Volcanic eruptions inject particles (tephra) and gases into the atmosphere, impacting air quality. To provide new insights into this process, we focus on the 3-month-long 2021 Tajogaite eruption, on La Palma in the Canary Islands, Spain. This eruption emplaced lava flows and produced tephra and gases in multiple sustained plumes. We examined the relationship between air quality, tephra dispersion and deposition, and eruption dynamics. We reconstructed the spatiotemporal variations in tephra deposition using a collection network deployed around the island and maintained throughout the eruption, while plume dispersion was tracked using satellite observations. These datasets were compared to the air quality monitoring data from the local regulatory network using time-series analyses. Our findings reveal distinct peaks in tephra deposition rates (a few g/m2/h 20 km away from the vent, up to more than 2000 g/m2/h at locations less than 3 km from the vent), related to both increased explosive activity at the volcanic vents and specific atmospheric conditions. We show that the fluctuations of tephra emission were the main driver of the particulate matter (PM) concentration variations, outweighing contributions from secondary aerosol formation through volcanic SO2 conversion. We evidence spatial disparity in the impact on air quality, with the western half of La Palma island experiencing higher amplitude and more frequent pollution peaks than the eastern half. We demonstrate that even low-explosivity basaltic eruptions can significantly affect air quality by generating and dispersing fine PM and gases over wide areas. Moreover, elevated PM concentrations persist beyond the duration of intense tephra deposition episodes, thereby extending the period of population exposure. These results have important implications for understanding and mitigating human exposure to volcanic pollutants.

Dense shelf water cascading (DSWC) in the northwestern Mediterranean Sea occurs due to the densification and overflow of shelf water in winter. This process ventilates the deep basin with waters that can be denser than those generated by open-ocean convection. Between 1987 and 2021 (i.e., 35 winter periods), shelf water reached depths greater than 1000 m on only 9 occasions, and open questions remain regarding the triggering factors and inhibitors for these deep DSWC events. Combining atmospheric and ocean reanalysis data, we found that, at interannual scales, the East Atlantic (EA) mode of climate variability is more strongly associated with the thermal components of the atmospheric forcing: air temperature, wind, and sea surface temperature, contributing to a strong connection between the negative phase of EA, and an increased heat loss and buoyancy loss. At shorter synoptic to subseasonal time scales, the dense shelf water formation in winter is linked to the local northerly winds and cold air outbursts. As important as the thermal atmospheric forcing, the evaporation-precipitation balance and river runoff play a key role in facilitating or preventing dense shelf water formation and cascading. Besides, the temperature of surface shelf water at the beginning of winter can be critical. In the years after an intense DSWC event, the favorable preconditioning by advected dense water and reduced intermediate stratification enhances deep cascading. These insights are meaningful for how the atmospheric and oceanic signals from a changing climate propagate into the deep Mediterranean Sea, which ultimately could affect the thermohaline circulation.

Dense shelf water cascading (DSWC) is an oceanographic process that occurs when dense shelf water overflows over the shelf edge downslope toward the deep sea. Monitored in the northwestern Mediterranean by moorings since 1993 in the Lacaze-Duthiers Canyon and since 2005 in the Cap de Creus Canyon, numerical modeling with reanalysis extends this timeline further into the past. This study investigates a regional reanalysis (1987-2021) validated against mooring observations at 750-1000 m depth. The reanalysis successfully reproduces observed intense DSWC (IDSWC) events from 1999, 2000, 2005, 2006, 2012, 2013, and 2018 while identifying one previously unreported event in 1987 and detecting no IDSWC between 1988 and 1998. The reanalysis effectively matches 84 % of observed IDSWC days within the same week and 56 % on the exact date. Instead of assimilating IDSWC events from mooring observations to resolve the cascading process, the model relies solely on the seawater density on the shelf and revealed the seawater properties along the canyon that caused IDSWC. This work highlights the importance of high-resolution reanalyses in investigating the impacts of mesoscale processes on larger scales in the deep ocean.

