Anomalies of Net Primary Productivity under Compound Marine Heatwaves and Microplastics

Marine heatwaves (MHW) and microplastics (MPs) pollution increasingly co-occur, yet the response of phytoplankton net primary production (NPP) to this compound condition remains incompletely characterized, in part because analyses confined to local conditions may overlook nonlocal influences. Here we developed an adaptive machine learning framework to evaluate global NPP anomalies under co-occurring MHW and MPs. The results indicate that comparable compound-stress regimes corresponded to divergent NPP outcomes depending on regional nutrient backgrounds: an anomalous increase coincided with nitrate replenishment in oligotrophic waters, whereas an anomalous decrease coincided with silicate accumulation in iron-limited, diatom-dominated waters. Furthermore, pronounced NPP anomalies frequently exhibited a geographic offset from heatwave cores, a spatial mismatch consistent with a shock-transmission-spillover (STS) framework, here interpreted as a spatial teleconnection between the thermal forcing and the ecological response. Pending in situ validation, these observed associations indicate that monitoring confined to thermal or pollution sources may misplace ecological risk. Consequently, these findings support a shift toward downstream monitoring along current pathways relevant to fisheries and carbon uptake.