title: Distinct patterns of seasonal Greenland glacier velocity.
abstract: Predicting Greenland Ice Sheet mass loss due to ice dynamics requires a complete understanding of spatiotemporal velocity fluctuations and related control mechanisms. We present a 5 year record of seasonal velocity measurements for 55 marine-terminating glaciers distributed around the ice sheet margin, along with ice-front position and runoff data sets for each glacier. Among glaciers with substantial speed variations, we find three distinct seasonal velocity patterns. One pattern indicates relatively high glacier sensitivity to ice-front position. The other two patterns are more prevalent and appear to be meltwater controlled. These patterns reveal differences in which some subglacial systems likely transition seasonally from inefficient, distributed hydrologic networks to efficient, channelized drainage, while others do not. The difference may be determined by meltwater availability, which in some regions may be influenced by perennial firn aquifers. Our results highlight the need to understand subglacial meltwater availability on an ice sheet-wide scale to predict future dynamic changes.
  
  
  CONCLUSIONS
  First multi-region seasonal velocity measurements show regional differencesSeasonal velocity fluctuations on most glaciers appear meltwater controlledSeasonal development of efficient subglacial drainage geographically divided.
authors.affiliation: Earth and Space Sciences, University of Washington Seattle, Washington, USA ; Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA ; National Snow and Ice Data Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado-Boulder Boulder, Colorado, USA.
authors.forename: Twila
authors.initials: T
authors.lastname: Moon
authors.affiliation: Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA.
authors.forename: Ian
authors.initials: I
authors.lastname: Joughin
authors.affiliation: Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA.
authors.forename: Ben
authors.initials: B
authors.lastname: Smith
authors.affiliation: Institute for Marine and Atmospheric Research, Utrecht University Utrecht, Netherlands.
authors.forename: Michiel R
authors.initials: MR
authors.lastname: van den Broeke
authors.affiliation: Institute for Marine and Atmospheric Research, Utrecht University Utrecht, Netherlands.
authors.forename: Willem Jan
authors.initials: WJ
authors.lastname: van de Berg
authors.affiliation: Institute for Marine and Atmospheric Research, Utrecht University Utrecht, Netherlands.
authors.forename: Brice
authors.initials: B
authors.lastname: Noël
authors.affiliation: Polar Science Center, Applied Physics Lab, University of Washington Seattle, Washington, USA.
authors.forename: Mika
authors.initials: M
authors.lastname: Usher
keywords: Greenland; interferometric synthetic aperture radar; meltwater; seasonal velocity; subglacial drainage; terminus
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