ABSTRACT: Hydroclimatic controls over the formation of varves in the Canadian High Arctic: do warmer temperatures produce thicker varves?

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Has the warmest recorded year in the Canadian Arctic produced the thickest varve? Conventional thinking would have argued for such an outcome from the 2005 season, but results from our long term monitoring at Cape Bounty, Melville Island, Nunavut, Canada, suggest that the climate-varve relationship is best described by hydrological factors (snowpack) rather than thermal conditions. The results from the three year study indicate that initial catchment snowpack is a more important factor than temperature for total seasonal sediment delivery to the lakes. Thus 2005, the warmest spring of the three years studied, did not yield the most sediment deposited. Rather, 2004, the year with the largest snowpack and runoff (and coolest) during our study, generated the highest suspended sediment discharge (SSQ) and resulted in greater sediment deposition in both lakes. In addition, 2003 and 2005 were similar with respect to snowpack, but sediment transfer and deposition was still significantly less in 2005. This is best explained by reduced suspended sediment concentrations (SSC) measured in 2005, which we attribute to sediment exhaustion caused by the large runoff in 2004. In 2003 and 2004, high SSC caused frequent underflows that likely delivered sediment directly and rapidly to the deepest parts of both lakes, resulting in high deposition rates. In 2005, SSC was reduced and underflows were relatively infrequent.Cape Bounty is situated on the south-central coast of Melville Island (74º54’N, 109º35’W) and is characterised by gently sloping plateaus with simple drainage patterns, sparse vegetation underlain by continuous permafrost. We studied two adjacent catchments of similar size and physiography that drain into deep lakes of similar size (West and East Lakes and Rivers, respectively, unofficial names). Hydrometeorological and sedimentological processes were measured in both lakes from 2003-5 in order to improve the interpretations of the long sedimentary records. Snow surveys and river gauging was undertaken to evaluate the hydrological inputs into each lake. As well, a network of weather stations was established within the two watersheds to monitor the meteorological conditions each season. Limnological processes were monitored through instruments moored within the lake and sediment deposition was measured using sediment traps recovered at 1-4 day intervals. A varve record was independently developed for both lakes and evaluated within the context of the process study results to reconstruct landscape and environmental variability for the past 500+ years. This is the first study developed that tests the reproducibility of varve records from the same site. Furthermore, it is one of a few studies to incorporate multi-year process work including snow surveys to facilitate interpretations of the sediment record. These conclusions suggest that caution may be necessary when interpreting temperature signals in varves from nival catchments.This work facilitates a greater understanding of the processes that form annual sedimentary layers that are often used to reconstruct climate variability. From these results, the two sedimentary records at Cape Bounty show sensitivity to snowpack variability and individual catchment sediment supply that can vary over multiple years. The results from the process work allow for analysis of the two independent sedimentary records to test whether the records are sensitive to regional climate change and variability or to what extent geomorphic processes mask the climate signal. More broadly, this study contributes baseline information which may assist our understanding of how sediment budgets and rivers will respond in future climate scenarios.

Bibliography of Canadian Geomorphology