Changes in late Neoglacial perennial snow and ice extent and climate in the Queen Elizabeth Islands, Arctic Canada.

摘要

The extent of snow and ice during the Little Ice Age (LIA, 1600-1900 AD) is used in this thesis to measure the impact of early twentieth century warming (1900-1960) on perennial snow/ice cover in the Queen Elizabeth Islands (QEI), and to investigate the climatic conditions that might have favoured snow/ice reduction. Techniques are developed for the regional scale mapping of trimlines surrounding former LIA perennial snow/ice in the QEI using multispectral classification approaches, applied to high-resolution satellite imagery. Where mapped trimlines outlining the former margins of thin plateau ice caps are accordant with trimlines marking former perennial snowfields, their common elevation is interpreted to record the LIA equilibrium-line altitude (ELA) for that locality. The LIA ELA trend surface is modeled over the QEI and used to estimate the total area formerly covered by perennial snow/ice and to determine the area reduction between the LIA and 1960. Between the end of the LIA and 1960, the QEI experienced a 37% (62,387 km2) reduction in perennial snow/ice cover, resulting from a 50 to >600 m increase in the ELA. The spatial distribution of ELA change reveals a high degree of local (20 km) variability in the mountainous regions, but a strong regional-scale (∼500--1,500 km) pattern of change over the QEI. Regional-scale spatial variation in ELA change is evaluated against Empirical Orthogonal Functions (EOFs) of meteorological variables computed from the NCEP-NCAR reanalysis (1949-2002). Warm and cold decadal episodes identified in the observational record are examined to determine their potential as modern analogs of early 20th century and LIA climates. The spatial pattern of ELA change between the LIA and 1960 shows the greatest change occurring in the eastern QEI (from Devon to N Ellesmere islands), which corresponds to EOF-1 of mean summer surface air temperature (SAT; 1949-2002), the positive (negative) phase of which is strongly in place during the warm (cold) decade. Temperature anomalies during the warm (cold) decade are positively correlated with a weak (strong) polar vortex, higher (lower) than normal SSTs in the North Atlantic, and one of the lowest (highest) periods of sea-ice extent during the 20th century.