Carbon Stores In Arctic Soil Surprisingly Unchanged By Warming Climate, Study Says

Because of increased temperatures resulting from climate change, researchers studying carbon sinks in the Arctic -- the world's most rapidly warming biome -- imagined that the region would have transformed from a carbon repository to a carbon emitter.

But the research into carbon storage in the Arctic revealed some unexpected revelations about the resiliency of the Arctic ecosystem.

When Seeta Sistla, a doctoral student at University of California, Irvine, went to the U.S. Arctic Long-Term Ecological Research site at Toolik Lake in northern Alaska, which has been in operation since 1989, she initially observed signs typical of warming climates, such as low-lying, shallow-rooted vegetation giving way to taller plants with deeper roots; greater wood shrub dominance; and increased thaw depth.

But what Sistla and her colleagues did not expect to find was that that two decades of slow and steady warming had not changed the amounts of carbon in the soil, despite changes in vegetation and even the soil food web.

"We expected that because of the long-term warming, we would have lost carbon stored in the soil to the atmosphere," said Sistla's advisor Josh Schimel.

Schimel said the expectation was that the gradual warming of the surface would accelerate the melting of the upper layers of frozen earth, releasing the greenhouse gas into the air. Because high latitudes contain nearly half of all global soil carbon in their ancient permafrost -- permanently frozen soil -- Schimel said even a few degrees' rise in temperature could be enough to release massive quantities, turning a carbon repository into a carbon emitter.

But in a piece of new research, Sistla reports that increased plant growth appears to have facilitated stabilizing of soil carbon loss.

"We hypothesize that net soil carbon hasn't changed after 20 years because warming-accelerated decomposition has been offset by increased carbon inputs to the soil due to a combination of increased plant growth and changing soil conditions," Sistla said.

She said that increased plant productivity caused by the rising temperatures is a reflection of the complexity of the biome.

"These changes reflect a complicated feedback," Sistla said. "Shrubs trap more snow than the lower-lying vegetation, creating warmer winter soil temperatures that further stimulate both decomposers and plant growth. Shrubs also increase summer shading, which appears to have reduced decomposer activity in the surface soil by reducing the greenhouse effect during the summer."

The study is published in the journal Nature.