CONTRIBUTION OF ACTIVE CARBON FLUX BY ZOOPLANKTON DIEL VERTICAL MIGRATION TO DEEP TOTAL FLUX IN THE NW MEDITERRANEAN

The diel vertical migration (DVM) of zooplankton contributes to the biological pump transporting material from surface to deep waters. We examined the DVM of the zooplankton community in five different size fractions in the open NW Mediterranean Sea. We found differences in DVM at three phases of the seasonal cycle: during the spring bloom, post-bloom, and strongly stratified oligotrophic conditions. DVM intensity was related to the composition of the zooplanktonic assemblage, which also varied between cruises. Euphausiids appeared as the most active migrants in all seasons, and their life cycle conditioned the observed pattern. We estimated active fluxes of dissolved carbon to the mesopelagic zone driven by migrant zooplankton. The amount of dissolved carbon exported was highest during post-bloom conditions (2.2 mmol C respired m-2 d-1, and up to 3.1 mmol C exported m-2 d-1 when DOC release estimations are added). Active transport by diel migrants represented a substantial contribution to total carbon export to deep waters, especially under stratified oligotrophic conditions, revealing the importance of zooplankton in the biological pump operating in the study area