The Antarctic Ice Sheet is an important indicator of climate change and driver of sea-level rise. Here we combine satellite observations of its changing volume, flow and gravitational attraction with modelling of its surface mass balance to show that it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). Over this period, ocean-driven melting has caused rates of ice loss from West Antarctica to increase from 53 ± 29 billion to 159 ± 26 billion tonnes per year; ice-shelf collapse has increased the rate of ice loss from the Antarctic Peninsula from 7 ± 13 billion to 33 ± 16 billion tonnes per year. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment for East Antarctica, with its average rate of mass gain over the period 1992–2017 (5 ± 46 billion tonnes per year) being the least certain.

/pdf/mass-balance-of-the-antarctic-ice-sheet-from-1992-to-2017-49s3lh63iz.pdf

Mass balance of the Antarctic ice sheet from 1992 to 2017.

VIIRS Data and Data Access at the NASA National Snow and Ice Data Center Distributed Active Archive Center

Mass changes of the Antarctic ice sheet impact sea-level rise as climate changes, but recent rates have been uncertain. Ice, Cloud and land Elevation Satellite (ICESat) data (2003–08) show mass gains from snow accumulation exceeded discharge losses by 82 ± 25 Gt a−1, reducing global sea-level rise by 0.23 mm a−1. European Remote-sensing Satellite (ERS) data (1992–2001) give a similar gain of 112 61 Gt a−1. Gains of 136 Gt a−1 in East Antarctica (EA) and 72 Gt a−1 in four drainage systems (WA2) in West Antarctic (WA) exceed losses of 97 Gt a−1 from three coastal drainage systems (WA1) and 29 Gt a−1 from the Antarctic Peninsula (AP). EA dynamic thickening of 147 Gt a−1 is a continuing response to increased accumulation (>50%) since the early Holocene. Recent accumulation loss of 11 Gt a−1 in EA indicates thickening is not from contemporaneous snowfall increases. Similarly, the WA2 gain is mainly (60 Gt a−1) dynamic thickening. In WA1 and the AP, increased losses of 66 ± 16 Gt a−1 from increased dynamic thinning from accelerating glaciers are 50% offset by greater WA snowfall. The decadal increase in dynamic thinning in WA1 and the AP is approximately one-third of the long-term dynamic thickening in EA and WA2, which should buffer additional dynamic thinning for decades.

/pdf/mass-gains-of-the-antarctic-ice-sheet-exceed-losses-2zd9chyyrr.pdf

Mass gains of the Antarctic ice sheet exceed losses

. We developed a multi-mission satellite altimetry analysis over the Antarctic
Ice Sheet which comprises Seasat, Geosat, ERS-1, ERS-2, Envisat, ICESat and
CryoSat-2. After a consistent reprocessing and a stepwise calibration of the
inter-mission offsets, we obtained monthly grids of multi-mission surface
elevation change (SEC) with respect to the reference epoch
09/2010 (in the format of month/year) from 1978 to 2017. A validation with independent elevation
changes from in situ and airborne observations as well as a comparison with a
firn model proves that the different missions and observation modes have been
successfully combined to a seamless multi-mission time series. For coastal
East Antarctica, even Seasat and Geosat provide reliable information and,
hence, allow for the analysis of four decades of elevation changes. The
spatial and temporal resolution of our result allows for the identification
of when and where significant changes in elevation occurred. These time
series add detailed information to the evolution of surface elevation in such
key regions as Pine Island Glacier, Totten Glacier, Dronning Maud Land or
Lake Vostok. After applying a density mask, we calculated time series of mass
changes and found that the Antarctic Ice Sheet north of 81.5 ∘  S was
losing mass at an average rate of - 85 ± 16  Gt yr −1 between 1992 and
2017, which accelerated to - 137 ± 25  Gt yr −1 after 2010.

/pdf/four-decades-of-antarctic-surface-elevation-changes-from-4kj1e0poq6.pdf

Four decades of Antarctic surface elevation changes from multi-mission satellite altimetry

Monitoring the variation of rivers and lakes is of great importance. Satellite radar altimetry is a promising technology to do this on a regional to global scale. Satellite radar altimetry data has been used successfully to observe water levels in lakes and (large) rivers, and has also been combined with hydrologic/hydrodynamic models. Except CryoSat-2, all radar altimetry missions have been operated in conventional low resolution mode with a short repeat orbit (35 days or less). CryoSat-2, carrying a Synthetic Aperture Radar (SAR) altimeter, has a 369-day repeat and a drifting ground track pattern and provides new opportunities for hydrologic research. The narrow inter-track distance (7.5 km at the equator) makes it possible to monitor many lakes and rivers and SAR mode provides a finer along-track resolution, higher return power and speckle reduction through multi-looks. However, CryoSat-2 challenges conventional ways of dealing with satellite inland water altimetry data because virtual station time series cannot be directly derived for rivers. We review the CryoSat-2 mission characteristics, data products, and its use and perspectives for inland water applications. We discuss all the important steps in the workflow for hydrologic analysis with CryoSat-2, and conclude with a discussion of promising future research directions.

