The biological carbon pump underpins the oceanic carbon sink and regulates climate change. However, its magnitude, efficiency, and drivers remain poorly constrained in oligotrophic subtropical gyres that cover vast areas of the global ocean. Here, we report particulate organic carbon (POC) export across the upper subtropical South Pacific using ²³⁴Th:²³⁸U disequilibrium, particle imaging, and a suite of biogeochemical measurements. Our results show POC fluxes ranging from 0.28 to 5.36 mmol C m⁻² d⁻¹, with export efficiencies (Ez-ratio) of 2–24%, consistently higher than predictions based on temperature-dependent models. Elevated Ez-ratios were mainly observed within the South Pacific Subtropical Gyre, despite the dominance of small particles in carbon export. Such efficient carbon export is likely driven by limited microbial remineralization and weak zooplankton grazing. A global synthesis of ²³⁴Th-derived Ez-ratios reveals that POC export efficiencies in subtropical gyres are generally low but exhibit substantial spatial heterogeneity, with localized hotspots of enhanced carbon export. We further estimate that subtropical gyres export ~1.3 Pg C yr⁻¹ below the euphotic zone, accounting for 11–22% of the global carbon export. These findings underscore the significant yet underappreciated role of subtropical gyres in global carbon sequestration.

暂无