Abstract

<p><span>Smith, Pope, and Kohler glaciers and the corresponding Crosson and Dotson ice shelves have undergone speedup, thinning, and rapid grounding-line retreat in recent years, leaving them in a state likely conducive to future retreat. We conducted a suite of numerical model simulations of these glaciers and compared the results to observations to determine the processes controlling their recent evolution. Simulations were forced using estimates of the distribution and intensity of melt from 1996-2014. The model simulations indicate that the state of these glaciers in the 1990s was not inherently unstable, i.e., that small perturbations to the grounding line would not necessarily have caused the large retreat that has been observed. Instead, sustained melt, at rates higher than the 1990s and concentrated at the grounding line, was needed to cause the observed retreat. Weakening of the margins of Crosson Ice Shelf may have hastened the onset of grounding-line retreat but is unlikely to have initiated these rapid changes without an accompanying increase in melt. In the simulations that most closely match the observed thinning, speedup, and retreat, modeled grounding-line retreat and ice loss continue unabated throughout the 21st century, and subsequent retreat along Smith Glacier's trough appears likely. Given the modeled retreat, thinning associated with the retreat of Smith Glacier may reach the ice divide and undermine a portion of the Thwaites catchment as quickly as changes initiated at the Thwaites terminus. Thus, while the Smith, Pope, Kohler catchment is small compared to Thwaites, these smaller glaciers may be important when considering the centennial-scale evolution of the Amundsen Sea region.</span></p>

Highlights

  • Glaciers along the Amundsen Sea Embayment (ASE) have long been thought to be vulnerable to catastrophic retreat (Hughes, 1981), and the major ice streams in the region have recently undergone significant speedup and grounding-line retreat (Mouginot et al, 2014; Rignot et al, 2014; Scheuchl et al, 2016)

  • Using reasonable melt intensity distributed with simple, depth-dependent parameterizations, our model simulations are able to reproduce the recent speedup, thinning, and retreat of Smith, Pope, and Kohler glaciers, albeit with some uncertainty in the timing

  • These simulations suggest that in 1996 Smith Glacier was in a state of precarious stability, but elevated melt rates were needed to cause the observed grounding-line retreat

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Summary

Introduction

Glaciers along the Amundsen Sea Embayment (ASE) have long been thought to be vulnerable to catastrophic retreat (Hughes, 1981), and the major ice streams in the region have recently undergone significant speedup and grounding-line retreat (Mouginot et al, 2014; Rignot et al, 2014; Scheuchl et al, 2016). Ice-flow modeling (e.g., Joughin et al, 2014) and glaciological observations (e.g., Rignot et al, 2014) suggest that the retreat of Thwaites Glacier and perhaps Pine Island Glacier, the largest glaciers along the ASE, will continue under all realistic melt scenarios (Favier et al, 2014; Joughin et al, 2010) Despite their lower ice discharge relative to Thwaites and Pine Island glaciers, Smith, Pope, and Kohler glaciers (see Fig. 1 for an overview of the area) have gained attention as some of the most rapidly changing outlets along the Amundsen Sea Embayment (Mouginot et al, 2014).

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