Spatiotemporal variability of Canadian High Arctic glacier surface albedo from MODIS data, 2001–2016

Colleen A Mortimer,Martin Sharp

doi:10.5194/tc-12-701-2018

Abstract

Abstract. Inter-annual variations and longer-term trends in the annual mass balance of glaciers in Canada's Queen Elizabeth Islands (QEI) are largely attributable to changes in summer melt. The largest source of melt energy in the QEI in summer is net shortwave radiation, which is modulated by changes in glacier surface albedo. We used measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors to investigate large-scale spatial patterns, temporal trends, and variability in the summer surface albedo of QEI glaciers from 2001 to 2016. Mean summer black-sky shortwave broadband albedo (BSA) decreased at a rate of 0.029±0.025 decade−1 over that period. Larger reductions in BSA occurred in July (−0.050±0.031 decade−1). No change in BSA was observed in either June or August. Most of the decrease in BSA, which was greatest at lower elevations around the margins of the ice masses, occurred between 2007 and 2012, when mean summer BSA was anomalously low. The first principal component of the 16-year record of mean summer BSA was well correlated with the mean summer North Atlantic Oscillation index, except in 2006, 2010, and 2016, when the mean summer BSA appears to have been dominated by the August BSA. During the period 2001–2016, the mean summer land surface temperature (LST) over the QEI glaciers and ice caps increased by 0.049±0.038 °C yr−1, and the BSA record was negatively correlated (r: −0.86) with the LST record, indicative of a positive ice-albedo feedback that would increase rates of mass loss from the QEI glaciers.

Highlights

The area of glaciers and ice caps in the Queen Elizabeth Islands (QEI, Fig. 1), Arctic Canada, in 2000 was ∼ 104 000 km2 (Arendt et al, 2012)
Mean summer black-sky albedo (BSA) is lower around the margins of the ice masses, where glacier ice is exposed in the summer, than it is in the higher-elevation interior regions, where snow or firn are exposed year-round (Fig. 2)
During years when the QEI-wide mean summer BSA was low (e.g. 2011), we observed a broad zone of low albedo values (< 0.4) around the margins of the major ice masses (Fig. 2)

Summary

Introduction

The area of glaciers and ice caps in the Queen Elizabeth Islands (QEI, Fig. 1), Arctic Canada, in 2000 was ∼ 104 000 km (Arendt et al, 2012). QEI summer mean air and glacier surface temperatures are strongly correlated with the annual and summer glacier mass balances, which have become increasingly negative since at least 2003 (Gardner et al, 2013; Lenaerts et al, 2013; Wolken et al, 2016). The high albedo of fresh snow declines naturally over time due to settling and grain growth (Warren, 1982). This initial decrease in albedo raises the shortwave energy absorption, leading to warming and/or melt, and a further lowering of the surface albedo. Warmer temperatures and increased snowpack water content further accelerate grain growth, causing a more rapid albedo decline that enhances surface warming and/or melt (Wiscombe and Warren, 1980; Colbeck, 1982). A positive snow/ice albedo feedback has been linked to accelerating high-latitude warming and is increasingly recognized as an important factor in explaining recent increases in Published by Copernicus Publications on behalf of the European Geosciences Union

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