Reconstructing Holocene glacier fluctuations from glaciolacustrine sediments : a new approach using modern analogues in southern Norway

• Main Author: Smith, J. G.
• Published: Swansea University 2003
• Subjects: 551.4
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639069

A new technique for reconstructing Holocene glacier variations was developed using a modern analogue approach on glaciolacustrine sediments. Glaciolacustrine sediments record alternations between minerogenic (active glaciers) and organic sedimentation (reduced glacier extent) with high resolution and have been used widely to infer regional glacier history. The approach has been particularly prevalent in southern Norway, where relatively extensive Little Ice Age glaciers destroyed much of the evidence for earlier episodes. Surface sediments from 53 pro-glacial lakes in southern and western Norway were sampled and variations in grain-size, organic matter and magnetic susceptibility were related to catchment variables through correlation and multiple regression analyses. This modern analogue sample was used to test directly the accepted model of glaciolacustrine sedimentation by investigating glacial signals in established sedimentary indicators on a quantitative basis. In relation to grain-size, percentage data were insensitive indicators of glacier extent, while <i>estimated sedimentation rates</i> (derived from an independent training set) were very sensitive. Glacial signal strength of up to 83 % for regional and other sub-sets and up to 50 % for the total data set were recorded. The <i>glacial signal</i> occurs in the fine size grades, particularly fine silt and clay. Organic matter and magnetic susceptibility are insensitive to glacier size and carry noisy signals with no systematic relationship to catchment variables. The analyses also identified and quantified non-glacial sediment sources. The optimum models for grain-size were applied to dated sediment cores from southern Norway in order to reconstruct Holocene glacier variations on a <i>quantitative</i> basis. The reconstructions were reasonably successful in Jotunheimen and Breheimen lakes, but unsuccessful in Jostedalsbreen, where the models were not applicable to the available sediment cores. The quantification of glacier size variations is a significant methodological advance in reconstructing Holocene glacier variations and its potentially a powerful tool for reconstructing Holocene climatic change.