Ocean Anoxic Event 1a (OAE 1a), occurring 119.5 million years ago during the Cretaceous period, saw Earth's oceans depleted of oxygen due to massive volcanic CO₂ emissions. This triggered global warming, marine extinctions, and black shale formation. Recent studies highlight parallels with modern climate change and its impact on marine ecosystems.
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By studying prehistoric rocks and fossils emerging from the side of Mount Ashibetsu in Japan, researchers have precisely refined the timing and duration of Ocean Anoxic Event 1a (OAE 1a).
Mount Ashibetsu is a mountain located on the border between Ashibetsu and Furano, Hokkaidō, Japan.
It is part of the Yūbari Mountains.
OAE 1a occurred during the Cretaceous period (145-66 million years ago), marking the time when Earth's oceans became depleted of oxygen. This has led to severe disruption of marine ecosystems.
Causes: Triggered by massive volcanic eruptions that released large amounts of carbon dioxide (CO₂), resulting in global warming and depleting oceans of oxygen.
These conditions created anoxic sea basins where oxygen levels were almost absent.
Impacts: The interaction of CO₂ and seawater produced carbonic acid, which dissolved the shells of marine organisms and reduced oxygen levels.
This led to the extinction of several marine species, especially plankton, and led to the formation of black shales, organic carbonaceous layers preserved in the geological record.
Anoxic sea basins: Bodies of water, often in deep ocean regions, where oxygen levels are extremely low or absent.
Characteristics: Favors the survival of specialized microbes and fungi while inhibiting most aerobic life forms.
Carbon sequestration: Low oxygen levels slow down the decomposition of organic matter, which aids in long-term carbon sequestration, helping to reduce CO₂ levels in the atmosphere.
Examples: Black Sea, Cariaco Basin (Caribbean Sea) and Orca Basin (Gulf of Mexico).
Timing: The event began 119.5 million years ago, confirmed by isotopic analysis of volcanic tuffs from the Japanese island of Hokkaido.
OAE 1a lasted approximately 1.1 million years, indicating an extended period of ocean recovery following CO₂-induced warming and anoxia.
Volcanic activity: Associated with massive volcanic eruptions, such as the Ontong Java Nui complex, which released significant amounts of CO₂ into the atmosphere and oceans.
Contemporary relevance: Highlights parallels between ancient volcanic CO₂ emissions and current human-induced warming.
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PRACTICE QUESTION Q.Consider the following statements regarding Ocean Anoxic Event 1a (OAE 1a):
Which of the statements given above is/are correct?
Answer: b Explanation: Statement 1 is incorrect: OAE 1a occurred during the Cretaceous period, not the Jurassic. Statements 2 and 3 are correct: Massive volcanic CO₂ emissions led to global warming, marine extinctions, and black shale formation during this event. |
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