Description: LiDAR scanning of the Yukon Coast and Herschel Island took place during the AIRMETH (AIRborne studies of METHane emissions from Arctic wetlands) campaigns (Kohnert et al., 2014) on 10 July 2012 and on 22 July 2013. Point cloud data were acquired with a RIEGL LMSVQ580 laser scanner instrument on board the Alfred Wegener Institute's POLAR-5 science aircraft. The laser scanner was operated with a 60° scan angle at a flight height of around 200 m above ground in 2012 and 500 m in 2013. This resulted in a scan width from 200 (2012) to 500 m (2013) and a mean point-to-point distance of 0.5–1.0 m. During the flight on July 10, 2012 the weather was cloudy with a cloud base around 200 m.a.s.l. . Air temperature ranged between 10 and 12 °C with wind speed ranging from 15 to 19 km/h from easterly direction (70–90°). The last recorded storm was on June 17. During the scanning on July 22, 2013, the weather was nearly cloudless with air temperature 9 °C. Wind speed was 15 km/h from easterly direction (60–80°). The last storm before the acquisition occurred on July 2. Raw laser data were calibrated, combined with the post-processed GPS trajectory, corrected for altitude, and referenced to the EGM (Earth Gravitational Model) 2008 geoid (Pavlis et al., 2008). The final georeferenced point cloud data accuracy was determined to be better than 0.15 ± 0.1 m. The loss of accuracy varied along the flight track because of the vertical accuracy of the post-processed GPS trajectory. The GPS datawere acquired in 50Hz resolutionwith aNovatel OEM4 receiver on board POLAR-5. The GPS trajectory was post-processed using precise ephemerides and the commercial software package Waypoint 8.5 (PPP [precise point positioning] processing). For the interpolation to the final DEM an inverse distance weighting (IDW) algorithm was applied using all cloud points within a 10 m radius of each point. Finally, the DEMs from the different acquisition years were interpolated toraster grids of 1 m horizontal resolution in NAD83 UTM zone 7 coordinate system. To quantify vertical change that is significant at the 99% confidence interval, we used three times RMS error procedure by Jaw (2001). Vertical accuracies for both datasets were estimated to be 0.15 m, which results in the threshold of 0.64 m for significant vertical elevation change. The accuracy of the datasets was additionally tested at locations characterized by the presence of anthropogenic features that presumably remain stable and are not affected by vertical movements because of artificial embankments underneath them. The differences between both DEM datasets were assessed along profiles and were within the previously-stated 0.15 m uncertainty.

Description: Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula (AP), foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic (EA) ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the AP, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal EA high temperatures are caused by persistent katabatic winds originating from the ice sheet's interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining 〉3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared to its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in-situ observation of supraglacial flow and englacial storage of meltwater suggests that ice shelf grounding zones in EA, like their AP counterparts, are vulnerable to hydrofracturing.

Description: Estimating the contribution of ice sheets to sea level change is a major goal of glaciologists and of high interest for the public. For this purpose we analyse altimeter data of different satellite-borne satellites with a main focus on CryoSat-2 and estimate by this the volume change and as a final product the mass change using a firn densification model. For the assessment of the contribution of ice sheets to sea level change robust, consistent processing, as well as the estimation of uncertainties is important. There are numerous sources for uncertainty, ranging from instrumental errors, different processing approaches towards the interpolation between sparsely distributed data. This presentation focuses on the present-day ice-volume changes of the Greenland and Antarctic ice sheets. Based on five years (January 2011 to January 2016) of CryoSat-2 data acquisition we derived elevation change maps and finally volume and mass change estimates for both ice sheets. We will present a set of estimates derived from different processing approaches and interpolation methods. Additional we will compare our results to elevation change rates obtained from ICESat data covering the time period from 2003 to 2009. In contrast to our study of 2014 we extended the time series of CryoSat-2 by two years, used the new data release 34 of ICESat and implemented the output of the firn densification models of the Institute for Marine and Atmospheric research Utrecht (IMAU). The new results will be presented and compared.

Description: Surface elevation measurements from CryoSat-2 data were examined to determine their utility for measuring ice sheet grounding line locations and ice thickness in Antarctica. The boundary between grounded and floating ice is an important glaciological parameter, because it delineates the lateral extent of an ice sheet and it marks the optimal location for computing ice discharge. We present a method for detecting the grounding line as the break in ice sheet surface slope, computed from CryoSat-2 elevation measurements using a plane-fitting solution. Furthermore we measure ice thickness at the grounding line using firn corrected CryoSat-2 data based on the theory of hydrostatic equilibrium. We apply these techniques to map the break in surface slope and ice shelf thickness at the grounding line in four topographically diverse sectors of Antarctica - the Filchner-Ronne ice shelf, the Ekström ice shelf, the Amundsen Sea Sector, and the Larsen-C ice shelf - using CryoSat-2 observations acquired between July 2010 and May 2014. An inter-comparison of the CryoSat-2 break in surface slope with independent measurements of the hinge line position determined from quadruple-difference synthetic aperture radar interferometry (QDInSAR) shows good overall agreement, with a mean separation of 4.5 km. In the Amundsen Sea Sector, where in places over 35 km of hinge line retreat has occurred since 1992. The CryoSat-2 break in surface slope coincides with the most recent hinge line position, recorded in 2011. Ice shelf ice thickness measurements are validated with Radio Echo Sounding (RES) point data and show good overall agreement with BEDMAP 2 ice thickness data. The techniques we have developed are automatic, computationally-efficient, and can be repeated in the future given further data acquisitions offering a complimentary approach to existing techniques.

