Whale-Mediated Iron Recycling

node · earth · Southern Ocean and other baleen whale feeding systems

The mechanism behind the krill paradox - the observation that removing the great whales did not leave more krill behind, it left less. Baleen whales feed at depth on iron-rich krill and defecate at the surface, returning iron to the sunlit layer where phytoplankton, the krill's own food, can use it. The 2021 consumption study estimates that Southern Ocean baleen whales recycled around 1.2 x 10⁴ tonnes of iron a year before whaling, against around 1.2 x 10³ tonnes a year today. On that reading the whales were not simply consumers of a krill stock but a large part of what kept it fertilised, and the ecosystem that was left after whaling was not the same ecosystem minus whales.