Highly temporally resolved response to seasonal surface melt of the Zachariae and 79N outlet glaciers in northeast Greenland

The seasonal response to surface melting of the Northeast Greenland Ice Stream outlets, Zachariae and 79N, is investigated using new highly temporally resolved surface velocity maps for 2016 combined with numerical modelling. The seasonal speed-up at 79N of 0.15km/yr is suggested to be driven by a decrease in effective basal pressure induced by surface melting, whereas for Zachariae its 0.11km/yr seasonal speed-up correlates equally well with the break-up of its large ice melange. We investigate the influence 76km long floating tongue at 79N, finding it provides little resistance and that most of it could be lost without impacting the dynamics of the area. Furthermore, we show that reducing the slipperiness along the tongue–wall interfaces produces a velocity change spatially inconsistent with the observed seasonal speed-up. Finally, we find that subglacial sticky spots such as bedrock bumps play a negligible role in the large-scale response to a seasonally enhanced basal slipperiness of the region.

[1]  Klaus Wyser,et al.  A 140-year simulation of European climate with the new version of the Rossby Centre regional atmospheric climate model (RCA3) , 2005 .

[2]  N. Reeh,et al.  Sea ice and the stability of north and northeast Greenland floating glaciers , 2001, Annals of Glaciology.

[3]  David M. Holland,et al.  Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters , 2008 .

[4]  O. Olesen,et al.  The Nioghalvfjerdsfjorden glacier project, North-East Greenland: a study of ice sheet response to climatic change , 1997 .

[5]  R. Jacobel,et al.  Fractures as the main pathways of water flow in temperate glaciers , 2005, Nature.

[6]  O. Olesen,et al.  Tidal movement of Nioghalvfjerdsfjorden glacier, northeast Greenland: observations and modelling , 2000, Annals of Glaciology.

[7]  Per Lötstedt,et al.  Dynamically coupling the non-linear Stokes equations with the shallow ice approximation in glaciology: Description and first applications of the ISCAL method , 2015, J. Comput. Phys..

[8]  B. Kamb,et al.  Stress-gradient Coupling in Glacier Flow: IV. Effects of the “T” Term , 1986, Journal of Glaciology.

[9]  S. Marshall,et al.  Paleofluvial Mega-Canyon Beneath the Central Greenland Ice Sheet , 2013, Science.

[10]  D. Dahl-Jensen,et al.  Response of the large-scale subglacial drainage system of Northeast Greenland to surface elevation changes , 2015 .

[11]  Jørgen Dall,et al.  Ice Velocity Mapping Using TOPS SAR Data and Offset Tracking , 2015 .

[12]  B. Scheuchl,et al.  Fast retreat of Zachariæ Isstrøm, northeast Greenland , 2015, Science.

[13]  H. Oerter,et al.  The subglacial cavity and implied dynamics under Nioghalvfjerdsfjorden Glacier, NE‐Greenland , 2000 .

[14]  Sridhar Anandakrishnan,et al.  Dilatant till facilitates ice-stream flow in northeast Greenland , 2014 .

[15]  A. Hubbard,et al.  Evolution of the subglacial drainage system beneath the Greenland Ice Sheet revealed by tracers , 2013 .

[16]  Martin Truffer,et al.  Of isbræ and ice streams , 2003, Annals of Glaciology.

[17]  Sivaprasad Gogineni,et al.  A new ice thickness and bed data set for the Greenland ice sheet: 1. Measurement, data reduction, and errors , 2001 .

[18]  I. Joughin,et al.  High Geothermal Heat Flow, Basal Melt, and the Origin of Rapid Ice Flow in Central Greenland , 2001, Science.

[19]  O. Gagliardini,et al.  The stability of grounding lines on retrograde slopes , 2012 .

[20]  Richard B. Alley,et al.  In search of ice-stream sticky spots , 1993, Journal of Glaciology.

[21]  Ian M. Howat,et al.  Rapid retreat and acceleration of Helheim Glacier, east Greenland , 2005 .

[22]  K. E. Rose,et al.  Characteristics of Ice Flow in Marie Byrd Land, Antarctica , 1979, Journal of Glaciology.

[23]  J. Box,et al.  Ice discharge uncertainties in Northeast Greenland from boundary conditions and climate forcing of an ice flow model , 2015 .

[24]  Ian Joughin,et al.  Fracture Propagation to the Base of the Greenland Ice Sheet During Supraglacial Lake Drainage , 2008, Science.

[25]  L. Stearns,et al.  Controls on the recent speed-up of Jakobshavn Isbræ, West Greenland , 2011, Journal of Glaciology.

[26]  D. Macayeal,et al.  Basal friction of Ice Stream E, West Antarctica , 1995 .

[27]  Eric Rignot,et al.  Deeply incised submarine glacial valleys beneath the Greenland ice sheet , 2014 .

