Factors Controlling Downward Fluxes of Particulate Matter in Glacier‐Contact and Non‐Glacier Contact Settings in a Subpolar Fjord (Billefjorden, Svalbard)

Abstract

Sedimentation from suspensions was quantified, and its primary controls were investigated in Billefjorden, a subpolar fjord in Svalbard. Measurements of fjord hydrology, suspended particulate matter concentration, vertical downward flux of particulate matter, and distribution of grain size in material collected in sediment traps were conducted in the summer and autumn. Measurements were performed in two settings: glacier-contact and non-glacier contact. The first, Adolfbukta, is a bay with a large tidewater glacier and the second, Petuniabukta, is an inlet supplied by meltwater rivers that cross the tidal flat. The vertical particulate matter fluxes in both settings are as high as several thousand g m-2 day-1 during the short summer season and tens of g m-2 day-1 in the autumn. Sedimentation is dominated by settling from surface turbid water plumes and is largely the result of flocculation. This results in poorly sorted sediments, most of which are trapped either within a few hundred metres proximal to the meltwater inlet in the case of rivers ending on tidal flats, since flocculation occurs on the tidal flat; or within the first few km in the case of tidewater glaciers, where flocculation occurs after the sediments reach fjord waters. In the autumn, the fluxes diminish more than the concentration of suspended particulate matter, and the residence time of the suspended matter in the water lengthens. The major factors controlling particulate matter flux are the positions of freshwater inlets (surface/subsurface), meltwater discharge, suspended matter concentration in meltwater rivers, local wind damming effects, and tidal range (enhanced fluxes during spring tides). In the waters near the fjord bottom, the fluxes are usually higher due to resuspension and possibly turbidity currents or slumps.