MAKING SENSE OF THE VARVE STRATIGRAPHY OF GLACIER-FED LAKE LINNé, SVALBARD, NORWAY

Glacial–lacustrine lamination stratigraphy is frequently used to infer late Holocene climate change. In most cases an assumption is made that varve thickness is related to glacier mass balance changes or mean summer (JJA) air temperatures and often times varve thickness is calibrated using local climate data. To better understand what specific factors influence long term and inter-annual sedimentation in a high Arctic lake we have been monitoring the glacier-river-lake system of the Linné Valley, Svalbard. Annual sediment trap stratigraphies indicate that the laminae represent varve deposition, however, correlation of varve thickness with the long term weather records fails to show a strong correlation with mean summer temperatures.

As part of the Svalbard REU we have been monitoring modern processes in the valley since 2004. Our results indicate that high discharge events associated with the annual spring snowmelt have delivered the majority of annual sediment. However, occasionally high discharge events associated with late summer/early fall rainstorms have dominated annual sediment accumulation. In contrast, river discharge from routine summer glacial ablation delivers minor amounts of fine-grained sediment. We believe that the fluvial system accumulates and stores glacially-produced sediment until large discharge events, however caused, rework and transport sediment to the lake. As such, the lamination stratigraphy is not directly related to summer ablation but instead is mostly a proxy for high discharge events. Further, inflow sediment plume dynamics within the lake can strongly influence the behavior of sediment plumes and thereby the location of sedimentation within a lake basin.

Cores recovered from both proximal and distal sites in the lake indicate marked changes in the thickness and texture of annual laminae deposited during and after the Little Ice Age. In proximal cores LIA varves are overall thinner and coarser (mostly due to reduced clay layer thickness). In contrast, distal cores similarly exhibit thinner varves, and generally the texture of the LIA varves is finer-grained. Our work indicates that varve records in glacier-fed lakes can be influenced by a variety of processes which can complicate paleoclimatic reconstructions.