Thursday 23rd May – 5.15pm, Castle Street, Thurso
Our Arctic: Amplification of Climate Change
Adrian Dye presents his research of rapidly retreating Arctic glaciers and iceberg calving after recent warm events (e.g. record breaking air temperatures of July 2018 in Scandinavia). He also presents a synthesis of the state of the Arctic, from declining reindeer herds to melting ice and breakdowns of the polar vortex. He explores the reasons behind the Arctic warming twice as fast as the Northern hemisphere and examines green news stories from other Nordic countries in the battle against climate change.
Cold Ice in a Warm Bath? Rapid retreat of a lake terminating Arctic glacier and warm proglacial lakes
Glaciers in contact with proglacial lakes show accelerated mass loss rates through mechanical and thermal processes, particularly through the formation of thermal notches in the ice front (Carrivick and Tweed, 2013). As glaciers retreat from their Little Ice Age maxima (~100 years ago) and respond to increasing air temperatures (particularly in Arctic Scandinavia: cf July 2018) they often develop proglacial lakes. However, the prevalence, status and role of proglacial lakes in Arctic glacial systems have received relatively little attention. As a consequence, despite significant increases in air temperatures, a common assumption persists that smaller proglacial lakes remain at a uniform 1oC.
We present the first recorded proglacial lake temperatures and time lapse imagery from the front of an actively calving Arctic glacier (67.954878°N, 18.561535°E), which rapidly lost 10,523m2 of ice (0.67% of area in RGI, 2008) between 2014 to 2018. The changing geometry of the glacier terminus (including calving bay evolution) during this retreat is recorded throughout the melt season via high spatial resolution multispectral satellite imagery. We present temperature observations directly from the ice front in July 2017 from the innovative use of thermal infrared imagery, supplemented by several detailed thermistor temperature surveys (using a remote controlled boat). Previous melt models for lacustrine terminating glaciers have been compromised by a lack of data from the hazardous water to ice contact point and assume a uniform temperature (e.g. 1oC). Here we report night time temperatures of 3oC directly at the ice-water contact point following numerous ice berg calving events above thermal notches (captured in time lapse imagery). Day time maximum proglacial lake surface temperatures of 8oC were observed during the fieldwork and surface skin temperatures of 8oC have been observed in ASTER satellite 2014 thermal image analysis.
We present thermistor data of lake surface temperatures that shows a strong validation (R2 = 0.9365) of the surface skin temperatures from the AST08 temperature product. At the regional scale, analysis of ASTER AST08 data demonstrate that 11 out of the 12 largest proglacial lakes in Arctic Sweden had daytime surface skin temperatures of >4oC in August 2014. The temperatures reported by this study are substantially warmer than expected from an Arctic proglacial lake. Combined with rapid thermal notch development and associated calving, this study provides the first direct evidence of proglacial lake temperatures directly impacting on the retreat of an Arctic glacier.
