Photosynthetic marine microbes are the foundation of ocean ecosystems¹. By virtue of their microscopic size, microbes experience the ocean as a viscous medium², and their motion is therefore determined by drift with the ocean currents. Temperature has a direct influence on microbial photosynthesis and metabolism³ and when the ambient temperature exceeds optima for individual species, this can result in sharp declines in growth^4,5. Up until now, the analytical framework for understanding the thermal exposure of microbes has typically involved a Eulerian view – evaluation of temperature fluctuations at fixed points in space. However, for ocean microbes, this framework does not take into account their transport in dynamic seascapes, implying that our current view of change for these critical biota may be inaccurate. In this presentation I will show that upper ocean microbes experience along-trajectory temperature variability up to 10 °C greater than the seasonal variability estimated in a static frame, and that this variability depends strongly on location. These findings demonstrate that advection has the capacity to influence marine microbial community assemblies, such that taxa with narrow temperature performance curves will potentially be restricted to regions of the global ocean where ocean currents are weak or along-trajectory temperature variation is low. The results shift our present understanding of microbial operational temperatures and have implications for understanding the costs and constraints of adaptation.