Suchergebnisse

18 pages, 6 figures, 1 table ; [EN] One possible path for exploring the Earth's far-from-equilibrium homeostasis is to assume that it results from the organisation of optimal pulsating systems, analogous to that in complex living beings. Under this premise it becomes natural to examine the Earth's organisation using physiological-like variables. Here we identify some of these main variables for the ocean's circulatory system: pump rate, stroke volume, carbon and nutrient arterial-venous differences, inorganic nutrients and carbon supply, and metabolic rate. The stroke volume is proportional to the water transported into the thermocline and deep oceans, and the arterial-venous differences occur between recently-upwelled deep waters and very productive high-latitudes waters, with atmospheric CO2 being an indicator of the arterial-venous inorganic carbon difference. The metabolic rate is the internal-energy flux (here expressed as flux of inorganic carbon in the upper ocean) required by the system's machinery, i.e. community respiration. We propose that the pump rate is set externally by the annual cycle, at one beat per year per hemisphere, and that the autotrophic ocean adjusts its stroke volume and arterial-venous differences to modify the internal-energy demand, triggered by long-period astronomical insolation cycles (external-energy supply). With this perspective we may conceive that the Earth's interglacial-glacial cycle responds to an internal organisation analogous to that occurring in living beings during an exercise-recovery cycle. We use an idealised double-state metabolic model of the upper ocean (with the inorganic carbon/nutrients supply specified through the overturning rate and the steady-state inorganic carbon/nutrients concentrations) to obtain the temporal evolution of its inorganic carbon concentration, which mimics the glacial-interglacial atmospheric CO2 pattern ; [ES] Un posible camino para el estudio de la homeóstasis fuera-de-equilibrio de la tierra es suponer que resulta de la organización de sistemas pulsátiles optimizados, análoga a aquélla en seres vivos complejos. Bajo esta premisa parece natural examinar la organización de la tierra utilizando variables de tipo fisiológico. Aquí identificamos algunas de las principales variables del sistema circulatorio oceánico: tasa de bombeo del corazón, volumen de latido, diferencias arteriovenosas de carbono y nutrientes, suministro de carbono y nutrientes inorgánicos, y tasa metabólica. El volumen de latido es proporcional al transporte de agua hacia la termoclina y océano profundo, y las diferencias arterio-venosas ocurren entre las aguas profundas recientemente afloradas y aquellas altamente productivas de altas latitudes, con el CO2 atmosférico siendo un indicador de la diferencia arterio-venosa de carbono inorgánico. La tasa metabólica es el flujo de energía interna (aquí expresado como flujo de carbono inorgánico en el océano superior) requerido por la maquinaria que sostiene el sistema, i.e. respiración total de la comunidad. Se propone que la tasa de latido está impuesta externamente, un latido por año por hemisferio, y que el océano autotrófico ajusta su volumen de latido y las diferencias arteriovenosas a cambios en la demanda de energía interna, inducido por ciclos de insolación astronómica de largo período (suministro de energía externa). Bajo esta perspectiva podemos concebir que el ciclo interglacial-glacial de la tierra responde a una organización interna análoga a la que ocurre en seres vivos durante un ciclo de ejercicio-recuperación. Se utiliza un modelo metabólico idealizado de dos estados para el océano superior (con el suministro de carbono/nutrientes inorgánicos especificado mediante la tasa de recirculación de aguas profundas y las concentraciones de carbono/nutrientes inorgánicos en estado estacionario) para obtener la evolución temporal de su concentración de carbono inorgánico, la cual mimetiza el patrón glacial-interglacial del CO2 atmosférico ; This work was supported by the Spanish government through the CANOA project (CTM2005-00444/MAR) ; Peer reviewed

