Dynamic Sinking and Surface-Area Based Decay Modeling Reduce Estimates of Gelatinous Zooplankton-Mediated Carbon Export to the Deep Sea

Gelatinous zooplankton (GZ) have been proposed as a potentially important but largely overlooked contributor to the biological carbon pump. However, estimates of GZ-derived carbon transfer efficiency to the ocean floor reflect uncertainties in key parameters that govern carbon export, leading to contrasting interpretations of the role of GZ in the biological carbon pump. This study addresses key simplifications in previous models, that is, constant sinking speed and mass-depending decay, by introducing (a) vertical sinking dynamically coupled to GZ biomass loss due to microbial decay and (b) a novel surface-area-dependent formulation of GZ biomass degradation. Under these new assumptions, global GZ carbon exports and transfer efficiencies are recomputed, capturing processes not considered in earlier models. While global GZ export from the euphotic zone remains similar to previous estimates (Formula presented.), accounting for (Formula presented.) of the total global particulate organic carbon (POC) export, introducing a sinking speed coupled to GZ biomass reduces GZ POC export to the seafloor by (Formula presented.) (to (Formula presented.)). Adding the surface-area based decay reduces export to the seafloor by (Formula presented.) (to (Formula presented.)). These results indicate that while GZ remains a major contributor to carbon export from the euphotic zone, earlier models overestimated GZ contribution to deep-ocean carbon sequestration. Our modeling assumptions are generic and transferable to other types of sinking and decaying particles and can be leveraged to improve estimates of POC export, thus advancing the understanding of the mechanical aspects of the biological carbon pump.