Abstract
We investigated the change in terminus position between 1985 and 2015 of 17 marine-terminating glaciers that drain into Disko and Uummannaq Bays, West Greenland, by manually digitizing over 5000 individual frontal positions from over 1200 Landsat images. We find that 15 of 17 glacier termini retreated over the study period, with ~80% of this retreat occurring since 2000. Increased frequency of Landsat observations since 2000 allowed for further investigation of the seasonal variability in terminus position. We identified 10 actively retreating glaciers based on a significant positive relationship between glaciers with cumulative retreat >300 m since 2000 and their average annual amplitude (seasonal range) in terminus position. Finally, using the Detecting Breakpoints and Estimating Segments in Trend (DBEST) program, we investigated whether the 2000–2015 trends in terminus position were explained by the occurrence of change points (significant trend transitions). Based on the change point analysis, we found that nine of 10 glaciers identified as actively retreating also underwent two or three periods of change, during which their terminus positions were characterized by increases in cumulative retreat. Previous literature suggests potential relationships between our identified change dates with anomalous ocean conditions, such as low sea ice concentration and high sea surface temperatures, and our change durations with individual fjord geometry.
Highlights
The Greenland Ice Sheet has undergone increasing rates of mass loss, a large component of which is the result of retreat and speed up of marine-terminating outlet glaciers that have been subject to both increasing atmospheric and oceanic temperatures
Challenges arise in determining a primary control on glacier terminus change, as the magnitude of retreat observed at the terminus is determined by the atmospheric and oceanic temperatures, and physical constraints unique to each glacier, such as ice mélange buttressing and glacial runoff [10], underlying bedrock topography [4], and fjord bathymetry [11]
These factors unique to each glacier have often led to asynchronous terminus retreat trends of glaciers in the same region in response to climate changes [2,3]. This temporally non-linear glacier behavior is seen at glaciers throughout the world, for example, marine-terminating glaciers in Novaya Zemlya underwent dramatic retreat between 2000 and 2013, corresponding with high air temperatures and low sea ice concentrations, yet subsequently retreat rates decreased between 2013 and 2015 [12]
Summary
The Greenland Ice Sheet has undergone increasing rates of mass loss, a large component of which is the result of retreat and speed up of marine-terminating outlet glaciers that have been subject to both increasing atmospheric and oceanic temperatures. Modelling studies suggest that the slow response rate of marine-terminating glaciers to recent atmospheric and oceanic forcings points to a continuation of current glacier change observations, and a commitment to even greater changes [18] Understanding both the short-term (seasonal) and long-term (decadal) glacier terminus variability prior to past transitions in their behavioral trends can help elucidate how current terminus retreat (advance) responds to recent atmospheric and oceanic conditions and how this response may be indicative of approaching a tipping point in the future. We assessed the relationship between the annual amplitude in position and the terminus retreat (advance) behavior in the context of the identified change points in order to understand glacier fluctuation during the different phases
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