Marine heatwave inhibition of gelatinous zooplankton carbon flux into the deep ocean

Once gelatinous zooplankton (GZ) organisms die, they begin to sink. During the sinking process they decay, with decay rates strongly dependent on ambient ocean temperature - warmer temperatures accelerate mass decay rates in the upper water column during the presence of a marine heatwave, leading to reduced GZ carbon flux into the deep ocean. We leverage this temperature dependence of the decay rates to quantify marine heatwave (MHW) related inhibition of vertical GZ mass fluxes out of the euphotic zone (at 200 m depth). We use established methodologies for MHW detection and quantification to isolate some of the strongest MHW events in the northwest Mediterranean in the past 20 years, specifically June 2003, July 2006 and July 2019 events. We present a new Lagrangian tracking class CarbonDrift for the OpenDrift environment, which couples mass decay and organism sinking rates while allowing for horizontal advection during sinking. We use this Lagrangian model for vertical tracking of the sinking organisms and compute the fraction of the sinking organism mass reaching the bottom of the euphotic zone under i) climatological temperature field and ii) during the three mentioned MHWs. The difference between climatological and MHW simulations allows  quantification of the impact of MHW on the vertical carbon flux out of the euphotic zone. We show that during each of these marine heatwaves, carbon export out of the euphotic zone (at 200 m) decreases by 2 - 6 % in comparison to exports in climatological conditions. The accumulated effect of this inhibition proportionally diminishes Mediterranean's capacity to act as a deep ocean carbon sink.