21 February, 2019

Large krill swarms in the Southern Ocean could help remove additional carbon from the atmosphere, in a way that is currently ‘hidden’ in global models. The new study is published today (21 February) in Nature Communications.

Antarctic krill form some of the highest concentrations of animal biomass in the world’s oceans. They produce carbon-rich faecal pellets, which sink in the water column and can transfer carbon from the atmosphere to the deep ocean. This study provides the first estimate of how much carbon large swarms of Antarctic krill, living at the edge of the sea ice, can draw down and store through their faecal pellets. The efficiency of this process has an important influence on our global climate.

Krill feed on single-celled plants known as phytoplankton, which drawn down carbon from the atmosphere. Krill generate carbon-rich faecal pellets which are ingested by other animals like zooplankton or sink to the ocean floor. This process is part of the biological carbon pump.

Results showed that Antarctic krill swarms are responsible for 35% of regional carbon removed from the surface water in the Southern Ocean, when compared to model estimates based on satellite and field measurements. The patchy nature of krill swarms means, at present, it is difficult to directly measure the contribution of krill to carbon storage. Global estimates based on these limited data are therefore likely to underestimate the contribution from the Southern Ocean.

Acoustic instruments are used to detect swarms of Antarctic Krill in the Southern Ocean. Scientists can calculate the depth, size and density of krill swarms from images like these. Photo Credit: Sophie Fielding.

Researchers estimated the krill density in the region using data from scientific net samples stored within the KRILLBASE scientific database. They combined this with estimates of krill faecal pellet production based on previous scientific research to gain an understanding of the potential ‘hidden’ carbon linked to Antarctic krill in the Southern Ocean.

Dr Anna Belcher, lead author and biogeochemist at British Antarctic Survey says:

“Our study reveals that large krill swarms in the Southern Ocean could remove a significant amount of carbon from the atmosphere. This is exciting because it highlights, for the first time, how important Antarctic krill may be for carbon storage on a global scale.

Currently, this process is not well represented in many global climate models, so the next steps are to test how including krill affects our estimates of ocean carbon storage.”

Krill faecal pellets drive hidden pulses of particulate organic carbon in the marginal ice zone by A. Belcher, S. A. Henson, C. Manno, S. L. Hill, A. Atkinson, S. E. Thorpe, P. Fretwell, L. Ireland, G. A. Tarling published in Nature Communications here.