A novel proxy for past ocean carbon concentration

The shells of ancient plankton hold a chemical fingerprint that could reveal how much carbon the ocean contained millions of years ago. Atmospheric CO₂ is higher now than at any point in the last three million years. To predict how the climate will respond, scientists look to past warm periods when CO₂ was similarly high. But existing chemical proxies for ancient CO₂ rely on uncertain assumptions about how the ocean’s total carbon content changed over time. There is currently no direct way to measure past ocean carbon concentrations, which limits the accuracy of long-term CO₂ reconstructions. This project aims to fill that gap by developing a new proxy based on the ratio of strontium to lithium in the shells of marine plankton. This is fundamental science. If successful, it will give climate modellers a more direct constraint on past ocean carbon, improving reconstructions of ancient CO₂ levels. Better reconstructions feed into the models used to project future warming, sea-level rise, and ocean acidification. While the research has no immediate practical application, similar fundamental advances in palaeoclimate proxies have underpinned the understanding of carbon-cycle feedbacks that now inform international climate policy.