Ocean Acidification Threatens Diatoms' Carbon Capture

Flinders University researchers have uncovered evidence that shifts in diatom communities—tiny microalgae that form the base of marine food webs—could compromise both the structure of oceanic ecosystems and the deep‑sea carbon sequestration process that helps regulate atmospheric CO₂. The study, published in *Nature Communications*, examined long‑term sediment cores and contemporary plankton samples across the Southern Ocean, revealing a trend toward larger, less calcifying diatom species in warming, acidifying waters. These species produce fewer calcium carbonate shells, which are a key component of the biological pump that transports carbon from surface waters to the deep sea.

The research team used high‑resolution imaging and molecular techniques to link changes in diatom size and composition to reduced food availability for higher trophic levels, including zooplankton, fish, and marine mammals. Simultaneously, the decline in calcifying diatoms weakens the ocean’s natural carbon sink, as fewer shells are formed and subsequently buried in sediments. Modeling projections suggest that if current warming trajectories continue, the Southern Ocean could lose up to 20 % of its diatom‑driven carbon export by mid‑century, potentially amplifying atmospheric CO₂ concentrations and disrupting marine food chains.

These findings underscore the interconnectedness of climate change, marine biology, and global carbon cycling. They highlight the need for integrated monitoring of diatom populations and more robust conservation strategies to preserve the ocean’s capacity to support biodiversity and mitigate climate change.