Bacteria as Passive Passengers in the Equatorial Pacific Biological Carbon Pump

Abstract Bacteria are important agents modulating the efficiency of the ocean's biological carbon pump (BCP). The long‐standing view considers bacteria as degraders of sinking particulate organic carbon (POC), yet underappreciates their contribution to carbon export. Here, using in situ pump sampling, particle imaging, and bacterial biomarker analysis across the equatorial Pacific, we show that bacteria primarily accompany carbon flux passively, rather than actively attenuating it. Despite rapid attenuation of POC flux with depth in large sinking particles, chemical signatures suggest minimal bacterial remineralization. Nevertheless, bacterial material constituted ∼30% of the POC flux. Bacterial‐mediated POC attenuation was only ∼35% of the bacterial POC export. Such a pattern can be explained by rapid particle sinking and steep vertical temperature gradients, which limit bacterial metabolism but facilitate bacterial biomass export. Our findings reveal that bacteria serve as passive passengers in the BCP, largely contributing to rather than attenuating carbon flux.