Intermediate Water Research Articles

Dynamics of wave-supported gravity currents in intermediate water

The dynamics of gravity currents propagating beneath intermediate water waves is investigated in the present study. Laboratory experiments were carried out in a wave flume, in which saltwater was released into freshwater by means of a point-release setup in the presence of a fully developed wave field. Results revealed a series of interesting features of the gravity current advancement and density distribution under the influence of the wave field. The advancing fronts oscillate with the same period of the wave, although front velocity appears not to be affected by increasing wave nonlinearity. The analysis of the density field highlighted the existence of an enhanced mixing process between ambient and gravity current fluid induced by the orbital motion, alongside a loss of symmetry between onshore and offshore fronts, in terms of front shape and density spatial distribution. Such an effect intensifies as wave height increases and wavelength decreases. Moreover, variations of the salinity concentration profiles during the wave phase revealed a “piston-type” oscillatory behavior of the gravity current concentration induced by the wave field, which oscillates accordingly to the wave phase.

Hierarchical Hydration Dynamics of RNA with Nano-Water-Pool at Its Core.

Many functional RNAs fold into a compact, roughly globular shape by minimizing the electrostatic repulsion between their negatively charged phosphodiester backbone. The fold of such close, compact RNA architecture is often so designed that its outer surface and complex core both are predominately populated by phosphate groups loosely sequestering bases in the intermediate layers. A number of helical junctions maintain the RNA core and its nano-water-pool. While the folding of RNA is manifested by its counterion environment composed of mixed mono- and divalent salts, the concerted role of ion and water in maintaining an RNA fold is yet to be explored. In this work, detailed atomistic simulations of SAM-I and Add Adenine riboswitch aptamers, and subgenomic flavivirus RNA (sfRNA) have been performed in a physiological mixed mono- and divalent salt environment. All three RNA systems have compact folds with a core diameter of range 1-1.7 nm. The spatiotemporal heterogeneity of RNA hydration was probed in a layer-wise manner by distinguishing the core, the intermediate, and the outer layers. The layer-wise decomposition of hydrogen bonds and collective single-particle reorientational dynamics reveal a nonmonotonic relaxation pattern with the slowest relaxation observed at the intermediate layers that involves functionally important tertiary motifs. The slowness of this intermediate layer is attributed to two types of long-resident water molecules: (i) water from ion-hydration layers and (ii) structurally trapped water (distant from ions). The relaxation kinetics of the core and the surface water essentially exposed to the phosphate groups show well-separated time scales from the intermediate layers. In the slow intermediate layers, site-specific ions and water control the functional dynamics of important RNA motifs like kink-turn, observed in different structure-probing experiments. Most interestingly, we find that as the size of the RNA core increases (SAM1 core < sfRNAcore < Add adenine core), its hydration tends to show faster relaxation. The hierarchical hydration and the layer-wise base-phosphate composition uniquely portray the globular RNA to act like a soft vesicle with a quasi-dynamic nano-water-pool at its core.

Altering the bio-inert properties of surfaces by fluorinated copolymers of mPEGMA

Hydrophilic materials display “bio-inert properties”, meaning that they are less recognized as foreign substances by proteins and cells. Such materials are often water soluble; therefore, one general approach to enable the use of these materials in various applications deals with copolymerizing hydrophilic monomers with hydrophobic ones to facilitate such resulting copolymers water insoluble. However, reducing the hydrophilic monomer amount may reduce the bio-inert properties of the material. The decrease in bio-inert properties can be avoided when small amounts of fluorine are used in copolymers with hydrophilic monomers, as presented in this article. Even in small quantities (7.9 wt%), the fluorinated monomer, 1,1,1,3,3,3-hexafluoropropan-2-yl 2-fluoroacrylate (FAHFiP), contributed to the improved hydrophobicity of the polymers of the long side-chain poly(ethylene glycol) methyl ether methacrylate (mPEGMA) bearing nine ethylene glycol units turning them water insoluble. As evidenced by the AFM deformation image, a phase separation between the FAHFiP and mPEGMA domains was observed. The copolymer with the highest amount of the fluorinated monomer (66.2 wt%) displayed also high (82 %) FAHFiP amount at the polymer–water interface. In contrast, the hydrated sample with the lowest FAHFiP/highest mPEGMA amount was enriched of three times more hydrophilic domains at the polymer–water interface compared to that of the sample with the highest FAHFiP content. Thus, by adding a small FAHFiP amount to mPEGMA copolymers, water insoluble in the bulk too, could be turned highly hydrophilic at the water interface. The high content of intermediate water contributed to their excellent bio-inert properties. Platelet adhesion and fibrinogen adsorption on their surfaces were even more decreased as compared to those on poly(2-methoxyethyl acrylate), which is typically used in medical devices.

