STABLE ISOTOPE ANALYSIS OF SEASONAL SEDIMENTATION PATTERNS OF ICELANDIC LAKE SEDIMENTS

The annual sedimentary records of four northwestern Icelandic lakes were studied to constrain seasonal sedimentation patterns. The characteristics and sources of lacustrine organic matter as well as the rate of accumulation and burial are integral proxies used to interpret a lake’s response to changing environmental conditions. In this study, productivity proxies were used to infer sediment source and delivery and to investigate annual variability of productivity and delivery to the sediment. Funnel-type sediment traps were deployed in the deepest portion of four lakes in July 2011 and recovered in July 2012. The sediment trap design magnified the accumulation and provided a stratigraphically continuous sample, similar to a core sample. Each sample tube was split, described, imaged and logged for volume magnetic susceptibility at 1 cm resolution with a Bartington point sensor. Traps were sub-sampled at 0.2 cm resolution and the elemental and isotopic concentrations of organic carbon, nitrogen and sulfur were quantified with an EA-IRMS. The rate of accumulation for each lake was calculated using total mass accumulation corrected for the area of the trap mouth and time of deployment. Mass accumulation rates reveal Thiđriksvallavatn to have a sedimentation rate an order of magnitude higher than the other three lakes studied. This higher accumulation can be attributed to the installation of a dam in 1953 AD, resulting in fluctuations in lake levels and erosion of shorelines (Azucena, 2013). Elemental and isotopic results show distinct correlative records among the productivity proxies. Variability within lakes Kaldbaksvatn, Rekavikurvatn and Vatnsdalsvatn are driven by productivity as interpreted from OC, δ¹³C, and the OC:N ratio. Erosional processes and influx of terrigenous material drive variance within Thiđriksvallavatn; OC concentration is diluted but δ¹³C, and the OC:N reveal increased productivity in the summer months when snowmelt and lake level changes associated with dam activity are significant. Documenting the natural and anthropogenic influences on nitrogen, sulfur and carbon cycles will provide insight into how the environment responds to change. A second year of sediment trap accumulation is currently being analyzed.