DOI: 10.5061/dryad.5hqbzkhg2
title: Ice-shelf melting around Antarctica

description: We compare the volume flux divergence of Antarctic ice shelves in 2007 and
 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to
 determine their rates of melting and mass balance. Basal melt of 1325 ±
 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139
 Gt/year, making ice-shelf melting the largest ablation process in
 Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves
 covering two-thirds of the total ice-shelf area account for only 15% of
 net melting. Half of the meltwater comes from 10 small, warm-cavity
 Southeast Pacific ice shelves occupying 8% of the area. A similar high
 melt/area ratio is found for six East Antarctic ice shelves,
 implying undocumented strong ocean thermal forcing on their deep grounding
 lines.
description: 1. Ice shelf thickness Ice thickness is from
 BEDMAP-2 (1) and NASA Operation IceBridge (OIB) (18-19), which are
 available, respectively, at www.antarctica.ac.uk › Projects AZ › Bedmap2
 and at the National Snow and Ice Data Center nsidc.org/data/icebridge/
 data_summaries.html. BEDMAP-2 merges measurements of ice thickness from
 airborne radio echo sounding with estimates derived from radar-altimetry
 observations of surface elevation from 1994 (20). The altimetry product
 uses the most inland grounding line positions from InSAR (21), MOA (36),
 or ASAID (37) to minimize the omission of floating sectors. Ice thickness
 may be erroneously high where ice is not in hydrostatic equilibrium, e.g.,
 in a transition region. Along most glaciers, MOA and ASAID grounding lines
 (GL) have lateral errors up to 50 km (21), which impact the calculation of
 ice thickness, volume flux, and basal melt rate. Here, we only rely on a
 systematic, precise mapping of GL with InSAR (available at
 nsidc.org/data/docs/measures/ nsidc0498_rignot/), and minimize the risk of
 including grounded ice sectors. Special cases: As GL
 ice thickness is not well known on Larsen D-G, we use balance discharge
 from RACMO2 for the GL flux. At the GL of Larsen C, Rayner/Thyer, Edward
 VIII, and the thickest parts of Shackleton (Denman Glacier) and Moscow
 University Ice Shelves, ice thickness assumes hydrostatic equilibrium. For
 Larsen B, we use ice velocity from 2000 and ice-shelf thickness from 1994,
 pre-dating its 2002 collapse. For the GL of Ross East, Nansen, Aviator,
 Mariner, Ninnis, Mertz, Dibble, Holmes, Totten, Wilma/Robert/Downer,
 Rayner/Thyer and Shirase in East Antarctica (EAIS), and Land, Nickerson,
 Sulzberger and Swinburne in West Antarctica (WAIS), we use (20); for David
 Glacier, we use OIB. For ice-front fluxes, we use BEDMAP-2, except for
 Rayner/Thyer, where ice thickness uses hydrostatic equilibrium.
 2. Ice shelf
 velocity Ice-shelf vector velocity data are from a
 mosaic of InSAR data from six sensors (22). Flow speeds are highest along
 the coast and on ice shelves. The error in speed is lowest in fast-moving
 areas mapped with multiple sensors and highest in slow-moving areas mapped
 using only Advanced Land Observing System (ALOS) Polarimetric Advanced
 L-band Synthetic Aperture Radar (PALSAR) data. The average errors in flow
 speed and direction are, respectively, 4 m/yr and 1.7. The velocity data
 are available online at
 nsidc.org/data/docs/measures/nsidc0484_rignot. 
 3. Drainage
 boundaries Drainage boundaries on continental ice are
 traditionally drawn using a digital elevation model of the ice sheet,
 assuming steady-state ice flow along the lines of steepest surface slope.
 This approach is not reliable on ice shelves due to their small surface
 slope. We use flow vector direction to delineate drainage boundaries
 between adjacent ice shelves. This approach helps to differentiate the ice
 flow into the Filchner Ice Shelf (East Antarctica Ice Sheet (EAIS)) from
 Academy Glacier versus ice flow into the Ronne Ice Shelf (West Antarctica
 Ice Sheet (WAIS)) from the Foundation Ice Stream. We also separate ice
 flow into Ross West (WAIS) versus Ross East (EAIS) and ice flow into
 Brunt-Stancomb versus Riiser-Larsen ice shelves. The transition between
 EAIS and WAIS is thus defined at the boundaries between Foundation Ice
 Stream and Academy Glacier in the Weddell Sea sector, and Mercer Ice
 Stream and Scott Glacier in the Ross Sea sector. 
