Global warming triggers abrupt regime shifts in island lake ecosystems in the Azores Archipelago

Global warming significantly alters lake ecosystems worldwide. However, the effects of warming at a regional scale are often overlooked due to the scarcity of multidecadal to centennial regional studies. Here, we examined diatom sedimentary records from five lakes on São Miguel Island (Azores archipelago) over the last 170 years. Our analysis using hierarchical generalised additive models revealed an abrupt shift in the island-wide diatom community around 1982 CE, when the Northern Hemisphere temperature exceeded 0.35 °C above the 20th-century mean. This community regime shift resulted in a 27% loss in regional diatom diversity across the Island. Furthermore, previous anthropogenic impacts may have enhanced lakes’ rapid response to warming. These findings highlight the vulnerability of freshwater island ecosystems to climate warming and emphasise the importance of transitioning from local to regional assessments to preserve regional resilience and prevent irreversible damage to these essential freshwater resources and their biodiversity. Analyses of five sedimentary records show that regional diatom diversity in São Miguel Island (Azores) decreased by nearly 30% around 1982, coinciding with a shift in communities and consistently above-average Northern Hemispheric temperatures.