WE HACK the climate at our peril. Volcanoes spewed so much sulphate into the atmosphere 94 million years ago that the oceans were starved of oxygen and 27 per cent of marine genera went extinct. Geoengineering our climate could inflict a similar fate on some lakes.
So claims Matthew Hurtgen at Northwestern University in Chicago, who with his colleagues measured sulphur isotopes in sediments on the floor of the Western Interior Seaway. The WIS was a vast body of water that divided the continent of North America down the middle at the time. The team also developed a model to simulate the impact of volcanoes on ocean chemistry.
Before oceanic oxygen levels tumbled, something caused a big change in atmospheric sulphate levels. 鈥淭hat something was probably volcanoes,鈥� says Hurtgen. He says their sulphate emissions triggered vast phytoplankton blooms and much of the ocean鈥檚 oxygen was gobbled up as these died and decomposed. According to the team鈥檚 model, oceanic sulphate was extremely low prior to the eruptions (Nature Geoscience, ).
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This has implications for geoengineering, says Hurtgen. 鈥淟ike the mid-Cretaceous ocean, most modern lakes are poor in sulphate, so it鈥檚 possible that geoengineering the climate [using sulphate aerosols to reflect sunlight] could trigger blooms and ultimately anoxia in some lakes.鈥�
