The Beagle Channel is a 300-km long passage connecting the Pacific and Atlantic Oceans at similar to 55 degrees S, where glaciers and river streams meet subantarctic waters. Here we present the first evaluation of downward fluxes and composition of particulate matter in the channel. Settling particle fluxes were collected by sequential sediment traps deployed in two contrasting areas: one in the western part of the channel, corresponding to an early post-glacial environment (site A) and a second, fully deglaciated, river-dominated environment (site B) in the eastern part. In early summer, fluxes at both sites are driven by organic matter produced in spring, with peak organic carbon fluxes of 289 and 413 mg C m(-2) d(-1) at sites A and B, respectively (C:N ratios of 7.3 and 6.3, respectively). During winter, the fluxes of fecal pellets, particulate organic carbon (POC) and particulate nitrogen (PON) were at their minimum. At site A (integrated annual POC flux of 74 g C m(-2) yr(-1)), seasonality was weak and the flux was driven by ballast material (>95% of total particle flux) of glacial origin year-around, which also promotes the POC export. According to isotopic and taxonomic analyses performed at site A, the low seasonality in the organic component of the flux appears to be mainly related to autochthonous production of nano- and pico-phytoplankton during autumn and winter, later replaced by microphytoplankton fluxes during spring and summer. At site B, ballast material accounted for <60% of total mass flux and the POC flux showed a marked seasonality with a well-defined maximum after the spring phytoplankton bloom. Regarding the contribution of zooplankton, fecal pellets of appendicularians dominated at the western sector of the channel (site A) while Munida gregaria pellets dominated the flux at the eastern site (site B). This work is a contribution to ongoing efforts to unveil the physical and biogeochemical variables driving the biological carbon pump and the land-sea connections in this high-latitude ecosystem threatened by climate change.

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.

In order to calculate budgets of particulate matter and sediment-bound contaminants leaving the continental shelf of the Gulf of Lion (GoL), settling particles were collected in March 2011 during a major storm, using sediment traps. The collecting devices were deployed in the Cap de Creus submarine canyon, which represents the main export route. Particulate matter samples were analyzed to obtain mass fluxes and contents in organic carbon, Al, Cr, Co, Ni, Cu, Zn, Cd, Pb and La, Nd and Sm. The natural or anthropogenic origin of trace metals was assessed using enrichment factors (EFs). Results are that Zn, Cu and Pb appeared to be of anthropogenic origin, whereas Ni, Co and Cr appeared to be strictly natural. The anthropogenic contribution of all elements (except Cd) was refined by acid-leaching (HCl 1 N) techniques, confirming that Zn, Cu and Pb are the elements that are the most enriched. However, although those elements are highly labile (59-77%), they do not reflect severe enrichment (EFs <4). Most particles originate from the Rhone River. This has been confirmed by two different tracing procedures using rare earth elements ratios and concentrations of acid-leaching residual trace metals. Our results hence indicate that even in this western extremity of the GoL, storm events mainly export Rhone-derived particles via the Cap de Creus submarine canyons to the deep-sea environments. This export of material is significant as it represents about a third of the annual PTM input from the Rhone River.