[28]  Son V. Nghiem,et al.  The melt anomaly of 2002 on the Greenland Ice Sheet from active and passive microwave satellite observations , 2004 .

[29]  M. Krabbendam.  Sliding of temperate basal ice on a rough, hard bed: creep mechanisms, pressure melting, and implications for ice streaming , 2016 .

[30]  R. Kwok,et al.  Ice-stream-related patterns of ice flow in the interior of northeast Greenland , 2001 .

[31]  R. Alley,et al.  Deformation of till beneath ice stream B, West Antarctica , 1986, Nature.

[32]  Chris D. Clark,et al.  Ice stream sticky spots: A review of their identification and influence beneath contemporary and palaeo-ice streams , 2007 .

[33]  C. Schoof.  Ice-sheet acceleration driven by melt supply variability , 2010, Nature.

[34]  S. P. Anderson,et al.  Response of glacier basal motion to transient water storage , 2007 .

[35]  R. Kwok,et al.  Detection of snowmelt regions on the Greenland ice sheet using diurnal backscatter change , 2001, Journal of Glaciology.

[36]  Ian M. Howat,et al.  Continued evolution of Jakobshavn Isbrae following its rapid speedup , 2008 .

[37]  Ian Joughin,et al.  Distinct patterns of seasonal Greenland glacier velocity , 2014, Geophysical research letters.

[38]  Leigh A. Stearns,et al.  Increased flow speed on a large East Antarctic outlet glacier caused by subglacial floods , 2008 .

[39]  Garry K. C. Clarke,et al.  Fast glacier flow: Ice streams, surging, and tidewater glaciers , 1987 .

[40]  M. Bevis,et al.  Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming , 2014 .

[41]  Baptiste Vandecrux,et al.  Liquid Water Flow and Retention on the Greenland Ice Sheet in the Regional Climate Model HIRHAM5: Local and Large-Scale Impacts , 2017, Front. Earth Sci..

[42]  R. Greve,et al.  The effect of the north-east ice stream on the Greenland ice sheet in changing climates , 2007 .

[43]  Ian Joughin,et al.  Seasonal Speedup Along the Western Flank of the Greenland Ice Sheet , 2008, Science.

[44]  R. Hindmarsh,et al.  Similarity of organized patterns in driving and basal stresses of Antarctic and Greenland ice sheets beneath extensive areas of basal sliding , 2014 .

[45]  Fabien Gillet-Chaulet,et al.  Simulations of the Greenland ice sheet 100 years into the future with the full Stokes model Elmer/Ice , 2011, Journal of Glaciology.

[46]  R. Alley,et al.  Basal conditions and ice dynamics inferred from radar-derived internal stratigraphy of the northeast Greenland ice stream , 2013, Annals of Glaciology.

[47]  M. Lüthi,et al.  Mechanisms of fast flow in Jakobshavn Isbræ, West Greenland. Part III. Measurements of ice deformation, temperature and cross-borehole conductivity in boreholes to the bedrock , 2002 .

[48]  Jonathan L. Bamber,et al.  A new ice thickness and bed data set for the Greenland ice sheet: 2. Relationship between dynamics and basal topography , 2001 .

[49]  R. Greve,et al.  Resolution of ice streams and outlet glaciers in large-scale simulations of the Greenland ice sheet , 2013, Annals of Glaciology.

[50]  John Paden,et al.  Deformation, warming and softening of Greenland’s ice by refreezing meltwater , 2014 .

[51]  J. Box,et al.  Decadal‐scale sensitivity of Northeast Greenland ice flow to errors in surface mass balance using ISSM , 2012 .

[52]  Prasad Gogineni,et al.  Observation and analysis of ice flow in the largest Greenland ice stream , 2001 .

[53]  S. Gollvik,et al.  HIRLAM experiments on surface energy balance across Vatnajökull, Iceland , 2009 .

[54]  Barclay Kamb,et al.  RHEOLOGICAL NONLINEARITY AND FLOW INSTABILITY IN THE DEFORMING BED MECHANISM OF ICE STREAM MOTION , 1991 .

[55]  Maik Thomas,et al.  Melting at the base of the Greenland ice sheet explained by Iceland hotspot history , 2016 .

[56]  Søren Rysgaard,et al.  Quantifying Energy and Mass Fluxes Controlling Godthåbsfjord Freshwater Input in a 5-km Simulation (1991–2012)*,+ , 2015 .

[57]  Ian M. Howat,et al.  Synchronous retreat and acceleration of southeast Greenland outlet glaciers 2000–06: ice dynamics and coupling to climate , 2008 .

[58]  Urs Wegmüller,et al.  Glacier motion estimation using SAR offset-tracking procedures , 2002, IEEE Trans. Geosci. Remote. Sens..