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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 different size fractions (53–200 μm, 200–500 μm, 500–1000 μm, 1000–2000 μm and > 2000 μm) during three cruises carried out in the open NW Mediterranean Sea. We assessed their metabolic rates from empirical published relationships and estimated the active fluxes of dissolved carbon to the mesopelagic zone driven by migrant zooplankton. Within the predominantly oligotrophic Mediterranean Sea, the NW region is one of the most productive ones, with a seasonal cycle characterized by a prominent spring bloom. The study area was visited at three different phases of the seasonal cycle: during the spring bloom, the post-bloom, and strongly stratified oligotrophic conditions. We found seasonal differences in DVM, less evident during the bloom. Changes in DVM intensity were 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. Immature stages, which are unable to perform large diel vertical movements, dominated during the bloom, in contrast to the higher relative importance of migrating adults in the other two sampling periods. The amount of dissolved carbon exported was determined by the migrant zooplankton biomass, being highest during the post-bloom (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). The 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., Spanish Ministry of Economy and Competitiveness. Proyecto FAMOSO CTM2008-06261-C03, SI

extended abstract del poster, In order to investigate the role of turbulence mixing on structuring marine phytoplankton communities, the CHAOS project included a multidisciplinary approach involving specifically designed field observations supported by remote sensing, database analyses, and modeling and laboratory chemostat experiments. Field observations carried out in the outer part of Ría de Vigo in summer 2013 showed that, as a result of increased mixing levels, nitrate diffusive input into the euphotic layer was approximately 4-fold higher during spring tides. This nitrate supply could contribute to explain the continuous dominance of large-sized phytoplankton during the upwelling favorable season. Simultaneous estimates of nitrate diffusive fluxes, derived from microturbulence observations, and picoplankton abundance collected in more than 100 stations, spanning widely different hydrographic regimes, showed that the contribution of eukaryotes to picoautotrophic biomass increases with nutrient supply, whereas that of picocyanobacteria shows the opposite trend. These findings were supported by laboratory and modeling chemostat experiments that reproduced the competitive dynamics between picoeukaryote and picocyanobacteria as a function of changing nutrient supply. The results derived from this project confirm that turbulence and mixing control the availability of light and nutrients, which in turn determine the structure of marine phytoplankton communities., RADIALES-20 (IEO), CHAOS (CTM 2012-30680), Malaspina-2010(CSD2008-00077)

The Margalef´s mandala (1978) is a simplified bottom-up control model that explains how mixing and nutrient concentration determine the composition of marine phytoplankton communities. Due to the difficulties of measuring turbulence in the field, previous attempts to verify this model have applied different proxies for nutrient supply, and very often used interchangeably the terms mixing and stratification. Moreover, because the mandala was conceived before the discovery of smaller phytoplankton groups (picoplankton

The effect of internal wave activity on nutrient supply to the euphotic layer and its potential impact on phytoplankton composition and size-structure remain unexplored in the shelf edge off NW Iberian Peninsula. In August 2013, continuous measurements (yo-yo) of dissipation rates of turbulent kinetic energy, obtained with a microstructure profiler, were carried out during spring and neap tides, covering a complete tidal cycle (25 hours). Every hour the yo-yo was interrupted to collect samples for inorganic nutrient concentration. Microturbulence and nutrient concentration data were combined to compute the nutrient input into the euphotic zone driven by vertical diffusivity. Size-fractionated chlorophyll-a and pigment composition samples were taken for the determination of phytoplankton community structure. As a result of increased mixing levels, nitrate transport to the euphotic layer during spring tides was approximately 4-fold higher (34.6 mmol m-2 d-1) than during neap tides (9.4 mmol m-2 d-1). However, the phytoplankton community was always dominated by large (>20 µm) chain-forming diatoms and seemed to be mainly controlled by the upwelling conditions predominating in late August.

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.