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https://doi.org/10.5194/tc-2020-5
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-5
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 16 Jan 2020

Submitted as: research article | 16 Jan 2020

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This preprint is currently under review for the journal TC.

Variability of glacier albedo and links to annual mass balance for the Gardens of Eden and Allah, Southern Alps, New Zealand

Angus J. Dowson1,2, Pascal Sirguey2, and Nicolas J. Cullen1 Angus J. Dowson et al.
  • 1School of Geography, University of Otago, Dunedin, 9016, New Zealand
  • 2National School of Surveying, University of Otago, Dunedin, 9016, New Zealand

Abstract. The Gardens of Eden and Allah (GoEA) are two of New Zealand's largest icefields. However, their remote location and protected conservation status has limited access and complicated monitoring and research efforts. As a result, the behaviour and dynamics of these unique glaciers are poorly understood. We use annual minimum glacier-wide albedo (αyrmin) derived from Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard the Terra and Aqua satellites over the period 2000-2018 to assess linkages between the spatial and temporal variability of αyrmin and glacier mass balance. The αyrmin for 12 individual glaciers, identified using a new objective glacier masking approach, ranges between 0.42 and 0.70, and can occur as early as mid-January and as late as the end of April. There is evidence that the timing of αyrmin has shifted to later in the summer over the 19-year period on 10 of the 12 glaciers. The largest negative departures in αyrmin (lower than average albedo) are consistent with high snow line altitudes (SLA) as determined from the End-of-Summer Snowline (EOSS) survey, which has monitored glaciers in the Southern Alps for over 40 years. While the record of αyrmin for Vertebrae Col 25, an index glacier of the EOSS survey and one of the GoEA glaciers, explains less than half of the variability observed in the corresponding EOSS SLA (R2 = 0.43, p = 0.003), the relationship is stronger when compared to other GoEA glaciers. Angel Glacier has the strongest relationship with EOSS observations at Vertebrae Col 25, accounting for 69% of its variance (p = 1.8 × 10−5). A key advantage in using the αyrmin approach is that it enables the variability in response of individual glaciers to be explored, revealing that topographic setting plays an important role in addition to the regional climate signal. MODIS imagery acquired from the Terra and Aqua platforms also provide insights about the spatial and temporal variability of clouds. The frequency of clouds in pixels west of the Main Divide is as high as 90 % during summer months, and reach a minimum of 35 % in some locations in winter. These complex cloud interactions deserve further attention as they are likely a contributing factor in controlling the spatial and temporal variability of glacier response observed in the GoEA. The observed variability of individual glacier response on the GoEA demonstrate that glaciers in the Southern Alps do not behave as a single climatic unit.

Angus J. Dowson et al.

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Angus J. Dowson et al.

Angus J. Dowson et al.

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Latest update: 05 Apr 2020
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Short summary
19 years of satellite observations are used to characterise the spatial and temporal variability of surface albedo across the Gardens of Eden and Allah, two of New Zealand’s largest icefields. The variability in response of individual glaciers reveals the role of topographic setting and suggests that glaciers in the Southern Alps do not behave as a single climatic unit. There is evidence that the timing of the minimum surface albedo has shifted to later in the summer on 10 of the 12 glaciers.
19 years of satellite observations are used to characterise the spatial and temporal variability...
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