Iron is very rare in the upper layers of the world´s oceans, where photosynthesis is possible and therefore biological activity and concentration of living biomass is highest, making the mineral a growth-limiting nutrient in 40 percent of the world’s oceans, including the Southern Ocean around Antarctica.

It is why geoengineering minds have suggested ocean iron feritilisation may be effective to spur plankton growth and thereby increase CO2 uptake. Around Antarctica, it turns out, nature already does that for us.

An international research group led by Kathrin Schmidt of the British Antarctic Survey [that we still owe a big thank you for accidently discovering the Antarctic ozone hole in 1985 – without Montreal we would have been toast by now] have researched Antarctic krill behaviour and found [publication in Limnology and Oceanography] the shrimp-like crustaceans have a different dining habit than previously assumed.

Ocean iron recycling

Indeed they do feed on phytoplankton in the upper layers of the water column, but year-round a big portion [an estimated 20 percent] of the krill population descends up to 2 kilometers to reach the ocean floor and – this was discovered by examining stomach content of krill at the ocean surface – feed on copepods [a much tinier type of crustacean] and ocean sediments, rich in iron.

‘Bio-geoengineering’

As the krill swims back up, it behaves like a tiny bio-geoengineer, refertilising the ocean ecosystem with iron – and allowing a bloom in phytoplankton that not only the krill and the many krill eaters depend on, but that may also be ‘beneficial’ to the world’s climate, as plankton growth is one of the most important mechanisms for CO2 uptake and – as long as there is some sort of deep sea sedimentation – structural CO2 storage as well.

Accelerating CO2 rise

Unfortunately the new findings are no good news. If krill is that important for the natural CO2 balance, the witnessed decline in krill populations is yet another disturbance of our planet’s carbon cycle, with increased emissions and decreased sequestration both adding up to rising atmospheric CO2 concentrations.

It is no longer just our fossil fuel consumption and last year’s associated record-breaking CO2 emissions – it may also be the Amazon drought as a positive climate feedback and indeed the krill decline that is co-responsible for the acceleration in the CO2 concentration rise – that according to NOAA reached +2.6 ppm in 2010.

© Rolf Schuttenhelm | www.bitsofscience.org