Model Thermohaline Trends in the Mediterranean Sea during the Last Years: A Change with Respect to the Last Decades?

Temperature and salinity outputs from ECCO (years 93–09) and GLORYS (years 03–09) models have been used to compute the thermohaline and steric sea level trends in the surface (0–150 m), intermediate (150 m–600 m), and deep (600 m–bottom) layers of the Mediterranean Sea. Some changes with respect to the second half of the 20th century have been observed: the cooling of the upper waters of the entire eastern basin since 1950 seems to have vanished; the warming of WMDW historically reported for the second half of the last century could have reversed, although there is no agreement between both models at this point (trends of different sign are predicted); the salinification of WMDW reported for the previous decades is not observed in the south-westernmost area in the period 93–09, and a clear change from positive to negative in the steric sea level trend with respect to the period 93–05 is detected due to the sharp decreasing steric sea level of years 02–06

The upper-oceanic response to overflows : a mechanism for the Azores Current

Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 880–895, doi:10.1175/2007JPO3750.1.The oceanic response to overflows is explored using a two-layer isopycnal model. Overflows enter the open ocean as dense gravity currents that flow along and down the continental slope. While descending the slope, overflows typically double their volume transport by entraining upper oceanic water. The upper oceanic layer must balance this loss of mass, and the resulting convergent flow produces significant vortex stretching. Overflows thus represent an intense and localized mass and vorticity forcing for the upper ocean. In this study, simulations show that the upper ocean responds to the overflow-induced forcing by establishing topographic β plumes that are aligned more or less along isobaths and that have a transport that is typically a few times larger than that of the overflows. For the topographic β plume driven by the Mediterranean overflow, the occurrence of eddies near Cape St. Vincent, Portugal, allows the topographic β plume to flow across isobaths. The modeled topographic β-plume circulation forms two transatlantic zonal jets that are analogous to the Azores Current and the Azores Countercurrent. In other cases (e.g., the Denmark Strait overflow), the same kind of circulation remains trapped along the western boundary and hence would not be readily detected.SK’s support during the time of his Ph.D. research in the MIT/WHOI Joint Program was provided by the National Science Foundation through Grant OCE04-24741. JP and JY have also received support from the Climate Process Team on Gravity Current Entrainment, NSF Grant OCE-0611530

Integrated monitoring of mola mola behaviour in space and time

Over the last decade, ocean sunfish movements have been monitored worldwide using various satellite tracking methods. This study reports the near-real time monitoring of finescale (< 10 m) behaviour of sunfish. The study was conducted in southern Portugal in May 2014 and involved satellite tags and underwater and surface robotic vehicles to measure both the movements and the contextual environment of the fish. A total of four individuals were tracked using custom-made GPS satellite tags providing geolocation estimates of fine-scale resolution. These accurate positions further informed sunfish areas of restricted search (ARS), which were directly correlated to steep thermal frontal zones. Simultaneously, and for two different occasions, an Autonomous Underwater Vehicle (AUV) videorecorded the path of the tracked fish and detected buoyant particles in the water column. Importantly, the densities of these particles were also directly correlated to steep thermal gradients. Thus, both sunfish foraging behaviour (ARS) and possibly prey densities, were found to be influenced by analogous environmental conditions. In addition, the dynamic structure of the water transited by the tracked individuals was described by a Lagrangian modelling approach. The model informed the distribution of zooplankton in the region, both horizontally and in the water column, and the resultant simulated densities positively correlated with sunfish ARS behaviour estimator (r(s) = 0.184, p < 0.001). The model also revealed that tracked fish opportunistically displace with respect to subsurface current flow. Thus, we show how physical forcing and current structure provide a rationale for a predator's finescale behaviour observed over a two weeks in May 2014

Variability in storm climate along the Gulf of Cadiz: the role of large scale atmospheric forcing and implications to coastal hazards

In the context of increased coastal hazards due to variability in storminess patterns, the danger of coastal damages and/or morphological changes is related to the sum of sea level conditions, storm surge, maximum wave height and run up values. In order to better understand the physical processes that cause the variability of the above parameters a 44 years reanalysis record (HIPOCAS) was used. The HIPOCAS time-series was validated with real wave and sea-level data using linear and vector correlation methods. In the present work changes in the magnitude, duration, frequency and approach direction of the Atlantic storms over the Gulf of Cadiz (SW Iberian Peninsula) were identified by computing various storm characteristics such as maximum wave height, total energy per storm wave direction and storm duration. The obtained time-series were compared with large-scale atmospheric indices such as the North Atlantic Oscillation (NAO) and the East Atlantic pattern. The results show a good correlation between negative NAO values and increased storminess over the entire Gulf of Cadiz. Furthermore, negative NAO values were correlated with high residual sea level values. Finally, a joint probability analysis of storm and sea level analysis resulted in increased probabilities of the two events happening at the same time indicating higher vulnerability of the coast and increased coastal risks. The above results were compared with coastal inundation events that took place over the last winter seasons in the province of Cadiz.info:eu-repo/semantics/publishedVersio

Climatic Indices over the Mediterranean Sea: A Review

This article belongs to the Section Earth Sciences and Geography.The Mediterranean Sea, strategically situated across a dynamic frontier line that separates two regions with different climates (Europe and North Africa), has been the focus of attention of many studies dealing with its thermohaline circulation, deep water formation processes or heat and freshwater budgets. Large-scale atmospheric forcing has been found to play an important role in these topics and attention has been renewed in climatic indices that can be used as a proxy for atmospheric variability. Among them, the North Atlantic oscillation, the East Atlantic or the East Atlantic–West Russia patterns have been widely addressed but much less attention has been devoted to a Mediterranean mode, the Mediterranean oscillation. This overview summarizes the recent advances that have been achieved in the understanding of these climatic indices and their influence on the functioning of the Mediterranean from a physical point of view. The important role of the Mediterranean oscillation is emphasized and the most relevant aspects of the other indices are revisited and discussed.Most of the work used for this review article was carried out for the authors in the frame of the P07-RNM-02938 and P12-RNM-01412 Junta de Andalucía Spanish-funded projects

