IDENTIFYING COHERENT LINKS BETWEEN SUBANNUAL SEDIMENT STRUCTURES AND DAILY WEATHER OBSERVATIONS IN PROGLACIAL CLASTIC VARVES

Annually laminated (varved) sediments from Devon Island, Nunavut, are examined for the potential information contained within their subannual records.  By identifying and cataloguing the physical characteristics of the subannual units (texture, colour, grain size), interpretations of the sediment delivery mechanisms are made and compared to regional weather conditions (temperature and rainfall).  Temperature data was reorganized to characterize the presence of ‘melt events' defined as periods of continuously positive mean daily temperature.  The duration and intensity of these events yielded a melt event magnitude, measured in melting degree-days.  Rainfall was treated semi-quantitatively (due to spatial inconsistencies), though large daily events (> 7.5 mm d^-1) were recognized as significant with regards to sedimentary inputs.

While correlations between varve thickness and annual climatic parameters were poor in this case, strong relationships existed between individual subannual sedimentary structures and the corresponding melt event magnitude (r² = 0.637, p < 0.01, n = 45).  Likewise, the occurrence of large rainfall events was reflected by the coincident deposition of coarse laminae and interrupted clay caps.  Thin basal sedimentary units were explained by early season temperature fluctuations producing minor amounts of snowmelt.  Sediment deposition associated with non-climate controls was rare, and likely explained by changes in lake-inflow interaction.

Using this framework for sedimentary deposition, sedimentary records can be used as tools to understand how past climate changes have affected the melt event characteristics, and provide insight into their potential future changes.  Climate models anticipate that surface temperatures in the high arctic will increase in the near future.  Based on our analysis, melt event characteristics (total number, duration, intensity) can all be expected to increase in the warmer environment.  Results from this study suggest that the anticipated temperature rise will be reflected more as a lengthening of the arctic summer and less so as an overall increase in high temperatures, though a combination of both can be expected.