Embayed beaches are laterally bounded by natural barriers such as rocky headlands or by artificial structures on human-altered coasts. They are commonly described as closed compartments because of limited sedimentary connection with other systems. However, this description is not accurate for many embayments, where sediment exchange can occur via headland bypassing. This study investigates natural sand bypassing between two embayed beaches along the Catalan coast, Pals and Sa Riera, and the influence of local stream-delivered sediment based on the analysis of repeated bathymetric surveys and surficial sediment samples. Sa Riera beach is a pocket beach separated from the Pals embayed beach by a rocky headland, and characterized by continuous progradation during the last decades. Comparison of bathymetric data spanning nearly two decades reveals sand bypassing between the beaches, supported by backscatter data and bottom sediment samples. Moreover, sediment samples highlight the significant contribution of local streams to sediment inputs at Sa Riera beach.

El principal objetivo de este trabajo es evaluar las variaciones espaciales y temporales de anchura y el comportamiento sedimentológico a medio-corto plazo (2004 a 2020) de las playas del norte del Golfo de Roses (NO Mediterráneo, España). La zona de estudio cubre 10 km en la parte norte del golfo. Se emplearon dos metodologías SIG para cuantificar los cambios costeros por transectos y por áreas. Se recolectaron muestras de sedimento tanto de la playa seca como de las áreas de lavado para cada transecto. El análisis basado en perfiles muestra una tasa anual promedio de -0,11 m•y-1 (que oscila entre 0,53 y -0,55 m•y-1), mientras que los resultados regionales indican una pérdida total de -20810 m2 ( -1300 m2•año-1). El tamaño del grano de sedimento disminuye hacia el norte (de 745 a 264 µm en la zona de balanceo). Los cambios en el ancho de la playa y el tamaño del grano ilustran el impacto de las estructuras antropogénicas en el comportamiento morfodinámico. Estas estructuras depositan preferentemente tamaños de grano específicos e impiden el transporte de sedimentos, lo que lleva a un aumento del ancho de la playa y del tamaño de los granos de sedimento aguas arriba y un proceso inverso aguas abajo, generando un comportamiento morfodinámico distinto.

This study conducts a morphodynamic analysis of beaches located in the northern sector of the Gulf of Roses (NW Mediterranean, Spain). The primary objective is to investigate mid-short (2004–2020) term spatial and temporal variations in shoreline position and sedimentological behaviour. The study area covers the northern part of the gulf, spanning 9.86 km, and includes both natural beaches and heavily anthropized ones. The following GIS methodologies were employed to study the variations in the coastline: QGIS for areas and DSAS-ArcGIS for transects, quantifying coastal changes from 2004 to 2020. Sediment samples were collected from both the dry beach and swash areas for each profile. The results reveal minor discrepancies in shoreline evolution data, depending on the method used (transects or areas). Profile-based analysis shows an average annual rate of −0.11 m·y−1 (ranging between 0.53 and −0.55 m·y−1), while areal-based results (2004–2020) indicate a total loss of −20,810 m2 (−1300 m2·y−1). Sediment grain size decreases northward (from 745 to 264 µm in the swash zone). Changes in shoreline position and grain size illustrate the impact of various anthropogenic structures on morphodynamic behaviour. These structures preferentially deposit specific grain sizes and impede sediment transport, which will cause an advance in the position of the shoreline and sediment grain sizes upstream and a reverse process downstream. This study underscores the influence of coastal anthropization on beach morphology and sedimentology, generating distinct morphodynamic behaviour.

The wide continental shelf of the Gulf of Lion in the NW Mediterranean is a region subject to pronounced atmospheric and oceanic interactions. Persistent cold northerly winds trigger progressive cooling of shelf waters, instigating a notable increase in seawater density. This dense water is forced to overflow by the slope, primarily channeled through the submarine canyons and especially through the southernmost Cap de Creus submarine canyon. Known as dense shelf water cascading, this intricate phenomenon exerts a pivotal influence not only on regional oceanographic dynamics but also on seafloor morphology and deep-sea living resources, warranting comprehensive investigation.To understand the interannual variability of cascading events spanning recent decades, we use the Med MFC physical reanalysis dataset, which encompasses the Mediterranean Sea. This dataset has proven invaluable, exhibiting robust correlations with in-situ observations of dense shelf water cascading via moored instrumentation, thereby offering unprecedented insights into the spatiotemporal evolution of water properties and dynamics within the Gulf of Lion.Our study quantifies the influence of the shelf water density modulation by the buoyancy fluxes in the air-sea interface. Leveraging data from atmospheric ERA5 and hydrological GloFAS reanalyses, we unveil a comprehensive understanding of the ocean-atmosphere interaction dynamics within this region. Specifically, we analyze the interannual variability in the buoyancy fluxes calculated from the main forcing agents impacting shelf water density: river freshwater input, wind speed, air-sea temperature contrast, absolute humidity, and precipitation.Our analysis reveals a significant correlation between these fluxes and the East Atlantic pattern (EA), which is one of the main modes of climate variability in the atmosphere. This underscores the intricate interplay between oceanic processes and broader atmospheric dynamics, particularly over the Gulf of Lion. Our findings offer insights into the mechanisms governing dense shelf water cascading and natural variability, thus augmenting our understanding of regional climate dynamics and enhancing predictive capabilities, and help foresee its occurrence and evolution in the context of climate change.

