Hydroclimatic Controls on Laminated Sediment Formation in Linnévatnet, Svalbard

Abstract:

Monitoring environmental processes in a glaciated watershed in Svalbard over a 12 year period provides insights into the controls on annually laminated sediment deposition in Linnévatnet, west Spitsbergen. This proglacial lake has a major inflow from nival and glacier meltwater and minor inflows from alluvial fans along the east and west shores of the lake. A synthesis of meteorological, hydrological and limnological measurements coupled with a composite stack of sediment grain size profiles from multiple traps and time lapse photography from 2004 to 2015 provides a detailed and complex record of inlet stream flow events and consequently the timing and amount of sediment deposited annually on the lake floor. Data is presented from temperature loggers, CTD’s and sediment traps spanning a 3 km proximal to distal transect across the central axis of the basin from the main inlet. Process studies and observations reveal that the annual nival melt is generally the high discharge event that delivers the greatest annual sediment flux to the lake (e.g. 2005, 2006, 2008 2009), however in several years (e.g. 2011, 2013), intense late summer and early fall rainfall events occurred when thawed active layer sediments were mobilized and residual sediment in stream channels, produced heavy sediment loads that exceeded the nival melt sediment delivery. Sediment cores recovered adjacent to mooring sites across the basin are annually laminated. The structure of laminae in proximal sediment traps mimics proximal varves seen in thin sections with multiple coarser grained events ( median up to 35 μm) overlain by fine-grained (median ~5 μm) “winter” layers. Annual couplets in distal traps are proportionally thinner and finer grained and their grain size profile records the major events seen in proximal sectors of the lake. Mineralogical and ITRAX scanning XRF analyses of trap sediments shows that late season events also activate sedimentation from alluvial fan sources that otherwise contribute little sediment to the lake floor.