Publications

This work evolved from a class example that I created to teach the analysis and interpretation of empirical orthogonal function (EOF) / principal component analysis (PCA).

Eric’s senior thesis work turned into a Journal of Glaciology paper!

Plain language summary: The speed of glacier ice flowing toward the ocean is influenced by timing and the amount of water flowing in moulins. Moulins are large vertical shafts that penetrate the entire ice thickness to transport water from the glacier’s surface to the bed. Water levels within moulins reflect the water pressure within channels that form underneath the glacier, transporting meltwater seaward. Most models that are used to simulate this water flow under the ice assume that moulins are cylindrical, but in reality, they are not. In this study, we show that noncylindrical moulins affect how the water level fluctuates within moulins and that what matters is the shape of the moulin within the range where the water level oscillates.

Short summary: This manuscript introduces a new, open-source physical for moulin geometry and uses it to study the time evolution of the shapes and sizes of Greenland moulins. This is timely, as manned exploration of moulins in Greenland are discovering a wide range of moulin geometries, and important, as recent work has found that the shapes and sizes of moulins modulate the efficiency of the local subglacial system, which controls ice flow. We find that moulins comprise 10–15% of the Greenland Ice Sheet englacial–subglacial hydrologic system and act as time-varying water storage reservoirs. Daily variations in modeled moulin size (~30%) exceed daily variations in modeled subglacial channel size (~10%), which affects subglacial pressure, especially during periods of rapidly varying supraglacial input such as the onset and end of the melt season. These findings lead us to advocate for including moulin geometry in future hydrologic models.

Short summary: We present a new science gateway, GHub, a collaboration space for ice sheet scientists. This web-accessible gateway hosts datasets and modeling workflows, and provides access to codes that enable tool building by the ice sheet science community. Using GHub, we collect and centralize existing datasets, creating data products that more completely catalog the ice sheets of Greenland and Antarctica. We build workflows for model validation and uncertainty quantification, extending existing ice sheet models. Finally, we host existing community codes, enabling scientists to build new tools utilizing them. With this new cyberinfrastructure, ice-sheet scientists will gain integrated tools to quantify the rate and extent of sea level rise, benefitting human societies around the globe.

Short summary: This study addresses Greenland glacier lake drainages, a major international research focus. We analyze ice deformation associated with lake drainages over 18 summers to assess whether precursor events consistently precede lake drainages. We find that currently available remote sensing data products cannot resolve these events and thus that we cannot predict future lake drainages. Thus, future avenues for evaluating this hypothesis will require major field-based GPS or photogrammetry efforts.

Short summary: We used a subglacial hydrology model (GlaDS, written by Mauro Werder) to test the effect of firn-aquifer water at the bed of an outlet glacier. We found that firn-aquifer water should actually dampen the seasonal variations in the hydrological system under the lower glacier. This is because firn-aquifer water can keep channels open year-round, which limits the ‘overwhelming’ event at the beginning of the melt season.
This paper was highlighted in an EOS Research Spotlight by Aaron Sidder on June 7, 2019. “Modeling the Subsurface Hydrology of the Greenland Ice Sheet”

This white paper is available at the U.S. Ice Drilling Program website. It was one of four topical white papers to come out of the 2019 Subglacial Access Working Group meeting in Herndon, Virginia, March 29-30, 2019.

This paper was highlighted by Phys.org: Climate change accelerating rise in sea levels.

A summary I wrote for growkudos.com is here:
“Water refreezing in Greenland may not affect global sea levels much”
What’s it about?
Each summer, water melts at the top surface of Greenland glaciers, and some of it trickles into crevasses, where it refreezes. This warms and softens the ice, leading to faster ice flow — just as it is easier to squeeze out warm honey than cold honey — and thus higher sea levels. However, we show here that this refreezing process is virtually absent in the fast-moving glaciers that contribute >60% of ice flow from Greenland into the ocean. Thus, other processes are likely more important in determining sea-level rise from Greenland.
Why is it important?
The recent IPCC report (a 2013 summary of current climate science) identified this mechanism (cryo-hydrologic warming) as an important unknown in how Greenland glaciers will respond to a warming climate. Our work constrains the influence that refreezing water will have on global sea level. It is important to note that our work DOES NOT indicate that Greenland glaciers are “safe” from climate change. Other mechanisms (warm ocean water, loss of ice shelves, warmer air temperatures) will continue to lay waste to the ice; we simply assert that our studied mechanism will have less influence than these others.
Author perspectives:
Field measurements of meltwater that refreezes in certain Greenland glaciers are quite striking — they show substantially warmer ice that does flow faster, just like warm honey. But in other Greenland glaciers, this does not occur. I wanted to combine these field measurements (taken by others) and physically based numeric model results (my own) to add perspective to how refreezing meltwater is likely to affect the health of all Greenland glaciers.

A great paper led by the future developer of the ice-sheet model icepack

This paper was featured in a SciWorthy blog post: Hydrofracturing in the Greenland Ice Sheet: New meltwater is not likely to further lubricate the Greenland Ice Sheet waterslide