IV Encuentro Oceanografía Física Española, celebrado del 20 al 22 de julio de 2016 en Alicante,España.-- 1 page, 1 figure ; Temperature-salinity (T-S) diagrams are widely used to spot the temperature (T) and salinity (S) relations at different places and times. They also help visualize how water masses with different T and S values mix up as they propagate away from the formation regions. Potential density (rho) is typically included in these diagrams to emphasize the vertical stability of a given hydrographic cast or to illustrate how two water masses remain at different density levels. Alternatively, we may introduce a new variable that sets a surrogate orthonormal space, with rho on one axis and spiciness (pi) on the other (Flament, 2002; but see Veronis, 1972, and Jackett and McDougall, 1985). Here we discuss how the rho and pi anomalies in this space may be interpreted as latent diapycnal and epipycnal mixing, or mixing yet feasible to take place, between two water masses. We illustrate these concepts with casts that sample the Mediterranean Outflow (MO) running under the North Atlantic Central Waters (NACW) stratum in the eastern Gulf of Cádiz (Fig. 1) ; This research has been supported by the Ministerio de Economía y Competitividad of the Spanish Government through project VA-DE-RETRO (CTM2014-56987-P) ; Peer Reviewed

Special volume: Planet Ocean. Scientia Marina 80(Suppl.1) 2016.-- 10 pages, 8 figures, 1 table ; [EN] Mediterranean Water lenses (meddies) in the eastern North Atlantic, north of the Canary Islands, appear to often have their salty and nutrient-poor core accompanied by relatively fresh and nutrient-rich waters on top. We describe several occurrences of freshwater halos and berets for meddies sampled north of the Canary Islands—with instrumented moorings, Argo floats and oceanographic cruises—and identify the source of these fresh anomalies as diluted Antarctic Intermediate Water (AAIW). We propose that this capping takes place off Northwest Africa, as the southward-advected meddy interacts with the northward-advected AAIW. This interpretation is consistent with a simple analysis of the relevant advective-diffusive time scales associated with the passage of meddies under a layer of AAIW, and suggests that meddies may be a mechanism for AAIW export far into the North Atlantic Ocean ; [ES] Los Meddies en el Atlántico Norte oriental, al norte de las Islas Canarias, a menudo parecen tener su núcleo salado y pobre en nutrientes acompañado de aguas relativamente frescas y ricas en nutrientes en la parte superior. Se describen varios casos de halos y boinas de agua dulce para meddies muestreados al norte de las Islas Canarias -con instrumentos anclados, perfiladores Argo y campañas oceanográficas- identificando así el origen de estas anomalías frescas como Agua Intermedia Antártica (AIAA) diluida. Proponemos que esta interacción se lleva a cabo en el noroeste de África, cuando el meddy advectado hacia el sur interactúa con el AIAA advectada hacia el norte. Esta interpretación es coherente con un simple análisis de las escalas de tiempo advectivo-difusivas asociadas con el paso de meddies bajo una capa de AIAA, y sugiere que los meddies pueden ser un mecanismo para exportar AIAA hacia el océano interior en el Atlántico Norte ; This work was supported by the projects CANOA (CTM2005-00444/MAR), TIC-MOC (CTM2011-28867) and VA-DE-RETRO (CTM2014-56987-P), funded by the Spanish government. [.] FM was partly supported by the Spanish Ministry of Education and Science through the Juan de la Cierva Programme ; Peer Reviewed

5 pages, 7 figures ; We apply an inverse model to a hydrographic cruise that completely closes the Canary Islands to investigate their effect on the water masses transports. Most central waters are transported south between the eastern islands and the African coast, with 2.5 Sv out of a total of 3.5 Sv. Intermediate waters are effectively blocked by the islands passages, with Mediterranean/Antarctic waters predominantly found north/south of the islands, and most deep waters loop around the archipelago plateau. A process model upholds the existence of intense two-way exchange between central and intermediate waters along the eastern passage, with vertical velocities of order 10−5 m s−1 ; This work has been funded by the Spanish goverment through Project CANOA (CTM2005-00444/MAR) and by European Union through projects CANIGO (MAS3-CT96-0060) and OASIS (EVK3-CT-2002-00073-OASIS) ; Peer reviewed

10 pages, 10 figures ; A historical set of expendable bathythermograph (XBT) and Pegasus sections across the Gulf Stream in natural coordinates is examined to investigate the isopycnic structure of the current off Cape Hatteras. In isopycnic-natural coordinates, the axis of the Stream remains vertically aligned, in contrast to its well-known offshore tilting when plotted as a function of depth. These results are confirmed using the geostrophic velocities obtained from a synthetic temperature field for the Gulf Stream. We prove that a baroclinic current aligned with density cannot be aligned with depth, and vice versa, and we show that the density alignment of the Gulf Stream results from the distortion of the density field and has negligible dependence on the choice of reference level. The invariable character of intense geophysical jets is supported through analogous representations for the upper level atmospheric jet stream in isentropic coordinates. These show that the atmospheric jet, when plotted on to a section normal to the direction of its maximum velocity core, is vertically aligned with potential temperature. Copyright © Blackwell Munksgaard, 2005 ; Part of this work was written while JLP was at the University of Wisconsin-Madison with funding from the Secretar´ıa de Estado de Educación y Universidades of the Spanish Government. This work has also been partly funded by the European Union through project OASIS (EVK3-CT-2002-00073-OASIS) ; Peer Reviewed

