Bathypelagic fauna as a main driver of carbon sequestration in the ocean

Abstract

Sequestration, in contrast to export, is a mechanism of the biological pump occurring when carbon cannot return to the atmosphere in at least 100 years, normally the carbon transported below 1000 m depth. Pelagic fauna release carbon at depth through respiration, egestion, excretion, moulting, lipid consumption and mortality supporting deep-sea food webs. Knowledge about this transport in the mesopelagic layer is growing. However, the role of the pelagic fauna to fuel the bathypelagic zone, the layer where effective carbon sequestration occurs, is largely unknown. Here we report net zooplankton biomass in the meso- and bathypelagic zones showing significant relationships with primary production (PP) at a global scale during the Malaspina Circumnavigation Expedition. We also reviewed available data on zooplankton biomass at the different biogeographical provinces also showing significant correlations with large-scale estimates of PP, implying the transference of a significant fraction of PP from the epipelagic to the deep ocean. Carbon sequestration assessed only from conservative estimates of zooplankton mortality in the bathypelagic was 0.43 PgC y-1, in the order of recent estimates of gravitational carbon sequestration. These values and those recently reviewed due to lipid consumption almost triples ocean carbon sequestration estimates in Westerlies and Polar biomes. These results point at a pivotal role of the pelagic fauna in ocean carbon sequestration as, besides zooplankton, downward transport by macroplankton and micronekton should also be accounted for. Our results raises the question of whether we are severely underestimating carbon sequestration in the ocean