Abstract

Dynamic changes of marine-terminating outlet glaciers are projected to be responsible for about half of future ice loss from the Greenland Ice Sheet. However, we lack a unified, process-based understanding that can explain the observed dynamic changes of all outlet glaciers. Many glaciers undergo seasonal dynamic thickness changes and classifying the patterns of seasonal thickness change can improve our understanding of the processes that drive glacier behavior. The Ice, Cloud and land Elevation Satellite (ICESat-2) provides the first space-based, seasonally repeating altimetry measurements of the ice sheets, allowing us to quantify near-termini seasonal dynamic thickness patterns of 34 outlet glaciers around the Greenland Ice Sheet. We classify the glaciers into seven common patterns of seasonal thickness change over a two-year period from 2019 to 2020. We find small groupings of neighboring glaciers with similar seasonal thickness change patterns but, within larger sectors of the ice sheet, seasonal thickness change patterns are heterogeneous. Comparing the seasonal thickness changes to average glacier ice flow speeds, we find that faster glaciers typically undergo patterns of spring and summer dynamic thickening, while slower glaciers exhibit a variety of thickness change patterns. Future studies can build upon our results by comparing seasonal dynamic thickness changes with external forcings, such as ocean temperature and meltwater runoff, and with other dynamic variables such as seasonal glacier velocity and terminus position changes.

Highlights

  • Understanding the complex nature of Earth’s ice sheets is of critical importance as they have undergone dynamic changes in recent decades (Church et al, 2013; Oppenheimer et al, 2019)

  • We measure dynamic ice sheet thickness near the termini of 34 Greenland Ice Sheet (GrIS) outlet glaciers at seasonal resolution for the first time using the ATL06 land ice along-track altimetry dataset from the Ice, Cloud and land Elevation Satellite-2 (ICESat-2; Markus et al, 2017; Neumann et al, 2019)

  • Large scale observational studies such as this allow for smaller, less studied, glaciers to be observed at the same time as more well-studied glaciers and 40 comparisons to be drawn into how these lesser-known glaciers compare with the seasonal thinning of larger glaciers, which is critical for better understanding the drivers of dynamic change in a changing climate across all outlet glaciers

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Summary

Introduction

Understanding the complex nature of Earth’s ice sheets is of critical importance as they have undergone dynamic changes in recent decades (Church et al, 2013; Oppenheimer et al, 2019). While multi-year and decadal changes of ice sheet discharge via outlet glaciers have been studied before 30 (Mouginot et al, 2019), patterns of seasonal thickness change have not yet been studied for a representative sample of GrIS outlet glaciers. Outlet glaciers exhibit seasonal fluctuations in velocity with distinct patterns (Moon et al, 2014; Vijay et al, 2019) but the lack of seasonal thickness change measurements contributes to a lack of understanding of what processes control glacier dynamics on seasonal time scales. Seasonal thickness changes of outlet glaciers are driven by both external forcings (e.g., precipitation, evaporation, runoff, terminus melt) and internal glacier dynamics (e.g., subglacial and englacial hydrology, 35 terminus calving) and classifying their patterns of seasonal thickness change is the first step towards a more holistic understanding of the processes that control them.

Data and methods
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Discussion and conclusions

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