[EN] We use several hydrographic and velocity sections crossing the Gulf Stream to examine how the gradient Richardson number, Ri, is modified due to both vertical smoothing of the hydrographic and/or velocity fields and the assumption of parallel or geostrophic flow. Vertical smoothing of the original (25 m interval) velocity field leads to a substantial increase in the Ri mean value, of the same order as the smoothing factor, while its standard deviation remains approximately constant. This contrasts with very minor changes in the distribution of the Ri values due to vertical smoothing of the density field over similar lengths. Mean geostrophic Ri values remain always above the actual unsmoothed Ri values, commonly one to two orders of magnitude larger, but the standard deviation is typically a factor of five larger in geostrophic than in actual Ri values. At high vertical wavenumbers (length scales below 3 m) the geostrophic shear only leads to near critical conditions in already rather mixed regions. At these scales, hence, the major contributor to shear mixing is likely to come from the interaction of the background flow with internal waves. At low vertical wavenumbers (scales above 25 m) the ageostrophic motions provide the main source for shear, with cross-stream movements having a minor but non-negligible contribution. These large-scale motions may be associated with local accelerations taking place during frontogenetic phases of meanders ; [ES] Hemos utilizado varias secciones hidrográficas y de velocidad, que atraviesan la Corriente del Golfo, con el fin de analizar como se modifica el número de gradiente de Richardson, Ri, debido tanto al suavizado vertical de los datos hidrográficos y de velocidad como a la aproximación de flujo geostrófico paralelo. El suavizado vertical de los datos originales de velocidad (intervalo de 25 m) conlleva un aumento substancial del valor medio de Ri, del mismo orden que el factor de suavizado, mientras que la desviación estándar permanece aproximadamente constante. Esto contrasta con los cambios muy pequeños en la distribución de los valores de Ri causados por el suavizado vertical del campo de densidades sobre distancias similares. Los valores medios geostróficos de Ri permanecen siempre por encima de los valores de Ri obtenidos mediante los datos originales de velocidad sin suavizar, típicamente uno o dos órdenes de magnitud mayores, mientras que la desviación estándar de los valores geostróficos usualmente es unas cinco veces mayor que la de los valores reales de Ri. En números de onda verticales altos (escalas de longitud por debajo de 3 m) la cizalla geostrófica solo ocasiona condiciones casi críticas in regiones que ya se encuentran bastante mezcladas. En estas escalas, por tanto, la mayor contribución a la mezcla por cizalla probablemente proviene de la interacción entre el flujo base y las ondas internas. En números de onda verticales bajos (escalas por arriba de 25 m) los movimientos geostróficos proporcionan la fuente principal de cizalla, teniendo los movimientos en la dirección normal al flujo medio una contribución pequeña pero no despreciable. Estos movimientos a escalas largas pueden estar asociados con aceleraciones locales que tienen lugar durante fases frontogenéticas de meandros ; Part of this work was written while J.L.P. was at University of Wisconsin-Madison with a grant from the Ministerio de Educación, Cultura y Deportes, Spanish Government. This work has been partly funded by the European Union through the OASIS project (contract No. EVK3-CT-2002-00073-OASIS). ; Peer reviewed