 4. Ice-front
 positions We identify ice-front positions in a radar
 mosaic of ALOS PALSAR data for the years 2007-2008 at a 150-m posting. The
 results are compared for consistency and quality control with MOA 2009,
 updated from (36). As an ice front migrates with ice flow and calving
 events, an exact agreement is not expected, but the comparison helps
 identify and resolve discrepancies. In the case of broken ice shelves,
 where icebergs are partially detached and glued together with an ice
 mélange of iceberg debris, sea ice, and blown snow, ice front delineation
 uses clues from both radar and visible imagery. The
 2007-2008 ice-front positions do not coincide with the boundaries of
 BEDMAP-2 because the data sets are from slightly different time periods.
 As a result, our ice front flux gates are slightly upstream of the
 2007-2008 ice front positions. The area in-between the ice-front flux
 gates and the actual ice front positions is 2% of the total ice shelf
 area. For ice walls and smaller ice shelves excluded
 from our survey, we assume a 50/50 partitioning between calving and basal
 melt to balance the incoming flux, as in the case of tidewater glaciers
 (39-40). 5. Ice shelf areas, rises, and
 islands Inflow from ice rises and ice islands along the
 ice shelf perimeter is included in the GL flux. Ice rises, rumples, and
 islands within the ice shelf perimeters are included in the SMB input but
 excluded from the ice shelf area used to calculate total meltwater
 production. 6. Grounding line fluxes
 We have compared our GL fluxes with the balance fluxes calculated
 using RACMO2 (16). GL fluxes are within error bars of the balance fluxes
 except in a few areas known to be thinning rapidly (23). This verification
 provides an evaluation of the quality of the thickness data at the
 grounding line and helps justify the selection of alternative ice
 thickness estimates, as per the discussion in section 1, “Special
 cases”. 7. Surface mass balance (SMB)
 We employ SMB products from the University of Utrecht’s Regional
 Atmospheric Climate Model (RACMO2) validated with in-situ data (16). An
 error rate has been quantified for each basin based on error propagation
 (17). We use an average SMB for the time period 1979-2010 to obtain a
 long-term average SMB. Employing SMB values for 2007-2008, the time period
 of velocity mapping, would introduce significant noise and assume that ice
 shelf velocities respond instantaneously to annual fluctuations in snow
 input. 
 8. Basal melt rates The actual basal melt
 rate, B, in meters per year is deduced from the equation of mass
 conservation (15): ∂H/∂t = SMB – B - ∇ (H v), where H is the ice
 thickness, v is the ice velocity vector, SMB the surface mass balance, and
 ∂H/∂t the rate of ice shelf thickening (positive for ice shelf
 growth). To take into account the spatial resolution of
 the thickness data, we calculate the derivative terms of the mass
 conservation equation with a 10-km baseline, and the final melt rate map
 is smoothed with a 10-km filter. As a result, we miss points along the ice
 shelf perimeters when mapping the freeze/melt distribution; but this does
 not affect the estimation of area-average melt rates, B, expressed in
 Gt/yr, because that calculation is based on the total inflow and outflow
 within the ice shelf perimeters, not the integration of point
 values. We also calculate melt rates Bss for ∂H/∂t = 0,
 i.e., the amount of freezing and melting that would be required to
 maintain the ice shelves in a steady state of velocity and thickness in
 2007-2008. For this calculation, we still use velocity data for 2007-2008.
 In reality, some of these glaciers have been accelerating in recent
 decades, e.g., several glaciers draining into the Amundsen Sea. For these
 glaciers, it would have been preferable to use ice velocities from an
 earlier time period, e.g., 1975, when the system seemed closer to steady
 state. As we do not have complete velocity and thickness data for that
 time period, we focus instead on the most complete data set.
