Tempestes bentòniques al Mar Català profund

Abstract

High-energy oceanographic processes on deep oceanic regions are poorly known. Large, episodic increases in bottom currents and water turbidity in the deep ocean were first documented in the Western North Atlantic, where the term “benthic storms” was initially coined by Gardner and Sullivan (1981). Similar events were studied on the continental rise and basins of the Atlantic Ocean. Although the origin of these events was not well identified, the accepted hypothesis is that benthic storms on the western North Atlantic often closely match the position of Gulf Stream meanders and rings, which energy is propagated downward, sometimes reaching the seafloor in the form of cyclones, anticyclones, or topographic waves, generating current speeds sufficient to resuspend and erode deep surface sediments. Time series recorded in the deep Catalan Sea and other north-western Mediterranean areas show several events causing high currents and suspended sediment concentration increases that could be defined as benthic storms but produced mainly by bottom-reaching dense water formation and the associated deep eddy activity. These events are generated by deep open sea convection that induce sediment resuspension and advection and also can be feed and enhanced by concurrent deep dense shelf water cascading pulses. These benthic storms increase near bottom fluxes by more than one order of magnitude and transport large amounts of particulate matter with marine and terrestrial OM to the northwestern Mediterranean Basin, feeding a quasi-permanent thick bottom nepheloid layer. This should contribute significantly to the “fertilization” of the deep pelagic and benthic ecosystems, playing a major role on global biogeochemistry