Abstract

Ocean biology is key to the uptake of carbon dioxide from the atmosphere, driving a flux of sinking organic particles through the deep ocean and ultimately to the sea bed. In fact, atmospheric levels of carbon dioxide would be 50% higher without the ocean carbon pump. Antarctic krill are a key part of Southern Ocean ecosystems and could act as a major highway for the transfer of carbon to the deep ocean through their swarming behaviour and bulk egestion of rapidly sinking faecal pellets. However, their contribution is difficult to measure directly because of the patchy nature of krill swarms, and is likely not well represented in global biogeochemical models. In this work, we model the potential hidden flux of carbon originating from Antarctic krill. Our model results suggest that krill faecal pellets sinking to 100 m depth in the marginal ice zone of the Southern Ocean transports 39 million tonnes of carbon seasonally. This corresponds to 17–61% (mean 35%) of current satellite-derived carbon export estimates for this zone. The magnitude of our conservatively estimated flux highlights the important role of krill in carbon export and, the need to incorporate such processes more mechanistically to improve climate model projections.