 The spatial pattern of the melt rate B appears noisy on some ice
 shelves, in particular on Brunt-Stancomb or Ross. Part of this signal is
 real and associated with rifts, cracks, and vertical undulations in
 surface elevation present on those shelves. Part of the signal is caused
 by the time difference between ice thickness and ice velocity data and the
 advection of heterogeneities in ice thickness along flow. Furthermore,
 basal melting is expected to be non-uniform across such zones, with
 melting dominant along the rift sides and freezing dominant at the rift
 center. We first calculate the basal melt rates in
 meters per year over the surveyed areas from the GL flux, ice front flux,
 SMB, and ∂H/∂t. The result is then applied to the actual ice shelf area to
 deduce the total ice shelf meltwater production. We then re-calculate SMB
 and ∂H/∂t over the actual ice shelf areas instead of the surveyed area;
 the grounding line fluxes are unchanged because surveyed and actual areas
 share identical GL positions. The ice front fluxes are, however, corrected
 for the adjustment in SMB and ∂H/∂t to ensure closure of the mass balance
 equation. This correction amounts to 30 Gt/yr, i.e., &lt; 3% of the
 total ice front flux, which covers 99.5% of the Antarctic ice shelf
 area. 
 9. Adjustments for ice shelf
 thickening Ice shelf thickening ∂H/∂t is derived using
 corrected ICESat-1 altimetry data for the period 2003-2008, and surface
 mass balance and firn correction data posted at
 dx.doi.org/10.1594/PANGAEA.775984. The analysis follows the method in
 (23). Firn depth corrections provided for 100 ice shelves are interpolated
 to all ice shelves using inverse distance weighting. The results are
 combined with the flux divergence and SMB data to calculate the melt rate
 B. The uncertainty in ice shelf thickening is from (23). Our results are
 consistent with (23). Early in 2013, the National Snow
 and Ice Data Center reported an error of omission in the processing of
 ICESat data that introduces a 5-10 cm error on a pulse-by-pulse basis.
 Application of inter-campaign corrections and averaging over the entire
 time period 2003-2008 reduces the impact of this correction, which should
 not affect the results of this study. 
 We have no estimates of ice shelf
 thickening for a few ice shelves. For Wordie and Ferrigno, we use the
 rates for the adjacent Wilkins and Venable shelves, respectively. Zero
 thickening is assumed for Lillie, Wilma/Robert/Downer, Rayner/Thyer,
 Edward VIII, and Shirase in East Antarctica. Ice shelf thickening for
 Larsen B is based on measurements collected over the remnant part of the
 ice shelf. We verified that if we calculate the sum of
 all ice shelf melt values over an ice shelf and compare that total with
 the difference between the incoming ice flux minus the outgoing calving
 flux plus the net surface balance, minus the net change in ice thickness,
 we find the same total net mass loss. In effect, our estimates conserve
 mass.  
 10. References 1. P. Fretwell et al., Bedmap2:
 Improved ice bed, surface and thickness datasets for Antarctica. The
 Cryosphere 7, 375 (2013). doi:10.5194/tc-7-375-2013 2.
 C. W. Swithinbank, Satellite Image Atlas of Glaciers of the World:
 Antarctica, R. S. Williams, J. G. Ferrigno, Eds. (USGS Prof. Paper 1386-B,
 1988). 3. N. I. Barkov, Ice Shelves of Antarctica (New
 Delhi, NY, Amerind Pub. Co., 1985). 4. R. LeB. Hooke,
 Principles of Glacier Mechanics (Cambridge University Press, Cambridge,
 2005). 5. K. M. Cuffey, W. S. B. Paterson, The Physics
 of Glaciers (Elsevier, Burlington, MA, ed. 4, 2010). 6.
 S. S. Jacobs, H. H. Hellmer, C. S. M. Doake, A. Jenkins, R. M. Frolich,
 Melting of ice shelves and the mass balance of Antarctica. J. Glaciol. 38,
 375 (1992). 7. H. H. Hellmer, Impact of Antarctic ice
 shelf basal melting on sea ice and deep ocean properties. Geophys. Res.
 Lett. 31, L10307 (2004). doi:10.1029/2004GL019506 8. A.
 Jenkins, S. S. Jacobs, Circulation and melting beneath George VI Ice
 Shelf, Antarctica. Geophys. Res. Lett. 113, (C4), C04013 (2008).
 doi:10.1029/2007JC004449 9. S. S. Jacobs, A. Jenkins,
 C. F. Giulivi, P. Dutrieux, Stronger ocean circulation and increased
 melting under Pine Island Glacier ice shelf. Nature Geosc. 4, 519 (2011).
 doi:10.1038/ngeo1188 10. A. Foldvik, T. Gammelsrod, E.
