What caused the ice ages? Tiny ocean fossils offer key evidence

Since the discovery that atmospheric carbon dioxide (CO2) concentrations were lower during past ice ages, the cause has been a mystery. Now, fossils of ocean algae reveal that a weakening in upwelling in the Antarctic Ocean kept more CO2 in the deep ocean during the ice ages. This brings scientists closer to a complete explanation for the glacial cycle and suggests that upwelling will strengthen under anthropogenic global warming, altering global climate and ocean ecosystems.

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