The global contribution of seasonally migrating copepods to the biological carbon pump

Every year, large numbers of zooplankton migrate from the surface ocean to depths of 500–2000 m to hibernate. Through this migration, they actively transport organic carbon to the deep ocean, where it is used to fuel metabolic needs. This active transport of carbon is thought to be highly efficient, as carbon metabolized by copepods is directly injected deep into the ocean's interior. The significance of this process in view of global carbon cycling remains an open question. Here, we focus on five representative, diapausing copepod species (Calanus finmarchicus, Calanus hyperboreus, Calanoides acutus, Calanoides natalis, and Neocalanus tonsus) distributed in the Arctic, Atlantic, Indian, and Southern Oceans. For each species, we compute both carbon injection (how much carbon is transported below the euphotic zone during zooplankton migration and left there as dissolved inorganic carbon) and carbon sequestration (the amount of carbon stored in the ocean's interior following diapausing zooplankton-mediated injection). In total, the five species considered here contribute 0.4–0.8% of total biological carbon export, and 0.8–3.3% of total carbon sequestration mediated by the biological pump (assuming a total carbon export of ~ 10 PgC yr and sequestration of ~ 1300 PgC). Including other species in this inventory would increase the contribution of diapausing copepods to the biological carbon pump, but requires more precise estimates of copepods' distribution, abundance, and metabolic requirements.