 Nygaard, S. Osterhus, Current measurements near Ronne Ice Shelf:
 Implications for circulation and melting. J. Geophys. Res. Oceans 106,
 (C3), 4463 (2001). doi:10.1029/2000JC000217 11. R.
 Timmermann, Q. Wang, H. H. Hellmer, Ice-shelf basal melting in a global
 finite-element sea-ice/ice-shelf/ocean model. Ann. Glaciol. 53, 303
 (2012). doi:10.3189/2012AoG60A156 12. I. Joughin, L.
 Padman, Melting and freezing beneath Filchner-Ronne Ice Shelf, Antarctica.
 Geophys. Res. Lett. 30, 1477 (2003). doi:10.1029/2003GL016941
 13. J. Wen et al., Basal melting and freezing under the Amery Ice
 Shelf, East Antarctica. J. Glaciol. 56, 81 (2010).
 doi:10.3189/002214310791190820 14. E. Rignot, S. S.
 Jacobs, Rapid bottom melting widespread near Antarctic Ice Sheet grounding
 lines. Science 296, 2020 (2002). doi:10.1126/science.1070942
 Medline 15. A. Jenkins, C. S. M. Doake, Ice ocean
 interaction on Ronne Ice Shelf, Antarctica. J. Geophys. Res. 96, (C1), 791
 (1991). doi:10.1029/90JC01952 16. J. T. M. Lenaerts et
 al., Modeling drifting snow in Antarctica with a regional climate model:
 1. Methods and model evaluation. J. Geophys. Res. 117, (D5), D05108
 (2012). doi:10.1029/2011JD016145 17. E. Rignot et al.,
 Recent mass loss of the Antarctic Ice Sheet from dynamic thinning. Nat.
 Geosci. 1, 106 (2008). doi:10.1038/ngeo102 18. C.
 Allen, IceBridge MCoRDS L2 Ice Thickness. Boulder, Colorado USA: NASA DAAC
 at the National Snow and Ice Data Center (2010). 19. D.
 D. Blankenship, S. Kempf, D. Young, IceBridge HiCARS 2 L2 Geolocated Ice
 Thickness. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice
 Data Center (2012). 20. J. A. Griggs, J. L. Bamber,
 Antarctic ice-shelf thickness from satellite radar altimetry. J. Glaciol.
 57, 485 (2011). doi:10.3189/002214311796905659 21. E.
 Rignot, J. Mouginot, B. Scheuchl, Antarctic grounding line mapping from
 differential satellite radar interferometry. Geophys. Res. Lett. 38,
 L10504 (2011). doi:10.1029/2011GL047109 22. E. Rignot,
 J. Mouginot, B. Scheuchl, Ice flow of the Antarctic ice sheet. Science
 333, 1427 (2011). doi:10.1126/science.1208336 Medline
 23. H. D. Pritchard et al., Antarctic ice-sheet loss driven by
 basal melting of ice shelves. Nature 484, 502 (2012).
 doi:10.1038/nature10968 Medline 24. K. Makinson, P. R.
 Holland, A. Jenkins, K. Nicholls, D. M. Holland, Influence of tides on
 melting and freezing beneath Filchner Ronne Ice Shelf, Antarctica.
 Geophys. Res. Lett. 38, L06601 (2011). doi:10.1029/2010GL046462
 25. H. J. Horgan, R. T. Walker, S. Anandakrishnan, R. B. Alley,
 Surface elevation changes at the front of the Ross Ice Shelf: Implications
 for basal melting. J. Geophys. Res. 116, (C2), C02005 (2011).
 doi:10.1029/2010JC006192 26. A. Shepherd et al., A
 reconciled estimate of ice-sheet mass balance. Science 338, 1183 (2012).
 doi:10.1126/science.1228102 Medline 27. S. Neshyba, E.
