4500 Years of Annual Sediment Accumulation Recorded in Lower Murray Lake in the Canadian High Arctic

A varved sediment record spanning the last 4500 years was recovered from Lower Murray Lake, northern Ellesmere Island, Nunavut, Canada (81°20'N, 69°30'W). The annually laminated sequence covers the upper 2.3m of a 12m core; similar patterns of sedimentation are not observed elsewhere in the record. The lower section of the record is characterized by irregular laminations and greater variability in grain size. Additionally, the transition at 2.3m is associated with a distinct shift in sediment geochemistry as observed in ITRAX scanning XRF results. Flatbead scanned images of sediment thin sections from the upper, laminated portion of the record were used to establish the varve chronology and measure lamination thicknesses for the past 4500 years. The annual nature of sedimentation in Lower Murray Lake is supported by the occurrence of additional laminations after a second set of cores was collected following a 5 year interval; comparison of the varve chronology with 137Cs and 210Pb profiles and comparison of the paleomagnetic characteristics of the Murray Lake sediments with those from other records that have been independently dated. The pattern of sedimentation in Lower Murray Lake is characterized by centennial scale variability in lamination thickness superimposed on a millennial scale trend of increasing lamination thickness from 4500 years BP to present. Three distinct periods, corresponding to the Little Ice Age (~150 to 300 years BP), ~2550 to 2900 years BP, and ~3750 to 4450 years BP, are characterized by below normal varve thicknesses and fewer extreme sedimentation events (i.e. anomalously thick beds of coarse grained sediment). Preliminary results also suggest that higher mean sediment accumulation observed over the last 30 years is unequaled during any thirty year period in the preceding 3500 years, and is only surpassed during two intervals (centered around ~3550 and 3700 yrs BP) in the entire 4500 year record.