Reconstruction of Holocene environmental signal in Linnédalen catchment, Svalbard - with a focus on the high-resolution lacustrine hydroclimate reconstruction from the recent 400 years of the late Holocene

Abstract

Rapid Arctic warming is causing an intensification of the hydrological cycle and Arctic precipitation is predicted to increase this century. Svalbard is located at the forefront of these environmental changes and can be a window into future climatic challenges. To better understand how future projections might affect the environment and Arctic settlements, information on the natural variability and the previous responses to similar conditions are needed. Warmer and wetter climate affect natural processes like mobilisation and accumulation of sediments. Proglacial lakes can be an excellent archive of past hydroclimatic conditions because they record the climate signal of the area through sedimentary deposition. This thesis investigates changes in Holocene environment using the proglacial lake of Linnévatnet, Svalbard, with a particular focus on the hydroclimate of the last ~400 years using high-resolution varve data. The catchment was mapped based on field observations and remote sensing to identify processes and sources of deposition material into Linnévatnet. Two sediment cores, one long core and one gravity core, were retrieved from Linnévatnet. Sedimentary structures of laminations (varves), were interpreted to reconstruct high- resolution hydroclimate and geochronology of the past 400 years, supported by radiometric dating of 239+240Pu and 210Pb. A multiproxy analysis consisting of computed tomography (CT), micro-X-ray fluorescence (XRF), magnetic susceptibility (MS) and geophysical parameters showed climatic and hydroclimatic variability in the sediment record. The environmental interpretations based on the XRF-data from the long core seams to support the pioneer research of Svendsen and Mangerud (1997). Rapid depositional events analysis indicates mild and humid climate at 1620 – 1650, 1770 – 1830 and 1980 to present, causing the deepening of the active layer to enable more sediment to be transported downslope into Linnévatnet by floods or mass-wasting events. Changes in the amount of μXRF Ca correlated well with varve thickness and increases of rapid depositional events. These rapid depositional events occur when there is higher temperature and a positive mode of NAO, which therefore indicates that the last part of the LIA glacial period was due to enhanced winter precipitation causing a positive winter mass balance, rather than cold summer temperatures. The recent trend in proxies in Linnévatnet shows an intensified hydrological cycle that can cause an increase in the amount and magnitude of natural hazards in Svalbard.