The greatest rise in marine biodiversity in all of Earth’s history surprisingly was not fuelled by ocean oxygenation. Instead, oceanic redox stability appears to have favoured increased ecosystem resilience and – ultimately – a massive rise in global biodiversity levels. Oxygen rise occurred later…

A drill core close to Kinnekulle in Sweden reveals the redox state of the global oceans 470-460 million years ago. Photo: Mikael Calner.

PhD student Alvaro del Rey measured the uranium isotope composition of Middle Ordovician carbonates in Kinnekulle, Sweden, and discovered that the radiation of animals coincided with stable, albeit still more deoxygenated ocean redox conditions than today. Marine oxygen levels increased after the main peak of the biodiversification episode, the study showed.

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The standing cumulative biodiversity dramatically increased at the Dapingian-Darriwilian boundary – in great part due to the lack of extinctions. Thus, animal ecosystems became more resilient than before. The new study suggest stability rather more oxygenated conditions in the oceans was an important factor in this. Previous studies have shown that the climate cooled at this time (Trotter et al. 2008; Rasmussen et al, Sci. Rep 2016). Climatic cooling will both increase O2 solubility and better ventilate the oceans – even if atmospheric pO2 levels were likely still lower than today (Dahl et al. PNAS 2010; Lenton et al. PNAS 2016).

The new study is published in Nature Communications Earth & Environment.

The official press release from University of Copenhagen is found here.