La climatología y la topografía del Estrecho de Gibraltar determinantes de las propiedades termohalinas del agua del Mar Mediterráneo

En este trabajo se revisan y reúnen resultados obtenidos a lo largo de los últimos años por la comunidad científica internacional sobre la importancia que tiene el Estrecho de Gibraltar en relación con la oceanografía del Mar Mediterráneo. En particular se muestra cómo las propiedades de las aguas Mediterráneas son el resultado de la acción conjunta de dos causas independientes: la climatología del Mar Mediterráneo que lo convierte en una cuenca de evaporación y la topografía del Estrecho de Gibraltar que limita las cantidades de agua que se pueden intercambiar a través de él para alimentar y renovar el contenido de la cuenca Mediterránea. La teoría del doble control hidráulico de un fluido bicapa, aplicada al Estrecho de Gibraltar con éxito en la década de 1980, conduce a resultados notablemente precisos a pesar de las distintas aproximaciones que asume. El tamaño de los flujos intercambiados y la salinidad de las aguas Mediterráneas que predice difieren de las observaciones en no más de un 20%. (A

Seasonal and interannual variability of the surface circulation in the eastern Gulf of Cadiz (SW Iberia)

11 páginas, 6 figuras, 1 tabla.An 11-year (1996–2007) time series of current meter observations representative of the open sea circulation; a 4-year (2001–2005) time series of current meter records over the continental shelf and in situ data during different seasons have been compared in order to study the seasonal and interannual variability of the surface circulation in the eastern Gulf of Cadiz. The open sea velocity observations indicate southeastward flow along the northern continental slope of the Gulf of Cadiz, compatible with anticyclonic circulation, during most of the year and more intense during summer months. Flow reversals (northwestward circulation) at seasonal time scales in late autumn and early winter (preferably December and January) are a rather recurrent feature with variable intensity depending on the year. Anticyclonic circulation is associated with westerlies, whereas flow reversals usually take place under easterly episodes, suggesting wind-driven circulation. Negative North Atlantic Oscillation indices (indicative of southward displacement of the Azores high) are also linked to the reversals. Changes in this mainly wind-driven large-scale surface circulation are echoed by the shelf circulation: the coastal countercurrent that closes the mesoscale cyclonic cell over the eastern shelf in spring-summer (upwelling season) is replaced by and eastward current in autumn and winter.We acknowledge CANIGO (MAS3-PL95-0443) European-funded project and, particularly, Guillermo Díaz Del Río for CTD data and the UIB-IMEDEA (Special Action CICYT, REN2000-2599-E) for the software used for the optimal interpolation. Partial support from CTM2006–02326 (Ministry of Science and Technology) and P07-RNM-02938 (Junta de Andalucía) Spanish-funded projects and the Consejeria de Agricultura y Pesca of the Junta de Andalucia are also acknowledged.Peer reviewe

The Mediterranean Oscillation Teleconnection Index: Station-Based versus Principal Component Paradigms

Two different paradigms of the Mediterranean Oscillation (MO) teleconnection index have been compared in this work: station-based definitions obtained by the difference of some climate variable between two selected points in the eastern and western basins (i.e., Algiers and Cairo, Gibraltar and Israel, Marseille and Jerusalem, or south France and Levantine basin) and the principal component (PC) approach in which the index is obtained as the time series of the first mode of normalised sea level pressure anomalies across the extended Mediterranean region. Interannual to interdecadal precipitation (P), evaporation (E), E-P, and net heat flux have been correlated with the different MO indices to compare their relative importance in the long-term variability of heat and freshwater budgets over the Mediterranean Sea. On an annual basis, the PC paradigm is the most effective tool to assess the effect of the large-scale atmospheric forcing in the Mediterranean Sea because the station-based indices exhibit a very poor correlation with all climatic variables and only influence a reduced fraction of the basin. In winter, the station-based indices highly improve their ability to represent the atmospheric forcing and results are fairly independent of the paradigm used

Basin-scale structures governing the position of the deep fluorescence maximum in the Gulf of Cádiz

21 páginas, 16 figuras, 4 tablas. The Gulf of Cadiz Oceanography: a multidisciplinary view.Physical and biological properties of the water column in the Gulf of Cádiz area were examined during a survey in May 2001. The sampling region was dominated by the presence of a central warm core and anticyclonic circulation in the open ocean, upwelling processes nearby both Cape Santa María and Cape San Vicente, and a coastal counter current along the continental shelf. These features determined the stratification of the water column and thereby nutrient distribution. A strong positive correlation between a particular isopycnal (with a density of 26.6 kg m−3) and the depth of the DeepFluorescenceMaximum (DFM) throughout the whole basin was found. This isopycnal marked the interface between the deepest limit of the Surface Atlantic Water (SAW) and the shallowest limit of the North Atlantic Central Water (NACW) and was characterized by nutrient concentrations non-limiting for phytoplankton growth. According to this analysis, the isopycnal can be considered as a nutrient tracer in the Gulf, determining the depth at which the DFM is invariably located, with the DFM intensity depending upon advective and diffusive fluxes arising around the interface.This work was supported by projects MAR99-0643-C03-02 and CTM2005-01091/MAR and G.N. by a F.P.I. fellowship from MEC.Peer reviewe