Enhanced pH‐Universal Hydrogen Evolution Reactions on the Ru/a–Ni–MoO3 Electrocatalysts

Green hydrogen production through the electrocatalytic hydrogen evolution reaction (HER) is a promising solution for transition from fossil fuels to renewable energy. To enable the use of a variety of electrolytes with different pH values, HER catalysts with pH universality are highly desirable but their performance remains mediocre. Herein, a pH‐universal HER catalyst composed of ruthenium nanoparticles decorated on amorphous Ni‐doped MoO3 (a–Ni–MoO3) nanowire support is reported, that is, Ru/a–Ni–MoO3, which achieves enhanced performance as compared to the commercial Ru/C catalyst. Electron transfer from Ru to a–Ni–MoO3 is identified by spectroscopic techniques, which results in a modified electronic structure of the Ru active sites with a reduced electron density of 4d states near the Fermi level. Density functional theory calculations further reveal that the modulated electronic structure weakens the interactions between the Ru active sites and the reaction intermediates, which facilitates the HER reaction steps including H intermediate desorption and water dissociation. Experimental and theoretical findings provide insight into enhancing pH‐universal HER performance through modulation of electrocatalyst electronic structure.

Unified analytical solution for group-induced infragravity waves based on Green's function

Short-wave group forcing is a major driving mechanism of infragravity waves. The subharmonic response to wave group forcing approaches resonance in shallow water where the group velocity is equal to the shallow-water wave-propagating speed. Currently, there is a lack of understanding of the connection between the free and bound components of group-induced infragravity waves and the consistency among existing solutions for off- and near-resonance conditions in intermediate and shallow water. Here, a unified solution of group-induced subharmonics is derived based on Green's function for the first time. The new solution is valid for any resonance intensity and is able to describe group-induced subharmonic behaviour at all water depths consistently from a new angle. The proposed solution reduces to existing solutions for intermediate depth (Longuet-Higgins &amp; Stewart, J. Fluid Mech., vol. 13, 1962, pp. 481–504; Zou, Phys. Oceanogr., vol. 41, 2011, pp. 1842–1859), shallow water and/or over a plane sloping beach (Van Leeuwen, PhD thesis, TU Delft, 1992; Schäffer, J. Fluid Mech., vol. 247, 1993, pp. 551–588; Janssen et al., J. Geophys. Res., vol. 108, 2003, p. 3252; Contardo et al., J. Phys. Oceanogr., vol. 51, 2021, pp. 1465–1487; Liao et al., J. Phys. Oceanogr., vol. 51, 2021, pp. 2749–2765). Unlike previous solutions, the Green's function-based solution describes all subharmonics as free subharmonics continuously radiated away from each point source in the group-induced forcing field determined by wave radiation stress gradients. The superposition of all these free subharmonics yields so-called bound subharmonics by previous studies due to group-modulated emission of each free subharmonic through the source field bound to the wave group. Therefore, this solution provides theoretical evidence that the group-induced subharmonic at any observation point is dependent on the surrounding radiation stress field and topography. Under full-resonance conditions in shallow water, downwave-propagating subharmonics excited at all source locations interfere with each other constructively; therefore, their superposed amplitude is proportional to the travel distance of wave groups. Combined with the conventional moving-breakpoint forcing model, the predicted amplitude of the subharmonic in the surf zone by the present solution is in good agreement with laboratory observations.

Effect of relative opening on the moving thin plate under the action of ocean wave in the surging direction: A numerical simulation approach

This paper aims to develop the simulated numerical methodology for sloping beach with nonlinear free-surface waves of sloshing water in a 2D rectangular tank. The current computational tool would be the first step in accurately modeling wave energy converters. The 2D tank model was developed by ANSYS FLUENT software, and Navier–Stokes equations are discretized on a regular structured grid based on the finite volume method (FVM). The model is validated for nonlinear sloshing cases. In addition, tank flexibility is analyzed for its impact on liquid sloshing. The test was conducted in five different wave steepness conditions. There were five conditions of wave steepness used in the test. This study looked at fluid–structure interaction around moving plates. The output power of the plate wave energy converter for different plate heights and streamline motion around the plate are important studies in the flow field. Variations of drag coefficient with the wave steepness are the important study in this paper. It shows that the drag coefficient increases with the increase in wave steepness and plate length. In particular, the new structure can give a new, highly accurate formula for determining the wave power of the ocean structures. Its application is seen in wave energy converter (WEC), where the interaction of solid objects, such as wind turbines with water waves, extracts renewable wave energy from the ocean. A highly efficient CFD approach method is introduced to capture the interaction of solid object with a two-phase flow. The effect of wave steepness using second-order stokes wave theory on a moving thin plate in intermediate water is a new discussion. This research is a highly relevant source of information in the development of many practical systems and has direct employment in the design of WEC in order to extract ocean energy.

