Sperm whales are doing their bit for the environment every time they defecate. When the giant mammals blast air from their blowholes, they pump carbon dioxide into the atmosphere, contributing to greenhouse gas emissions. But a new study of sperm whales in the Southern Ocean indicates that they pay back their carbon debt—and then some. The whales feed at great depths, ingesting squid, octopus, and other animals rich in iron, and then defecate near the water surface where this iron-rich waste fertilizes phytoplankton. The phytoplankton in turn use more carbon for photosynthesis, removing 240,000 metric tons more carbon from the atmosphere annually than the sperm whales respire, the researchers report online tomorrow in the Proceedings of the Royal Society B. Other marine mammals, such as pygmy and dwarf sperm whales, may also be eco-warriors, the team reports, highlighting another downside to commercial whaling.
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