Modeling of gelatinous zooplankton related carbon export into the deep ocean

Gelatinous zooplankton (GZ) has recently been proposed as one of the potential key contributors to the global biological carbon pump, a process that sequesters substantial amounts of CO2 in the deep ocean through sinking organic matter. However, estimates of GZ contributions to global vertical carbon export vary significantly, due to underestimation of GZ abundance and a limited understanding of GZ-derived organic matter release rates, as well as processes affecting vertical GZ export and degradation rates. Here we derive a first dynamically consistent physical model coupling GZ sinking speed to its mass, to provide high-resolution visualization of global vertical transport of GZ-derived carbon. This contrasts with other works, which have used constant sinking speed dynamics. Furthermore, we propose an improvement to microbial decay modeling, where the GZ biomass degradation rate is a function of its area rather than mass. We solved both models, using constant and variable sinking speeds, inside our newly developed Lagrangian particle tracking OpenDrift python environment, which enables numerically fast vertical and horizontal advection of GZ. We use previously published initial GZ-carbon content data and average GZ carcasses sinking speed measurements as our initial speed values. To model the GZ biomass decay, we use published decay rate dependencies and make use of annual climatological temperature fields. We find that, depending on the model, the carbon exports are between (3.83−4.50) Pg C Y^-1, (1.53 −2.20) Pg C Y⁻¹ and (0.77 − 1.53) Pg C Y⁻¹ at depths of 100 m, 1000 m and at the seafloor, respectively.  In comparison to previous estimates these values are from 8-27 % larger at depths of 100 m, from 16 % lower and up to 20 % larger at depths of 1000 m and from 32 % lower and up to 35 % larger at the seafloor. Finally, we estimate that the inclusion of horizontal advection does not play any major role in the model outcome. This study represents a step towards our understanding of GZ-derived carbon fluxes across ocean depths, the global biological carbon pump and carbon budgets in the ocean.