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Submesoscale features, characterised by a low salinity layer originating from river discharges, enhance water column stability in a New Zealand shelf sea - the Greater Cook Strait. Using a combination of data from multiple ocean glider surveys and regional modelling, we show that low salinity submesoscale features (LSMFs) can cause increased stratification on the order of 10^-4. Modelled oceanographic conditions compared well to observations, especially in austral spring. Stably stratified LSMFs can replace the previously well mixed layer in the water column up to a distance of 100 km offshore before getting entrained by the regional barotropic current in Greater Cook Strait. LSMFs observed from glider surveys and reproduced from modelled results generate strong vertical and horizontal salinity differences of ~0.45 psu. These salinity differences define density fronts and stratification in the upper ~30 m. Temperature differences of up to ~1.4°C associated with LSMFs were not large enough to entirely cancel the density effect of salinity. The offshore advection reach of LSMFs is partly constrained by the variability of the barotropic d'Urville Current. Its presence and strong winds inhibit the propagation of LSMFs offshore in Greater Cook Strait, leaving the water column unstable while enhancing mixing and deepening the mixed layer depth. In contrast, moderate winds and weak current enable the propagation of LSMFs furthest offshore in Greater Cook Strait, where the water column becomes stably stratified. A stably stratified regime inhibits vertical mixing of nutrients and phytoplankton, which may lead to enhanced primary production in the region.

The physical reanalysis component of the Mediterranean Forecasting System is used to construct a high-resolution three-dimensional atlas of the Turner Angle. An assessment of the model quality shows a maximum degree of agreement with observations in the water column between 150 and 1000 m depth. The mean state of the favourable conditions for double diffusion processes is evaluated and the recent decadal variability is studied in terms of changes in the water mass properties. The results show that approximately 50% of the Mediterranean Sea is favourable to double diffusion processes, from which around 47% is associated with salt fingering. The Tyrrhenian, Ionian and southwestern Mediterranean are the most vulnerable basins to salt fingering, and the strongest processes can occur in the Tyrrhenian deep waters. Diffusive convection is most likely to occur in the Ionian, Aegean and eastern Mediterranean at vertical levels deeper than 1000 m. The observed gradual warming and salinification of the Mediterranean after 1997 decreased and increased the possibilities of the occurrence of salt fingers and double diffusive convections, respectively. The climatological atlas that is presented in this paper provides a three-dimensional picture of the regions that are either doubly stable or favourable to double diffusion instability and allows for the characterization of the diffusive properties of the water masses.

Special volume: Advances in Spanish physical oceanography. Scientia Marina 76(Suppl.1) 2012.-- 19 pages, 15 figures, 3 tables, [EN] We use three transatlantic cruises (1957, 1993 and 2010) along 7.5°N to analyse inter-decadal variations of the neutral buoyancy frequency (with neutral density replacing potential density) and Turner angle. We also use Argo data from the 2003-2011 period to show that, within central and intermediate waters, the changes between the three sections are slightly greater than the seasonal and inter-annual variations, so they may be interpreted as actual inter-decadal variations. The results point to a generalized sinking of isoneutrals between 1957 and 2010, with maximum zonally-averaged values of about 100 m in the central and upper deep layers. They also reveal the occurrence of substantial changes in the intermediate and neighbouring water strata, with differential vertical sinking of isoneutrals and the transformation of their thermohaline characteristics. The neutral buoyancy frequency increased in the lower central and upper intermediate layers and decreased in the lower intermediate and upper deep layers. The distributions of Turner angle highlight a predominance of salt-fingering in the North Atlantic, except for a gravitationally doubly-stable layer located immediately below the intermediate water core; this stable layer thinned substantially between 1957 and 2010 because of the sinking of the lower intermediate isoneutrals acting together with actual water transformations from Antarctic Intermediate Waters into North Atlantic Deep Waters. We conclude that a significant portion of the water column underwent both increased vertical stratification and enhanced salt-fingering, two mechanisms with opposite effects on the effective vertical diffusion, [ES] Usamos tres campañas transatlánticas (1957, 1993 y 2010) a lo largo de 7.5°N para analizar las variaciones interdecadales de la frecuencia de flotabilidad neutra (con la densidad neutra reemplazando a la densidad potencial) y el ángulo de Turner. También utilizamos datos Argo del periodo 2003-2011 para mostrar que, en las aguas centrales e intermedias, los cambios entre las tres secciones son algo superiores a las variaciones estacionales o interanuales, de modo que pueden interpretarse como cambios interdecadales. Los resultados indican un hundimiento generalizado de las isoneutras entre 1957 y 2010, con valores máximos promediados zonalmente de unos 100 m en las aguas centrales y profundas superiores. También revelan la existencia de cambios substanciales en las aguas intermedias y los estratos vecinos, con desplazamientos verticales diferenciales de las distintas isoneutras, y la transformación de sus características termohalinas. La frecuencia de flotabilidad neutra aumentó en las capas centrales inferiores e intermedias superiores y disminuyó en las capas intermedias inferiores y profundas superiores. Las distribuciones del ángulo de Turner enfatizan la predominancia de dedos de sal en el Atlántico Norte, excepto en una capa gravitacionalmente estable ubicada inmediatamente por debajo del núcleo de aguas intermedias; esta capa estable se estrechó entre 1957 y 2010 debido al efecto conjunto del hundimiento de las isoneutrasintermedias más profundas y la transformación de las Aguas Antárticas Intermedias en Aguas Noratlánticas Profundas. Concluimos que una porción significativa de la columna de agua experimentó tanto un aumento en la estratificación vertical como un incremento en el régimen de dedos de sal, dos mecanismos con efectos opuestos en la difusión vertical efectiva, This research was supported by the Spanish National R&D Plan, in the framework of projects MOC2 (CTM2008-06438-C02-01) and TIC-MOC (CTM2011-28867). The authors are grateful to the BIO Hespérides scientists, technicians and crew for making it possible to gather the 2010 data set