Study of a monopile with pre-tensioned tethers for offshore wind turbines at deeper waters

Currently, monopiles are the industry's first choice to support offshore wind turbines (OWTs) due to the complexities associated with fabrication, transportation and installation of various foundation solutions. These are, however, considered suitable for water depths up to ∼30–35 m, beyond which they become massive and complex to handle. Increasing the application range of monopiles without making them too large by adopting some suitable means may significantly impact the rapid growth of OWTs at intermediate water depths (∼50 m), where existing solutions such as jackets or concrete gravity foundations involve large capital expenditure. In this work, a novel approach of utilising pre-tensioned tethers along with a 6.0 m wide monopile was explored for 50 m water depth. Under an extreme load case, the stress ratio was found to be reduced from 1.17 to 0.44 when pre-tensioned tethers are used. Similarly, it was found that by adjusting parameters associated with the proposed concept, fatigue damage can be brought down from a very high value to 0.63 or less. The results thus show that the proposed approach can open new avenues to bring competitiveness to the cost of offshore wind energy at intermediate water depths.

Deglacial temperature and carbonate saturation state variability in the tropical Atlantic at Antarctic Intermediate Water Depths

Deglacial temperature and carbonate saturation state variability in the tropical Atlantic at Antarctic Intermediate Water Depths

Spatio-temporal accumulation and sources of anthropogenic Pb in Ulleung Basin sediments, East/Japan Sea, based on stable Pb isotope ratios.

The accumulation, pathways, and sources of anthropogenic lead (Pb) in Ulleung Basin sediments were investigated based on the temporal and spatial variations in the Pb concentration and stable Pb isotopes for 21 dated box core sediments collected from the shelf, slope, and basin in the southern East/Japan Sea. Leached (1M HCl) Pb concentrations and isotope ratios (207Pb/206Pb and 208Pb/206Pb) were nearly constant before 1930, but have increased rapidly until the present. The primary source of anthropogenic Pb is considered to be atmospheric deposition, showing the signature of a mixture of leaded gasoline and coals, which was the major anthropogenic source in the basin. However, after the 1990s, anthropogenic Pb from dumping materials added as much as 10-25% to the slope sediment and has been spreading out from the water column accompanied by the movement of the East Sea Intermediate Water. In shelf areas, inputs from nonferrous refineries in the coastal industrial complexes play an important role in pollution from anthropogenic Pb.

A Lagrangian Estimate of the Mediterranean Outflow's Origin

AbstractThe origin of the Mediterranean Outflow is investigated by deploying six millions virtual Lagrangian parcels at the Strait of Gibraltar, and tracing them backward in time using velocity estimates from an eddy‐permitting reanalysis. The Lagrangian parcels are followed until they intercept one of three sections. The hypothesis is that each section is associated with distinct water masses: the Gulf of Lions, related to Western Mediterranean Deep Water and Western Intermediate Water, carries 86% of the Outflow's transport; the Northern Tyrrhenian, related to Tyrrhenian Deep and Intermediate Waters, carries 1% of the transport; the Strait of Sicily, related to Levantine Intermediate Waters, carries 13% of the transport. The median transit times from the sections to the Strait of Gibraltar range from 5 years (Gulf of Lions) to 8 years (Strait of Sicily).

