Species → Sperm Whale
Sperm Whale
Physeter macrocephalus
What if it disappeared?
Impact HighWithout sperm whales feeding at depth and then defecating near the surface, in the photic zone, the Southern Ocean would lose an annual input of about 50 tonnes of iron — a natural fertilizer that today fuels phytoplankton production and the net export of roughly 200,000 tonnes of carbon to the depths each year, more than these same whales emit by breathing.
DocumentedDetail
Lavery, T.J. et al. (2010). Iron defecation by sperm whales stimulates carbon export in the Southern Ocean. Proceedings of the Royal Society B, 277(1699), 3527–3531.
The mechanism differs from the one documented in the North Atlantic right whale (see that entry): where the general "whale pump" relies on nitrogen and nutrients brought up from all depths, this one specifically targets iron, a micronutrient that limits phytoplankton growth in the Southern Ocean. The authors' calculations, based on a population of about 12,000 sperm whales in that ocean, show that the iron input exceeds what would be needed to offset the carbon the whales themselves respire — a net negative carbon balance, making them a sink rather than a source.
If the Southern Ocean's carbon-sink capacity scaled proportionally with the sperm whale population, industrial whaling — which reduced the species from about two million individuals before exploitation to roughly 840,000 worldwide today — would have considerably weakened this service, though its exact scale remains difficult to quantify.
ExtrapolatedDetail
Extrapolation à partir de Lavery et al. 2010 et des estimations de population préindustrielle et actuelle.
The inference assumes a proportional relationship between the number of sperm whales and the iron they defecate, plausible but not measured directly over so long a period. The relevant figure would be the Southern Ocean's specific sperm whale population (12,000 individuals) rather than the global population, and its own historical trajectory is less well reconstructed than the world total.
What's missing to confirm it: A historical reconstruction of the sperm whale population specifically in the Southern Ocean over the industrial whaling period would confirm the true scale of the loss and recovery of this particular carbon sink.
Documentation
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Lavery et al. (2010) — Iron defecation by sperm whales stimulates carbon export in the Southern Ocean, Proceedings of the Royal Society B
Accessed August 7, 2026
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Current global population size, post-whaling trend and historical trajectory of sperm whales, Scientific Reports
Accessed August 7, 2026
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IUCN — Red List Updates Published for Sperm Whales (2025)
Accessed August 7, 2026
Last verified: August 7, 2026