The research, led by Professor Jordon Hemingway, overturns long-standing assumptions about carbon storage during critical geobiological eras. Analysis revealed that between 1,000 and 541 million years ago, oceans held 90 to 99 percent less dissolved organic carbon than today, not more as previously believed. This challenges prevailing explanations for the link between ice ages, oxygen surges and the rise of complex life.
Dissolved organic carbon, generated by photosynthetic organisms and recycled by microbes, is today a massive reservoir containing 200 times more carbon than is found in living marine organisms. For decades, scientists argued that this pool must have been especially large during the Proterozoic era to drive major climate and biological shifts. The new findings suggest the opposite.
According to the team, the decline in ancient dissolved carbon likely resulted from larger organisms sinking rapidly to the seafloor, bypassing recycling processes in the oxygen-poor deep ocean. Only after the second great oxygenation event did marine oxygen levels rise sufficiently to restore the reservoir to modern levels of around 660 billion tonnes of carbon.
Lead author Nir Galili emphasized the wider implications: "We need new explanations for how ice ages, complex life and oxygen increase are related." The study also carries relevance for today, as human-driven warming and ocean deoxygenation could echo conditions that reshaped Earth's biosphere in deep time.
Research Report:The geologic history of marine dissolved organic carbon from iron oxides
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