Novel configuration of dual-temperature condensation and dual-temperature evaporation high-temperature heat pump system: Carbon footprint, energy consumption, and financial assessment

To achieve the goal of carbon neutrality for the application of industrial heating by recovery waste heat, the concept of dual-temperature condensation and dual-temperature evaporation is proposed for the high-temperature heat pump (HTHP) by introducing the techniques of ejector and two-stage compression. The energy, exergy, emission, and economic models are developed and optimized for the two new proposed systems. Then, the energy consumption, CO2 emissions and cost (LCC) during the whole life cycle are compared with five existing heat pumps and four traditional boilers. The highest coefficient of performance (COP) of heat pump (HP) can be got when intermediate water temperature on the heat sink side is optimum. The new proposed systems have better performances than the other five HTHPs. During the rated working condition, discharge temperature decreases by the use of dual-temperature condensation and dual-temperature evaporation HP with an ejector (Ej-DCDE). The optimal COP of Ej-DCDE-2 is 4.25, which is 11.55% and 1.43% higher than dual-temperature condensation and single-temperature evaporation HP and Ej-DCDE-1, respectively. The exergy destruction of Ej-DCDE-2 is reduced by 27.88% compared with basic heat pump (Base). Moreover, Ej-DCDE-2 has the lowest primary energy consumption of 14.62 ktoe, 22.19% and 25.09% lower than Base and oil-fired boiler during the total working period, respectively. In general, HTHPs have lower carbon dioxide, gaseous and particular pollutant emissions compared with boilers, especially Ej-DCDE-2. Finally, Ej-DCDE-2 has the minimum LCC, which is 14.67% and 11.75% less than Base and coal-fired boiler. Ej-DCDE-2 shows the most potential advantages of all the heating solutions and is recommended to replace traditional boilers for industrial heating.

Non-homogeneous approximation for the kurtosis evolution of shoaling rogue waves

Bathymetric changes have been experimentally shown to affect the occurrence of rogue waves. We recently derived a non-homogeneous correction to the spectral analysis, allowing us to describe the evolution of the rogue wave probability over a shoal. Here, we extend this work to the evolution of the excess kurtosis of the surface elevation, that plays a central role in estimating rare event probabilities. Furthermore, we provide an upper bound to the excess kurtosis. In intermediate and deep water regimes, a shoal does not affect wave steepness nor bandwidth significantly, so that the vertical asymmetry between crests and troughs, the excess kurtosis and the exceedance probability of wave height stay rather constant. In contrast, in shallower water, a sharp increase in wave steepness increases the vertical asymmetry, resulting in a growth of both the tail of the exceedance probability and the excess kurtosis.

Can Oxygen Utilization Rate Be Used to Track the Long‐Term Changes of Aerobic Respiration in the Mesopelagic Atlantic Ocean?

AbstractQuantifying changes in oceanic aerobic respiration is essential for understanding marine deoxygenation. Here we use an Earth system model to investigate if and to what extent oxygen utilization rate (OUR) can be used to track the temporal change of true respiration (Rtrue). Rtrue results from the degradation of particulate and dissolved organic matter in the model ocean, acting as ground truth to evaluate the accuracy of OUR. Results show that in thermocline and intermediate waters of the North Atlantic Subtropical Gyre (200–1,000 m), vertically integrated OUR and Rtrue both decrease by 0.2 molO2/m2/yr from 1850 to 2100 under global warming. However, in the mesopelagic Tropical South Atlantic, integrated OUR increases by 0.2 molO2/m2/yr, while the Rtrue integral decreases by 0.3 molO2/m2/yr. A possible reason for the diverging OUR and Rtrue is ocean mixing, which affects water mass composition and maps remote respiration changes to the study region.

Late Pleistocene boreal molluscs in the Gulf of Cadiz: Past and current oceanographic implications

Remains of molluscs were collected from the seafloor on the north-eastern margin of the Gulf of Cadiz, between 300 and 1000 m water depth, using different sampling methods (e.g. dredging, trawling and box-coring), during several deep-sea expeditions. Samples contained a suite of species which nowadays mostly occur northwards of the English Channel, together with other widespread species. Species now locally extinct in the Gulf of Cadiz and restricted to northern latitudes, which unequivocally indicate a faunal shift, include the gastropods Buccinum undatum, Colus gracilis, Liomesus ovum and Neptunea antiqua, the bivalves Arctica islandica, Chlamys islandica, Modiolus modiolus, Mya truncata and Nuculana pernula and the scaphopod Antalis entalis. These species represent “Boreal Guests” of marked palaeoclimatic significance, some of which are reported for the first time in the Gulf of Cadiz. The boreal species collected were mostly large (>5 cm) whereas smaller boreal species were extremely scarce, probably winnowed away by strong bottom currents. The pteropod Limacina retroversa, at present restricted to water masses northwards of the Iberian Peninsula but widespread in Mediterranean sediments of the last glaciation, was also recorded. Accelerator mass spectrometry (AMS) 14C dates obtained from nine specimens of molluscs ranged between 26.1 and 14.6 kyr B.P., thus confirming their attribution to a last glacial assemblage. The abundance of these molluscan remains in the present Mediterranean Outflow Water pathway could be explained if this outflow was reduced in intensity or more likely shifted to a deeper level, leaving the upper slope in contact with suitable Atlantic intermediate waters. The findings of Boreal Guests in the Gulf of Cadiz document the continuity of the faunal shift which is well-known in the Mediterranean basin. Species still living in the Gulf of Cadiz and the Alboran Sea nevertheless account for 84.6% of specimens among the larger species.

