9 research outputs found
Informe de les afectacions produïdes pel temporal Glòria sobre la població i les activitats econòmiques a les platges de Barcelona
Sol·licitant de l'informe: Barcelona Cicle de l'Aigua, S.A
External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea
Particle fluxes (including major components and grain size), and oceanographic parameters (near-bottom water temperature, current speed and suspended sediment concentration) were measured along the Cap de Creus submarine canyon in the Gulf of Lions (GoL; NW Mediterranean Sea) during two consecutive winter-spring periods (2009 2010 and 2010 2011). The comparison of data obtained with the measurements of meteorological and hydrological parameters (wind speed, turbulent heat flux, river discharge) have shown the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea. Indeed, atmospheric forcing during 2009 2010 and 2010 2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14.2 × 103 W m−2) in winter 2009 2010 that triggered a pronounced sea surface cooling compared to winter 2010 2011 (1.6 × 103 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009 2010, which cascaded at high speed (up to ∼1 m s−1) down Cap de Creus Canyon as measured by a current-meter in the head of the canyon. The lower heat losses recorded in winter 2010 2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation and downslope transport of dense shelf water. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter-spring 2009 2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to the middle canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010 2011. The dominance of the lithogenic fraction in mass fluxes during the two winter-spring periods points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated with the plankton spring bloom during March and April of both years.This research has been supported by the ECfunded HERMIONE (FP7-ENV-2008-1-226354
Particle fluxes in submarine canyons along a sediment-starved continental margin and in the adjacent open slope and basin in the SW Mediterranean Sea
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
Deep-water formation variability in the north-western Mediterranean Sea during the last 2500yr: A proxy validation with present-day data
Here we investigate the sensitivity of deep-water formation in the north-western Mediterranean Sea to climate variability during the last 2500 yr. With this purpose, the grain-size parameter UP10 (fraction > 10 μm) is used as a proxy for intensity of deep-water circulation. Such a proxy is first validated through the analysis of oceanographic data collected from October 2012 to October 2014 by means of two deep-water mooring lines equipped with sediment traps and currentmeters in the Gulf of Lion and north of Minorca Island. Enhancements of deep current speed resulted from dense shelf water cascading and open-sea deep convection in February 2013 leading to dense-water formation. The grain-size distribution of settling particles from sediment traps collected during 2012-2013 shows a distinctive particle mode and high UP10 values correlated to deep-water formation. These data are consistent with grain-size values in sediment cores from the north of Minorca, thus supporting the validity of the UP10 parameter to reconstruct changes of intensity in deep-water formation and associated near-bottom currents. The deep-water sediment record of the north of Minorca for the last 2.5 kyr shows that the strongest deep-water formation events occurred during relatively warm intervals, such as the Roman Period (123 BCE-470 CE2), the end of the Medieval Climate Anomaly (900-1275 CE) and the first part of the Little Ice Age (1275-1850 CE). By contrast, our data indicate a progressive reduction in the overturning conditions during the Early Middle Ages (470-900 CE) resulting in weaker deep-water formation events during most of the Medieval Climate Anomaly. Intense deep-water formation events appear to be mostly associated with periods of enhanced Evaporation-Precipitation balance rather than to buoyancy loss due to winter cooling only. Our results suggest that warm sea surface temperature during spring months could have played an important role by increasing the Evaporation-Precipitation balance and favouring buoyany loss by increased of salinity. The comparison our data with other oceanographic and climatic records indicates a change in the proxy relation before and after the Early Middle Ages. Western Mediterranean Deep Water and Levantine Intermediate Water behave in opposite way after the Early Middle Ages, thus indicating that the previously proposed Mediterranean see-saw pattern in the Evaporation-Precipitation balance also influenced convection patterns in the basins during the last 1500 yr. These changes are discussed in the frame of different configurations of the North Atlantic Oscillation and East Atlantic/ West Russian modes of atmospheric variation
