Reconstruction of climate and glacial history based on a comparison of varve and tree-ring records from Mirror Lake, Northwest Territories, Canada

Abstract

This study compared the hydroclimatic signals recorded in annually laminated (varved) sediments and tree rings within a small study area in the Selwyn Mountains of the southwestern Northwest Territories/southeastern Yukon Territory border region of Canada. The records were located immediately adjacent to each other and within 6 km of instrumental meteorological and hydrometric records, which permitted a detailed analysis of climate in the area from AD 1704 to 1996. This study explored the challenges of annually-resolved multi-proxy hydroclimate analyses and examined how best to interpret the climate record given the differences in proxy formation and the respective signals. The high-frequency (annual) variability from both proxies showed a good match for some parts of the record (e.g., mid-1700s and much of the 1900s) but revealed different sensitivities at other times (e.g., 1800s). However, both records contained a common low-frequency (decadal) summer climate signal. Glacier dynamics influenced varve formation through altered sediment availability during the inferred Little Ice Age (LIA) maximum ice stand in the catchment from AD 1778 to 1892 and subsequent recession after this maximum. As a result of reduced LIA sedimentation, July mean temperatures reconstructed from varve thickness during the 1800s were underestimated compared to the tree-ring estimates. Other instances of low-frequency divergence were apparent, particularly during parts of the twentieth century, despite the overall similarities. The extended varve record also provided a glacial history for the southern Selwyn Mountains, indicating probable glacier advances during AD 1300–1450 and AD 1600–1670, maximum ice stand during the 1800s, followed by twentieth-century recession.