Grounding line migration through the calving season at Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry

Abstract. Ice velocity variations near the terminus of Jakobshavn Isbrae, Greenland, were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. We estimate a  ∼  1 km wide floating zone near the calving front in early summer of 2015 and 2016, where ice moves in phase with ocean tides. Digital elevation models (DEMs) generated by the TRI show that the glacier front here was much thinner (within 1 km of the glacier front, average ice surface is  ∼  100 and  ∼  110 m above local sea level in 2015 and 2016, respectively) than ice upstream (average ice surface is  >  150 m above local sea level at 2–3 km to the glacier front in 2015 and 2016). However, in late summer 2012, there is no evidence of a floating ice tongue in the TRI observations. Average ice surface elevation near the glacier front was also higher,  ∼  125 m above local sea level within 1 km of the glacier front. We hypothesize that during Jakobshavn Isbrae's recent calving seasons the ice front advances  ∼  3 km from winter to spring, forming a  >  1 km long floating ice tongue. During the subsequent calving season in mid- and late summer, the glacier retreats by losing its floating portion through a sequence of calving events. By late summer, the entire glacier is likely grounded. In addition to ice velocity variation driven by tides, we also observed a velocity variation in the melange and floating ice front that is non-parallel to long-term ice flow motion. This cross-flow-line signal is in phase with the first time derivative of tidal height and is likely associated with tidal currents or bed topography.

[1]  I. Joughin,et al.  Outlet glacier response to forcing over hourly to interannual timescales, Jakobshavn Isbræ, Greenland , 2012, Journal of Glaciology.

[2]  M. Lüthi,et al.  Ice mélange dynamics and implications for terminus stability, Jakobshavn Isbræ, Greenland , 2010 .

[3]  Dana Floricioiu,et al.  Brief Communication: Further summer speedup of Jakobshavn Isbræ , 2014 .

[4]  R. Alley,et al.  Tidal forcing of basal seismicity of ice stream C , 1997 .

[5]  G. Gudmundsson,et al.  Tidal controls on the flow of ice streams , 2016 .

[6]  Eric Rignot,et al.  Antarctic grounding line mapping from differential satellite radar interferometry , 2011 .

[7]  Ian M. Howat,et al.  Submarine melting of the 1985 Jakobshavn Isbræ floating tongue and the triggering of the current retreat , 2009 .

[8]  Martin Funk,et al.  Flow dynamics of tidewater glaciers: a numerical modelling approach , 2001, Journal of Glaciology.

[9]  Roy A. WaIters.  Small-amplitude, short-period variations in the speed of a tide-water glacier in south-central Alaska, U.S.A , 1989 .

[10]  Matt A. King,et al.  Diurnal and semidiurnal tide‐induced lateral movement of Ronne Ice Shelf, Antarctica , 2012 .

[11]  P. Myers,et al.  Warming of the Polar Water Layer in Disko Bay and Potential Impact on Jakobshavn Isbrae , 2013 .

[12]  B. Riedel,et al.  Parametric modelling of the geometrical ice-ocean interaction in the Ekstroemisen grounding zone based on short time-series , 2007 .

[13]  Urs Wegmüller,et al.  Topography Mapping With a Portable Real-Aperture Radar Interferometer , 2012, IEEE Geoscience and Remote Sensing Letters.

[14]  Adrian Jenkins,et al.  Tide‐induced lateral movement of Brunt Ice Shelf, Antarctica , 2002 .

[15]  T. Dixon,et al.  Acquisition of a 3 min, two-dimensional glacier velocity field with terrestrial radar interferometry , 2017, Journal of Glaciology.

[16]  M. Lüthi,et al.  Quantifying velocity response to ocean tides and calving near the terminus of Jakobshavn Isbræ, Greenland , 2014 .

[17]  Martin Truffer,et al.  Where glaciers meet water: Subaqueous melt and its relevance to glaciers in various settings , 2016 .

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

[19]  Ian M. Howat,et al.  Observations of inertial currents in a lagoon in southeastern Iceland using terrestrial radar interferometry and automated iceberg tracking , 2015, Comput. Geosci..

[20]  J. Paden,et al.  Bed elevation of Jakobshavn Isbræ, West Greenland, from high‐resolution airborne gravity and other data , 2017 .

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

[22]  Ian M. Howat,et al.  Multi-year observations of Breiðamerkurjökull, a marine-terminating glacier in southeastern Iceland, using terrestrial radar interferometry , 2015, Journal of Glaciology.

[23]  T. Dixon,et al.  Tidally driven ice speed variation at Helheim Glacier, Greenland, observed with terrestrial radar interferometry , 2015 .

[24]  E. Rignot,et al.  Changes in the Velocity Structure of the Greenland Ice Sheet , 2006, Science.

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

[26]  J. de Juan,et al.  Evidence for non-tidal diurnal velocity variations of Helheim Glacier, East Greenland , 2014, Journal of Glaciology.

[27]  H. Maas,et al.  Grounding line migration and high‐resolution calving dynamics of Jakobshavn Isbræ, West Greenland , 2013 .

[28]  T. Dixon,et al.  An Intensive Observation of Calving at Helheim Glacier, East Greenland. , 2016, Oceanography.

[29]  Ian M. Howat,et al.  Mass balance of Greenland's three largest outlet glaciers, 2000–2010 , 2011 .

[30]  M. Fahnestock,et al.  Dynamic jamming of iceberg‐choked fjords , 2014, 1412.1467.

[31]  Matt A. King,et al.  Tidal influence on Rutford Ice Stream, West Antarctica: observations of surface flow and basal processes from closely spaced GPS and passive seismic stations , 2008 .

[32]  T. Dixon,et al.  Precursor motion to iceberg calving at Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry , 2016, Journal of Glaciology.

[33]  I. Howat,et al.  Submarine melt rate estimates for floating termini of Greenland outlet glaciers (2000–2010) , 2013, Journal of Glaciology.

[34]  A. Richter,et al.  Coastal tides in West Greenland derived from tide gauge records , 2011 .

[35]  Sivaprasad Gogineni,et al.  Bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica , 2014 .

[36]  C. Werner,et al.  GAMMA ’ S PORTABLE RADAR INTERFEROMETER , 2008 .

[37]  J. Scargle.  Studies in astronomical time series analysis. II - Statistical aspects of spectral analysis of unevenly spaced data , 1982 .

[38]  R. Forsberg,et al.  Sudden increase in tidal response linked to calving and acceleration at a large Greenland outlet glacier , 2010 .

[39]  R. Thomas.  Tide-induced perturbations of glacier velocities , 2007 .

[40]  Ian Joughin,et al.  Large fluctuations in speed on Greenland's Jakobshavn Isbræ glacier , 2004, Nature.

[41]  Sridhar Anandakrishnan,et al.  Ice-Shelf Tidal Flexure and Subglacial Pressure Variations , 2013 .

[42]  Teri A. Crosby,et al.  How to Detect and Handle Outliers , 1993 .

[43]  T. S. Clarke,et al.  Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland , 1996 .

[44]  C. Schoof.  Ice sheet grounding line dynamics: Steady states, stability, and hysteresis , 2007 .