Joaquín Tintoré

The role of straits and channels in understanding the characteristics of Mediterranean circulation

Abstract Straits in the Mediterranean Sea form an important network from which one can determine the characteristics of the water exchange between all the constituent sub-basins. This includes the definition of water masses and water transport and their time variability. From 1994, all the major straits in the Mediterranean Sea (Gibraltar, Sicily, Otranto, Balearic Sea Straits, Cretan Arc Straits and Corsica) were subject to long term observations as part of various research projects. Besides adding new elements to the knowledge of internal strait conditions, the data sets collected allow us to propose a fairly consistent representation of the Mediterranean circulation and budgets in key points within the basin. The amplitude of the annual water transport measured at these straits was about 1 Sv and it appears to be modulated by a significant low-frequency and seasonal variability. For the first time, a seasonal component was identified at Gibraltar, thus raising new questions on the actual state of the Mediterranean. Also, the very likely existence of a significant interannual component was documented. In the Corsica Channel, this component was found to be related to the interannual variability of the North Atlantic Oscillation. The observations in the Cretan Arc Straits have provided a more comprehensive representation of the recent changes in the Eastern Mediterranean thermohaline cell. It is noteworthy that the effects of these changes have been observed both in the Otranto and Sicily Straits, and are now affecting the adjacent sea regions. The presence of a stream of Modified Atlantic Water in the Balearic Sea Channels indicates that part of the Atlantic inflow may be diverted directly into the northern region of the Western Mediterranean. Finally, data gathered in the Sardinia Channel indicate that the central Mediterranean region plays a critical role in controlling exchanges between the Eastern and the Western Mediterranean, while it is emphasized that the Tyrrhenian Sea area plays a role in strongly modifying some of the water masses that contribute to the large scale basin circulation. Their mixing creates new water types which modify the currently known pattern and composition of the Mediterranean circulation.

HYMEX , a 10-year Multidisciplinary Program on the mediterranean water cycle.

The Mediterranean countries are experiencing important challenges related to the water cycle, including water shortages and floods, extreme winds, and ice/snow storms, that impact critically the socioeconomic vitality in the area (causing damage to property, threatening lives, affecting the energy and transportation sectors, etc.). There are gaps in our understanding of the Mediterranean water cycle and its dynamics that include the variability of the Mediterranean Sea water budget and its feedback on the variability of the continental precipitation through air–sea interactions, the impact of precipitation variability on aquifer recharge, river discharge, and soil water content and vegetation characteristics specific to the Mediterranean basin and the mechanisms that control the location and intensity of heavy precipitating systems that often produce floods. The Hydrological Cycle in Mediterranean Experiment (HyMeX) program is a 10-yr concerted experimental effort at the international level that aims to advance the scientific knowledge of the water cycle variability in all compartments (land, sea, and atmosphere) and at various time and spatial scales. It also aims to improve the processes-based models needed for forecasting hydrometeorological extremes and the models of the regional climate system for predicting regional climate variability and evolution. Finally, it aims to assess the social and economic vulnerability to hydrometeorological natural hazards in the Mediterranean and the adaptation capacity of the territories and populations therein to provide support to policy makers to cope with water-related problems under the influence of climate change, by linking scientific outcomes with related policy requirements.

Mesoscale Dynamics and Vertical Motion in the Alborán Sea

Abstract The inflow of Atlantic water through the strait of Gilbraltar usually exhibits a stationary wavelike pattern in the Alboran sea. We use an objective analysis technique for quantitative scale separation to investigate the interaction of scales in the region. The large scale is clearly dominated by an anticyclonic gyre. Smaller scale analysis shows the existence of several mesoscale cyclonic eddies along the northern boundary of the western Alboran sea anticyclonic gyre. The relationship between the large-scale/mesoscale variability and the induced ageostrophic vertical motion is established using the Q vector formulation. We find that on the macroscale, upward motion occurs upstream of the anticyclonic gyre (upstream of a wave crest) while downward motion takes place downstream (upstream of a trough). We also show that the vertical motion associated with the mesoscale eddies is an order of magnitude higher than the large-scale vertical motion. These patterns of large-scale and mesoscale vertical m...