Modern and past mercury (Hg) fluxes in the oceanic water column and abyssal sediments are poorly quantified. Here, we investigated the particulate transfer of Hg in the water column of the ultra-oligotrophic Ionian Sea (Eastern Mediterranean) with sediment traps during a one-year period, and its accumulation in the deep central abyssal plain using sediment cores comprising the last 10 ka. The Hg concentrations in the particles collected in the sediment traps varied from 112 to 401 ng g(-1) and enabled quantifying annual Hg fluxes of 2.0, 2.5, and 2.5 mu g m(- 2) a(-1), for traps deployed at 250, 1440, and 2820 m deep, respectively. Hg collected in the upper trap originates from atmospheric deposition, including Saharan dust, which is scavenged by the biological pump. Higher Hg fluxes found at mid-depth and near-bottom than in the upper water layer are attributed to lateral advection under the mixed layer of Hg-rich resuspended sediments from the Adriatic continental margin. In the abyssal sediment, Hg concentrations range from 15 to 134 ng g(-1) with the highest levels in the Sapropel S1. Methylmercury concentrations varied from 0.06 to 0.24 ng g(-1) following the distribution of total Hg, with evidence of its specific accumulation at the oxidized front of the sapropel. We estimated that <1.8% of the total Hg in the sedimentary column was diagenetically reallocated. The reconstruction of historical Hg accumulation rates (HgAR) during the Holocene shows low pre-anthropogenic values (similar to 0.3 mu g m(2)a(- 1) before 4 ka BP), increasing up to similar to 0.9 mu g m(2)a(- 1) during the late Iron Age and the Roman period (1.5-2.5 ka BP), and up to 2.9 mu g m(2)a(- 1) during the Industrial Era. During the Sapropel S1 period (similar to 6-10 ka BP), HgARs rose to 6.4 mu g m(- 2) a(-1) likely due to the intensity of the Hg removal by the biological pump, the organic matter preservation, along with high inputs of Hg-rich terrigenous matter and a possible restricted recycling in the atmosphere. Hg accumulation in the Ionian Sea deep sediment is found similar to 3-fold lower than those in the western Mediterranean abyssal plain.

Continental margins play a key role in the cycling of natural and anthropogenic trace metals (TMs) as pathways at the interface between landmasses and deep ocean basins but also as sinks. Knowledge of how short-lived forcings alter the export dynamics of TMs is essential for our understanding of their fate in that setting. Here we report time series of particulate metal fluxes in three submarine canyons -namely Escombreras, Almeria and the Garrucha-Almanzora system- of the South-Western Mediterranean Sea. Our research focuses on combining multi-elemental TMs (Al, Fe, Ti, Co, Cu, Mn, Ni, Pb and Zn) and As (a metalloid) contents of settling particles collected near the bottom by automated particle traps during one year, and seafloor sediment samples from below the traps. We assess the role of storms and bottom trawling in the off-shelf transport of particulate TMs and As, and the natural and anthropogenic contributions of TMs by using enrichment factors (EFs).The TM export fluxes and composition changed over the study period, from March 2015 to March 2016. TM fluxes increase in early spring 2015 in association with short-lived storm events and during calm months in the Garrucha-Almanzora Canyon system, likely due to sediment resuspension triggered by bottom trawling. In terms of composition, TMs in the sinking fluxes appear to be closely associated with lithogenic (Al, Fe and Ti) and authigenic (Mn) particles' proxies. During storm events, the mass of settling particles in Escombreras and Almeria canyons was impoverished in Al, Fe, As, Co, Cu, Mn and Ni compared to other periods. The Garrucha-Almanzora Canyon system behaves differently as the above-described differences, are not observed there. Moreover, the TM composition of the sediments -with higher contents of Fe, Ti and several other TMs- in this canyon is barely tied to the composition of the settling particles. Finally, Cu and Zn contents, together with Pb in the northernmost Escombreras Canyon, are best explained by referring to anthropogenic sources. This work provides insights into the profound influence of the natural and anthropogenic forcings controlling the distributions and seasonal dynamics of particulate TMs and As in submarine canyons.

