New research from the University of Oxford reveals that sea level changes have played a key role in stabilizing Earth's climate over the past 60 million years. The study shows that rising and falling sea levels controlled the availability of phosphate, an essential ocean nutrient, which in turn influenced how much organic carbon was buried in marine sediments. When sea levels dropped, phosphate was released from continental shelves, fueling marine life blooms that pulled carbon dioxide out of the atmosphere and buried it in low-oxygen zones. The feedback loop worked strongest when sea levels were 10 to 40 meters above today's level, aligning oxygen minimum zones with carbon-rich sediments. During the Eocene epoch, high sea levels shut down this mechanism, keeping carbon in the atmosphere and the planet warm. Over time, the system has become more resilient, narrowing the window for carbon burial and stabilizing both oxygen and CO2 levels. This research helps explain a long-standing gap in climate science: where atmospheric carbon went as Earth cooled. It also highlights the natural processes that have kept the planet livable for millions of years, offering insights into how carbon cycles operate on geological timescales.
