Sedimentary Processes and Environmental Signals from Paired High Arctic Lakes
Climate Change , Varves , Hydrology
Suspended sediment delivery dynamics in two watersheds at Cape Bounty, Melville Island, Nunavut, Canada were studied to characterize the hydroclimate conditions in which laminated sediments formed. Process work over three years determined snow-water equivalence was the primary factor that controlled sediment yield in both catchments. Cool springs (2003, 2004) enhanced runoff potential and intensity because channelized meltwater was delayed as it tunneled through the snowpack and reached the river channel (sediment supply) within 1-2 days. In warm springs (2005), meltwater channelized on the snowpack and did not immediately reach the river bed (7-10 days). Sediment transport was reduced because flow competence was lower and sediment supplies limited. Sediment deposition in the West Lake depended on surface runoff intensity. Short-lived, intense episodes of turbid inflow generated underflow activity which delivered the majority of seasonal sediment. In 2005, runoff was less intense and few underflows were detected compared to the cooler, underflow dominated 2004 runoff season. As well, grain-size analysis of trapped sediment indicated that deposition rates and maximum grain-size were decoupled, indicative of varied sediment supplies and delivery within the fluvial system. These decoupled conditions have important implications for paleohydrological interpretations from downstream sedimentary records. Two similar 600-year varve records were constructed from the lakes at Cape Bounty. Although these series were highly correlated throughout, time-dependent correlation analysis identified divergence in the early 19th century. Because the varve records were from adjacent watersheds and subject to the same hydroclimatic conditions, the divergence suggests watershed-level changes, such as increased local active layer detachments. The varve record from West Lake was highly correlated with lagged autumn snowfall and spring temperature. Similar relationships between these variables and East Lake were not as strong or significant. Long-term climatic interpretations should be carefully assessed. A single record from either of these lakes might lead to autumn snowfall and/or spring-melt intensity reconstructions, given the process work and weather record correlations. The recent divergence reveals potential changes likely to occur as warming increases variability within the Arctic System. Multidisciplinary monitoring and observations should continue in order to quantify future variability and evaluate the impact on these systems.