Larsen, Darren J 1 ; Miller, Gifford H 2 ; Geirsdóttir, Áslaug 3
1 INSTAAR, University of Colorado
2 INSTAAR, University of Colorado
3 University of Iceland
It is widely accepted that 20th century warming has had the most profound effects in the Arctic, where strong positive feedbacks amplify global or hemispheric forcings. Reconstructing the behavior of the Arctic system to modest changes in forcings in the recent past improves our understanding of the sensitivity of the climate system to human induced perturbations in the future. Changes in glacier length offer one of the most reliable paleoclimate proxies, and the size and accessibility of Iceland’s ice caps present a practical model for reconstructing changes in climates of the past. The goal of this project is to use varved lake sediments from proglacial lake Hvítárvatn to produce an annually resolved record of late Holocene ice-sheet activity in Iceland. Hvítárvatn is a large, glacially dominated lake situated beneath Langjökull, the second largest icecap in Iceland (Fig. 1). In 2003, four long cores spanning the last 10ka were recovered from the northern basin of Hvítárvatn. All of the cores exhibit beautifully preserved laminations as well as multiple diagnostic tephra layers. Using tephrochronology and cross-correlating techniques on distinctive tephra and laminae patterns, the cores have been linked across the basin and it was found that the lake contains annually laminated varves. It has been demonstrated that the varve record (sediment flux to lake) in this system is controlled by the activity of Langjökull and the two outlet glaciers that drain into the lake. In this manner, cold times are reflected in the sediment record due to glacier growth and erosion to the bedrock resulting thicker varves. Physical and biological proxies associated with these sediments (including ice-rafted debris, C:N, δ13C, and varve thickness) record local and regional climate fluctuations and environmental conditions with unprecedented resolution. A project focus is the transition into and out of Little Ice Age (LIA) and the regional effects of explosive volcanism on the catchment environment and regional climate.