts and rivers on the Arctic carbon cycle. About half of the Arctic Ocean consists of coastal waters, where the interaction between land and sea is complex. The insights gained from this study extend beyond the study area and provide a broader perspective on environmental change in the Arctic.
Scientists are closely monitoring these changes, including increased river flow and increased runoff of organic matter, as well as the positive effects of open-water phytoplankton blooms due to retreating sea ice. The ECCO-Darwin model plays a central role in the study of these phenomena and their interrelationships in the arctic environment. Because ocean waters act as a critical buffer against climate change, sequestering up to 48% of the carbon from burning fossil fuels, understanding and mitigating these changes remains critically important.
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