It has been suggested that the seafloor may be a sink for the plastic debris that enters the ocean. Therefore, the collection of data in the seafloor sediments regarding the co-presence of microplastics (MPs) and contaminants associated to plastic is considered a relevant topic. However, the number of studies addressing their possible correlation in this environment is still limited, and very little is known about the mechanisms that determine the release of plastic additives from plastic items. Starting from this basis, we investigated the presence of MPs and eleven phthalic acid esters (PAEs) in the continental shelf offshore Barcelona. Following a shelf-slope continuum approach, we sampled sediments from five stations, and we performed analysis by means of infrared micro spectroscopy (µFTIR) and liquid chromatography tandem mass spectrometry (LC–MS/MS). MPs were found to range from 62.0 to 931.1 items/kg d.w. with maximum concentration in the submarine canyon Besòs and at the highest depth. Moreover, different trends in the size distribution of fibers and non-fibers were observed, indicating the occurrence of a size dependent selection mechanism during transport and accumulation. PAEs resulted comprised between 1.35 to 2.41 mg/kg with Di(2-ethylhexyl)phthalate (DEHP) the most abundant congeners (1.04 mg/kg). Statistical analysis revealed no correlation between the Σ 11 PAEs and the total MPs concentration, but correlation between DEHP and fibers (σ = 0.667, p = 0,037), that resulted both correlated to the distance to the coast (ρ = 0.941 with p = 0,008 and ρ = 0.673 with p = 0.035, respectively).

Investigating the transfer of particulate matter from the continental shelf to the deep basin is critical to understand the functioning of deep sea ecosystems. In this paper we present novel results on the temporal variability of particle fluxes to the deep in three physiographic domains of a 240 km long margin segment and nearby basin off Murcia and Almeria provinces in the SW Mediterranean Sea, which are submarine canyons forming a rather diverse set (namely Escombreras, Garrucha-Almanzora and Almeria), the adjacent open slope and the deep basin. This margin is located off one of the driest regions in Europe and, therefore, its study may help understanding how mainland aridity translates into the export of particles to deep margin environments. Five mooring lines equipped with currentmeters, turbidity-meters and sediment traps were deployed for one entire annual cycle, from March 2015 to March 2016. We combine oceanographic, hydrological and meteorological data with grain size and bulk elemental data (organic carbon, opal, CaCO3, lithogenic) from the collected sinking particles to understand what drives particle transfers in such an under-studied setting, and to quantify the resulting fluxes and assess their spatio-temporal variability. Weighted total mass fluxes in canyons range from 1.64 g m(- 2) d(-1) in Almeria Canyon to 7.33 g m(- 2) d(-1) in Garrucha-Almanzora Canyon system, which are rather low values compared to other submarine canyons in the Western Mediterranean Sea. This results from the absence of extreme wind-storm events during the investigated time period combined with the reduced sediment input to the inner shelf by river systems in the study area. Our results also show that wind-storms are the main trigger for off-shelf particle transport to the deep margin, both within submarine canyons and over the open slope. The most significant transfer period is associated to a set of north-eastern storms in early spring 2015, when the off-shelf transport likely was promoted by storm-induced downwelling. However, the prevailing oceanographic conditions restricts the advection of water down the canyon heads to a few hundred meters, thus promoting a bottom-detached transport of particles seaward. Overall physiography, canyon head incision into the continental shelf and the distance of the canyon head to the shoreline (e.g. very short in Garrucha Canyon) play a key role in particle trapping capability and, therefore, in easing downslope particle transport. Further, bottom trawling activities around the Garrucha-Almanzora Canyon system, feed a nepheloid layer at depths in excess of 400 m, subsequently enhancing particle fluxes throughout the study period. In contrast, maximum particle fluxes in the deep basin respond to seasonal phytoplankton blooms. Our study shows that particle export from the shallow inner margin to the deep outer margin in sediment starved settings, even if limited, does occur as dominated by atmosphere and ocean driven short-lived events. However, that export does not reach too far as at several tens of kilometres from the shelf edge advective fluxes are replaced by vertical ones impelled by phytoplankton dynamics.

