About Ocean Anoxic Event 1a (OAE 1a):

• OAE 1a occurred during the Cretaceous Period (145–66 million years ago), marking a time when Earth’s oceans became depleted of oxygen. This led to severe disruptions in marine ecosystems.
• It was triggered by massive volcanic eruptions, which released large amounts of carbon dioxide (CO₂), resulting in global warming and oxygen depletion in the oceans.
• These conditions created anoxic marine basins, where oxygen levels were nearly absent.
• Impacts: The interaction of CO₂ and seawater formed carbonic acid, dissolving marine organisms’ shells and reducing oxygen levels.
• Resulted in the extinction of several marine species, particularly plankton, and led to the formation of black shales, organic carbon-rich layers preserved in geological records.
• Anoxic marine basins: Bodies of water, often in deep ocean regions, where oxygen levels are extremely low or absent.
• Characteristics: Favor the survival of specialized microbes and fungi while inhibiting most aerobic life forms.
• Carbon Sequestration: Low oxygen levels slow the decomposition of organic matter, aiding in long-term carbon sequestration, which helps reduce atmospheric CO₂ levels.
• Examples: Black Sea, Cariaco Basin (Caribbean Sea), and Orca Basin (Gulf of Mexico).

Key Highlights of the Recent Study:

• Timing: The event began 119.5 million years ago, confirmed through isotopic analysis of volcanic tuffs from Japan’s Hokkaido Island.

• OAE 1a lasted approximately 1.1 million years, indicating the extended recovery period for oceans after CO₂-driven warming and anoxia.
• Volcanic activity: Linked to massive volcanic eruptions, such as the Ontong Java Nui complex, which released significant CO₂ into the atmosphere and oceans.
• Modern relevance: Highlights parallels between ancient volcanic CO₂ emissions and current human-induced warming.
• Warns that rapid modern warming could trigger similar disruptions in marine ecosystems and potentially lead to a Holocene extinction event.