Recent studies have revealed that variations in ocean density significantly influence the efficiency with which marine plankton incorporate carbon into their shells. This finding has important implications for carbon cycling and the ocean’s ability to reduce atmospheric CO2 levels in the context of climate change. Traditionally, research has focused on the impacts of ocean chemistry and acidification on the biomineralization process of marine plankton. Nonetheless, this pioneering study redirects attention to the essential role of physical ocean characteristics on this important process.