Special volume: Advances in Spanish physical oceanography. Scientia Marina 76(Suppl.1) 2012.-- 16 pages, 10 figures, 1 table ; [EN] The regional ocean circulation within the Canary Upwelling System between 31°N and 35°N is studied using numerical tools. Seasonal mean and near-instantaneous velocity fields from a previously-generated climatological Regional Ocean Modelling System (ROMS) solution of the Canary Basin are used to force a series of offline Lagrangian particle-tracking experiments. The primary objective is to identify the pathways through which water parcels arrive at the upwelling region north of Cape Ghir. Examining year-long pathways, the Azores Current contributes over 80% of particles annually, of which a large proportion arrive directly from offshore (from the northwest), while others travel along the shelf and slope from the Gulf of Cadiz. The remaining ~20% originate within the Gulf of Cadiz or come from the south, although the southern contribution is only significant in autumn and winter. When season-long pathways are considered, the alongshore contributions become increasingly important: northern contributions reach 40% in spring and summer, while southern values exceed 35% in winter. This study also shows that coastal upwelling changes both spatially and temporally. Upwelling becomes intensified near Cape Beddouza, with most upwelling occurring within ~40 km from shore although significant values may reach as far as 120 km offshore north of Cape Beddouza; at these locations the offshore integrated upwelling reaches as much as 4 times the offshore Ekman transport. In the Cape Beddouza area (32°N to 33°N), upwelling is negligible in February but intensifies in autumn, reaching as much as 3 times the offshore Ekman transport ; [ES] Se estudia la circulación oceánica regional en el Sistema de Afloramiento de Canarias entre 31 y 35°N mediante herramientas numéricas. Con este fin se realizan una serie de experimentos de seguimientos de partículas Lagrangianas mediante los campos de velocidad, tanto los medios estacionales como los cuasi-instantáneos, obtenidos a partir de una solución previamente generada del Sistema de Modelado Oceánico Regional (ROMS). El objetivo principal es identificar las rutas mediante las cuales las parcelas de agua llegan a la región de afloramiento al norte de Cabo Ghir. Al examinar las rutas anuales se aprecia que la Corriente de Azores contribuye con más del 80% de las partículas, una gran proporción de las cuales llega directamente desde costa afuera (desde el noroeste) mientras que otras siguen la plataforma y el talud continental desde el Golfo de Cádiz. Las restantes ~20% se originan en el Golfo de Cádiz o vienen desde el sur, aunque la contribución sureña solo es significativa en otoño e invierno. Al examinar las rutas estacionales se observa que las contribuciones a lo largo de la costa se tornan más importantes: la contribución norteña alcanza el 40% en primavera y verano mientras que las partículas originadas al sur exceden un 35% en invierno. Este estudio también muestra que el afloramiento costero cambia temporal y espacialmente. El afloramiento se intensifica cerca de Cabo Beddouza, con la mayor parte del afloramiento teniendo lugar en unos ~40 km desde la costa, aunque se obtienen valores significativos a distancias de hasta 120 km fuera de costa al norte de Cabo Beddouza; en estas mismas localidades el afloramiento integrado costa afuera alcanza hasta 4 veces el transporte de Ekman perpendicular a costa. En el área de Cabo Beddouza (32 a 33°N), el afloramiento es despreciable en febrero pero se intensifica en otoño, alcanzando hasta 3 veces el transporte de Ekman perpendicular a costa ; This research was supported by the Spanish government through projects MOC2 (CTM2008-06438-C02-01) and TIC-MOC (CTM2011-28867) ; Peer reviewed

IV Encuentro Oceanografía Física Española, celebrado del 20 al 22 de julio de 2016 en Alicante,España.-- 2 pages, 2 figures ; Recent studies have shown that sea surface temperature (SST) and surface wind speed (SWS) are directly related at ocean mesoscales (10-100 km). Here we examine this relationship in the Brazil-Malvinas Confluence region, where we find one of the most intense regional-scale SST gradients in the world's oceans. We analyze SST and SWS collected in situ during an oceanographic cruise done in March 2015. Data is processed to emphasize the variability of SST and SWS associated with oceanic fronts, both at regional and mesoscalar scales, taking into account the latitudinal SST gradients, the passage of atmospheric synoptic disturbances, and the diurnal variability of SWS. We observe that SST has an influence on SWS - a temperature raise of 1ºC involves a wind-speed increase of 0.36 m s-1, with a correlation coefficient of 0.43 and a 95% confidence level - a relationship that is corroborated using wind data from the European Copernicus Project. Finally, we assess the influence of SST on the lower atmosphere through the changes in sensible and latent heat fluxes across the front. The results point at the existence of significant coupling between the upper ocean and the lower atmosphere ; This research has been supported by the Ministerio de Economía y Competitividad of the Spanish Government through projects TIC-MOC (CTM2011-28867) and VA-DE-RETRO (CTM2014-56987-P) ; Peer Reviewed

