| Summary: | Abstract: This study uses changes in the chemistry and mineralogy of lake and surface sediments in a small lake in Kongress Valley (Kongressdalen), to interpret Late Holocene climate change in Western Spitsbergen, Svalbard. Changes in clay mineralogy across an inactive outwash fan (Black Fan) in the valley reflect weathering since the fan’s formation during the Little Ice Age (LIA) (1550-1920). X-Ray Diffraction analysis of clay samples from the meltwater channels and the Kapp Starostin rocks that compose the fan reveal a strong 10 Å peak, unaffected by ethylene glycol solvation or heating to 375°C and 550 °C, indicative of illite. However, samples collected from vegetated debris flows between the meltwater channels reveal a diminished 10 Å phase and a slightly expandable peak at approximately 14 Å, unaffected by magnesium and glycerol saturation (d 060 of 1.54 Å), indicative of vermiculite. The inverse relationship between these peaks reflects the weathering of illite to vermiculite, suggesting an early period of Kapp Starostin Fm. deposition subsequently eroded by meltwater from Kongressbreen (glacier) during the LIA. Changes in lake sediment chemistry should reflect changing sources of sediment inflow as meltwater from an advancing ice activated the Black Fan. X-Ray Fluorescence analysis of the White and Black Fan, which are the only sources of sediment inflow to the lake, reveals that the Black Fan sediments have greater concentrations of K2O, Fe2O3,Zr, and Cr, while the White Fan is characterized by higher concentrations of MgO, CaO, Sr, and U. However, analysis of sediment cores from the central part of the lake reveals a chemical composition that resembles only that of the White Fan sediment, indicating almost no Black Fan input into Kongressvatnet. The most likely hypothesis to explain this absence is that Kongressbreen was a cold-based glacier and therefore did not produce fine glacial flour from scour of bedrock. Despite the dominant White Fan signature in the core sediments, ITRAX Scanning XRay Fluorescence analysis reveals significant variations in core chemistry with depth, which is likely due to changes in climate. Periodic, massive high calcium layers, lacking internal laminations characterize the upper 200 mm of the core, which correlates using MS to cores dated to the LIA (Guilizzoni et al., 2006). Preliminary SEM analysis reveals the presence of euhedral, sharp-edged rhombohedra and fibrous needles of calcite, high-Mg calcite, and dolomite, suggesting the precipitation of carbonate. The current supersaturation of Kongressvatnet waters below the chemocline with respect to calcite further supports this hypothesis. Alternatively, periods of extended ice cover during which the formation of lake ice concentrates the calcium in the underlying lake water, and may result in the formation of cryogenic calcite. Anomalous peaks in iron and sulfur characterize the lower core (300-400 mm), which MS correlations indicate corresponds to the Medieval Warm Period (Guilizzoni et al., 2006). An increase in organic terriginous inflow during this period likely spurs the activity of sulfur reducing bacteria, resulting in reducing conditions and the precipitation of iron sulfides. This analysis suggests that although provenance cannot be used in Kongressvatnet to constrain the timing of the Little Ice Age, changes in climate are intimately associated with fluctuations in lake chemistry and thelake’s biogeochemical cycles, providing the opportunity to interpret past climate change from lake sediment chemistry.
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