Echogram of an Antarctic krill (Euphausia superba) ball in the Southern Ocean. Colours represent reflected sound (and so density), with red showing the largest amount of reflection and white representing empty water. This krill ball was 100 metres deep and measured one kilometre in length. Krill play an important role in transferring carbon into the deep ocean, where it is stored for hundreds of years. However, increases in ocean temperature caused by global warming are damaging krill populations.