(CN) – Scientists announced Friday the discovery of a previously unknown significant source of carbon hidden in the Arctic that has researchers concerned over what it may mean amid the era of climate crisis.
This paper, published in the journal Nature Communication, presents new evidence of significant, undetected concentrations and fluxes of dissolved organic matter entering Arctic coastal waters, with the source being groundwater flow atop of frozen permafrost.
This groundwater can travel from land to sea practically invisibly, but now researchers believe that it carries significant concentrations of carbon and other nutrients to Arctic coastal food webs.
Groundwater is known worldwide to be an important conduit for delivering carbon and various other nutrients to oceans, but it’s a different story in the Arctic. Most of the water in this region remains trapped under the ice that blankets the land, so it’s role here has been relatively unclear.
Scientists were pleasantly surprised to find that this groundwater may be contributing an amount of dissolved organic matter to the Alaskan Beaufort Sea that is nearly equal to what comes from neighboring rivers during the summer.
"We have to start thinking differently about groundwater," said senior author Jim McClelland, professor of marine sciences at UT Austin. "The water that flows from rivers to the Arctic Ocean is pretty well accounted for, but until now the groundwater flowing to this ocean hasn't been."
The research community surrounding this topic has generally assumed that groundwater inputs from land to sea are small in the Arctic because of the perennially frozen ground, or the permafrost, that constrains the flow of water below the tundra surface.
The study explains the process in which the research team sampled the concentration and age of dissolved carbon, as well as nitrogen, in the groundwater flowing beneath the land's surface in the Arctic during the summer.
They discovered that as shallow groundwater flows beneath the surface in different locations in northern Alaska, it picks up new, young organic carbon and nitrogen as expected.
However, they also found that while this groundwater is flowing toward the ocean, it is mixing with layers of deeper soils and thawing permafrost, picking up and transporting century-to-millennia old organic carbon and nitrogen.
This matured carbon being transported by groundwater is suspected to be minimally decomposed and has probably never seen the light of day before it meets the ocean.
"Groundwater inputs are unique because this material is a direct shot to the ocean without seeing or being photodegraded by light," McClelland said. "Sunlight on the water can decompose organic carbon as it travels downstream in rivers. Organic matter delivered to the coastal ocean in groundwater is not subject to this process, and thus may be valuable as a food source to bacteria and higher organisms that live in Arctic coastal waters."
Based on the results from their samples, the research team concluded that the supply of leachable organic carbon from groundwater adds up to about 70% of the dissolved organic matter flux from rivers to the Alaska Beaufort Sea during the summer.
"Despite its ancient age, dissolved organic carbon in groundwater provides a new and potentially important source of fuel and energy for local coastal food webs each summer," said lead author Craig Connolly, a recent graduate of UT Austin's Marine Science Institute.
He added, "The role that groundwater inputs play in carbon and nutrient cycling in Arctic coastal ecosystems, now and in the future as climate changes and permafrost continues to thaw, is something we hope will spark research interest for years to come."
Co-author M. Bayani Cardenas, a professor in the Jackson School of Geosciences, agrees with his colleague’s sentiment, and believes that the effect that climate change has on the Arctic only makes groundwater research even more important.
"The Arctic is heating up twice as much as the rest of the planet. With that comes permafrost thawing and the birth of aquifers," Cardenas said. "It is likely that groundwater transport in the Arctic will be more and more important in the future."
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