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

Joep E A Storms,Nicolas Waldmann,Louise Hansen,Achim A Beylich

doi:10.1002/dep2.101

Joep E A Storms, Nicolas Waldmann + Show 2 more

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https://doi.org/10.1002/dep2.101

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Abstract

AbstractThis 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.

Highlights

Understanding sedimentation patterns in fjords and fjordlake systems is important for palaeoenvironemental and palaeoclimate reconstructions
The focus of this paper is on Lake Strynevatnet, a 220 m deep lake characterized by high sediment trapping efficiency
This study indicates the value of combining detailed mapping of lake infill sediments and a thorough understanding of the associated hydrodynamic processes in the lake

Summary

Introduction

Understanding sedimentation patterns in fjords and fjordlake systems is important for palaeoenvironemental and palaeoclimate reconstructions. Lakes in glaciated areas provide an ideal setting to study their response to Late Holocene climate changes and glacial fluctuations. The focus of this paper is on Lake Strynevatnet, a 220 m deep lake characterized by high sediment trapping efficiency. By characterizing the sedimentary infill geometry the aim is to increase our understanding of the interaction between sedimentation rates, sediment dispersal patterns and glacier activity over the past ca 8150 years. The sediment dispersal patterns in Lake Strynevatnet are likely driven by wind-induced circulation patterns in the absence of other main driving forces for sediment dispersal such as large fluvial systems and slope failures. There has been little research on the effects of palaeowind conditions on Holocene lake sedimentation

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