Source to sink reconstruction of a Holocene Fjord-infill: Depositional patterns, suspended sediment yields, wind-induced circulation patterns and trapping efficiency for Lake Strynevatnet, inner Nordfjord, Norway

This paper reconstructs the sedimentation volumes and patterns, suspended sediment yields, wind-induced circulation patterns and sediment trapping efficiency of Lake Strynevatnet, western Norway as an integrated source to sink system. The lake became deglaciated ca 11 ky cal bp, with glacio-isostatic uplift isolating the basin from the nearby fjord (Nordfjord) ca 9.2 ky cal bp. Based on geophysical data collected in 2010, the upper 15–20 m of Holocene sediment accumulation in the lake was mapped. A sediment body in the centre of the lake indicates a depositional mechanism dominated by suspension sedimentation. The source of this sediment is associated with the adjacent glaciated catchments westward of the lake. Three seismic units were identified based on seismic facies generating an evolutionary model utilizing three depositional units (U1, U2 and U3), in which unit U2 represents the Storegga tsunami event. Unit U3 is further divided into three subunits; U3a, U3b and U3c based on their spatial continuity and subtle downlapping and onlapping relationships. The degree to which wind conditions could have affected the lake depositional patterns were studied utilizing an open-source coupled hydrodynamic and sediment transport model. The results show that fluvial discharge alone is incapable of generating a circulation pattern in the lake currents. Suspended sediment concentrations in the lake are highest for strong winds. Modelled sediment accumulation on the lake floor shows that mild or absent winds lead to a proximal to distal sediment thickness trend, while strong winds result in uniform sediment thickness. Based on this it is argued that the thickness trends of seismic subunits U3a-c are related to a variable palaeowind climate. As such, seismic data of lake infills, in combination with numerical modelling, may provide valuable palaeoclimatic information on wind patterns.