Mass imbalance and climate sensitivity of Arctic glaciers and ice caps
Item statusRestricted Access
Embargo end date31/07/2022
Tepes, Paul Dan
Glaciers and ice caps are prominent features in the landscapes surrounding the Greenland Ice Sheet and in the archipelagos of the Arctic seas. Their dynamic response in mass and flow to climate variability makes them a visible and important expression of the changes that are affecting the Earth’s climate system. Arctic glaciers and ice caps are losing mass rapidly, a trend sustained over recent decades and that is expected to continue into the 21st century driven by climatic change and exacerbated by the amplification of polar warming relative to the planetary mean. Mass imbalance of Arctic land ice is a source of major concern given its impact on global sea level rise, ocean circulation, regional hydrology, and on the local ecosystems and communities, which are also impacted by these changes, with increased ecological, socio-economic and geopolitical pressures afflicting the region. To effectively mitigate and adapt to these environmental changes, the large-scale, continuous monitoring of the Arctic cryosphere has become essential, and satellite geodesy is a critical tool for estimating glacier and ice cap mass balance. In this thesis, seven years of CryoSat-2 high-resolution swath interferometric altimetry were utilised to investigate changes in the volume of Arctic glaciers and ice caps outside of Greenland between 2010 and 2017. From these data, a pan-Arctic assessment of mass imbalance was produced, and losses partitioned into signals associated with atmospheric processes and glacier dynamics. The sampled satellite observations provide a detailed picture of the response of Arctic glaciers and ice caps to climate forcing, eliciting contrasting patterns of change that are driven by a combination of oceanic and atmospheric forcing and by internal instabilities (glacier surges). Results show that between 2010 and 2017, Arctic glaciers and ice caps lost 609 ± 7 gigatonnes of ice, contributing 0.240 ± 0.007 millimetres per year to global sea level rise. While surface ablation is responsible for 87 % of losses across the Arctic, dynamic imbalance is increasing in the Barents and Kara Sea region where it now accounts for almost half of the total ice loss. This dynamic imbalance is associated with a northward shift of Atlantic climate and is sustained by a range of climate-dynamic feedbacks and processes that have been amplified in areas adjacent to the archipelagos of the Eurasian Shelf. The thesis builds on these initial pan-Arctic findings to further investigate, in Chapter 5, the processes that shape the current response to forcing of the glaciers and ice caps in the Eurasian High Arctic, with a particular focus on glacier fluctuations in the Russian archipelagos of Novaya Zemlya and Severnaya Zemlya. Time series of surface elevation change between 2010 and 2018 in conjunction with concurrent climate anomaly trends provide insights into the contrasting cryospheric changes affecting these two regions, as well as their association with contemporary atmospheric and oceanic forcing. While both frontal ablation of tidewater glaciers and surface melt are found to jointly contribute to volume changes in Novaya Zemlya, ice dynamics are entirely responsible for the recent net ice loss from Severnaya Zemlya. A quasi-linear relationship between coupled ocean-atmosphere forcing and volumetric changes in Novaya Zemlya is found to be appropriate in explaining the overall regional trends in ice loss at decadal scale, in agreement with previous findings from tidewater glaciers in east Greenland. In Severnaya Zemlya, the role of ocean warming is found to be the key factor in driving dynamic ice loss, owing to the intrusion of warmer Atlantic Water circulating along the Eurasian continental margin. Together these results suggest that meteorological processes will continue to dominate glacier loss throughout the Arctic, while warming of the Arctic Ocean will increasingly affect the dynamic stability of tidewater glaciers in the Barents and Kara Sea regions, with unpredictable and possibly abrupt shifts in mass balance. In this region, as well as globally, ice dynamics represent the largest source of uncertainty in climate models predicting how land ice will respond to future climatic fluctuations. The findings from this thesis support the principle that linear relationships between environmental forcings and glacier change may be sufficiently accurate to parametrise ice loss in regions where synchronous, coupled ocean-atmospheric forcing prevails. The results therefore provide important support to current efforts aimed at estimating future ice loss, freshwater budgets, and sea level contributions from Arctic glaciers and ice caps in a changing climate.