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Research Article

Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet

Laurence C. Smith, Vena W. Chu, Kang Yang, Colin J. Gleason, Lincoln H. Pitcher, Asa K. Rennermalm, Carl J. Legleiter, Alberto E. Behar, Brandon T. Overstreet, Samiah E. Moustafa, Marco Tedesco, Richard R. Forster, Adam L. LeWinter, David C. Finnegan, Yongwei Sheng, and James Balog
PNAS first published January 12, 2015; https://doi.org/10.1073/pnas.1413024112
Laurence C. Smith
aDepartment of Geography, University of California, Los Angeles, CA 90095;
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  • For correspondence: lsmith@geog.ucla.edu
Vena W. Chu
aDepartment of Geography, University of California, Los Angeles, CA 90095;
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Kang Yang
aDepartment of Geography, University of California, Los Angeles, CA 90095;
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Colin J. Gleason
aDepartment of Geography, University of California, Los Angeles, CA 90095;
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Lincoln H. Pitcher
aDepartment of Geography, University of California, Los Angeles, CA 90095;
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Asa K. Rennermalm
bDepartment of Geography, Rutgers University, Piscataway, NJ 08854;
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Carl J. Legleiter
cDepartment of Geography, University of Wyoming, Laramie, WY 82071;
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Alberto E. Behar
dNASA Jet Propulsion Laboratory, Pasadena, CA 91109;
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Brandon T. Overstreet
cDepartment of Geography, University of Wyoming, Laramie, WY 82071;
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Samiah E. Moustafa
bDepartment of Geography, Rutgers University, Piscataway, NJ 08854;
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Marco Tedesco
eDepartment of Earth and Atmospheric Science, The City College of New York, NY, 10031;
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Richard R. Forster
fDepartment of Geography, University of Utah, Salt Lake City, UT 84112;
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Adam L. LeWinter
gU.S. Army Cold Regions Research & Engineering Laboratory, Hanover, NH 03755; and
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David C. Finnegan
gU.S. Army Cold Regions Research & Engineering Laboratory, Hanover, NH 03755; and
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Yongwei Sheng
aDepartment of Geography, University of California, Los Angeles, CA 90095;
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James Balog
hEarth Vision Trust, Boulder, CO 80304
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  1. Edited by John H. England, University of Alberta, Edmonton, Canada, and accepted by the Editorial Board November 13, 2014 (received for review July 10, 2014)

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Significance

Meltwater runoff from the Greenland ice sheet is a key contributor to global sea level rise and is expected to increase in the future, but it has received little observational study. We used satellite and in situ technologies to assess surface drainage conditions on the southwestern ablation surface after an extreme 2012 melting event. We conclude that the ice sheet surface is efficiently drained under optimal conditions, that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater release from the ice sheet.

Abstract

Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km2 of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54–2.81 cm⋅d−1) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41–98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056–0.112 km3⋅d−1 vs. ∼0.103 km3⋅d−1), and when integrated over the melt season, totaled just 37–75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.

  • Greenland ice sheet
  • supraglacial hydrology
  • meltwater runoff
  • mass balance
  • remote sensing

Footnotes

  • ↵1To whom correspondence should be addressed. Email: lsmith{at}geog.ucla.edu.
  • ↵2Deceased January 9, 2015.

  • Author contributions: L.C.S. conceived the project; L.C.S., V.W.C., K.Y., C.J.G., L.H.P., A.K.R., C.J.L., and Y.S. designed research; A.E.B., A.L.L., D.C.F., and J.B. designed instrumentation; L.C.S., V.W.C., K.Y., C.J.G., L.H.P., A.K.R., C.J.L., A.E.B., B.T.O., S.E.M., M.T., R.R.F., A.L.L., and D.C.F. performed field work; V.W.C., K.Y., C.J.G., and L.H.P. conducted analyses; L.C.S. wrote the paper; and V.W.C., K.Y., C.J.G., and L.H.P. helped write the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission. J.H.E. is a guest editor invited by the Editorial Board.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1413024112/-/DCSupplemental.

Freely available online through the PNAS open access option.

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Efficient melt drainage on the Greenland ice sheet
Laurence C. Smith, Vena W. Chu, Kang Yang, Colin J. Gleason, Lincoln H. Pitcher, Asa K. Rennermalm, Carl J. Legleiter, Alberto E. Behar, Brandon T. Overstreet, Samiah E. Moustafa, Marco Tedesco, Richard R. Forster, Adam L. LeWinter, David C. Finnegan, Yongwei Sheng, James Balog
Proceedings of the National Academy of Sciences Jan 2015, 201413024; DOI: 10.1073/pnas.1413024112

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Efficient melt drainage on the Greenland ice sheet
Laurence C. Smith, Vena W. Chu, Kang Yang, Colin J. Gleason, Lincoln H. Pitcher, Asa K. Rennermalm, Carl J. Legleiter, Alberto E. Behar, Brandon T. Overstreet, Samiah E. Moustafa, Marco Tedesco, Richard R. Forster, Adam L. LeWinter, David C. Finnegan, Yongwei Sheng, James Balog
Proceedings of the National Academy of Sciences Jan 2015, 201413024; DOI: 10.1073/pnas.1413024112
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