Current velocities and vertical sediment fluxes in the Var submarine canyon were assessed at three stationsrespectively at 800 m, 1200 m and 1800 m depth, using moorings deployed for 4 months duringwinter 2008–2009. During this period, we observed three major sediment gravity flows, all characterizedby sudden increases in current velocity that lasted 2–5 h and by downward particle fluxes. Each gravityflow, described using a high frequency current meter and two Acoustic Doppler Current Profiler (75 and300 kHz ADCP) showed distinctive features. The first event, triggered during a flood of the Var River, wasdetermined to be a hyperpycnal current with a large vertical extent (>100 m high) and relatively lowvelocity (40 cm s 1). The second event, observed after a Var River flood, was more energetic with a maximumhorizontal current peak of 60 cm s 1 but with a low vertical extent (30 m high). This event wasconsidered to be a turbidity landslide. The third was the result of a local canyon wall failure. It was characterizedby a speed of >85 cm s 1. These peaks of current speed were associated with large clouds ofmaterial that transported sediment along the canyon and reached up to 200 g m 2 d 1 of sediment(>1 g m 2 d 1 of organic carbon). Our measurements in the Var canyon show the important role of gravityflows transporting particulate matter to the deep-sea floor. These large inputs of sediment and organiccarbon may have a significant impact on deep-sea carbon storage in the Mediterranean Sea.
展开▼
