A study published by the University of Florida shows that the chemistry of the six main Arctic rivers is changing, with a potential impact on all the planet’s oceans.
A team of American, Russian, Canadian and French researchers from the Arctic Great River Observatory recently published in the journal Nature Geosciences on the chemical changes in Arctic rivers. Conducted over a period of more than 15 years, between 2003 and 2019, the study is based on sampling results from the six main rivers flowing into the Arctic Ocean: the Russian rivers Ob, Yenisei, Lena and Kolyma, and the North American rivers Mackenzie and Yukon. The results show that the waters of Arctic rivers are undergoing a process of chemical change.
The authors underline the importance of such large river systems for the Arctic Ocean. “Rivers integrate processes occurring throughout their watersheds and are therefore sentinels of change across broad spatial scales, ” the authors state in the article. “Nowhere is this more consequential than in the Arctic, where around 11% of the Earth’s river flow flows into a closed basin containing 1% of the world’s ocean volume.”
As the rivers’ chemistry regulates ecosystem functions across the land-ocean continuum of our planet, they also influence both food webs and the global carbon cycle. Simply put, river water and its chemical composition alter the physics of the oceans. What’s more, chemical changes in rivers can also affect the amount of CO2 released into the air, in addition to the way plants and animals can thrive in the oceans.
The scientists focused in particular on three components: dissolved organic carbon, alkalinity and nitrates, showing significant changes in the last two. Alkalinity in Far North rivers increased by 18% over a 17-year period. This means more weathering and decomposition of rocks and greater weathering in watersheds. As for nitrates, which serve as nutrients for plants and animals such as algae and fish, their levels have dropped by 32%. Ultimately, this raises the question of the balance of life in the oceans.
While the study revealed broad trends, pointing to a large-scale disturbance throughout the Arctic, the individual results were not uniform. For example, alkalinity increased in all the rivers studied, except for the Mackenzie, which showed a downward trend. This points to variable mechanisms of change from one river to the next.
Global warming is to blame for these changes: “The Arctic is warming faster than anywhere else on Earth, leading to a multitude of changes, from the thawing of permafrost, which mobilizes long-stored carbon, to changes in vegetation and the transformation of nutrients and carbon in rivers,” says Robert G.M. Spencer, professor and biogeochemist at the University of Florida and one of the study’s authors. All of these phenomena lead to chemical changes in rivers, which in turn have an impact not only on the Arctic Ocean, but on the world’s oceans as a whole.
The permafrost thawing by thermokarst, i.e. the collapse of the landscape, can in particular have an impact on the long-term change in the chemistry of a river depending on the nature of the soil and the extent of the thaw. Thus, the presence of some inorganic nutrients may increase while others, such as dissolved organic carbon, may decrease.
The results show profound and rapid changes, and should open the door to new projects, as it is crucial to understand not only how the Arctic is evolving, but also the pace of this change: “Our results clearly call for continuous and integrated observation of the Arctic land-ocean system in all the different jurisdictions that make up the pan-Arctic territory. But, just as importantly, they reinforce the need for rapid attention to the warming of the Earth’s climate and its multiplier effects in the North”, conclude the researchers.
Link to the study : Tank, S.E., McClelland, J.W., Spencer, R.G.M. et al. Recent trends in the chemistry of major northern rivers signal widespread Arctic change. Nat. Geosci. (2023). https://doi.org/10.1038/s41561-023-01247-7
Mirjana Binggeli, PolarJournal