Summary Dune systems, generally, have high porosity and permeability and good lateral continuity, constituting excellent reservoirs around the world. The use of geophysical data to study dune systems can provide useful information to characterize these reservoirs. This project is focused on the study of a continental dune system of El Baix Empordà (Girona, Spain), to understand the system architecture, as well as to analyse his potential as a reservoir analogue. In the present work, we present the results of different profiles of ERT (Electric Resistivity Tomography) and GPR (Ground Penetrating Radar) that has enabled us to characterize the internal structure of the dune system, allowing us to differentiate dune and interdune deposits. Moreover, several sediment cores and surface samples were extracted in order to analyse porosity, water permeability and others physical characteristics of the system.

Research on microplastics has rapidly expanded in recent years and has led to the discovery of vast amounts of microplastics floating offshore in all main oceanic gyres and including the Mediterranean Sea. However, there is a lack of information from a few meters from the coastline where the largest plastic mass flux is suspected to occur. The reason behind is the general use of manta trawls towed by boats or research vessels to obtain samples, which hinders nearshore sampling. We have designed a manta trawl to collect samples in the nearshore from any type of recreational sports floating gear like kayaks, sailboats, rowing boats, windsurf boards and others. Data generated is comparable to that obtained with traditional scientific equipment towed from boats. During one year, starting from October 2020, 12 social, environmental and sports associations along the NW Mediterranean coast are acquiring scientific samples in the nearshore within the frame of two citizen science monitoring projects lead by the Spanish delegation of the non-governmental organization Surfrider Foundation Europe and the University of Barcelona. The projects represent a paradigm shift in microplastic research, allowing to fill the gap in knowledge of this transition coastal area, and actively involving citizens in the generation of new monitoring data (https://surfingforscience.org/).Our results reveal that densities of floating plastics in the nearshore along the NW Mediterranean coast are on average similar to those found offshore. However, we observe high variability due to meteorological and oceanographic conditions (i.e. the occurrence of eastern storms). We also observe that whereas floating microplastics dominate offshore, greater proportions of mesoplastics and macroplastics dominate at the nearshore waters, especially in between the breakwaters in Barcelona city. Indeed, the breakwaters, that protect Barcelona beaches against wave action and coastal erosion, behave as plastic traps. This is an indication of the importance of the nearshore as a source of plastic fragments to the open sea and calls for increased research in this area.

Sinking particles are a critical conduit for the export of organic material from surface waters to the deep ocean. Despite their importance in oceanic carbon cycling, little is known about the biotic composition and seasonal variability of sinking particles reaching abyssal depths. Herein, sinking particle flux data, collected in the deep Ierapetra Basin for a three-year period (June 2010 to June 2013), have been examined at the light of atmospheric and oceanographic parameters and main mass components (lithogenic, opal, carbonates, nitrogen, and organic carbon), stable isotopes of particulate organic carbon (POC) and source-specific lipid biomarkers. Our aim is to improve the current understanding of the dynamics of particle fluxes and the linkages between atmospheric dynamics and ocean biogeochemistry shaping the export of organic matter in the deep Eastern Mediterranean Sea. Overall, particle fluxes showed seasonality and interannual variability over the studied period. POC fluxes peaked in spring April–May 2012 (12.2 mg m−2 d−1) related with extreme atmospheric forcing. Summer export was approximately fourfold higher than mean wintertime, fall and springtime (except for the episodic event of spring 2012), fueling efficient organic carbon sequestration. Lipid biomarkers indicate a high relative contribution of natural and anthropogenic, marine- and land-derived POC during both spring (April–May) and summer (June–July) reaching the deep-sea floor. Moreover, our results highlight that both seasonal and episodic pulses are crucial for POC export, while the coupling of extreme weather events and atmospheric deposition can trigger the influx of both marine labile carbon and anthropogenic compounds to the deep Levantine Sea. Finally, the comparison of time series data of sinking particulate flux with the corresponding biogeochemical parameters data previously reported for surface sediment samples from the deep-sea shed light on the benthic–pelagic coupling in the study area. Thus, this study underscores that accounting the seasonal and episodic pulses of organic carbon into the deep sea is critical in modeling the depth and intensity of natural and anthropogenic POC sequestration, and for a better understanding of the global carbon cycle.