IV Encuentro Oceanografía Física Española, celebrado del 20 al 22 de julio de 2016 en Alicante,España.-- 2 pages, 2 figures, 1 table ; The Brazil Current (BC) and the Malvinas Current (MC) meet at the Brazil-Malvinas Confluence (BMC) region. This encounter is characterized by a complex mesoscale structure, with numerous eddies, filaments and thermohaline intrusions that lead to meridional exchange of mass, heat and salt between both currents. Therefore, the BMC is the site where the subtropical gyre and the ACC exchange key properties, thus playing a fundamental role in the Earth's climate. During March 2015, the R/V Hespérides carried out the TIC-MOC cruise in the BMC with the objective of sampling the BMC with high resolution. Here we use 28 hydrographic sections from this cruise that, together with the South American coast, constitute a closed ocean volume with sides about 400 km, and build an inverse box model to quantify the mass exchange through its contour. We find that mass enters the region predominantly from the north, carried by the BC, and leave through the eastern section; most of the flow from the south also leaves the region through the southern boundary. The results are consistent with the velocity field as measured during the cruise ; This research has been supported by the Ministerio de Economía y Competitividad of the Spanish Government through projects TIC-MOC (CTM2011-28867) and VA-DE-RETRO (CTM2014-56987-P). Dorleta Orue-Echeverría has been funded through a FPU contract of the Ministerio de Educación y Ciencia ; Peer Reviewed

IV Encuentro Oceanografía Física Española, celebrado del 20 al 22 de julio de 2016 en Alicante,España.-- 1 page, 1 figure ; Maps of velocity vectors and streamlines, calculated after integration from some reference contour, can be very useful to illustrate the gross characteristics of the changing velocities. Nevertheless, they are only snapshots of the velocity field that cannot be used to directly infer exchange between different oceanic regions. In order to do so, we must use of a Lagrangian approach, where we actually track water parcels as they move under the influence of the spatially and temporally changing velocity fields. Here we present a simple model that integrates monthly velocity fields in time, either forward or backward, in order to track the origin or fate of water parcels. In our case, the velocity fields are inferred from the positions of Argo floats. We illustrate the model by examining the recirculation of intermediate waters in the southern South Atlantic Ocean. The model allows us tracking whether and how the water parcels at these intermediate depths recirculate zonally or drift meridionally. In this application, we carefully explore the important role of the Brazil-Malvinas Confluence and the Agulhas Leakage. We estimate that most of the intermediate waters recirculate across the ocean in time periods between about 15 and 30 years, eventually meeting at the Brazil-Malvinas Confluence region. Our results show no water transfer from the Indian Ocean, i.e. they show no Agulhas Leakage, although this may be an artefact caused by the absence of rings in the mean fields. A remarkable feature is the presence of a meridionally pulsating behaviour in the transoceanic trajectories, best visible in an accompanying video ; This research has been supported by the Ministerio de Economía y Competitividad of the Spanish Government through project VA-DE-RETRO (CTM2014-56987-P) ; Peer Reviewed

IV Encuentro Oceanografía Física Española, celebrado del 20 al 22 de julio de 2016 en Alicante,España.-- 1 page, 1 figure ; Since 2007, in the world's oceans there are over 3000 Argo floats that transmit position data typically once every 10 days. This represents some 100.000 positions yearly that lead to an equivalent number of velocity vectors. This massive amount of velocity data allows us constructing monthly-mean fields with spatial resolution of the order of 1º in latitude-longitude. Here we present, for the first time, the monthly sea-surface velocity fields for all oceans, unravelling the spatial distribution of the seasonally evolving fields. The velocity fields are predominantly zonal except for the western boundary subtropical regions. Further, these zonal fields change spatially following the evolution of the Intertropical Convergence Zone and the accompanying low- and high-pressure centres in both hemispheres. The resulting patterns appear as a transoceanic meridional seasonal pulse, typically propagating from south to north and from east to west. This work illustrates the potential of the Argo-inferred velocity data for an improved description of the surface currents at regional and, most remarkably, global scales ; This research has been supported by the Ministerio de Economía y Competitividad of the Spanish Government through project VA-DE-RETRO (CTM2014-56987-P) ; Peer Reviewed

