Oxygen, the life-sustaining element crucial for marine ecosystems, is under threat as our planet warms. The ocean, which relies on its upper layers for oxygen exchange with the atmosphere, faces significant challenges due to climate change. Understanding how ocean oxygen levels redistribute across its interior is essential, yet remains a complex puzzle.
In a groundbreaking study published in Science, researchers led by scientists from the Max Planck Institute for Chemistry and Princeton University delved into the Paleocene-Eocene Thermal Maximum (PETM) to unravel the response of tropical ocean oxygenation. By analyzing microscopic fossils called foraminifera, preserved in marine sediments over millions of years, the team reconstructed past oxygen dynamics.
Nitrogen isotopes within these fossils provided insights into changes in column denitrification, a process indicative of oxygen-depleted zones in the ocean. Surprisingly, the study revealed a decrease in denitrification during the PETM, suggesting a contraction of oxygen-deficient zones despite global warming.
Additionally, the size of foraminifera fossils proved critical. Models correlating body size with environmental factors indicated an unexpected increase in the size of planktonic foraminifera in the central tropical Pacific during the PETM. This phenomenon suggests a rise in tropical ocean oxygenation in the upper layers, contrary to previous assumptions.
The study’s findings shed light on the PETM’s impact on marine biodiversity. While the event triggered significant extinction among deep-sea organisms, surface ocean fauna were relatively less affected. The transient increase in tropical ocean oxygenation likely played a role in preserving habitability, although surface ecosystems still endured substantial disruption.
Despite this oxygenation, it took over a hundred thousand years for surface ocean ecosystems to recover fully. The study underscores the complex interplay between climate change, ocean oxygenation, and marine biodiversity, highlighting the need for continued research to understand and mitigate the consequences of global warming on marine ecosystems.
