Dynamic sedimentary environments of an Arctic glacier-fed river estuary (Adventfjorden, Svalbard). I. Flux, deposition, and sediment dynamics

The spatial patterns of the transport, settling, and deposition of sediments were studied in a small Arctic glacier-fed river estuary (Adventfjorden, west Spitsbergen, Svalbard). Salinity and temperature, suspended solids concentration, and particle fluxes in the water column were measured at seven stations situated on the tidal flat formed at the river mouth, the delta slope, and along the fjord axis down to the fjord mouth. Turbidity currents were measured in situ using a current meter combined with a turbidity meter. The sediments collected with a Niemisto gravity corer were x-rayed and analyzed for granulometric composition. The results of the major sampling campaign undertaken in July 2002 were supplemented with winter hydrological data from January 1996. Since the river is frozen in winter, no fresh water or fluvial sediment supply is observed in the fjord water column. A hypopycnal plume of brackish water (1.5 m thick) extends in summer as far as 0.8 km from the river mouth. The highest concentration (826 mg l 1) and vertical flux (over 1000 g m 2 day 1) of suspended solids were noted at the edge of the tidal flat and over the upper slope of the delta. Both concentrations and the solid particle flux decreased as distance from the river mouth increased. Local peaks of turbidity in the intermediate and deep water layers in the central fjord indicated the presence of hyperpycnal plumes. Tidal flat sediments are rhythmically laminated by the tidally controlled resuspension/redeposition cycles and occasionally eroded by catastrophic events such as intense storms or winter ice cover scouring. The steep inclination of the bottom of the slope (15e19 ) promotes the gravity-driven processes of sediment transport (debris flows). Frequent resuspension and redeposition events can be traced on x-radiographs and in the granulometric composition of the sediment cores collected on the slope. Turbidity currents are observed throughout the fjord, although their intensity and frequency of occurrence change as distance from the river mouth increases. The near bottom hyperpycnal flows transport the finest sediment over the slope and into the low energy environment of the central basin of Adventfjorden. The current study shows that the patterns of sediment storage and sedimentary dynamics in a glacier-fed river estuary are driven by gravity flows and turbidity currents rather than by the patterns of the vertical sedimentation of suspensions in the water column.