Ice Mass Balance Research Articles

Ice and groundwater effects on long term polar motion (1979–2010)

We examine Earth’s polar motion (PM) for the years 1979–2010 to understand climate related sources of PM excitation at periods longer than a year, and to investigate Antarctic and Greenland ice mass balance contributions to long period PM. There is particular interest in years prior to the GRACE mission (prior to 2002). Although long period PM is dominantly a measure of changes in two spherical harmonic Stokes coefficients (ΔC21 and ΔS21), we remove excitations due to winds and currents by estimating them from ERA-Interim winds and GECCO2 currents. PM estimates of ΔC21 and ΔS21 are compared with model estimates of contributions from the atmosphere, oceans, water stored on the continents, and polar ice sheets. We also include contributions from groundwater depletion and mountain glaciers. PM Stokes coefficient variations agree very well with model estimates over inter-annual time scales. For ΔC21 we find good agreement at long periods, with a common long-period (quadratic) variation, but not for ΔS21. This suggests deficiencies in understanding long period ice mass variations in Antarctica and/or groundwater mass changes in Eurasia and North America.

Uncertainty of GRACE-borne long periodic and secular ice mass variations in Antarctica

Glacial ice mass balance of Antarctica can be observed by the twin satellites of the gravity recovery and climate experiment (GRACE). The gravity fields with monthly resolution enable efficient detection of annual, long periodic and secular variations. The present study delivers an error estimation of the long-periodic and secular variations by determining the linear trend of the observed surface mass anomaly series. Among the error sources, the error of the timing of the trend fitting, the error of the glacial isostatic adjustment correction, and the error of the atmospheric correction of the GRACE monthly solutions are discussed. The investigation concludes that apart from West Antarctica, Wilkes Land, Queen Maud Land and Enderby Land no reliable trend estimates of ice mass variation can be expected, thus any results should be treated with care.

Contributions of growth and deformation to monthly variability in sea ice thickness north of the coasts of Greenland and the Canadian Arctic Archipelago

AbstractRegional variability in monthly CryoSat‐2 sea ice thickness is partitioned into contributions from dynamics and thermodynamics using ice deformation calculated from large‐scale ice drift. For five winters (December to April, 2011–2015), over a region of persistent convergence north of the coasts of Greenland and the Canadian Arctic Archipelago, deformation explains ~34% of the overall variance (up to 69% in 2014/2015) in monthly thickness changes. Approximately 42–56% (or ~ 0.6 m) of the seasonal changes in mean regional ice thickness can be attributed to divergence and shear. The estimated area‐averaged growth of 0.12 ± 0.03 m/month compares favorably with measurements from ice mass balance buoys. Examination of the time‐variable thickness distributions shows areas covered by ice < 3 m are reduced, while areas of thicker ice (>3 m) increased. Albeit at fairly coarse resolution, this coupled analysis of thickness changes and deformation offered a first look at the character of the regional thickness redistribution process.

Discovery of relict subglacial lakes and their geometry and mechanism of drainage.

Recent proxy measurements reveal that subglacial lakes beneath modern ice sheets periodically store and release large volumes of water, providing an important but poorly understood influence on contemporary ice dynamics and mass balance. This is because direct observations of how lake drainage initiates and proceeds are lacking. Here we present physical evidence of the mechanism and geometry of lake drainage from the discovery of relict subglacial lakes formed during the last glaciation in Canada. These palaeo-subglacial lakes comprised shallow (<10 m) lenses of water perched behind ridges orientated transverse to ice flow. We show that lakes periodically drained through channels incised into bed substrate (canals). Canals sometimes trend into eskers that represent the depositional imprint of the last high-magnitude lake outburst. The subglacial lakes and channels are preserved on top of glacial lineations, indicating long-term re-organization of the subglacial drainage system and coupling to ice flow.

