Throughout the Arctic, fallen trees make their way from forests to the ocean by way of rivers. Those logs can stack up as the river twists and turns, resulting in long-term carbon storage. A new study has mapped the largest known woody deposit, covering 51 square kilometers (20 square miles) of the Mackenzie River Delta in Nunavut, Canada, and calculated that the logs store about 3.4 million tons (about 3.1 million metric tons) of carbon.