Boosting interfacial solar steam generation by three-dimensional bilayer cellulose aerogels

Interfacial solar steam generation (ISSG) provides a sustainable approach of clean water production through desalination and water purification. It is still needed to pursue a fast evaporation rate, high-quality freshwater production, and low-cost evaporators. Herein, a three-dimensional (3D) bilayer aerogel was fabricated using cellulose nanofiber (CNF) as a skeleton filled with polyvinyl alcohol phosphate ester (PVAP), and carbon nanotubes (CNT) as a light absorbing material in the top layer. The CNF/PVAP/CNT aerogel (CPC) had broadband light absorption ability and exhibited an ultrafast water transfer rate. The lower thermal conductivity of CPC effectively confined the convert heat in the top surface and minimized heat loss. Additionally, a large amount of intermediate water caused by water activation decreased the evaporation enthalpy. Under 1 sun irradiation, the CPC-3 (3.0 cm height of CPC) achieved a high evaporation rate of 4.02 kg m−2 h−1 with an energy conversion efficiency of 125.1%. The additional convective flow and environmental energy made CPC achieve an ultrahigh evaporation rate of 11.37 kg m−2 h−1, surpassing 673% of the solar input energy. More importantly, the continuous solar desalination and higher evaporation rate (10.70 kg m−2 h−1) in seawater revealed that CPC was a promising candidate for practical desalination. Outdoor cumulative evaporation was up to 73.2 kg m−2 d−1 in weak sunlight and lower temperature, which would meet the daily drinking water demands of 20 people. The excellent cost-effectiveness of 1.085 L h−1 $−1 presented its potential for a wide range of practical applications, such as solar desalination, wastewater treatment, and metal extractions.

Dense water formation in the eastern Mediterranean under a global warming scenario

Abstract. Dense water formation in the eastern Mediterranean (EMed) is essential in sustaining the Mediterranean overturning circulation. Changes in the sources of dense water in the EMed point to changes in the circulation and water properties of the Mediterranean Sea. Here we examine with a regional climate system model the changes in the dense water formation in the EMed through the 21st century under the RCP8.5 emission scenario. Our results show a shift in the dominant source of Eastern Mediterranean Deep Water (EMDW) from the Adriatic Sea to the Aegean Sea in the first half of the 21st century. The projected dense water formation is reduced by 75 % for the Adriatic Sea, 84 % for the Aegean Sea, and 83 % for the Levantine Sea by the end of the century. The reduction in the intensity of deep water formation is related to hydrographic changes in surface and intermediate water that strengthen the vertical stratification, hampering vertical mixing and thus convection. Those changes have an impact on the water that flows through the Strait of Sicily to the western Mediterranean and therefore on the whole Mediterranean system.

Intense anticyclones at the global Argentine Basin array of the Ocean Observatory Initiative

Abstract. We analyzed physical oceanic parameters gathered by a mooring array at mesoscale spatial sampling deployed in the Argentine Basin within the Ocean Observatory Initiative, a National Science Foundation major research facility. The array was maintained at 42∘ S and 42∘ W, a historically sparsely sampled region with small ocean variability, over 34 months from March 2015 to January 2018. The data documented four anticyclonic extreme-structure events in 2016. The four anticyclonic structures had different characteristics (size, vertical extension, origin, lifetime and Rossby number). They all featured near-inertial waves (NIWs) trapped at depth and low Richardson values well below the mixed layer. Low Richardson values suggest favorable conditions for mixing. The anticyclonic features likely act as mixing structures at the pycnocline, bringing heat and salt from the South Atlantic Central Water to the Antarctic Intermediate Waters. The intense structures were unique in the 29-year-long satellite altimetry record at the mooring site. The Argentine Basin is populated with many anticyclones, and mixing associated with trapped NIWs probably plays an important role in setting up the upper-water-mass characteristics in the basin.

