Blue Carbon Sinks on Polar Seabeds and Their Feedbacks on Climate Change

Abstract

Blue carbon held in polar organisms has been little considered in terms of global carbon sinks and impacts on climate change. Although the magnitude of sinks is small compared with elsewhere, they are amongst the biggest negative feedbacks on climate. As polar seas lose seasonal sea ice, ice shelves and glaciers retreat, new and longer phytoplankton blooms are occurring. This in turn supports the growing and extensive, long-lived, benthic biomass which is effective at storing and ultimately sequestering carbon. By far, the biggest impact per area is ice shelf collapse—a new giant iceberg may generate a million tons of blue carbon. However, losses of seasonal sea ice occurs over a far bigger area across the Arctic and West Antarctic shelves and thus is more important feedback. Blue carbon gains from glacier retreat are likely to be highly productive and efficient hotspots but ultimately occupy only small areas relative to a total shelf space. Small increases in temperature, as has happened to date, seem likely to increase polar blue carbon gains but big (2 °C) changes, ocean acidification and plastic pollution are all considerable threats to polar blue carbon natural capital.