title: Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland 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 km(2) 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 km(3)⋅d(-1) vs. ∼0.103 km(3)⋅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.
authors.affiliation: Department of Geography, University of California, Los Angeles, CA 90095; lsmith@geog.ucla.edu.
authors.forename: Laurence C
authors.initials: LC
authors.lastname: Smith
authors.affiliation: Department of Geography, University of California, Los Angeles, CA 90095;
authors.forename: Vena W
authors.initials: VW
authors.lastname: Chu
authors.affiliation: Department of Geography, University of California, Los Angeles, CA 90095;
authors.forename: Kang
authors.initials: K
authors.lastname: Yang
authors.affiliation: Department of Geography, University of California, Los Angeles, CA 90095;
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Gleason
authors.affiliation: Department of Geography, University of California, Los Angeles, CA 90095;
authors.forename: Lincoln H
authors.initials: LH
authors.lastname: Pitcher
authors.affiliation: Department of Geography, Rutgers University, Piscataway, NJ 08854;
authors.forename: Asa K
authors.initials: AK
authors.lastname: Rennermalm
authors.affiliation: Department of Geography, University of Wyoming, Laramie, WY 82071;
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Legleiter
authors.affiliation: NASA Jet Propulsion Laboratory, Pasadena, CA 91109;
authors.forename: Alberto E
authors.initials: AE
authors.lastname: Behar
authors.affiliation: Department of Geography, University of Wyoming, Laramie, WY 82071;
authors.forename: Brandon T
authors.initials: BT
authors.lastname: Overstreet
authors.affiliation: Department of Geography, Rutgers University, Piscataway, NJ 08854;
authors.forename: Samiah E
authors.initials: SE
authors.lastname: Moustafa
authors.affiliation: Department of Earth and Atmospheric Science, The City College of New York, NY, 10031;
authors.forename: Marco
authors.initials: M
authors.lastname: Tedesco
authors.affiliation: Department of Geography, University of Utah, Salt Lake City, UT 84112;
authors.forename: Richard R
authors.initials: RR
authors.lastname: Forster
authors.affiliation: U.S. Army Cold Regions Research & Engineering Laboratory, Hanover, NH 03755; and.
authors.forename: Adam L
authors.initials: AL
authors.lastname: LeWinter
authors.affiliation: U.S. Army Cold Regions Research & Engineering Laboratory, Hanover, NH 03755; and.
authors.forename: David C
authors.initials: DC
authors.lastname: Finnegan
authors.affiliation: Department of Geography, University of California, Los Angeles, CA 90095;
authors.forename: Yongwei
authors.initials: Y
authors.lastname: Sheng
authors.affiliation: Earth Vision Trust, Boulder, CO 80304.
authors.forename: James
authors.initials: J
authors.lastname: Balog
keywords: Greenland ice sheet; mass balance; meltwater runoff; remote sensing; supraglacial hydrology