Teleconnexions atmosfèriques i resposta oceanogràfica a les mars Mediterrània Nordoccidental i Cantàbrica
[cat] Hom considera que els oceans són sistemes altament complexos, la dinàmica dels quals depèn de la interrelació de processos físics, químics i biològics. En aquests context, l’estudi dels intercanvis verticals de matèria i energia des de la superfície cap a l’oceà profund esdevé essencial per a entendre i predir l’impacte dels canvis en el sistema climàtic de la Terra sobre la dinàmica oceànica i els l'ecosistema marins. Aquesta Tesi està centrada en el reconeixement del paper dels forçaments externs (règim de vents, pèrdues de calor, aportacions fluvials, acció de l’onatge, i altres), inclosa llur variabilitat intra- i interanual, damunt la hidrografia i les transferències de matèria i energia des de la plataforma cap al talús i els ambients més profunds a través dels canyons submarins. En aquest context, ens hem centrat en l’estudi un canyó mediterrani altament actiu, el canyó del cap de Creus, i en un gran canyó de la mar Cantàbrica, el canyó d’Avilés. El fet que tots dos canyons es trobin gairebé a la mateixa latitud, sotmesos recurrentment als mateixos règims atmosfèrics regionals, ens ha permès investigar les teleconnexions atmosfèriques entre ambdues àrees i llurs conseqüències oceanogràfiques i ecosistèmiques. L’anàlisi combinada de la variabilitat temporal dels fluxos de partícules i dels paràmetres meteorològics, hidrològics i oceanogràfics en tots dos canyons ha permès determinar les seves respostes als forçaments físics. Els principals processos que governen la transferència de matèria particulada més enllà de la plataforma continental a través del canyó del cap de Creus són: (1) les cascades d’aigua densa de plataforma (DSWC, de l’anglès Dense Shelf Water Cascading), desencadenades pel refredament sobtat, l’evaporació i la salinització de les aigües superficials de la plataforma continental durant episodis perllongats de vents del nord, freds i secs, i (2) els episodis d’enfonsament d'aigua (downwelling) que tenen lloc durant les llevantades, les quals provoquen l’augment de l’alçada de les ones, el reforçament de la circulació ciclònica i l’apilament massiu d'aigua carregada de sediment contra la costa que acaba provocant el seu enfonsament cap al talús. En canvi, la transferència de matèria particulada més enllà de la plataforma a través del canyó d’Avilés, ocorre majoritàriament durant els episodis de resuspensió de matèria particulada que tenen lloc amb motiu del desenvolupament de temporals i degut a l’augment de l’alçada de les ones i els corrents prop del fons. La direcció del vent i dels corrents que impulsa determinen si la matèria resuspesa arriba al canyó majoritàriament per la superfície o pel fons. El present estudi confirma que els canyons submarins del cap de Creus i d’Avilés són conductes preferents per al transport de matèria particulada esmentat adés i palesa el seu potencial com a vectors preferents per a la transferència del senyal dels forçaments externs des de la plataforma cap als respectius marges i conques profundes. La prevalença de la fracció terrígena en els fluxos de matèria particulada enregistrats en ambdós canyons, revela que la resuspensió de dipòsits terrígens a la plataforma continental representa la principal font de partícules vers els canyons del cap de Creus i d’Avilés. La segona font de matèria particulada a tots dos canyons és la producció marina primària, els fluxos procedents de la qual (matèria orgànica, carbonat de calci i òpal) mostren una gran variabilitat que depèn sobretot del règim hidrodinàmic i de les explosions (blooms) estacionals de fitoplàncton. D’altra banda, a més dels episodis de downwelling associats a tempestes marines i de les DSWC (al canyó del cap de Creus), i dels episodis de resuspensió i transport de matèria particulada que tenen lloc associats al desenvolupament de temporals (al canyó d’Avilés), els processos oceanogràfics més energètics a les dues àrees estudiades són la convecció profunda (al golf de Lleó) i la convecció intermèdia (a la mar Cantàbrica). Quan