Description: Recovery Glacier reaches far into the East Antarctic Ice Sheet. Recent projections point out that its dynamic behaviour has a considerable impact on future Antarctic ice loss (Golledge et al. 2017). Subglacial lakes are thought to play a major role in the initiation of the rapid ice flow (Bell et al. 2007). Satellite altimetry observations have even suggested several actively filling and draining subglacial lakes beneath the main trunk (Smith et al. 2009). We present new data of the geometry of this glacier and investigate its basal properties employing radio-echo sounding. Using ice-sheet modelling, we were able to constrain estimates of radar absorption in the ice, but uncertainties remain large. The magnitude of the basal reflection coefficient is thus still poorly known. However, its spatial variability, in conjunction with additional indicators, can be used to infer the presence of subglacial water. We find no clear evidence of water at most of the previously proposed lake sites. Especially locations where altimetry detected active lakes, do not exhibit lake characteristics in RES. We argue that lakes far upstream the main trunk are not triggering enhanced ice flow, which is also supported by modeled subglacial hydrology.

Description: We assess the basal conditions of the onset region of the Northeast Greenland Ice Stream (NEGIS) in a systematic analysis of airborne ultra-wideband radar data. We evaluate basal roughness and basal return echoes as well as hydraulic pathways in the context of the current ice stream geometry and ice surface velocity. The data comprises three individual datasets: 1) Spectral subglacial bed roughness data 2) Bed return power (BRP) and waveform abruptness data 3) Hydropotential and subglacial water routing data (geotiff and nc files) Email address of the provider: steven.franke@awi.de, daniela.jansen@awi.de, olaf.eisen@awi.de

Description: Support Force Glacier (SFG) is a large ice stream feeding into the Filchner Ice Shelf. The active seismic survey is recorded at the sheet-shelf transition of SFG. We map the bed while grounded, the ocean cavity around a surface channel at the ice shelf and its counterpart at the base, the basal channel, and the seabed. The survey consists of 5 seismic reflection profiles, 2 along-flow profiles and 3 across-flow profiles. The 2.42GB seismic data were recorded with a 300 m long streamer consisting of 96 30Hz p-wave sensors. The sample rate is 0.5 ms, record length 3000 ms. The data is single fold, shot spacing is 150 m: line name: profile TC paper: direction: #shots: - 20170501 profile I along-flow 291 shots - 20170502 profile III across-flow 28 shots - 20170503 profile II along-flow 71 shots - 20170504 profile IV across-flow 40 shots - 20170506 profile V across-flow 50 shots Presented are for each line (20170501 used as example): - The raw shots: 20170501_RAW_SHOTS_EDITS_GEOM.segy - The Kirchhoff migrated and depth converted profiles: 20170501stat_TXmig_Zconv.segy - The shot x,y,z coordinates in longitude, latitude and surface height in meters above sea level (z, WGS84 ellipsoid): 20170501_GPS.txt

Description: We introduce the coupled model of the Green- land glacial system IGLOO 1.0, including the polythermal ice sheet model SICOPOLIS (version 3.3) with hybrid dy- namics, the model of basal hydrology HYDRO and a param- eterization of submarine melt for marine-terminated outlet glaciers. The aim of this glacial system model is to gain a better understanding of the processes important for the future contribution of the Greenland ice sheet to sea level rise under future climate change scenarios. The ice sheet is initialized via a relaxation towards observed surface elevation, impos- ing the palaeo-surface temperature over the last glacial cycle. As a present-day reference, we use the 1961–1990 standard climatology derived from simulations of the regional atmo- sphere model MAR with ERA reanalysis boundary condi- tions. For the palaeo-part of the spin-up, we add the temper- ature anomaly derived from the GRIP ice core to the years 1961–1990 average surface temperature field. For our pro- jections, we apply surface temperature and surface mass bal- ance anomalies derived from RCP 4.5 and RCP 8.5 scenar- ios created by MAR with boundary conditions from simula- tions with three CMIP5 models. The hybrid ice sheet model is fully coupled with the model of basal hydrology. With this model and the MAR scenarios, we perform simulations to estimate the contribution of the Greenland ice sheet to future sea level rise until the end of the 21st and 23rd centuries. Fur- ther on, the impact of elevation–surface mass balance feed- back, introduced via the MAR data, on future sea level rise is inspected. In our projections, we found the Greenland ice sheet to contribute between 1.9 and 13.0 cm to global sea level rise until the year 2100 and between 3.5 and 76.4 cm until the year 2300, including our simulated additional sea level rise due to elevation–surface mass balance feedback. Translated into additional sea level rise, the strength of this feedback in the year 2100 varies from 0.4 to 1.7 cm, and in the year 2300 it ranges from 1.7 to 21.8 cm. Additionally, taking the Helheim and Store glaciers as examples, we inves- tigate the role of ocean warming and surface runoff change for the melting of outlet glaciers. It shows that ocean temper- ature and subglacial discharge are about equally important for the melting of the examined outlet glaciers.

Description: Subglacial hydrology plays an important role in ice sheet dynamics as it determines the sliding velocity. It also drives freshwater into the ocean, leading to undercutting of calving fronts by plumes. Modeling subglacial water has been a challenge for decades. Only recently have new approaches been developed such as representing subglacial channels and thin water sheets by separate layers of variable hydraulic conductivity. We extend this concept by modeling a confined–unconfined aquifer system (CUAS) in a single layer of an equivalent porous medium (EPM). The advantage of this formulation is that it prevents unphysical values of pressure at reasonable computational cost. We performed sensitivity tests to investigate the effect of different model parameters. The strongest influence of model parameters was detected in terms of governing the opening and closure of the system. Furthermore, we applied the model to the Northeast Greenland Ice Stream, where an efficient system independent of seasonal input was identified about 500km downstream from the ice divide. Using the effective pressure from the hydrology model, the Ice Sheet System Model (ISSM) showed considerable improvements in modeled velocities in the coastal region.