PHOTOGRAMMETRIC ACCURACY AND MODELING OF ROLLING SHUTTER CAMERAS

Abstract. Global climate change is one of the major challenges that all nations are commonly facing. Long-term observations of the Antarctic ice sheet have been playing a critical role in quantitatively estimating and predicting effects resulting from the global changes. The film-based ARGON reconnaissance imagery provides a remarkable data source for studying the Antarctic ice-sheet in 1960s, thus greatly extending the time period of Antarctica surface observations. To deal with the low-quality images and the unavailability of camera poses, a systematic photogrammetric approach is proposed to reconstruct the interior and exterior orientation information for further glacial mapping applications, including ice flow velocity mapping and mass balance estimation. Some noteworthy details while performing geometric modelling using the ARGON images were introduced, including methods and results for handling specific effects of film deformation, damaged or missing fiducial marks and calibration report, automatic fiducial mark detection, control point selection through Antarctic shadow and ice surface terrain analysis, and others. Several sites in East Antarctica were tested. As an example, four images in the Byrd glacier region were used to assess the accuracy of the geometric modelling. A digital elevation model (DEM) and an orthophoto map of Byrd glacier were generated. The accuracy of the ground positions estimated by using independent check points is within one nominal pixel of 140 m of ARGON imagery. Furthermore, a number of significant features, such as ice flow velocity and regional change patterns, will be extracted and analysed.

PHOTOGRAMMETRIC ACCURACY AND MODELING OF ROLLING SHUTTER CAMERAS

Global climate change is one of the major challenges that all nations are commonly facing. Long-term observations of the Antarctic ice sheet have been playing a critical role in quantitatively estimating and predicting effects resulting from the global changes. The film-based ARGON reconnaissance imagery provides a remarkable data source for studying the Antarctic ice-sheet in 1960s, thus greatly extending the time period of Antarctica surface observations. To deal with the low-quality images and the unavailability of camera poses, a systematic photogrammetric approach is proposed to reconstruct the interior and exterior orientation information for further glacial mapping applications, including ice flow velocity mapping and mass balance estimation. Some noteworthy details while performing geometric modelling using the ARGON images were introduced, including methods and results for handling specific effects of film deformation, damaged or missing fiducial marks and calibration report, automatic fiducial mark detection, control point selection through Antarctic shadow and ice surface terrain analysis, and others. Several sites in East Antarctica were tested. As an example, four images in the Byrd glacier region were used to assess the accuracy of the geometric modelling. A digital elevation model (DEM) and an orthophoto map of Byrd glacier were generated. The accuracy of the ground positions estimated by using independent check points is within one nominal pixel of 140 m of ARGON imagery. Furthermore, a number of significant features, such as ice flow velocity and regional change patterns, will be extracted and analysed.

Characterizing Arctic sea ice topography using high-resolution IceBridge data.

We present an analysis of Arctic sea ice topography using high resolution, three-dimensional, surface elevation data from the Airborne Topographic Mapper, flown as part of NASA's Operation IceBridge mission. Surface features in the sea ice cover are detected using a newly developed surface feature picking algorithm. We derive information regarding the height, volume and geometry of surface features from 2009-2014 within the Beaufort/Chukchi and Central Arctic regions. The results are delineated by ice type to estimate the topographic variability across first-year and multi-year ice regimes. The results demonstrate that Arctic sea ice topography exhibits significant spatial variability, mainly driven by the increased surface feature height and volume (per unit area) of the multi-year ice that dominates the Central Arctic region. The multi-year ice topography exhibits greater interannual variability compared to the first-year ice regimes, which dominates the total ice topography variability across both regions. The ice topography also shows a clear coastal dependency, with the feature height and volume increasing as a function of proximity to the nearest coastline, especially north of Greenland and the Canadian Archipelago. A strong correlation between ice topography and ice thickness (from the IceBridge sea ice product) is found, using a square-root relationship. The results allude to the importance of ice deformation variability in the total sea ice mass balance, and provide crucial information regarding the tail of the ice thickness distribution across the western Arctic. Future research priorities associated with this new dataset are presented and discussed, especially in relation to calculations of atmospheric form drag.