Recent advances in observing the physical oceanography of the western Mediterranean Sea

The Mediterranean Sea has been investigated intensively since the early nineties, using modern techniques and collaborative approaches. This overview summarizes some of the resulting advances that were made concerning the physical oceanography of the western Mediterranean. The water mass formation processes are now much better understood and have been quantified to a large extent. The boundary conditions of the system in terms of surface fluxes and strait transports can be determined with improved accuracy, thus enabling future investigation of interannual variability. The dynamics of the surface and intermediate layers have revealed a variety of eddy and mesoscale processes that are important for the circulation and spreading of water masses. The deep circulation is being investigated with Lagrangian techniques (tracers and floats). First results show a large component of the deep water originating from the Tyrrhenian Sea and intense cyclonic and anticyclonic eddy flows.

Circulation in the Alboran Sea as determined by quasi-synoptic hydrographic observations. Part I: Three-dimensional structure of the two anticyclonic gyres

Abstract The circulation and dynamics of the Modified Atlantic Water have been studied using data from an intensive field experiment carried out between 22 September and 7 October 1992. Data included 134 CTD casts, ADCP, and satellite imagery. A well-defined wavelike front was observed with two significant anticyclonic gyres in the western and eastern Alboran Sea. Smaller-scale cyclonic eddies were also observed. The front separates the more saline, older modified Atlantic water (S>38) in the northern region from the fresher, more recent modified Atlantic water (S<36.8) in the south. The associated baroclinic jet had a mean transport of 1 Sv and maximum geostrophic velocities of 1.0 ms−1. The three-dimensional structure and spatial scales of both gyres were similar, that is, 90 km long and 220 m deep. In the eastern Alboran, northeast of Oran, the origin of the Algerian Current was also detected with an eastward transport of 1.8 Sv. The general picture can be presented as a structure formed by a wavelike ...

Innovation in the Tourism Sector: Results from a Pilot Study in the Balearic Islands

This paper provides empirical evidence on innovation in various tourism firms in the Balearic Islands. The main results from this pilot study are as follows. Innovation is common in Balearic touris...

Multivariate analysis of the surface circulation in the Balearic Sea

Abstract This study gives a comprehensive view of the regional surface circulation of the Balearic Sea in early summer. Its spatial variability and dynamics are described from a multivariate analysis of AXBT, CTD and ADCP data collected during the mesoscale experiment FE-91 (May 22 – June 2, 1991). The results provide evidence of two energetic frontal jets that drive the circulation over the slopes: the southward Continental current (0.9Sv) and the northward Balearic current (0.5Sv). In the southern Balearic basin, to the north of the Ibiza sill, the analyses show that the slope circulation is drastically modified by a wide pool (≈70km) of Winter Intermediate Waters (WIW). In this region, both the Continental and Balearic currents leave the slopes and merge offshore. As a result, the Continental current veers cyclonically to the north and flows along the insular slope. Numerous mesoscale structures (eddies, meanders and filaments) are found in the centre of the basin, directly related to instabilities of the frontal jets often induced by sharp topographic irregularities and subsurface eddies, and involving significant offshore transport of slope waters. Assuming stationarity of the velocity field, a Lagrangian integration is performed to establish the trajectories and time scales associated with the analysed velocity field. The calculations indicate that a drifter released in the core of the Continental current at 22m depth drifts cyclonically around the Balearic basin and reaches the north of Mallorca in less than 40 days. This is consistent with data from an in situ surface drifter deployed in June 1993, and suggests that the velocity field obtained from FE-91 data is representative of the summer circulation of the Balearic Sea. All these results are discussed in the perspective of the general circulation of the Western Mediterranean.

