Abstract

Marine-terminating outlet glacier terminus traces, mapped from satellite and aerial imagery, have been used extensively in understanding how outlet glaciers adjust to climate change variability over a range of time scales. Numerous studies have digitized termini manually, but this process is labor-intensive, and no consistent approach exists. A lack of coordination leads to duplication of efforts, particularly for Greenland, which is a major scientific research focus. At the same time, machine learning techniques are rapidly making progress in their ability to automate accurate extraction of glacier termini, with promising developments across a number of optical and SAR satellite sensors. These techniques rely on high quality, manually digitized terminus traces to be used as training data for robust automatic traces. Here we present a database of manually digitized terminus traces for machine learning and scientific applications. These data have been collected, cleaned, assigned with appropriate metadata including image scenes, and compiled so they can be easily accessed by scientists. The TermPicks data set includes 39,060 individual terminus traces for 278 glaciers with a mean and median number of traces per glacier of 136 ± 190 and 93, respectively. Across all glaciers, 32,567 dates have been picked, of which 4,467 have traces from more than one author (duplication of 14 %). We find a median error of ∼100 m among manually-traced termini. Most traces are obtained after 1999, when Landsat 7 was launched. We also provide an overview of an updated version of The Google Earth Engine Digitization Tool (GEEDiT), which has been developed specifically for future manual picking of the Greenland Ice Sheet.

Highlights

  • Since the 1980s, the Greenland Ice Sheet (GrIS) has been in negative mass balance due to increased surface melt and ice discharge (Mouginot et al, 2019; Enderlin et al, 2014) with projected increases in sea level of 5 to 33 cm by 2100 from Greenland alone (Aschwanden et al, 2019; Goelzer et al, 2020)

  • We provide an overview of an updated version of The Google Earth Engine Digitization Tool (GEEDiT), which has been developed for future manual picking of the Greenland Ice Sheet

  • Long-term historical trends in ice sheet mass loss show that approximately 50% of the total mass loss since the ∼1990s is from ice dynamics alone, via fast-moving outlet glaciers that 20 drain into to the ocean (Enderlin et al, 2014; Mouginot et al, 2019; King et al, 2020)

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Summary

Introduction

Since the 1980s, the Greenland Ice Sheet (GrIS) has been in negative mass balance due to increased surface melt and ice discharge (Mouginot et al, 2019; Enderlin et al, 2014) with projected increases in sea level of 5 to 33 cm by 2100 from Greenland alone (Aschwanden et al, 2019; Goelzer et al, 2020). Outlet glaciers can change at sub-annual timescales and examination of terminus change on shorter time scales (∼seasonal) aids interpretation of the specific environmental and glaciological processes that influence glaciers (Fried 35 et al, 2018; Moon et al, 2015; Schild and Hamilton, 2013; Cassotto et al, 2015; Ritchie et al, 2008; Howat et al, 2010; Carr et al, 2014; Moon et al, 2014, 2015; Brough et al, 2019; Kehrl et al, 2017; Bevan et al, 2019) Such studies are valuable because glacier termini respond to a diverse set of mechanisms related to the geometry of the glacier-fjord system, inland ice dynamics, and the strength of climate forcing (Moon and Joughin, 2008; Carr et al, 2017; Catania et al, 2018; Bunce et al, 2018; Porter et al, 2018). Such studies demonstrate the need for detailed terminus tracing (map-view, full terminus width) at as high a temporal resolution as possible

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