Scientists have solved a 66-million-year-old climate mystery, revealing how Earth transitioned from a tropical “greenhouse” state to today’s ice-capped world. A team led by the University of Southampton found that ocean calcium levels fell by more than half over this period. The new analysis, published in the journal Proceedings of the National Academy of Sciences (PNAS), suggests that this calcium decline drew carbon dioxide from the atmosphere and drove long-term cooling.
Ocean chemistry and climate
According to the new study, the researchers examined the chemical signals present in the ancient sea fossils (minute organisms) present in the ancient oceans. Their study indicated that the Cenozoic oceans held about twice the level of dissolved calcium compared with the current ocean.
Computer simulations indicated that high levels of calcium meant the oceans held less carbon and released more CO2 into the atmosphere, while falling levels meant the oceans held more carbon, hence more greenhouse gases.
Marine life and carbon storage
This was confirmed by the co-author, Professor Xiaoli Zhou from Tongji University, who indicated that as calcium levels went down, sea life changed the way they formed calcium carbonate, which effectively harvested CO2 from the sky.
Similarly, Prof. Yair Rosenthal of Rutgers University said that the timing of the fall in calcium levels correlates with a decrease in the speed of seafloor spreading, the creation of new ocean floor, which altered rock water chemistry. This indicates the important role of changes in the chemistry of the deep Earth in controlling past climate change.
According to him, changes in ocean chemistry themselves were the cause of past changes in the climate.