Pressure-Forced Seiches of Large Amplitude in Inlets of the Balearic Islands

Large-amplitude harbor seiches usually occur in summer in the Balearic Islands. A significant correlation between sea level oscillations and atmospheric pressure disturbances has been found, though a proved physical mechanism to account for this atmosphere-ocean interaction is still missing. Using a flat bottom, shallow water model, we show that a direct coupling between atmospheric pressure and the free mode of an inlet is unlikely but that an oceanic wave of atmospheric origin can act as an intermediate mechanism and adequately force the inlet by resonance. The phase relationship derived from this mechanism is in good agreement with observations, provided the whole spectrum of oceanic waves is in opposite phase to the generating atmospheric disturbance. We also show that the very large oscillations observed at Ciutadella (an elongated, shallow inlet in the west coast of Menorca, Balearic Islands) can be explained in terms of the particular shape of this inlet.

Thermal Lag Correction on Slocum CTD Glider Data

AbstractIn this work a new methodology is proposed to correct the thermal lag error in data from unpumped CTD sensors installed on Slocum gliders. The advantage of the new approach is twofold: first, it takes into account the variable speed of the glider; and second, it can be applied to CTD profiles from an autonomous platform either with or without a reference cast. The proposed methodology finds values for four correction parameters that minimize the area between two temperature–salinity curves given by two CTD profiles. A field experiment with a Slocum glider and a standard CTD was conducted to test the method. Thermal lag–induced salinity error of about 0.3 psu was found and successfully corrected.

Effectiveness of protection of seagrass (Posidonia oceanica) populations in Cabrera National Park (Spain)

Posidonia oceanica, the dominant seagrass species in the Mediterranean, appears to be experiencing widespread loss. Efforts to conserve Posidonia oceanica are increasing, as reflected in the increase in the number of marine protected areas in the Mediterranean. However, the effectiveness of these measures to conserve seagrass meadows is unknown. In this study, the present status of the Posidonia oceanica meadows in the Cabrera National Park (Mediterranean), the only marine national park in Spain, was assessed, and the effectiveness of the conservation measures adopted was tested. This was done by reconstruction of past and present growth, quantification of the demographic status of the established meadows, and quantification of patch formation and growth rates in areas where recolonization is occurring. The meadows extended from 1-43m deep at Santa Maria bay and from 1-33 m at Es Port. Leaf production rate of the stands examined ranged between 6.5 and 7.8 leaves shoot -1 yr -1 , with higher rates in Santa Maria than in Es Port. Vertical rhizomes elongated at rates ranging from 5.39-10.12 mm yr -1 , annual vertical growth in Santa Maria stands being larger than that in the stands developing at Es Port. Horizontal rhizomes elongated slowly (from 2.6-6.1 cm yr -1 ), and branching was sparse (<0.25 branches yr -1 axis -1 ), with maximum elongation and branching rates in areas where patches were actively colonizing. Flowering was a rare event in all the stands (<0.015 flowers shoot -1 yr -1 ). Patch formation and patch growth rates in active colonizing areas were slow, but they increased after implementation of mooring regulations in the Park. Similarly, the leaf production tended to increase, and vertical rhizome growth to decrease, in both bays following the onset of regulation measures. However, the decrease in vertical growth detected was greater at Santa Maria, where access is prohibited to visitors, than at Es Port, where boats are allowed to moor, attached to permanent weights. Shoot mortality rate was generally low (mean 0.10 ± 0.02 In units yr -1 ) but exceeded the recruitment rate (<0.009 and 0.17 In units yr -1 ) in 55% of the meadows examined, indicative of negative net population growth rates. Regulation of mooring activities has improved the status of the P. oceanica meadows at Cabrera National Park. The demographic analysis, however, indicated that while P. oceanica meadows at Santa Maria are in good shape, those at Es Port seem to be compromised. The observed differences in meadow status reflect the large differences in circulation inside the bays (water residence time at Santa Maria = 4 days, water residence time at Es Port = 11 days) and the anthropogenic pressure both bays support.