The role of diel vertical migrants in the oceanic carbon pump

Abstract

Active flux performed by migrant biota is still a gap in the knowledge of the biological pump in the ocean. These organisms feed upon epipelagic zooplankton and transport this carbon due to their feeding at the shallower layers and their defecation, respiration, excretion and mortality at depth. Diel vertical migrants (DVMs) in subtropical waters promote a lunar cycle in epipelagic zooplankton biomass, and a rough estimation of this mortality by predation suggests values similar to the mean passive flux. The recent finding that mesopelagic fish biomass in the ocean is one order of magnitude higher, and the discovery of high acoustic backscatter from the surface to bathypelagic depths (4000 m depth) in the equatorial waters of the Atlantic and Pacific Oceans, suggests that active flux is barely known. Evidence of the so-called “Ladder of Migration” below 1000 m depth is presented, shedding some light about the capacity of DVMs to promote true carbon sequestration in the ocean.