Climate controls on the mass balance of Brewster Glacier, Southern Alps
Glaciers are highly sensitive indicators of climate variability. From the 1980’s to the early 2000’s, some glaciers in the Southern Alps experienced periods of advance; counter to global trends of glacier recession. These anomalous advances demonstrate the complexity of glacier-climate interactions and indicate the need to understand the physical drivers of glacier mass balance; particularly in the Southern Hemisphere, where long-term mass balance records are limited. To this end, the atmospheric and oceanic drivers of mass balance variability at Brewster Glacier in the Southern Alps are examined in this thesis. These drivers are examined across long and short-term periods, each at hemispheric, synoptic, and glacier spatial scales, using a mass balance record derived from the MODerate-resolution Imaging Spectroradiometer (1979-2013), 22-months of daily weather station data from the ablation zone of Brewster Glacier, as well as reanalysis, statistically downscaled, and station-based climate data sets. The highest mass gain (loss) years are on average driven by negative (positive) anomalies of geopotential height surrounding New Zealand, sea surface temperature, and atmospheric water vapour. The El Niño Southern Oscillation (ENSO) is found to be an important driver of mass balance, with mass gain (loss) years coincident with El Niño (La Niña) episodes. Elevated annual precipitation totals are not found during mass gain years, rather the increased proportion of snowfall and reduced proportion of rainfall as governed by temperature are responsible for mass gain. In terms of regional atmospheric circulation, the occurrence of north westerly airflow is critical for mass balance, delivering cold, wet conditions for accumulation in winter, and warm, wet conditions for melt in summer. The combined turbulent heat fluxes provide the largest source of energy for melt during extreme melt events (60%). For three of the most extreme melt and snowfall events, north westerly circulation is associated with high rates of water vapour flux, which resemble atmospheric river-type structures, the first time such features have been linked to glacier mass balance in New Zealand. The identification of regional scale atmospheric conditions, link to ENSO, and importance of north westerly circulation and associated vapour flux for both extreme melt and snow have contributed to a more holistic understanding of the relationships between mountain glaciers in the Southern Alps and the climate system.
Advisor: Kingston, Daniel; Cullen, Nicolas; Sirguey, Pascal
Degree Name: Master of Science
Degree Discipline: Geography
Publisher: University of Otago
Keywords: Glacier; Brewster Glacier; glacier-climate relationships; Southern Alps; New Zealand; mass balance; climate; MODIS; north westerly; accumulation; ablation; extreme events; snowfall; melt; atmospheric river; hemispheric circulation; atmospheric water vapour flux; synoptic circulation
Research Type: Thesis