The existence and properties of mesoscopic self-assembly structures formed by surfactants in protic ionic liquid solutions are reported. Micellar aggregates of n-alkyltrimethylammonium (n = 10, 12, 14, 16) chlorides and bromides and of n-alkylpyridinium (n = 12, 16) chlorides in ethylammonium nitrate and propylammonium nitrate were observed by means of several experimental techniques, including surface tension, transmission electron micrography, dynamic light scattering, and potentiometry using surfactant-selective electrodes. The effect of the alkyl chain length of both solute and solvent molecules on the critical micelle concentration is discussed, and a Stauff-Klevens law is seen to apply to surfactant solutions in both protic ionic liquids. The counterion role is also a matter of study in the case of alkyltrimethylammonium-based surfactants, and the presently reported evidence suggests that the place of the surfactant counterion in the Hoffmeister's series could determine its effect on micellization in IL solution. The size distribution of the aggregates is also analyzed together with the Gibbs free energies of micellization and the minimum surface area per monomer in all of the studied cases. All of the hereby reported evidence suggests that the negative entropic contribution arising from the release of the solvent layer upon micellization is also the driving force of conventional surfactant self-association in protic ionic liquids.

The input of new nitrogen into the euphotic zone constrains the export of organic carbon to the deep ocean and thereby the biologically mediated long-term CO2 exchange between the ocean and atmosphere. In low-latitude open-ocean regions, turbulence-driven nitrate diffusion from the ocean's interior and biological fixation of atmospheric N2 are the main sources of new nitrogen for phytoplankton productivity. With measurements across the tropical and subtropical Atlantic, Pacific and Indian oceans, we show that nitrate diffusion (171±190 μmol m−2 d−1) dominates over N2 fixation (9.0±9.4 μmol m−2 d−1) at the time of sampling. Nitrate diffusion mediated by salt fingers is responsible for ca. 20% of the new nitrogen supply in several provinces of the Atlantic and Indian Oceans. Our results indicate that salt finger diffusion should be considered in present and future ocean nitrogen budgets, as it could supply globally 0.23–1.00 Tmol N yr−1 to the euphotic zone.

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Picoplankton (ca. < 2 µm in diameter) are the most abundant organisms in the ocean. They often dominate planktonic biomass and primary production (Chis holm 1992, Marañón 2015, and could represent

Despite evidence of internal waves in the NW Iberian upwelling region, their action and role on nutrient supply dynamics and phytoplankton community structure remain unexplored. A multidisciplinary approach, combining analysis of Synthetic Aperture Radar (SAR) images acquired during the summer months of 2008-2011, together with high-frequency samplings carried out in the R ıa de Vigo in August 2013 during spring (CHAOS1) and neap tides (CHAOS2), was used to characterize: (1) the internal wave activity, (2) its influence on mixing and nutrient supply, and (3) its role on phytoplankton community. SAR images revealed that internal waves were more energetic during spring tides. Turbulent mixing was higher during CHAOS1-springs (Kz 51.3 [1.0-2.0, 95% confidence interval] 3 10 23 m 2 s 21 ) compared to CHAOS2-neaps (Kz 5 0.7 [0.5-1.0] 3 10 23 m 2 s 21 ), and as a result nitrate diffusive fluxes were approximately fourfold higher (35 [17-73] mmol m 22 d 21 ) during CHAOS1-springs. The sampling covered a transition from relaxation-stratification (CHAOS1springs) to intensifying upwelling (CHAOS2-neaps) conditions, resulting in nitrate supply (including both diffusive and advective fluxes) being about 50% higher during CHAOS2-neaps. The phytoplankton community, which was overwhelmingly dominated by diatoms in both cruises, exhibited a shift in species composition, with an increase in the abundance of large Chaetoceros spp. during CHAOS2-neaps. About 50% of the primary production in the ecosystem during periods of upwelling relaxation-stratification could be sustained by enhanced nitrate diffusive fluxes during spring tides. Therefore, even in coastal upwelling regions, turbulent mixing driven by internal waves could play an important role in controlling phytoplankton productivity and community structure.

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Abstract. The effect of inorganic nutrients on planktonic assemblages has traditionally relied on concentrations rather than estimates of nutrient supply. We combined a novel dataset of hydrographic properties, turbulent mixing, nutrient concentration, and picoplankton community composition with the aims of (i) quantifying the role of temperature, light, and nitrate fluxes as factors controlling the distribution of autotrophic and heterotrophic picoplankton subgroups, as determined by flow cytometry, and (ii) describing the ecological niches of the various components of the picoplankton community. Data were collected at 97 stations in the Atlantic Ocean, including tropical and subtropical open-ocean waters, the northwestern Mediterranean Sea, and the Galician coastal upwelling system of the northwest Iberian Peninsula. A generalized additive model (GAM) approach was used to predict depth-integrated biomass of each picoplankton subgroup based on three niche predictors: sea surface temperature, averaged daily surface irradiance, and the transport of nitrate into the euphotic zone, through both diffusion and advection. In addition, niche overlap among different picoplankton subgroups was computed using nonparametric kernel density functions. Temperature and nitrate supply were more relevant than light in predicting the biomass of most picoplankton subgroups, except for Prochlorococcus and low-nucleic-acid (LNA) prokaryotes, for which irradiance also played a significant role. Nitrate supply was the only factor that allowed the distinction among the ecological niches of all autotrophic and heterotrophic picoplankton subgroups. Prochlorococcus and LNA prokaryotes were more abundant in warmer waters (>20 ∘C) where the nitrate fluxes were low, whereas Synechococcus and high-nucleic-acid (HNA) prokaryotes prevailed mainly in cooler environments characterized by intermediate or high levels of nitrate supply. Finally, the niche of picoeukaryotes was defined by low temperatures and high nitrate supply. These results support the key role of nitrate supply, as it not only promotes the growth of large phytoplankton, but it also controls the structure of marine picoplankton communities.