We discuss the experimental methodology and present the results of several experiments on the onset and growth of instabilities in stratified shear flow. Our results include the assessment of the effective diffusivity prior to the development of the Kelvin-Helmholtz (K-H) type instability and the measurement of the velocity field. This allows us to determine that the onset of the instability takes place when the Richardson number is close to 0.25, this value slightly decreasing with increasing initial interface thickness. The formation of a fine layered structure at the interface is suggested by density profiles taken immediately after the generation of K-H billows, but the size of the full interface as well as the layers themselves decrease in the following few seconds. We hypothesize that the time scale of the K-H billows in our laboratory experiments is so short that there is no time for added mixing to further distribute and smoothen the initial layer structure ; This work has been supported by the Spanish government throught CICYT´s grant number MAR96-1893 ; Peer reviewed

IV Encuentro Oceanografía Física Española, celebrado del 20 al 22 de julio de 2016 en Alicante,España.-- 2 pages, 2 figues ; The Earth's climate is the outcome of numerous feedback energetic mechanisms. Paleoclimatic data tells us that the Earth has shifted between glacial and interglacial periods during the last 3 Myr, alternating between different temperature and atmospheric-CO2 states. Variations in key global processes are responsible for these transitions: CO2 atmospheric concentration, incoming solar radiation, meridional overturning circulation and albedo. Here we propose two simple box-models in order to analyze the effect of these processes on the heat content of the atmosphere and the upper-ocean during the last 450 kyr. The simplest model has only three boxes: atmosphere, upper-ocean and deep-ocean. The atmosphere and upper-ocean are allowed to exchange heat while the upper and deep oceans are connected through the meridional overturning circulation (MOC); it allows assessing the effects of cloud cover, greenhouse gases and MOC on climate but presents several important limitations, e.g. in the absence of a cooling mechanism, the deep ocean would warm up in times scales of order 10 kyr. Hence, we move to a more realistic five-box model, distinguishing now between high- and low-latitude atmospheric and upper-ocean compartments. This model, which adequately reproduces current estimates of preindustrial temperatures and heat fluxes, is used to estimate how these variables changed during glacial periods. Most important, the model helps us assess the relevance of the different physical processes on the Earth's climate, such as the latitudinal exchange within the ocean and atmospheric compartments, the intensity of the MOC and the reflecting power of albedo at high latitudes ; This research has been supported by the Ministerio de Economía y Competitividad of the Spanish Government through project VA-DE-RETRO (CTM2014-56987-P). Dorleta Orúe-Echeverría has been funded through a FPU contract of the Ministerio de Educación y Ciencia ; Peer Reviewed

We analysed historical data (Fraga and Manríquez, 1974; Manríquez and Fraga, 1978) to investigate the relation between the position of the Cape Verde frontal region and the geostrophic velocity field in summer and winter. The position of the front is well determined in the plotting of the salinity and nutrient distributions in isopycnic coordinates. The geostrophic velocity shows sharp gradients as a function of density and distance on sections normal to the coast. These gradients are reasonable well correlated with the frontal position and indicate the existence of strong meridional interleaving. The flow field relative to 400 m illustrates this interleaving as fluctuations on a westward mean flow. The surface temperature distribution undergoes very large latitudinal displacements but may help to locate the presence of north and south surface water ; This work was supported by the Spanish government through CICYT´s project MAR96-1893. The principal author, PPR, wishes to thank the Ministerio de Educación y Ciencia of the Spanish government for funding during this work ; Peer reviewed

Publicación online disponible en: http://www.icm.csic.es/scimar/index.php ; This paper shows observational evidence of internal wave generation and mixing in the southwest shelf-break region of Gran Canaria Island. Signals of periodic internal motion and related mixing events were detected through large pycnocline variations and subcritical gradient Richardson events. Broad areas of homogeneous dense water over the slope, where the vertical temperature field displays a wave-like pattern, provide further evidences of internal wave mixing in this region. The observed diapycnal chlorophyll transport matches with mixing events, suggesting a periodic nutrient supply to the euphotic zone through internal wave mixing. We postulate that internal wave mixing may be an important mechanism contributing to the biological enhancement reported southwest of Gran Canaria Island. ; This research was supported by Canary islans government throught project OMIAC (91/08 GAC). ; Peer reviewed