els forçaments d’origen atmosfèric que impliquen l’arribada de masses d’aire fred i sec són prou intensos i afecten alhora totes dues àrees, es produeix una resposta oceanogràfica simultània que palesa l’existència de teleconnexions atmosfèriques. Creiem que aquesta Tesi presenta un alt interès per la comunitat científica i també per la gestió dels recursos marins, doncs és fruit d’un nou enfocament en l’estudi de les relacions entre l’atmosfera i la dinàmica oceànica, la biogeoquímica marina i el funcionament dels ecosistemes marins entesos en sentit ampli. I té el valor afegit de demostrar que aitals relacions poden establir-se entre àrees separades per masses continentals, com és el cas del golf de Lleó i de la mar Cantàbrica, situats a banda i banda de la península Ibèrica. La integració de dades provinents de l’observació meteorològica i oceanogràfica, i del modelat numèric, que s’ha dut a terme en aquesta Tesi podria fer-se extensible, en el futur, a les dades de pesca de les mars del nord la península Ibèrica. Aquest esforç permetria segurament assolir una millor comprensió dels vincles entre els processos físics i biogeoquímics i la variabilitat dels recursos vius fins al punt, en una situació ideal, de poder plantejar models de gestió paral·lels entre les dues àrees, els quals incorporessin plenament els coneixements assolits.[eng] The oceans are considered to be highly complex systems, whose dynamics depend on the interrelation of physical, chemical and biological processes. In this context, the study of the vertical exchanges of matter and energy from the surface to the deep ocean is essential for understanding and predicting the impact of changes in the Earth's climate system on ocean dynamics and marine ecosystems. This Thesis aims at understanding the role of external forcings (wind regime, heat losses, riverine inputs, wave action, and others), including their intra- and interanual variability, on the hydrography and the transfer of matter and energy from the continental shelf to the slope and the deeper environments through submarine canyons. In this context, we have focused on a highly active Mediterranean canyon, the Cap de Creus Canyon, and in a large canyon of the Cantabrian Sea, the Aviles Canyon. The fact that the two canyons are practically at the same latitude, thus recurrently subjected to the same regional atmospheric regimes, has allowed us to investigate the atmospheric teleconnections between both areas and their oceanographic and ecosystemic consequences. The integrated analysis of the temporal variability of particle fluxes together with meteorological, hydrological and oceanographic parameters in both submarine canyons, has allowed to determine their response to physical forcings. The principal processes that govern the transfer of particulate matter beyond the continental shelf through the Cap de Creus Canyon are: (1) Dense Shelf Water Cascading (DSWC), triggered by cooling, evaporation or salinization in the surface layer of shallow areas of the continental shelf during events of cold, dry, and persistent northerly winds, and (2) downwelling events related to the occurrence of eastern storms that cause increased wave height, the strengthening of the cyclonic circulation and the massive stacking of sediment-laden water against the coast, which ultimately ends up sinking downslope. In contrast, the off-shelf transfer of particulate matter through the Aviles canyon principally occurs during resuspension events caused by large waves and near bottom currents developing at the occasion of severe northern storms. Wind direction and subsequent wind- driven currents determine if resuspended matter reach the canyon mainly by surface or bottom transport. This study confirms that the Cap de Creus and the Aviles submarine canyons act as preferential pathways for transporting particulate matter, and proves their potential as preferential vectors for transferring the signal of the external forcings from the shelf to their respective margins and deep basins. The dominance of the terrigenous fraction in the particulate matter fluxes recorded in both canyons reveals that the resuspension of terrigenous deposits on the continental shelf represent the main source of particles. Marine primary production is the second main source of particulate matter in both canyons. Its fluxes of major components (organic matter, opal and calcium carbonate) show high variability, which depend mainly on the hydrodynamic regime and the seasonal development of