Biogeochemistry of particle fluxes in submarine canyons of the northwestern mediterranean sea: the effects of dense shelf water cascading
- Autores: Catalina Pascual Mas
- Directores de la Tesis: Antonio Calafat Frau (dir. tes.), Anna Sanchez Vidal (codir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2011
- Idioma: español
- Tribunal Calificador de la Tesis: Joan Grimalt Obrador (presid.), A. Sáez (secret.), Joan B. Company (voc.)
- Materias:
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- Resumen
Particle flux studies aim at quantifying the amount of carbon and other components that are exported into deep ocean, which controls the long term atmospheric CO2 sequestration. Continental margins play an important role in this oceanic cycle as they pump carbon and nutrients from aerial ecosystems to the interior of the ocean. This work analyzes the transference of material along the continental margin of the Gulf of Lion. This margin, located in the northwestern Mediterranean, is a broad platform that extends to a slope cut by a large number of submarine canyons. Most of the sediments entering the system by rivers or resuspension in the shelf travel to the southwest due to the cyclonic circulation where are deflected mainly through the Cap de Creus and Lacaze-Duthiers submarine canyons to the deep basin. This process occurs mainly during winter sea storms and dense shelf water cascading events.
The pourpose of this study is to analyze the temporal and spatial variability of particle fluxes and the source and degree of degradation of the organic matter within the Lacaze-Duthiers and Cap de Creus submarine canyons and the southern slope, in the Gulf of Lion. Direct flux measurements has been carried out by the deployment of 9 instrumented lines equipped with sediment traps and currentmeters along three transects along the axis of the Lacaze-Duthiers and Cap de Creus canyons and the southern slope. Data indicate that there is a quick response of the system to physical forcings, with a close relation among atmospheric drivers (that trigger the dense water cascade, waving and river and atmospheric inputs), primary production, and the quantity and quality of settling material across the continental margin.
The severe dense shelf water cascading (DSWC) event observed during January-March 2006 was the main fac-tor controlling the sedimentation in the studied area. The dense waters escaped the lower canyon where it widens to flow along the isobaths and impacted the southern open slope. This denotes the capacity of such events to funnel and spread southwardly shelf eroded material through canyons. Therefore DSWC may become an important factor for the sedimentation in the middle and lower slope of the northwestern Mediterranean. Upper and middle canyon was primarily affected by continuous cross-slope exchanges with the shelf. The deeper ones were less affected by horizontal transferences and shelf material arrived only associated to the DSWC event, whereas outside the DSWC period pelagic fluxes become a significant part of the total mass flux.
The severe DSWC event controlled also the arrival of organic matter to the sea floor, with the transfer of large quantities of land derived organic matter in January 2006 (from shelf deposits), and marine derived organic matter in March-April 2006 (from the concomitant spring bloom). Therefore, the timing of the dispersion of both terrigenous and marine derived organic material was controlled by the energetic conditions that enhance the resuspension and off-shore transport of material in the shelf. In addition, this organic matter was degraded not only during its transport along the canyons but also in the water column before reaching the canyon mouth and open slope, as indicated by trends in amino acid and chloropigment concentrations and compositions. Furthermore, although lateral input of organic matter from the adjacent shelf predominated during DSWC events, sporadic primary production events and constant advection of land derived material were also evident during low energy and low-flux periods.
