Nature Climate Change, Published online: 25 July 2025; doi:10.1038/s41558-025-02379-xThe authors use a machine learning approach and in situ pigment samples to identify summer shifts (1997â2023) in the abundance and composition of Antarctic phytoplankton. While smaller phytoplankton groups generally increased, diatom chlorophyll a broadly decreased, with putative impacts on food webs and the carbon sink.