/pdf/cryosat-2-altimetry-applications-over-rivers-and-lakes-2pmxgwqclf.pdf

CryoSat-2 Altimetry Applications over Rivers and Lakes

. Ice-surface elevation profiles of more than 30 000 km in total length are derived from kinematic GNSS (GPS and the Russian GLONASS) observations on sledge convoy vehicles along traverses between Vostok Station and the East Antarctic coast. These profiles have accuracies between 4 and 9 cm. They are used to validate elevation data sets from both radar and laser satellite altimetry as well as four digital elevation models. A crossover analysis with three different processing versions of Envisat radar altimetry elevation profiles yields a clear preference for the relocation method over the direct method of slope correction and for threshold retrackers over functional fit algorithms. The validation of CryoSat-2 low-resolution mode and SARIn mode data sets documents the progress made from baseline B to C elevation products. ICESat laser altimetry data are demonstrated to be accurate to a few decimetres over a wide range of surface slopes. A crossover adjustment in the region of subglacial Lake Vostok combining ICESat elevation data with our GNSS profiles yields a new set of ICESat laser campaign biases and provides new, independent evidence for the stability of the ice-surface elevation above the lake. The evaluation of the digital elevation models reveals the benefits of combining laser and radar altimetry.

/pdf/validation-of-satellite-altimetry-by-kinematic-gnss-in-41f3kxmh0s.pdf

Validation of satellite altimetry by kinematic GNSS in central East Antarctica

Height changes of the ice surface above subglacial Lake Vostok, East Antarctica, reflect the integral effect of different processes within the subglacial environment and the ice sheet. Repeated GNSS (Global Navigation Satellite Systems) observations on 56 surface markers in the Lake Vostok region spanning 11 years and continuous GNSS observations at Vostok station over 5 years are used to determine the vertical firn particle movement. Vertical marker velocities are derived with an accuracy of 1 cm/yr or better. Repeated measurements of surface height profiles around Vostok station using kinematic GNSS observations on a snowmobile allow the quantification of surface height changes at 308 crossover points. The height change rate was determined at 1 ± 5 mm/yr, thus indicating a stable ice surface height over the last decade. It is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period. The continuous GNSS observations demonstrate that the particle heights vary linearly with time. Nonlinear height changes do not exceed ±1 cm at Vostok station and constrain the magnitude of spatiotemporal lake-level variations. ICESat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters. Assuming the ice sheet to be in steady state over the entire lake, estimates for the surface accumulation, on basal accretion/melt rates and on flux divergence, are derived.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014JF003228

Height changes over subglacial Lake Vostok, East Antarctica: Insights from GNSS observations

. We present the results of glaciological investigations in the megadune area located 30 km to the east of Vostok Station (central East Antarctica) implemented during the 58th, 59th and 60th Russian Antarctic Expedition (January 2013–2015). Snow accumulation rate and isotope content (δD, δ18O and δ17O) were measured along the 2 km profile across the megadune ridge accompanied by precise GPS altitude measurements and ground penetrating radar (GPR) survey. It is shown that the spatial variability of snow accumulation and isotope content covaries with the surface slope. The accumulation rate regularly changes by 1 order of magnitude within the distance

/pdf/non-climatic-signal-in-ice-core-records-lessons-from-1bmy5gt4tu.pdf

Non-climatic signal in ice core records: lessons from Antarctic megadunes

Ocean tides are an important phenomenon that has to be considered in a variety of geoscientific investigations in polar regions. Using ocean tide models, appropriate corrections can be calculated and applied in the different analyses, e.g. to infer temporal mass variations from satellite data, to investigate ice-shelf dynamics and deformation, to come up with precise station positions and velocities within a terrestrial reference system. However, those models show larger uncertainties in the polar seas and at areas covered by ice shelves and, therefore, need to be improved. Within this context, tidal gravimetry provides a powerful tool to validate ocean tide models. Sensing the cumulative signal of different effects (solid earth tides, ocean tidal loading, atmospheric loading) tidal gravimetry can be regarded as an independent observation technique and thus complements continuous GPS measurements. This paper reviews the background and the work done so far by the authors in Greenland and in Antarctica. Within a current project tidal gravimetry is applied at the Argentine Antarctic stations Belgrano II and San Martin. This joint Argentine-German project is a contribution to the IPY project POLENET. The set-up of the instruments in Belgrano II as well as first results of the ongoing observations, started February 2007, are presented. We discuss the problem of observing ocean tides in the area of the glacier near Belgrano II, which is – at least in parts – freely floating.

Lutz Eberlein

Papers

Validation of satellite altimetry by kinematic GNSS in central East Antarctica

Height changes over subglacial Lake Vostok, East Antarctica: Insights from GNSS observations

Non-climatic signal in ice core records: lessons from Antarctic megadunes

Tidal Gravimetry in Polar Regions: An Observation Tool Complementary to Continuous GPS for the Validation of Ocean Tide Models

Geodetic GNSS measurements as a basis for geodynamic and glaciological research in Antarctica