Publications

  1. L. C. Andrews, K. Poinar, and C. Trunz.  “Controls on Greenland moulin geometry and evolution from the Moulin Shape model”. The Cryosphere Discussions, doi:10.5194/tc-2021-41.
    • 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.
  2. J. M. Sperhac, K. Poinar, R. Jones-Ivey, E. Snitzer, J. Briner, B. Csatho, S. Nowicki, E. Simon, A.  Patra. “GHub: Building a Glaciology Gateway to Unify a Community”. Concurrency and Computation: Practice and Experience. e6130, 2020, doi:10.1002/cpe.6130.
    • 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.
  3. K. Poinar and L. C. Andrews.  “Challenges in predicting Greenland supraglacial lake drainages at the regional scale”.  The Cryosphere, doi:10.5194/tc-2020-251.
    • 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.
  4. K. Poinar, C. Dow, L. Andrews. “Long‐Term Support of an Active Subglacial Hydrologic System in Southeast Greenland by Firn Aquifers.” Geophysical Research Letters 57(204), doi:10.1029/2019GL082786.
    • In a nutshell, 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.
    • Preprint available at the University at Buffalo Institutional Repository (UBIR)
    • 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”
  5. K. Poinar, J. Lamp, A. Balter, C. Gustafson, P. Spector, D. Winebrenner, S.Tulaczyk. “Subglacial Access Working Group (SAWG): Access Drilling Priorities in Greenland.” White paper drafted for the U.S. Ice Drilling Program.
    • 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.
  6. C. Dow, W. Lee, J. Greenbaum, C. Greene, D. Blankenship, K. Poinar, A. Forrest, D. Young, and C. Zappa. “Basal channels drive active surface hydrology and transverse ice-shelf fracture.” Science Advances 4(6). doi:10.1126/sciadv.aao7212.
  7. J.P. Briner, R. B. Alley, M. L. Bender, B. Csatho, K. Poinar, and J. M. Schaefer, 2017. “How stable is the Greenland Ice Sheet?” A white paper nucleated from presentations and discussions held at a NSF-sponsored workshop in Buffalo, 10–12 September 2017.
  8. K. Poinar, I. Joughin, D. Lilien, L. Brucker, L. Kehrl, and S. Nowicki, 2017. “Drainage of Southeast Greenland Firn-Aquifer Water through Crevasses to the Bed.” Frontiers in Earth Science special issue “Melt Water Retention Processes in Snow and Firn on Ice Sheets and Glaciers: Observations and Modeling” 5, 8–15. doi:10.3389/feart.2017.00005.
    • The above paper was featured in a very nice NASA press release: NASA study identifies new pathway for Greenland meltwater to reach ocean
    • I was also lucky enough to present this work at the annual TED conference (2017): What’s hidden under the Greenland Ice Sheet?
    • A summary I wrote for growkudos.com is reproduced below.
      “New Pathway for Greenland Meltwater to Reach the Ocean”

      What’s it about?

      Picture a grotto: a low cave containing a lake of still water. In certain parts of Southeast Greenland, liquid water sits inside the glacier, similar to a 0° grotto. These glacial aquifers exist in the top hundred feet of the glacier, where summertime meltwater is trapped by huge wintertime snow drifts. Directly downhill of one such aquifer, we found a number of wide crevasses. This suggests that the aquifer water flows, invisibly under the snow, into these crevasses. Using a new, physically based fracture-mechanics model that predicts the shape and size of water-filled crevasses, we found that the water fractures the crevasses all the way to the bottom of the ice sheet, 1000 meters below. Thus, the crevasses give the aquifer water an easy path (under the ice sheet) to the global ocean. Without the aquifer and crevasses, this water would not reach the ocean.

      Why is it important?

      Most ice-sheet / climate models generally assume that meltwater runs off into the global ocean, raising sea levels. We did not know whether this was true of meltwater in the glacier aquifer — does it reach sea level, or does it refreeze within the ice sheet? We have now shown that meltwater in our study area *does* reach the ocean and contribute to global sea level, although there is a delay of some months to years as it travels through the aquifer – crevasse system.

      Author perspectives:
      I had developed a model for the fracture of crevasses over long time periods, but for a different project. At a conference, I learned that a separate research team, who specializes in the glacier aquifer, suspected that the water drained into crevasses, but could not tell whether the water reached the bottom of the ice sheet and, consequently, eventually the global ocean. It was straightforward to adapt my model to answer this important question.

  9. K. Poinar, I. Joughin, J. T. M. Lenaerts, and M. R. van den Broeke, 2016. “Englacial Latent-Heat Transfer Has Limited Influence on Seaward Ice Flux in Western Greenland.” Journal of Glaciology 62(235), 1–16.  doi:10.1017/jog2016.103.
    • 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.
  10. D. Shapero, I. Joughin, K. Poinar, M. Morlighem, F. Gillet-Chaulet, 2016. “Basal Resistance for Three of the Largest Greenland Outlet Glaciers.” Journal of Geophysical Research 121, 1–13. doi:10.1002/2015JF003643.
    • A great paper led by the future developer of the ice-sheet model icepack
  11. K. Poinar, I. Joughin, S. B. Das, M. D. Behn, J. T. M. Lenaerts, and M. R. van den Broeke, 2015. “Limits to Future Expansion of Surface-Melt-Enhanced Ice Flow into the Interior of Western Greenland.” Geophysical Research Letters42(6), 1800–1807. doi:10.1002/2015GL063192.