Study Links 60 Million Years of Sea-Level Swings to CO2 Regulation
Updated
Updated · Earth.com · Jul 20
Study Links 60 Million Years of Sea-Level Swings to CO2 Regulation
3 articles · Updated · Earth.com · Jul 20
Summary
A new PNAS study says sea-level changes governed phosphate supply in the oceans over the past 60 million years, helping control how much CO2 stayed in the atmosphere.
At low sea levels, shrinking continental shelves released phosphate, boosting marine productivity and organic carbon burial; the resulting low-oxygen waters then freed still more phosphate, reinforcing CO2 drawdown.
The feedback was strongest when sea level sat about 10 to 40 meters above today’s level, a range where oxygen minimum zones aligned with carbon-rich shelf sediments and maximized carbon burial for millions of years.
Data from carbon isotopes, phosphorus accumulation and an iodine-to-calcium proxy for ancient ocean oxygen showed the mechanism largely shut down in the warm Eocene, about 56 million to 34 million years ago, when high seas trapped phosphate on flooded shelves.
The researchers say the carbon-burial window has narrowed over geological time as oxygen minimum zones deepened, making swings in atmospheric oxygen and CO2 less extreme and Earth’s climate more resilient.