phytoplanktonic blooms. On the other hand, besides the downwellig episodes linked to the occurrence of marine storms and the DSWC (in the Cap de Creus submarine canyon), and the resuspension and transport episodes occurring during the occasion of severe storms (in the Avilés submarine canyon), the most energetic oceanographic processes in both studied areas are deep convection (in the Gulf of Lion) and intermediate depth convection (in the Cantabrian Sea). When atmospheric forcing involving the arrival of cold and dry air masses is severe enough and spreads over the two areas, a simultaneous oceanographic response occurs, which in turn evidences the existence of atmospheric teleconnections. We believe that this Thesis is of great interest for the scientific community and also for the management of marine resources, as it is the result of a new approach in the study of the relations between the atmosphere and the ocean dynamics, marine biogeochemistry and the marine ecosystems functioning understood in a broad sense. It also has the added value of demonstrating that such relations can be established between areas separated by continental masses, as is the case of the Gulf of Lion and the Cantabrian Sea, located at each side of the Iberian Peninsula. The integration of meteorological and oceanographic observations, and numerical modeling that has been carried out in this Thesis could be extended, in the future, to the fisheries data of the seas to the north of the Iberian Peninsula. This effort would lead to an improved understanding of the links between physical and biogeochemical processes, and resource variability to the point that, ideally, management plans could fully integrate such knowledge.[spa] Los océanos son sistemas altamente complejos, cuya dinámica viene determinada por la interrelación de diversos procesos físicos, químicos y biológicos. Por ello, el estudio de los intercambios verticales de materia y energía desde la superficie hacia el océano profundo resulta esencial para entender y predecir el impacto de los cambios en el sistema climático de la Tierra sobre la dinámica oceánica y los ecosistemas marinos.
Esta Tesis está centrada en el reconocimiento del papel que ejercen los forzamientos externos (régimen de viento, pérdidas de calor, aportes fluviales, acción del oleaje, y otros), incluida su variabilidad intra- e interanual, sobre la hidrografía y las transferencias de materia y energía desde la plataforma hacia el talud y los ambientes más profundos a través de los cañones submarinos. En este contexto, nos hemos centrado en el estudio de un cañón mediterráneo altamente activo, el cañón del cabo de Creus, y en un gran cañón del mar Cantábrico, el cañón de Avilés. El hecho de que los dos cañones se encuentren prácticamente a la misma latitud, sometidos recurrentemente a los mismos regímenes atmosféricos regionales, nos ha permitido investigar las teleconexiones atmosféricas entre ambas áreas y sus consecuencias oceanográficas y ecosistémicas.
A partir del análisis combinado de la variabilidad temporal de los flujos de partículas y de los parámetros meteorológicos, hidrológicos y oceanográficos en los dos cañones hemos podido determinar sus respuestas a los forzamientos físicos. Los principales procesos que gobiernan la transferencia de materia particulada más allá de la plataforma continental a través del cañón del cabo de Creus son: (1) las cascadas de agua densa de plataforma (DSWC, del inglés Dense Shelf Water Cascading), desencadenadas por el enfriamiento súbito, la evaporación y la salinización de las aguas superficiales de la plataforma continental durante episodios prolongados de vientos del norte, fríos y secos, y (2) los episodios de hundimiento de agua (downwelling) que tienen lugar durante las tormentas de levante, las cuales provocan el aumento de la altura del oleaje, el reforzamiento de la circulación ciclónica y el apilamiento masivo de agua cargada de sedimentos contra la costa que acaba provocando su hundimiento hacia el talud. Por el contrario, la transferencia de materia particulada más allá de la plataforma a través del cañón de Avilés, ocurre principalmente durante los episodios de
resuspensión de materia particulada que tienen lugar con motivo del desarrollo de temporales y debido al aumento de la altura del oleaje y de las corrientes cerca del fondo. La dirección del viento y de las corrientes que impulsa tras estos periodos, determinan si la materia resuspendida llega al cañón mayoritariamente por la superficie o por el fondo.
