ObsSea4Clim Spotlight on Marine Heatwaves - a quick glimpse into the science, challenges, and project activities related to studying marine heatwaves (MHWs). ObsSea4Clim Spotlight ObsSea4Clim Spotlight is a series of infosheets designed to provide a quick overview of scientific themes addressed in the project. Each document breaks down a key science theme - why it matters, the challenges scientists are tackling, and what ObsSea4Clim is doing about it. Alongside the background, each document provides a handy list of project outputs: publications, presentations, and posters, with direct links to dive deeper into the topic.