 G. Josberger, On the estimation of Antarctic iceberg melt rate. J. Phys.
 Oceanogr. 10, 1681 (1980).
 doi:10.1175/1520-0485(1980)010&lt;1681:OTEOAI&gt;2.0.CO;2 28. K. Grosfeld et al., Marine ice beneath Filchner Ice Shelf: Evidence from a multi-disciplinary approach. Antarct. Res. Ser. 75, 319 (1998). doi:10.1029/AR075p0319 29. M. P. Schodlok, D. Menemenlis, E. Rignot, M. Studinger, Sensitivity of the ice shelf ocean system to the sub-ice shelf cavity shape measured by NASA IceBridge in Pine Island Glacier, West Antarctica. Ann. Glaciol. 53, 156 (2012). doi:10.3189/2012AoG60A073 30. G. D. Williams et al., Late winter oceanography off the Sabrina and BANZARE coast (117– 1281°E), East Antarctica. Deep Sea Res. Part II Top. Stud. Oceanogr. 58, 1194 (2011). doi:10.1016/j.dsr2.2010.10.035 31. P. R. Holland, A. Jenkins, D. Holland, Ice and ocean processes in the Bellingshausen Sea, Antarctica. Geophys. Res. Lett. 115, (C5), C05020 (2010). doi:10.1029/2008JC005219 32. L. Padman et al., Oceanic controls on the mass balance of Wilkins Ice Shelf, Antarctica. J. Geophys. Res. 117, (C1), C01010 (2012). doi:10.1029/2011JC007301 33. P. R. Holland, H. F. J. Corr, D. G. Vaughan, A. Jenkins, P. Skvarca, Marine ice in Larsen Ice Shelf. Geophys. Res. Lett. 36, L11604 (2009). doi:10.1029/2009GL038162 34. P. R. Holland, A. Jenkins, D. M. Holland, The response of ice shelf basal melting to variations in ocean temperature. J. Clim. 21, 2558 (2008). doi:10.1175/2007JCLI1909.1 35. H. H. Hellmer, F. Kauker, R. Timmermann, J. Determann, J. Rae, Twenty-first-century warming of a large Antarctic ice-shelf cavity by a redirected coastal current. Nature 485, 225 (2012). doi:10.1038/nature11064 Medline 36. T. A. Scambos, T. M. Haran, M. A. Fahnestock, T. H. Painter, J. Bohlander, MODIS-based Mosaic of Antarctica (MOA) data sets: Continent-wide surface morphology and snow grain size. Remote Sens. Environ. 111, 242 (2007). doi:10.1016/j.rse.2006.12.020 37. R. A. Bindschadler et al., Getting around Antarctica: New high-resolution mappings of the grounded and freely-floating boundaries of the Antarctic Ice Sheet created for the International Polar Year. The Cryosphere 5, 569 (2011). doi:10.5194/tc-5-569-2011 38. J. Mouginot, B. Scheuchl, E. Rignot, Mapping of ice motion in Antarctica using synthetic- aperture radar data. Remote Sens. 4, 2753 (2012). doi:10.3390/rs4092753 39. R. J. Motyka, L. Hunter, K. A. Echelmeyer, C. Connor, Submarine melting at the terminus of a temperate tide-water glacier, LeConte Glacier, Alaska. Ann. Glaciol. 36, 57 (2003). doi:10.3189/172756403781816374 40. E. Rignot, M. Koppes, I. Velicogna, Rapid submarine melting of the calving faces of west Greenland glaciers. Nat. Geosci. 3, 187 (2010). doi:10.1038/ngeo765 41. A. J. Fox, A. Paul, R. Cooper, Measured properties of the Antarctic Ice Sheet derived from the SCAR Antarctic digital database. Polar Rec. (Gr. Brit.) 30, 201 (1994). doi:10.1017/S0032247400024268 42. A. J. Cook, D. G. Vaughan, Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere 4, 77 (2010). doi:10.5194/tc-4-77-2010 43. T. Gammelsrød et al., Distribution of water masses on the continental shelf in the southern Weddell Sea, in The Polar Oceans and Their Role in Shaping the Global Environment, Geophys. Monogr. Ser., vol. 85, O. M. Johannessen, R. D. Muench, J. E. Overland (Eds.), pp. 159–176 (AGU, Washington, D. C., 1994), pp. 159–176; doi:10.1029/GM085p0159. 44. P. Schlosser et al., Oxygen 18 and helium as tracers of ice shelf water and water/ice interaction in the Weddell Sea. J. Geophys. Res. 95, (C3), 3253 (1990). doi:10.1029/JC095iC03p03253 45. A. S. Shepherd et al., Recent loss of floating ice and the consequent sea level contribution. Geophys. Res. Lett. 37, L13503 (2010). doi:10.1029/2010GL042496 46. R. H. Thomas et al., A comparison of Greenland ice-sheet volume changes derived from altimetry measurements. J. Glaciol. 