El presente estudio confirma además que los cañones submarinos del cabo de Creus y de Avilés son conductos preferentes para el transporte de materia particulada, demostrando su potencial como vectores preferentes para la transferencia de la señal de los forzamientos externos desde la plataforma hacia los respectivos márgenes y cuencas profundas. La prevalencia de la fracción terrígena en los flujos de materia particulada registrados en ambos cañones revela que la resuspension de depósitos terrígenos en la plataforma continental representa la principal fuente de partículas de los cañones del cabo de Creus y de Avilés. La segunda fuente de materia particulada en ambos cañones es la producción marina primaria, los flujos procedentes de la cual (materia orgánica, carbonato de calcio y ópalo) muestran una gran variabilidad que depende sobretodo del régimen hidrodinámico y de las explosiones (blooms) estacionales de fitoplancton.
Por otro lado, además de los episodios de downwelling asociados a tormentas marinas y las DSWC (en el cañón del cabo de Creus), y de los episodios de resuspensión y transporte de materia particulada que tienen lugar con motivo del desarrollo de temporales (en el cañón de Avilés), los procesos oceanográficos más energéticos en las dos áreas estudiadas son la convección profunda (en el golfo de León) y la convección intermedia (en el mar Cantábrico). Cuando los forzamientos de origen atmosférico que implican la llegada de masas de aire frío y seco son suficientemente intensos y afectan de manera sincrónica a las dos áreas, se produce una respuesta oceanográfica simultánea que evidencia la existencia de teleconexiones atmosféricas.
Creemos que esta Tesis presenta un elevado interés para la comunidad científica y también para la gestión de los recursos marinos, pues es fruto de un nuevo enfoque en el estudio de las relaciones entre la atmósfera y la dinámica oceánica, la biogeoquímica marina y el funcionamiento de los ecosistemas marinos entendidos en sentido amplio. I tiene el valor añadido de demostrar que tales relaciones pueden establecerse entre áreas separadas por masas continentales,
como es el caso del golfo de León y del mar Cantábrico, situados a un lado y otro de la península Ibérica.
Así, la integración de datos provenientes de la observación meteorológica y oceanográfica, y del modelado numérico llevado a cabo en esta Tesis podría hacerse extensible, en el futuro, a los datos de pesca de los mares del norte de la península Ibérica. Este esfuerzo facilitaría una mejor comprensión de los vínculos entre los procesos físicos y biogeoquímicos, y de la variabilidad de los recursos vivos. En una situación ideal, se podrían incluso plantear modelos de gestión paralelos entre las dos áreas, incorporando para ello todos los conocimientos logrados
Particle fluxes in submarine canyons along a sediment-starved continental margin and in the adjacent open slope and basin in the SW Mediterranean Sea
© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Tarrés, M., Cerdà-Domènech, M., Pedrosa-Pàmies, R., Rumín-Caparrós, A., Calafat, A., Canals, M., & Sanchez-Vidal, A. Particle fluxes in submarine canyons along a sediment-starved continental margin and in the adjacent open slope and basin in the SW Mediterranean Sea. Progress in Oceanography, 203, (2022): 102783, https://doi.org/10.1016/j.pocean.2022.102783.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.This work was supported by research projects NUREIEV (ref. CTM2013-44598-R) and NUREIEVA (ref. CTM2016-75953-C2-1-R). GRC Geociències Marines is funded by the Catalan Government within its excellence research groups program (ref. 2017 SGR 315). M.Tarrés was supported by a FPI grant from Ministerio de Ciencia, Innovación y Universidades of the Spanish Government
External forcings, oceanographic processes and particle flux dynamics in Cap de Creus submarine canyon, NW Mediterranean Sea
