A relict forest biome, once covering a large tract of Brazil, continues to export significant quantities of charred carbon to the ocean each year, reports a study published online this week in Nature Geoscience. On entering the deep ocean, charred carbon remains largely resistant to degradation, and release into the atmosphere, on timescales of centuries to millennia.

Before being destroyed by slash and burn practices, Brazil’s Atlantic Forest was one of the largest tropical forest biomes on Earth. Thorsten Dittmar and colleagues combined historical records of land cover with satellite data to assess the amount of charred carbon generated by the burning of this biome, which started in the sixteenth century and ceased in 1973. They estimate that burning generated 200-500 million tonnes of charred carbon. Measurements from a river draining the region show that significant quantities of this charred carbon continue to be exported to the ocean each year.