Thawing Arctic permafrost is releasing ancient carbon into the ocean, raising fears that microbes could turn it into greenhouse gases and accelerate climate change. But sediment cores collected near Canada’s Herschel Island reveal a more reassuring twist: most of this land-based carbon becomes buried in the seafloor, while only about 10 percent is converted into gases.

Permafrost in the Arctic stores large quantities of organic carbon. When the frozen ground thaws or coastal sections erode, this carbon can enter the sea, where microorganisms can…

Thawing Arctic permafrost is releasing ancient carbon into the ocean, raising fears that microbes could turn it into greenhouse gases and accelerate climate change. But sediment…