Kelp forests are losing their capacity to trap carbon

Kelp forms vast seaweed forests along temperate coastlines, sequestering large amounts of carbon from the atmosphere. However, according to a new study led by the University of Western Australia, warming oceans will likely reduce kelp forests’ capacity to trap atmospheric carbon for extended periods of time in deep ocean stores, thus exacerbating the effects of climate change.

Carbon sequestered by kelp forests can feed other organisms during decomposition, or it can remain trapped in the deep ocean for hundreds or even thousands of years. To better understand how the capacity of kelp forests to build long-term carbon stores will change as oceans warm, the scientists examined kelp decomposition rates at 35 different locations across the Northern Hemisphere. 

By collecting fragments of fresh kelp and placing them inside a mesh bag within a plastic cage tethered to the sea floor for four to 18 weeks, they found that sea temperature has a strong influence on the rate of decomposition, with kelp fragments in cooler waters degrading more slowly. 

On the other hand, sea temperature rises caused by climate change could accelerate decomposition, reducing the amount of stored carbon. The researchers estimate that projected increases in sea temperature of 0.4 degrees Celsius by 2050 could reduce the carbon sequestration potential of decomposing kelp by nine percent.

Fortunately, kelp forests are predicted to expand in higher latitudes as the climate warms. There, slower decompositions rates will likely make these new forests major contributors to long-term ocean carbon sequestration. 

“Our experiment measured kelp carbon turnover across twelve regions throughout the northern hemisphere and found that carbon breakdown was strongly linked to ocean temperature. This suggests that kelp carbon storage could be reduced as the ocean warms and that kelp forests in cool polar environments have potential to be important blue carbon ecosystems,” concluded study lead author Karen Filbee-Dexter, a marine ecologist at the University of Western Australia.

The study is published in the journal PLoS Biology.

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By Andrei Ionescu, Earth.com Staff Writer