Fjords Act as Major Carbon Sinks, Study Says

Fjords, such as those in Norway, don't just make for beautiful landscapes but also act as major carbon sinks that likely play an important role in regulating the planet's climate, a new study says.

After analyzing data from 573 surface sediment samples and 124 sediment cores from fjords around the world, researchers estimate that about 18 million tons of organic carbon is buried in fjords each year - that's the equivalent of 11 percent of annual marine carbon burial globally.

In addition, calculations indicate that per unit area, fjord organic carbon burial rates are twice as large as the ocean average.

"Therefore, even though they account for only 0.1% of the surface area of oceans globally, fjords act as hotspots for organic carbon burial," Dr. Candida Savage of New Zealand's University of Otago said in a press release.

Fjords are long, deep and narrow estuaries formed at high latitudes during glacial periods as advancing glaciers carve out major valleys near the coast. While most people picture Norway when they think of fjords, they are also found in North Western Europe, Greenland, North America, New Zealand, and Antarctica.

These tranquil estuaries provide deep, often low-oxygen marine environments that are ideal for the build-up of carbon-rich sediments. Thus, carbon burial is a natural process that occurs in fjords. It also provides the largest carbon sink on the planet and influences atmospheric carbon dioxide (CO2) levels at multi-thousand-year time scales.

Therefore, according to the new study published in the journal Nature Geoscience, fjords may play an especially important role as a driver of atmospheric CO2 levels during times when ice sheets are advancing or retreating.

The last time ice sheets retreated by around 11,700 years ago - Earth is currently in an interglacial period. But during glacial retreats, fjords would trap and prevent large volumes of organic carbon from flowing out to the continental shelf, where chemical processes would generate CO2.

Once glaciers started advancing again this material would likely then be pushed out onto the shelf and CO2 production would increase.

"In essence," Savage concluded, "fjords appear to act as a major temporary storage site for organic carbon in between glacial periods. This finding has important implications for improving our understanding of global carbon cycling and climate change."

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