Marine heatwave and climate change impacts on gelatinous zooplankton carbon flux in the global ocean

In this study we investigate how marine heatwaves (MHWs) and future ocean warming scenarios affect the vertical carbon export mediated by gelatinous zooplankton (GZ) in the global ocean. The physical mechanism of MHW impact on carbon export is based on strong temperature dependence of zooplankton decay rates: warmer ocean accelerates the decay while colder environment inhibits it. Building on prior modeling frameworks, we introduce CarbonDrift, a new Lagrangian tracking module of the OpenDrift framework, developed specifically to simulate GZ sinking and decay. A key innovation is the coupling of sinking speed to organism mass, and the inclusion of modeled decay as either proportional to total mass or to the organism surface area. This dual approach allows for more realistic estimates of how warming influences vertical transport. We apply CarbonDrift globally to quantify GZ-mediated carbon fluxes under both recent MHW events and projected 21st-century ocean warming scenarios (SSP245 and SSP585). We show that MHWs locally inhibit carbon export by accelerating GZ decay and reducing sinking efficiency, although global impacts remain modest due to regional compensation. In contrast, long-term ocean warming leads to substantial reductions in deep carbon export, particularly below 1000 m and to the seafloor. Area-dependent decay models predict even stronger reductions than mass-based models. We further introduce the concept of a minimum initial sinking speed required for GZ biomass to reach deep ocean layers — a threshold that increases with ocean warming. Although the transfer efficiency (deep vs. surface export) remains high, it declines modestly under warming scenarios, pointing to a weakening of the soft-tissue biological carbon pump in a warming ocean.