Spatial and temporal variations in basal melting at Nivlisen ice 1 shelf , East Antarctica , derived from phase-sensitive radars 2

13 Thinning rates of ice shelves vary widely around Antarctica and basal melting is a major 14 component in ice shelf mass loss. In this study, we present records of basal melting, at unique 15 spatial and temporal resolution for East Antarctica, derived from autonomous phase-sensitive 16 radars. These records show spatial and temporal variations of ice shelf basal melting in 2017 and 17 2018 at Nivlisen, central Dronning Maud Land. The annually averaged melt rates are in general 18 moderate (0.8 m yr). Radar profiling of the ice-shelf shows variable ice thickness from 19 smooth beds to basal crevasses and channels. The highest melt rates (3.9 m yr) were observed 20 close to a grounded feature near the ice shelf front. Daily time-varying measurements reveal a 21 seasonal melt signal 4 km from the ice shelf front, at an ice draft of 130 m, where the highest 22 daily melt rates occurred in summer (up to 5.6 m yr). This seasonality indicates that summer23 warmed ocean surface water was pushed by wind beneath the ice shelf front. We observed a 24 different melt regime 35 km into the ice-shelf cavity, at an ice draft of 280 m, with considerably 25 lower melt rates (annual average of 0.4 m yr) and no seasonality. We conclude that warm deep 26 The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-108 Manuscript under review for journal The Cryosphere Discussion started: 24 May 2019 c © Author(s) 2019. CC BY 4.0 License.

[1]  P. Christoffersen,et al.  Basal melting of Ross Ice Shelf from solar heat absorption in an ice-front polynya , 2019, Nature Geoscience.

[2]  Eric Rignot,et al.  Four decades of Antarctic Ice Sheet mass balance from 1979–2017 , 2019, Proceedings of the National Academy of Sciences.

[3]  A. Thompson,et al.  The Antarctic Slope Current in a Changing Climate , 2018, Reviews of Geophysics.

[4]  N. Gillett,et al.  Recent Southern Ocean warming and freshening driven by greenhouse gas emissions and ozone depletion , 2018, Nature Geoscience.

[5]  D. Holland,et al.  Vertical Structure of Diurnal Englacial Hydrology Cycle at Helheim Glacier, East Greenland , 2018, Geophysical Research Letters.

[6]  Eric Rignot,et al.  Mass balance of the Antarctic Ice Sheet from 1992 to 2017 , 2018, Nature.

[7]  H. Fricker,et al.  Trends and connections across the Antarctic cryosphere , 2018, Nature.

[8]  Susheel Adusumilli,et al.  Variable Basal Melt Rates of Antarctic Peninsula Ice Shelves, 1994–2016 , 2018 .

[9]  H. Fricker,et al.  Ocean Tide Influences on the Antarctic and Greenland Ice Sheets , 2018 .

[10]  C. Bitz,et al.  Conditions leading to the unprecedented low Antarctic sea ice extent during the 2016 austral spring season , 2017 .

[11]  Rodrigo Gómez,et al.  Antarctica, 1979–2016 sea ice extent: total versus regional trends, anomalies, and correlation with climatological variables , 2017 .

[12]  T. Hattermann,et al.  Tidal influences on a future evolution of the Filchner–Ronne Ice Shelf cavity in the Weddell Sea, Antarctica , 2017 .

[13]  A. Thompson,et al.  Eddy Generation and Jet Formation via Dense Water Outflows across the Antarctic Continental Slope , 2016 .

[14]  S. Rintoul,et al.  Ocean heat drives rapid basal melt of the Totten Ice Shelf , 2016, Science Advances.

[15]  John Turner,et al.  Absence of 21st century warming on Antarctic Peninsula consistent with natural variability , 2016, Nature.

[16]  L. B. Lok,et al.  Instruments and methods:A ground-based radar for measuring vertical strain rates and time-varying basal melt rates in ice sheets and shelves , 2015 .

[17]  Gaël Durand,et al.  Antarctic ice rises and rumples: Their properties and significance for ice-sheet dynamics and evolution , 2015 .

[18]  Fernando S. Paolo,et al.  Volume loss from Antarctic ice shelves is accelerating , 2015, Science.

[19]  A. Thompson,et al.  Eddy transport as a key component of the Antarctic overturning circulation , 2014 .

[20]  M. Biuw,et al.  Wind‐driven spreading of fresh surface water beneath ice shelves in the Eastern Weddell Sea , 2014 .

[21]  B. Scheuchl,et al.  Widespread, rapid grounding line retreat of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica, from 1992 to 2011 , 2014 .

[22]  David M. Holland,et al.  Intrusion of warm surface water beneath the McMurdo Ice Shelf, Antarctica , 2013 .

[23]  Adrian Jenkins,et al.  The effect of basal channels on oceanic ice‐shelf melting , 2013 .

[24]  Helen Amanda Fricker,et al.  Impact of tide‐topography interactions on basal melting of Larsen C Ice Shelf, Antarctica , 2012 .

[25]  D. Vaughan,et al.  Antarctic ice-sheet loss driven by basal melting of ice shelves , 2012, Nature.

[26]  M. Biuw,et al.  Eddy overturning of the Antarctic Slope Front controls glacial melting in the Eastern Weddell Sea , 2011 .

[27]  Gwyn Griffiths,et al.  Measurements beneath an Antarctic ice shelf using an autonomous underwater vehicle , 2006 .

[28]  S. Gille.  Warming of the Southern Ocean Since the 1950s , 2002, Science.

[29]  T. Schreiber,et al.  Surrogate time series , 1999, chao-dyn/9909037.

[30]  R. Reese,et al.  The far reach of ice-shelf thinning in Antarctica , 2017, Nature Climate Change.

[31]  R. Timmermann,et al.  On the warm inflow at the eastern boundary of the Weddell Gyre , 2016 .

[32]  D. McGrath,et al.  Basal crevasses and associated surface crevassing on the Larsen C ice shelf, Antarctica, and their role in ice-shelf instability , 2012, Annals of Glaciology.

[33]  H. Sverdrup.  The Currents off the Coast of Queen Maud Land , 1953 .