An intermediate water gravity wavelength and wave height measurement inside a large wave flume tank

This paper discusses an intermediate water gravity wavelength and wave height measurement method. Three methods were used to obtain wave height, wavelength, and period. Firstly, conventional methods used two Honeywell pressure sensors mounted at the bottom of the wave tank at two different locations. Secondly, using the transfer function of the flap wavemaker (the relationship between wave height and the wave paddle stroke). Thirdly, the Laser Sheet technique (PIV image processing technique). The significant wave height and period from pressure reading sensors of regular gravity waves were obtained from the Raleigh distribution and Zero up crossing technique. Wavelength was obtained indirectly by using a dispersion relationship that was solved by using the Newton Raphson numerical method from both the pressure sensors and the transfer function of the flap wavemaker. This experiment was focused on getting the direct value of wave measurements by developing an image processing technique in a clear large wave flume tank to replace the conventional methods and eliminate the error that may produce by using the numerical methods. The PIV setup with the CCD camera was used to capture wave images. The image processing technique based on Canny edge detection with constant threshold value was used to detect the edge of the waves. The experimental result showed a good agreement between the results obtained from these three methods, with the percent of error up to 8.683%.

Observations in the Spanish Mediterranean Waters: A Review and Update of Results of 30-Year Monitoring

The Instituto Español de Oceanografía (IEO, Spanish Institute of Oceanography) has maintained different monitoring programs in the Spanish Mediterranean waters (Western Mediterranean) since 1992. All these monitoring programs were unified in 2007 under the current program RADMED (series temporales de datos oceanográficos en el Mediterráneo), which is devoted to the in situ multidisciplinary sampling of the water column of coastal and open-sea waters by means of periodic oceanographic campaigns. These campaigns, together with a network of tide-gauges, are part of the IEO Observing system (IEOOS). In some cases, the temperature and salinity time series collected in the frame of these monitoring programs are now more than 30 years long, whereas sea level time series date to the beginning of the 1940s. This information has been complemented with international databases and has been analyzed in numerous works by the Grupo mediterráneo de Cambio Climático (GCC; Mediterranean Climate Change Group) for more than 20 years. These works have been devoted to the detection and quantification of the changes that climate change is producing on the physical, chemical, and biological properties of the Spanish Mediterranean waters. In this work, we review the results obtained by the GCC since 2005 in relation to the changes in the physical properties of the sea: water column temperature, salinity, and density, heat content, mixed layer depth, and sea level. Time series and results are updated from the last works, and the reliability of the existing time series for the detection of climatologies and long-term trends are analyzed. Furthermore, the different sources of uncertainty in the estimation of linear trends are considered in the present work. Besides this review and update of the results obtained from the data collected in the frame of the IEOOS, we conduct a review of the existing monitoring capabilities from other institutions in the Spanish Mediterranean waters and a review of results dealing with climate change in the Spanish Mediterranean obtained by such institutions. In particular, we include a review of the results obtained by SOCIB (Servicio de Observación y Predicción Costero de las Islas Baleares; Balearic Islands costal observing and forecasting system) in relation to the study of marine heat waves and the warming of the sea surface, and the results corresponding to the intense warming of the Catalan continental shelf at L’Estartit oceanographic station. All these results evidence that the surface Spanish Mediterranean waters are warming up at a rate higher than that affecting the global ocean (&gt;2 °C/100 years). This warming and a salinity increase are also observed along the whole water column. Marine heat waves are increasing their intensity, frequency, and duration since 1982, and coastal sea level is increasing at a rate of 2.5 mm/yr. The salinity increase seems to have compensated for the warming, at least at surface and intermediate waters where no significant trends have been detected for the density. This could also be the reason for the lack of significant trends in the evolution of the mixed layer depth. All these results highlight the importance of monitoring the water column and the necessity of maintaining in situ sampling programs, which are essential for the study of changes that are occurring throughout the Spanish Mediterranean waters.

Hydraulic suppression of basal glacier melt in sill fjords

Abstract. Using a conceptual model, we examine how hydraulically controlled exchange flows in silled fjords affect the relationship between the basal glacier melt and the features of warm intermediate Atlantic Water (AW) outside the fjords. We show that an exchange flow can be forced to transit into the hydraulic regime if the AW interface height decreases, the AW temperature increases, or the production of glacially modified water is boosted by subglacial discharge. In the hydraulic regime, the heat transport across the sill becomes a rate-limiting factor for the basal melt, which is suppressed. An interplay between processes near the ice–ocean boundary and the hydraulically controlled exchange flow determines the melt dynamics, and the sensitivity of the basal melt to changes in the AW temperature is reduced. The model results are discussed in relation to observations from the Petermann, Ryder, and 79∘ N glaciers in northern Greenland.