Particle fluxes (including major components and grain size), and oceanographic parameters (near-bottom water temperature, current speed and suspended sediment concentration) were measured along the Cap de Creus submarine canyon in the Gulf of Lions (GoL; NW Mediterranean Sea) during two consecutive winter-spring periods (2009 2010 and 2010 2011). The comparison of data obtained with the measurements of meteorological and hydrological parameters (wind speed, turbulent heat flux, river discharge) have shown the important role of atmospheric forcings in transporting particulate matter through the submarine canyon and towards the deep sea. Indeed, atmospheric forcing during 2009 2010 and 2010 2011 winter months showed differences in both intensity and persistence that led to distinct oceanographic responses. Persistent dry northern winds caused strong heat losses (14.2 × 103 W m−2) in winter 2009 2010 that triggered a pronounced sea surface cooling compared to winter 2010 2011 (1.6 × 103 W m−2 lower). As a consequence, a large volume of dense shelf water formed in winter 2009 2010, which cascaded at high speed (up to ∼1 m s−1) down Cap de Creus Canyon as measured by a current-meter in the head of the canyon. The lower heat losses recorded in winter 2010 2011, together with an increased river discharge, resulted in lowered density waters over the shelf, thus preventing the formation and downslope transport of dense shelf water. High total mass fluxes (up to 84.9 g m−2 d−1) recorded in winter-spring 2009 2010 indicate that dense shelf water cascading resuspended and transported sediments at least down to the middle canyon. Sediment fluxes were lower (28.9 g m−2 d−1) under the quieter conditions of winter 2010 2011. The dominance of the lithogenic fraction in mass fluxes during the two winter-spring periods points to a resuspension origin for most of the particles transported down canyon. The variability in organic matter and opal contents relates to seasonally controlled inputs associated with the plankton spring bloom during March and April of both years.This research has been supported by the ECfunded HERMIONE (FP7-ENV-2008-1-226354
Deep-water formation variability in the north-western Mediterranean Sea during the last 2500yr: A proxy validation with present-day data
Here we investigate the sensitivity of deep-water formation in the north-western Mediterranean Sea to climate variability during the last 2500 yr. With this purpose, the grain-size parameter UP10 (fraction > 10 μm) is used as a proxy for intensity of deep-water circulation. Such a proxy is first validated through the analysis of oceanographic data collected from October 2012 to October 2014 by means of two deep-water mooring lines equipped with sediment traps and currentmeters in the Gulf of Lion and north of Minorca Island. Enhancements of deep current speed resulted from dense shelf water cascading and open-sea deep convection in February 2013 leading to dense-water formation. The grain-size distribution of settling particles from sediment traps collected during 2012-2013 shows a distinctive particle mode and high UP10 values correlated to deep-water formation. These data are consistent with grain-size values in sediment cores from the north of Minorca, thus supporting the validity of the UP10 parameter to reconstruct changes of intensity in deep-water formation and associated near-bottom currents. The deep-water sediment record of the north of Minorca for the last 2.5 kyr shows that the strongest deep-water formation events occurred during relatively warm intervals, such as the Roman Period (123 BCE-470 CE2), the end of the Medieval Climate Anomaly (900-1275 CE) and the first part of the Little Ice Age (1275-1850 CE). By contrast, our data indicate a progressive reduction in the overturning conditions during the Early Middle Ages (470-900 CE) resulting in weaker deep-water formation events during most of the Medieval Climate Anomaly. Intense deep-water formation events appear to be mostly associated with periods of enhanced Evaporation-Precipitation balance rather than to buoyancy loss due to winter cooling only. Our results suggest that warm sea surface temperature during spring months could have played an important role by increasing the Evaporation-Precipitation balance and favouring buoyany loss by increased of salinity. The comparison our data with other oceanographic and climatic records indicates a change in the proxy relation before and after the Early Middle Ages. Western Mediterranean Deep Water and Levantine Intermediate Water behave in opposite way after the Early Middle Ages, thus indicating that the previously proposed Mediterranean see-saw pattern in the Evaporation-Precipitation balance also influenced convection patterns in the basins during the last 1500 yr. These changes are discussed in the frame of different configurations of the North Atlantic Oscillation and East Atlantic/ West Russian modes of atmospheric variation