Sedimentology and paleoenvironmental indicators in a High Arctic meromictic lake
Tomkins, Jessica Diane
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High Arctic meromictic lakes are frequently used to generate detailed records of past environmental variability within their sedimentary profiles. However, without detailed analyses of sedimentation influences over time, their paleoclimate records cannot be accurately interpreted. This thesis presents a comprehensive examination of the sedimentology and paleoenvironmental records of meromictic Lake A, Ellesmere Island (83°00’N, 75°30’W), including detailed analysis of the sedimentary history, development and evaluation of several paleoclimate records. The sedimentary record was primarily composed of clastic material but varying inputs of authigenic components from biological and chemical processes in the water column resulted in a complex history of lake sedimentation. Under chemically stratified conditions during the past millennium, annual laminae (varves) formed and were used to develop a sedimentary chronology. Sedimentary pellets were most likely formed by ice-rafting processes and were deposited during high melt years in this perennially ice-covered lake. The pellet frequency record indicated that the twentieth century contained the most frequent reduced ice cover summers during the past millennium, although the 1500s and 1600s were also inferred warm periods. Comparison with instrumental climate data indicated that varve thickness was primarily related to late summer and autumn snowfall in the previous year, which highlighted the importance of snow availability in spring rather than melt energy in sediment transfer to the lake in this non-glacial catchment. The varve thickness and grain size records suggested increased flow competency and autumn snowfall particularly during the late-1000s to early-1100s and first half of the 1900s. Paleoenvironmental records from Lake A corresponded well with many regional proxy records and provided a long-term framework within which to examine observed environmental change along the northern Ellesmere Island coast during the past century. Finally, these analyses would not have been possible without obtaining high quality sediment cores. This research also investigated the effectiveness of a gel seal method for preserving the fragile sediment-water interface during transport and its results could be useful for other sediment core studies.