Abstract
The Gravity Recovery and Climate Experiment (GRACE) satellites have measured anomalies in the Earth’s time- variable gravity field since 2002, allowing for the measurement of the melting of glaciers due to climate change. Many techniques used with GRACE data have difficulty constraining mass change in small regions such as Iceland, often requiring broad averaging functions in order to capture trends. These techniques also capture data from nearby regions, causing signal leakage. Alternatively, Slepian functions may solve this problem by optimally concentrating data both in the spatial domain (e.g., Iceland) and spectral domain (i.e., the bandwidth of the data). We use synthetic experiments to show that Slepian functions can capture trends over Iceland without meaningful leakage and influence from ice changes in Greenland. We estimate a mass change over Iceland from GRACE data of approximately -9.3 ± 1.0 Gt/yr between March 2002 and November 2016, with an acceleration of 1.1 ± 0.5 Gt/yr 2 .
Highlights
Earth’s mountain glaciers and ice caps have been losing mass in response to climate change (Stocker et al, 2013), and in 2014 this mass loss accounted for ∼25% of current observed global mean sea level rise (Chen et al, 2017)
In order to examine signals in Iceland separately from other mass changes we use a method of spatio-spectral localization on the sphere in which we transform the data onto a basis of spherical Slepian functions (Slepian, 1983; Simons et al, 2006). This technique has previously been applied to various spatial domains including Greenland (Harig and Simons, 2012, 2016), Antarctica (Harig and Simons, 2015), and the High Plains Aquifer in the USA (Longuevergne et al, 2010). It is an open question how well Slepian functions perform for small regions, and we address that question with the case-study of Iceland
As buffer extent starts increasing above roughly 2.0◦, the Iceland region begins to intersect with the Greenland region resulting in the larger negative trend values at large buffers
Summary
Earth’s mountain glaciers and ice caps have been losing mass in response to climate change (Stocker et al, 2013), and in 2014 this mass loss accounted for ∼25% of current observed global mean sea level rise (Chen et al, 2017). Between 1995 and 2013, Iceland experienced −9.5 ± 1.5 Gt/yr of average ice mass change, with negative acceleration (meaning an increasing rate of mass loss) (Björnsson et al, 2013). In Iceland, ice mass changes and volcanic activity are linked, as unloading caused by ice melt can affect the frequency and character of volcanic eruptions (e.g., Jull and McKenzie, 1996; Gee et al, 1998; Pagli and Sigmundsson, 2008; Schmidt et al, 2013). Detailed and accurate measurements of glacier mass balance are important to understand sea level rise, and volcanic activity in Iceland and potential international consequences. The 2010 Eyjafjallajòkull eruption stranded over 8.5 million passengers of 108,000 canceled flights, costing airlines 1.7 billion USD (Alexander, 2013)
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