Alaska’s groundwater releases a huge amount of carbon into the ocean

The Arctic’s frozen ground has long kept its secrets locked away beneath layers of ice and snow. But as researchers dive deeper into the complex workings of this remote landscape, they’re uncovering startling revelations about how water moves beneath the surface.

A seemingly minor trickle of groundwater beneath Alaska’s tundra is quietly releasing vast amounts of carbon into the ocean.

This finding comes from researchers at The University of Texas at Austin, who discovered that this hidden process is adding an estimated 230 tons of organic carbon per day into the Beaufort Sea during summer.

Groundwater releasing carbon

Although groundwater accounts for only a small portion of the total water reaching the ocean, it is delivering as much carbon as the region’s rivers during the warmer months.

Cansu Demir, who led the research while completing her doctoral degree at the UT Jackson School of Geoscience, now works as a postdoctoral research associate at Los Alamos National Laboratory.

“This study shows that there’s humongous amounts of organic carbon and carbon dioxide released via fresh groundwater discharge in summer,” said Demir.

The researchers found that groundwater discharge in the Arctic is not only significant but may also play an increasing role in carbon release as permafrost continues to thaw.

Role of groundwater in climate change

While carbon emissions from rivers, melting ice, and thawing permafrost are well documented, this study sheds light on a less recognized but equally important contributor.

As fresh groundwater reaches the ocean, it releases carbon dioxide (CO2) that can contribute to climate change. The presence of CO2 in seawater can also lead to ocean acidification, which has long-term consequences for marine ecosystems.

As the Arctic warms, the natural movement of groundwater is changing. The study shows that fresh groundwater is actively flowing into submarine environments along the coastline where the land meets the sea.

This contradicts earlier assumptions that freshwater submarine groundwater discharge in this region was extremely limited. The discovery raises concerns about the long-term effects of increasing groundwater discharge on carbon levels in the Arctic Ocean.

Demir and her team went further by separating freshwater from other groundwater sources. Unlike previous studies, which included recirculated saltwater that had seeped into the ground from the ocean, this research specifically identified sources of fresh groundwater.

The freshwater likely originates from rain, melting snow, thawed shallow ground ice, and possibly deeper permafrost layers.

Groundwater’s contribution to carbon release

Through direct observations and numerical modeling, the researchers measured the volume of fresh groundwater entering the Beaufort Sea and compared it to river discharge.

They found that fresh groundwater accounts for 3-7% of the total discharge from three major rivers in the region during summer. This volume is surprisingly high for an Arctic environment and is comparable to groundwater discharge levels in temperate regions at lower latitudes.

What makes this discovery even more striking is the amount of organic carbon and nitrogen contained in the groundwater. Despite its relatively small volume, groundwater carries nearly as much organic carbon and nitrogen as the rivers in the region.

“In that small amount of water, that groundwater carries almost the same amount of organic carbon and nitrogen as rivers,” Demir explained.

This means that even as Arctic rivers continue to flow and release carbon into the ocean, groundwater is quietly doing the same, adding to the overall impact of carbon release in the region.

Permafrost and its impact

Groundwater does not simply move through soil and sediment on its way to the sea. It interacts with permafrost, a frozen layer of soil and organic matter that has stored carbon for thousands of years.

When permafrost melts, it releases stored carbon into the moving groundwater, which then transports it into the ocean.

This process is similar to how estuaries function, acting as natural reservoirs of organic matter and nutrients. However, permafrost is unique in that it holds a massive amount of trapped carbon.

When it melts, this carbon is no longer locked away but instead becomes part of the natural carbon cycle. The result is a significant increase in the amount of carbon reaching the ocean, which can further contribute to climate change.

“The Arctic coast is changing in front of our eyes,” said Bayani Cardenas, a co-author of the study and professor at the Jackson School’s Department of Earth and Planetary Sciences.

“As permafrost thaws, it turns into coastal and submarine aquifers. Even without this thawing, our studies are among the first to directly show the existence of such aquifers.”

This transformation has far-reaching implications. If warming continues, even more permafrost will melt, increasing the amount of freshwater that moves underground and carrying even more carbon into the ocean.

Potential ecological consequences

The effects of this newly recognized carbon pathway go beyond climate change. The increase in CO2 levels due to groundwater discharge is likely to impact marine ecosystems, particularly in Arctic coastal environments.

One of the most concerning impacts of groundwater contributing to carbon levels is ocean acidification. As more carbon dioxide enters the ocean, it lowers the pH of seawater, making it more acidic.

This shift in acidity can weaken marine organisms such as crustaceans, clams, and snails, which rely on calcium carbonate to build their shells. Acidification can make these creatures more vulnerable, disrupting food chains that support both marine and human communities.

In addition to acidification, the large influx of organic carbon and nitrogen may alter nutrient balances in coastal waters. Changes in nutrient levels can affect marine plant life, algae growth, and the availability of food for larger marine species.

Such disruptions could have cascading effects throughout Arctic marine ecosystems, affecting everything from microscopic organisms to larger fish and mammals.

Growing concern for the Arctic’s future

As climate change accelerates permafrost thaw, the natural movement of groundwater is likely to increase. This means that more carbon will enter the ocean through submarine groundwater discharge, adding to the carbon already released by rivers and melting ice.

Understanding this process is essential for predicting future climate trends and ecological changes in the Arctic. Researchers are continuing to investigate how groundwater moves through permafrost regions and how its carbon content interacts with the ocean.

The findings from this study provide an important foundation for future research, highlighting the need to consider groundwater as a key factor in Arctic climate models.

While much remains to be explored, one thing is clear: groundwater is playing a larger role in Arctic carbon emissions than previously thought.

As the Arctic landscape continues to change, scientists will need to keep a close watch on how these hidden water flows influence both regional and global climate systems.

The study is published in the journal Geophysical Research Letters.

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