Physical and biogeochemical processes in the Southern Ocean are fundamental for modulating global climate. In this context, a process-based understanding of how Antarctic diatoms control primary production and carbon export, and hence global-ocean carbon sequestration, has been identified as a scientific priority. Here we use novel sediment trap observations in combination with a data-assimilative ocean biogeochemistry model (ECCO-Darwin) to understand how environmental conditions trigger diatom ecology in the iron-fertilized southern Scotia Sea. We unravel the role of diatoms assemblage in controlling the biogeochemistry of sinking material escaping from the euphotic zone, and discuss the link between changes in upper-ocean environmental conditions and the composition of settling material exported from the surface to 1,000 m depth from March 2012 to January 2013. The combined analysis of in situ observations and model simulation suggests that an anomalous sea-ice episode in early summer 2012–2013 favored (via restratification due to sea-ice melt) an early massive bloom of Corethron pennatum that rapidly sank to depth. This event drove high biogenic silicon to organic carbon export ratios, while modulating the carbon and nitrogen isotopic signals of sinking organic matter reaching the deep ocean. Our findings highlight the role of diatom ecology in modulating silicon vs. carbon sequestration efficiency, a critical factor for determining the stoichiometric relationship of limiting nutrients in the Southern Ocean.

The Remolar beach-dune system (700 m long and more than 100 m wide, 070N direction) borders a campground that was closed (2003), due to the Barcelona airport expansion. In order to recover and restore the dune ecosystem, a series of soft measures were performed. After 10 years, a study of the morphology, sedimentology, and vegetation of the ecosystem was carried out to evaluate the results of these measures. For this purpose, a series of topographic and ground-penetrating radar (GPR) profiles, grain-size analysis, and an analysis of plant communities found along the profiles were carried out. The data obtained were compared with data from a former 2004 study. The results show that the morphology of the dunes recovered, and a new primary dune has arisen. The system now has a greater process of aggradation than of progradation. The vegetation has recovered the global composition of dune systems, with a typical community of embryo dunes and others of primary dunes that are set in strips parallel to the coast. Despite this improvement, the opportunistic and ruderal component in the primary dune vegetation evidences a strong anthropic inheritance in the system.

Nuria Roca, Dept. Biologia Evolutiva, Ecologia i Ciències Ambiental, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, 08028 Barcelona, Spain Maite Garcia-Valles, Dept. de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n 08028 Barcelona, Spain Pura Alfonso, Dept. Enginyeria Minera, Industrial i TIC, Universitat Politècnica de Catalunya, Edifici MN1. Av. de les Bases de Manresa, 61-73, 08242 Manresa, Barcelona, Spain Antoni Calafat, Dept. de Dinàmica de la Terra i de l’Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n 08028 Barcelona, Spain Telm Bover-Arnal, Dept. de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n 08028 Barcelona, Spain Ma Teresa Calvet-Pallas, Dept. de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n 08028 Barcelona, Spain Elisabet Playà, Dept. de Mineralogia, Petrologia i Geologia Aplicada, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n 08028 Barcelona, Spain Marta Guinau, Dept. de Dinàmica de la Terra i de l’Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n 08028 Barcelona, Spain Xavier Delclòs, Dept. de Dinàmica de la Terra i de l’Oceà, Facultat de Ciències de la Terra, Universitat de Barcelona, Carrer Martí i Franquès, s/n 08028 Barcelona, Spain Martin Rios, Dept. Genètica, Microbiologia i Estadística, Facultat de Biologia,