| 23 Feb 2026
Impacts of ridge-induced upwelling on the biological carbon pump in the tropical Northwestern Pacific
Abstract. Submarine ridges are prominent topographic features in the global ocean, yet their role in regulating the biological carbon pump remains underexplored. In this study, we investigated the spatial variability of phytoplankton production, particle dynamics, and carbon export along a meridional transect in the tropical Northwestern Pacific, spanning a warm eddy (WE), a cold eddy (CE), and the Kyushu-Palau Ridge (KPR). A suite of in situ measurements, including 14C-based primary production, HPLC pigment analysis, and particle profiling via Underwater Vision Profiler (UVP5-HD), was used to assess regional differences in biological carbon pump processes. Marked thermocline shoaling and nutrient uplift were observed in both the CE and KPR regions, but the KPR-derived upwelling waters had higher nutrient concentrations, resulting in the highest nutrient inventories in the upper 200 m and supporting elevated primary production (142.05 mg C m-2 d-1) and phytoplankton biomass there. Correspondingly, the KPR region exhibited the highest particle volume concentrations in the upper 200 m, followed by the CE, with the WE and background regions showing the lowest values. The 0–2000 m water column in the KPR region was also characterized by a substantially greater contribution of large particles (ESD ≥ 500 μm), which in turn supported enhanced particulate organic carbon (POC) export in this area. POC fluxes in the KPR region reached 9.04 ± 6.74, 5.52 ± 0.10, and 3.09 ± 1.96 mg C m-2 d-1 at 200 m, 1000 m, and 2000 m, respectively, which were 2.8 to 5.7 times higher than those in the CE region and 5.9 to 11.4 times higher than in the background region. Consistently, export efficiency (e-ratio) peaked in the KPR region (10 %), exceeding those in the CE (3 %), WE (3 %), and background (5 %) regions. Using the KPR as a representative case, our results highlight the critical role of ridge-induced upwelling in regulating phytoplankton production and particle dynamics, as well as enhancing biological carbon export and surface–deep coupling in oligotrophic oceans. These findings underscore the importance of incorporating such topographic processes into global oceanic carbon cycle research.
Review of Impacts of ridge-induced upwelling on the biological carbon pump in the tropical Northwestern Pacific by Guo et al.
General comments
This is an important contribution showing the impact of oceanic topographic features on POC fluxes, as these are often overlooked in flux assessments. However, there are substantial methodological considerations that I detail below.
Detailed comments
L32. It is unclear what you mean by background regions.
L57-61. These few sentences could be streamlined.
L63. Could you here mention a depth horizon to measure the efficiency of the BCP?
L85. “The strength of the BCP” has not been defined.
L135. Please correct to UVP5.
L142. There should be a DOI associated with the product.
L149. D3 seems to be at the edge of the eddy. Why did you choose to include it in BR rather than WE?
L174. By samples, do you mean filters or filtrates?
L224-225. Why not use Zooprocess? Will the custom scripts be made available?
L225. Please change equivalent spherical diameter to equivalent circular diameter throughout the manuscript.
L263. This set of parameters may not be adequate for your study area. If you want to use globally estimated parameters, then you could also consider the parameters determined in Clements et al. 2023 (https://doi.org/10.1029%2F2022GB007633). I suggest using several sets of parameters from the literature so to see how it may impact your flux estimates. Or the use of this particular set of coefficients and how it may impact your results should at least be discussed.
L269. Why do you use the UVP flux at 150 m and not at the base of the euphotic zone?
L292-293. How does that tell you that the water column is stratified? What is the temperature below?
Figure 2. It could be useful to display the MLD on the figures. It is also really hard to read salinity values on the upper right plot.
L332. Are you referring to integrated values? Can you also say in the method how you integrate nutrient concentrations over the water column?
L353-359. What is the confidence in determining phytoplankton groups?
Figure 4. What does “Haptophytes-6” mean?
L385. Would it be relevant to also compare this with attenuation here?
L407. It would be interesting to compare metrics between stations, such as the attenuation coefficient or the transfer efficiency.
L424. “POC flux was significantly positively correlated with PVC” since it is estimated from particle size distribution, this is expected. This is a spurious correlation.
Figure 8. You show many correlations that you don’t mention in the text. I would also suggest to not show correlation values if not significant. It would be interesting however to compare nutrient concentration to the metrics mentioned above, or to also relate them to fluxes below. This figure also needs to be described more in depth or removed. Right now this looks like a lot of information and it is hard to extract a clear message from it. For example, is it useful to have the correlation of POC fluxes with depth or salinity?
L551-553. Is there literature data for the area about grazing rates?
L530-532. Could it also be due to lateral transport along the ridge?
L532-533. Here the transfer efficiency would be useful to support this statement.
L542-546. Can you relate that to phytoplankton community structure? What type of particles do we expect? Here a bit of literature regarding the role of the dominant phytoplankton groups in promoting export would be useful.