The Biological Gravitational Pump (BGP) and Physical Particle Injection Pumps (PIPs) are key pathways for deep-ocean POC transport, yet their spatial patterns and impacts on mesopelagic carbon transfer efficiency remain unclear. Using the Northwestern and Equatorial Pacific as a natural laboratory, this study integrates BGC-Argo float data, CbPM-derived NPP, and historical sediment trap records to quantitatively reconstruct carbon flux from the surface to the twilight zone base (1000 m).
The results indicate that although the BGP is the dominant mechanism for POC export from the euphotic zone (contributing approximately 85%–95%), the synergistic effects of the mixed-layer pump (5%–15%) and the eddy subduction pump (3%–10%) in the subpolar and transition zones significantly enhance POC export. This synergy raises the total annual mean carbon flux in the euphotic zone of this region to 2.9–3.0 mol C m⁻² yr⁻¹. Notably, while the eddy pump has a limited contribution to the annual carbon budget, it acts as a powerful intermittent transport mechanism capable of exporting up to 130–140 mmol C m⁻² d⁻¹ of POC over a short period during summer frontal events.
Furthermore, this study reveals significant spatial heterogeneity and an "Export-Transfer Efficiency Paradox": oligotrophic low-latitude regions (e.g., the Eastern Equatorial Pacific), despite having a lower euphotic carbon export (~1.4 mol C m⁻² yr⁻¹) and extremely low export efficiency (~3%), exhibit a relatively high mesopelagic transfer efficiency (~10%). Conversely, high-latitude carbon export hotspots demonstrate exceptionally high export efficiency (15%–18%), yet their deep transfer efficiency is markedly reduced (only 4%–7.5%). Specifically, deep carbon transfer efficiency and the diatom community exhibit a significant latitudinal dependence. In low-latitude regions, diatom abundance is positively correlated with transfer efficiency; their heavily silicified frustules generate a strong "ballast effect," effectively protecting particles from mesopelagic degradation. In contrast, in high-latitude regions, transfer efficiency is negatively correlated with diatom abundance. The massive export of fresh, labile organic matter from diatom blooms provides abundant substrates for mesopelagic microbes, thereby exacerbating remineralization. Concurrently, the alleviation of iron limitation in the subpolar mesopelagic ocean further activates the metabolic activity of heterotrophic bacteria and enhances respiration, emerging as a critical bottleneck that limits deep-sea carbon sequestration efficiency at high latitudes.
This highly quantified, physico-biologically coupled framework provides a scalable foundation for predicting global mesopelagic carbon cycling and transport efficiency.