54, 203 (2008). doi:10.3189/002214308784886225 47. E. J. Rignot, Fast recession of a west Antarctic glacier. Science 281, 549 (1998). doi:10.1126/science.281.5376.549 Medline 48. A. J. Payne et al., Numerical modeling of ocean-ice interactions under Pine Island Bay’s ice shelf. J. Geophys. Res. 112, (C10), C10019 (2007). doi:10.1029/2006JC003733 49. C. S. M. Doake, Glaciological Evidence: Antarctic Peninsula, Weddell Sea; Glaciers, Ice Sheets, and Sea Level: Effect of a CO2-induced Climatic Change, Seattle Workshop, Washington, 13-15 Sep 1984, USDOE/ER/60235-1, 197-209, (1985) 50. S. S. Jacobs, H. H. Hellmer, A. Jenkins, Antarctic ice sheet melting in the southeast Pacific. Geophys. Res. Lett. 23, 957 (1996). doi:10.1029/96GL00723 51. R. Gerdes, J. Determann, K. Grosfeld, Ocean circulation beneath Filchner-Ronne Ice Shelf from three-dimensional model results. J. Geophys. Res. 104, (C7), 15,827 (1999). doi:10.1029/1999JC900053 52. K. W. Nicholls et al., Water mass modification over the continental shelf north of Ronne Ice Shelf, Antarctica. J. Geophys. Res. 108, (C8), 3260 (2003). doi:10.1029/2002JC001713 53. A. Jenkins, D. G. Vaughan, S. S. Jacobs, H. H. Hellmer, J. R. Keys, Glaciological and oceanographic evidence of high melt rates beneath Pine Island Glacier, West Antarctica. J. Glaciol. 43, 114 (1997). 54. H. H. Hellmer, S. S. Jacobs, A. Jenkins, Oceanic erosion of a floating Antarctic glacier in the Amundsen Sea. Antarct. Res. Ser. 75, 83 (1998). doi:10.1029/AR075p0083 55. A. Shepherd, D. Wingham, E. Rignot, Warm ocean is eroding West Antarctic Ice Sheet. Geophys. Res. Lett. 31, L23402 (2004). doi:10.1029/2004GL021106 56. R. A. Bindschadler, D. G. Vaughan, P. Vornberger, Variability of basal melt beneath the Pine Island Glacier ice shelf, West Antarctica. J. Glaciol. 57, 581 (2011). doi:10.3189/002214311797409802 57. P. Heimbach, M. Losch, Adjoint sensitivities of sub-ice-shelf melt rates to ocean circulation under the Pine Island Ice Shelf, West Antarctica. Ann. Glaciol. 53, 59 (2012). doi:10.3189/2012/AoG60A025 58. T. Hughes, The Stability of the West Antarctic Ice Sheet: What has happened and what will happen, Proceedings, Carbon Dioxide Research Conference: CO2, Science and Consensus, Berkeley Springs Workshop, 19-23 Sep 1982, USDOE, 820970-021, DE- AC05-76OR00033, 021, IV.62 (1983).
description: # Ice-shelf melting around Antarctica
 [https://doi.org/10.5061/dryad.5hqbzkhg2](https://doi.org/10.5061/dryad.5hqbzkhg2) ## Description of the data and file structure #### File: Ant\_MeltingRate.v2.nc **Ice-Shelf Melting Around Antarctica** The file is a netcdf file in Polar Stereographic format, with a coordinate reference system (CRS) EPSG:3031, 5,000 meters posting, 5601 columns x 5601 rows, origin at -2,800,000 meters, +2,800,000 meters. 1. lat: Latitude of grid points in degrees, 2d array, floating point, from -90 to -54.7 deg.  2. lon: Longitude of grid points in degrees, 2d array, floating point, from 0 to 360 degrees.  3. melt_actual: Actual melt rate B in meters per year, 2d array, floating point, from -10.44724 to +158.4632 m/yr 4. melt_steadystate: Steady state (no thickening) melt rate B in meters per year, 2d array, floating point, from -9.025163 to +152.8616 m/yr 5. xaxis: x values of grid in meters, 1d array, floating point, from -2,800,000 meters, +2,800,000 meters. 6. yaxis: y values of grid in meters, 1d array, floating point, from -2,800,000 meters, +2,800,000 meters. ## Code/software NA  ## Access information NA