measures indicate that the most dramatic increases in diversity relative to current conditions are expected for photosynthetic eukaryotes and copepods in the Arctic Ocean . However, component eukaryotic taxa, for example diatoms , are projected to lose diversity by 2100 under RCP8.5. Ecosystem models project a decline in nutrient supply that drives the disappearance of less-competitive and larger phytoplankton types, leading to extinction of up to 30% of diatom types, particularly in the Northern Hemisphere, by 2100 under RCP8.5 . Models further suggest that high latitudes are likely to encounter entirely novel phytoplankton communities by 2100 under RCP8.5 . At the polar edges, the increased richness is projected to coincide with high species turnover and increasing dominance of smaller phytoplankton types . These imply pronounced changes to both the oceans' ecological and biogeochemical function, as regions dominated by small phytoplankton typically support less-productive food webs  and sequester less particulate organic carbon  in the deep ocean
IPCC
Climate Change 2022: Impacts, Adaptation and Vulnerability
IPCC Report