Earth's natural climate thermostat explained: sea level, phosphate, and carbon burial

Scientists have identified a feedback loop that helps explain how Earth regulated its climate for tens of millions of years. The mechanism involves sea level changes controlling phosphate availability in the ocean, which in turn affects marine productivity and the burial of organic carbon in seafloor sediments. When sea levels were high, phosphate got trapped on continental shelves, reducing marine growth and allowing CO2 to build up in the atmosphere. When sea levels dropped, more phosphate reached the open ocean, boosting marine life and carbon burial, which pulled CO2 out of the atmosphere and cooled the planet. The research, published in Proceedings of the National Academy of Sciences, found that this carbon burial process was most effective when sea level stood roughly 10 to 40 meters above modern levels. At that sweet spot, low-oxygen waters overlapped with organic-rich shelf sediments, allowing unusually large amounts of carbon to be buried for millions of years. The study used iodine-to-calcium measurements from ancient foraminifera to reconstruct ocean oxygen levels over the past 60 million years. This natural thermostat helps explain why Earth remained warm during the Eocene epoch and gradually cooled afterward. The findings add to our understanding of long-term climate regulation and the role of ocean nutrients in the carbon cycle. For those tracking natural carbon removal processes, this research provides a clearer picture of how geological timescale climate control actually works.