Impact of Dense Water Formation on the Transfer of Particles and Trace Metals from the Coast to the Deep in the Northwestern Mediterranean

Abstract

This study aimed to describe the interannual variability of dense shelf water cascading and open ocean convection in the Gulf of Lions (NW Mediterranean) based on long-term temperature and current records and its impact on particle fluxes and associated metals. These observations highlight the predominant role of the rare intense events of dense shelf water cascading (1999/2000, 2005/2006, 2012/2013) in the basinward export of particles, which are mainly brought by rivers. Measurements of particulate trace metals in 2012 indicate that the monitored intense cascading event may be responsible for a significant fraction (~15%) of the annual input to the shelf. To this first process is added the effect of somehow more recurrent deep convection events (2005, 2009–2013) that remobilize the deep sediments, receptacle of coastal inputs, and disperse them rapidly at the scale of the northern Mediterranean basin, and gradually over the entire western basin. Coastal and oceanic dense water formations are key physical processes in the Mediterranean margins, whose reduction in intensity and recurrence has already been observed and also anticipate in climate scenarios that will likely change the dispersion pathways of chemical particles in this region.

Sources, Transport, and accumulation of Mercury in the northwestern Mediterranean margin sediments during the Industrial Era and influence of turbiditic events

“…First, particles with low Corg (<1%) and HgT (<0.13 µg g -1 ) concentrations are those of the material trapped at Sta. HD during the cascading event recorded in winter/spring 2005, which brought resuspended material (Canals et al, 2006;Puig et al, 2008;Tesi et al, 2010;Stabholz et al, 2013;Durrieu de Madron et al, 2023) mostly composed of carbonate broken shells and OM of terrigenous origin as indicated by the low δ 13 C values (Fig. 2).…”

“…The 210 Pb inventories in continental rise sediments (cores I and L) suggest that they receive most of their material from downward settling in the upper water column, but also from particles episodically advected from the margin during deep cascading pulses (Tesi et al, 2010;Palanques et al, 2012;Puig et al, 2013;Durrieu de Madron et al, 2023). The presence of planktonic material is attested by the coarse carbonate material, including foraminifera and pteropods, in core I, and finer planktonic-derived material in core L (Cossa et al, 2014a).…”

“…On the GoL shelf, storms and dense shelf-water cascading events prevent long-term sediment deposition (Guillen et al, 2006;Durrieu de Madron et al, 2008;Durrieu de Madron et al, 2023). The general westward water mass circulation directs most of the export of suspended sediment towards the southwestern exit of the GoL through re-suspension and deposition cycles along the inner shelf induced by waves and an anti-clockwise circulation (Millot, 1991;Durrieu de Madron et al, 2008).…”

Sources and Fate of Sedimentary Organic Matter in the Western Mediterranean Sea

“…Sediments are drained by canyons to the deep basin by sediment gravity flows. The latter mainly include turbidity currents, as observed in the Valencia Trough (Amblas et al., 2011; O'Connell et al., 1985), but also dense shelf water cascading, as in the Gulf of Lions (Durrieu de Madron et al., 2023). Here, intense winter storms coupled with the overflow of cold, dense‐shelf waters that are channeled through submarine canyons, drive large volumes of eroded sediment and aged OC toward the deep‐sea (Canals et al., 2006; Tesi et al., 2010), although the OC signal of these events on the slope is masked by the intrinsic heterogeneity of surface sediments (Durrieu de Madron et al., 2020).…”