Fig. 1: Mesopelagic transformations of downward POC flux at multiple depths investigated across contrasting regions.

a, Schematic of the cumulative transformations of settling particles (denoted by solid vertical bars) due to zooplankton flux-feeding (FF), DVM and MR before particle interception by C-RESPIRE during the initial collection phase at each of three depths (Extended Data Fig. 2). MR (in blue) represents the subsequent incubation phase of C-RESPIRE in which only MR acts on the intercepted particles to decrease POC. b, Deconstruction of the main drivers of the POC flux attenuation. MR (blue areas) is as described in a and is inferred from measured O₂ consumption and a fixed RQ (Methods). Dissolved organic C accumulation rates during incubation were low (representing on average 21 ± 16% of MR; Extended Data Table 4), supporting a close coupling between solubilization and MR. The residual POC flux (open circles) corresponds to the (intercepted) POC measured at the end of the multi-day in situ incubation. Cumulative POC flux (filled circles) is reconstructed using the sum of the residual POC and MR (that is, residual POC flux + MR) and should reflect a Martin curve, represented by the solid black line (Methods). c, Locations of C-RESPIRE deployments overlaid on a map of satellite-derived net primary productivity (NPP) climatology (2003–2018) (obtained from the NASA Ocean Color website and the CAFE algorithm). Green, SG; brown, BEN; red, SAZ; orange, PAPA; blue, MED; purple, SPSG.