Description: User documentation of the AWI CryoSat-2 sea ice data product (v1.2, July 2016)

Description: Knowledge about Antarctic sea-ice volume and its changes over the past decades has been sparse due to the lack of systematic sea-ice thickness measurements in this remote area. Recently, first attempts have been made to develop a sea-ice thickness product over the Southern Ocean from space-borne radar altimetry and results look promising. Today, more than 20 years of radar altimeter data are potentially available for such products. However, the characteristics of individual radar types differ for the available altimeter missions. Hence, it is important and our goal to study the consistency between single sensors in order to develop long and consistent time series. Here, the consistency between freeboard measurements of the Radar Altimeter 2 on board Envisat and freeboard measurements from the Synthetic-Aperture Interferometric Radar Altimeter on board CryoSat-2 is tested for their overlap period in 2011. Results indicate that mean and modal values are in reasonable agreement over the sea-ice growth season (May–October) and partly also beyond. In general, Envisat data show higher freeboards in the first-year ice zone while CryoSat-2 freeboards are higher in the multiyear ice zone and near the coasts. This has consequences for the agreement in individual sectors of the Southern Ocean, where one or the other ice class may dominate. Nevertheless, over the growth season, mean freeboard for the entire (regionally separated) Southern Ocean differs generally by not more than 3 cm (8 cm, with few exceptions) between Envisat and CryoSat-2, and the differences between modal freeboards lie generally within ±10 cm and often even below.

Description: Arctic coastal infrastructure, cultural, and archeological sites are increasingly vulnerable to erosion and flooding due to amplified warming of the Arctic, sea level rise, lengthening of open water periods, and a predicted increase in frequency of major storms. Mitigating these hazards necessitates decision-making tools at an appropriate scale. The objectives of this study were to assess potential erosion and flood hazards at Herschel Island, a UNESCO World Heritage candidate site, and produce a map to be used as a decision making tool. The study focused on Simpson Point and the adjacent coastal sections, because of their archeological, historical, and cultural significance. Shoreline movement was analyzed using the Digital Shoreline Analysis System (DSAS) after digitizing shorelines from 1952, 1970, 2000, and 2011. For purposes of this analysis, the coast was divided in seven coastal reaches (CRs) reflecting different morphologies and/or exposures. Using linear regression rates obtained from these data, projections of shoreline position were made for 20 and 50 years into the future. Flood hazard was assessed using a least cost-path analysis based on a high-resolution Light Detection and Ranging (LiDAR) dataset and current Intergovernmental Panel on Climate Change sea level estimates. Widespread erosion characterizes the study area. The rate of shoreline movement in different periods of the study ranges from -5.5 to 2.7 m·a-1 (mean -0.6 m·a-1). Mean coastal retreat decreased from -0.6 m·a-1 to -0.5 m·a-1, for 1952-1970 and 1970-2000, respectively, and increased to -1.3 m·a-1 in the period 2000-2011. Ice-rich coastal sections most exposed to wave attack exhibited the highest rates of coastal retreat. The geohazard map combines shoreline projections and flood hazard analyses to show that most of the spit area has extreme or very high flood hazard potential, and some buildings are vulnerable to coastal erosion.

Description: We present spatiotemporal mass balance trends for the Antarctic Ice Sheet from a statistical inversion of satellite altimetry, gravimetry, and elastic-corrected GPS data for the period 2003–2013. Our method simultaneously determines annual trends in ice dynamics, surface mass balance anomalies, and a time-invariant solution for glacio-isostatic adjustment while remaining largely independent of forward models. We establish that over the period 2003–2013, Antarctica has been losing mass at a rate of −84 ± 22 Gt yr−1, with a sustained negative mean trend of dynamic imbalance of −111 ± 13 Gt yr−1. West Antarctica is the largest contributor with −112 ± 10 Gt yr−1, mainly triggered by high thinning rates of glaciers draining into the Amundsen Sea Embayment. The Antarctic Peninsula has experienced a dramatic increase in mass loss in the last decade, with a mean rate of −28 ± 7 Gt yr−1 and significantly higher values for the most recent years following the destabilization of the Southern Antarctic Peninsula around 2010. The total mass loss is partly compensated by a significant mass gain of 56 ± 18 Gt yr−1 in East Antarctica due to a positive trend of surface mass balance anomalies.