Signal Shelf sediments hold about 360 billion tonnes of organic carbon

Summary

The report regards marine sediments as one of the largest active carbon reservoirs in the Earth system. The top metre of continental shelf sediments holds about 360 billion tonnes of organic carbon, which makes up 75 to 90 percent of global marine carbon burial. Before the Anthropocene these sediments faced only natural disturbance, but today they are repeatedly stirred up by bottom trawling, marine mining, anchoring and shipping. When the sediments meet oxygen-rich water, the stored carbon can break down and escape as carbon dioxide. The report names minimizing physical disturbance in depositional settings such as shelves, where organic carbon builds up over long periods, as a top priority. Such places are hotspots of biological productivity and key sites for long-term carbon storage and nitrogen removal.