Marine plankton size spectra are increasingly used to characterize energy transfer and to estimate carbon export in the ocean. However, the mechanistic pathways linking plankton size structure to carbon export across different oceanic regimes remain poorly constrained. Here, we combine field observations from the western Pacific Ocean, including phytoplankton pigment, zooplankton communities, and particle imagery, to investigate how the coupled size structures of phytoplankton and zooplankton regulate the pathways, magnitude, and efficiency of particulate organic carbon export. To place these regional findings in a broader context, we further integrate a global dataset of zooplankton images derived from scanner and Underwater vision profile systems spanning 1996 to 2022. This allows us to examine, at the global scale, how variations in plankton size structure are linked to carbon export across contrasting productivity regimes. Our results provide new insights into size-based controls on the biological carbon pump and highlight the importance of trophic structure in modulating carbon export efficiency.