HIGH RESOLUTION THERMAL RECORD OF SEDIMENT PLUMES INTO ARCTIC GLACIER-FED LAKE LINNÉ, SVALBARD, NORWAY

Paleoclimate may be inferred from laminated lake sediments, but often the processes causing sediment transport and deposition in lakes are not well documented. Since 2003, the Svalbard REU program (http://www.mtholyoke.edu/go/svalbard) has been monitoring sedimentation in and environmental conditions around Lake Linné of western Spitsbergen (78˚N, 12˚E). In order to understand the processes controlling lake sedimentation during the spring melt, we developed a monitoring network of sensors and dataloggers in the watershed and within the lake. Outside the lake, meteorological stations record weather conditions and automated cameras quantify snow cover and lake ice extent. Temperature loggers record river water temperature. At several mooring sites in the lake, we installed temperature dataloggers every 1 meter through the water column. We also moored CTD & turbidity dataloggers near the bottom to continuously record water turbidity, as well as tilt meters to record water currents.

By combining our data, we can reconstruct a detailed sequence of events during the spring melt period that help explain how varves form each year. Results from 2008, for example, show that lake water temperature was between 0.3 and 0.5 ˚C and largely free of suspended sediment prior to the melt season. Rapid warming of the entire water column occurred as solar insolation and snow melt increased. Interflows of turbid meltwater were recorded by the CTD turbidity sensor and also registered as thermal anomalies by the temperature loggers and as currents by the tiltmeters. As the melt season progressed, more temperature anomalies interpreted as inflows coincided with high solar insolation and warm river flows. Subsequently, the lake was well mixed with only minor thermal anomalies that represented weak interflows or diffuse homopycnal flows.

Our results indicate that simple temperature and tilt loggers are effective at identifying the timing and distribution of turbid sediment plumes in the lake. Conditions external to the lake – specific weather conditions, the extent and rate of snowpack melt, and river discharge all influence the amount of sediment deposited each year. Sediment distribution in the lake is an interplay of lake thermal stratification, inflow river discharge volume, temperature, and suspended sediment concentration.