Comparison of modelled- and remote sensing- derived daily snow line altitudes at Ulugh Muztagh, northern Tibetan Plateau

The ice cap Ulugh Muztagh in the central Kunlun Shan at the northern fringe of the Tibetan Plateau is a very isolated region with arid cold conditions. No observational, meteorological or glaciological ground truth data is available. Using the Moderate-resolution Imaging Spectroradiometer (MODIS) Level 1 radiance Swath Data (MOD02QKM) with a spatial resolution of 250 m, transient snow lines during the months of July to September in 2001 to 2014 are derived. Results are used to calibrate the physical based Coupled Snowpack and Ice surface energy and Mass balance model (COSIMA). The model runs on a representative detail region of Ulugh Muztagh (UM) on a digital elevation model with the same spatial resolution as the MODIS bands. In the absence of field observations, the model is driven solely by dynamically downscaled global analysis data from the High Asia Refined analysis (HAR). We compare remote sensing derived and modelled mean regional transient snow line altitudes in the course of consecutive summer seasons in 2008 to 2010. The resulting snow line altitude (SLA) and annual equilibrium line altitude (ELA) proxy of both methods coincide very well in their interannual variability in accordance with interannual variability of climatic conditions. Since SLAs of both methods do not consistently agree on a daily basis a usage of remote sensing derived SLAs for model calibration in the absence of field observation data is only limitedly feasible for daily analysis. ELA approximation using the highest SLA at the end of ablation period may not be applied to UM because the negative winter mass balance (MB) is not reflected in the summer SLA. The study reveals moderate negative MB for UM throughout the modelling period. The mean regional MB of UM accounts for -523±410 mm w.e. a-1 in the modelling period. Hence UM seems not to belong to the area of the ‘Karakorum anomaly’ comprising a region of positive mass balances in recent years which has its centre presumably in the Western Kunlun Shan.

Modeling of Store Gletscher's calving dynamics, West Greenland, in response to ocean thermal forcing

AbstractGlacier‐front dynamics is an important control on Greenland's ice mass balance. Warmer ocean waters trigger ice‐front retreats of marine‐terminating glaciers, and the corresponding loss in resistive stress leads to glacier acceleration and thinning. Here we present an approach to quantify the sensitivity and vulnerability of marine‐terminating glaciers to ocean‐induced melt. We develop a plan view model of Store Gletscher that includes a level set‐based moving boundary capability, a parameterized ocean‐induced melt, and a calving law with complete and precise land and fjord topographies to model the response of the glacier to increased melt. We find that the glacier is stabilized by a sill at its terminus. The glacier is dislodged from the sill when ocean‐induced melt quadruples, at which point the glacier retreats irreversibly for 27 km into a reverse bed. The model suggests that ice‐ocean interactions are the triggering mechanism of glacier retreat, but the bed controls its magnitude.

Atmospheric conditions in the central Arctic Ocean through the melt seasons of 2012 and 2013: Impact on surface conditions and solar energy deposition into the ice‐ocean system

AbstractSpectral Radiation Buoys and ice mass balance buoys were deployed on first‐year ice near the North Pole in April 2012 and 2013, collecting in‐band (350–800 nm) solar radiation and ice and snow mass balance data over the complete summer melt seasons. With complementary European ERA‐Interim reanalysis, National Centers for Environmental Prediction (NCEP) Climate forecast system version 2 (CFSv2) analysis and satellite passive microwave data, we examine the evolution of atmospheric and surface melt conditions in the two differing melt seasons. Prevailing atmospheric conditions contributed to a longer and more continuous melt season in summer 2012 than in 2013, which was corroborated by in situ observations. ERA‐Interim reanalysis data showed that longwave radiation likely played a key role in delaying the snowmelt onset in 2013. The earlier melt onset in 2012 reduced the albedo, providing a positive ice‐albedo feedback at a time when solar insolation was high. Due to earlier melt onset and later freeze‐up in 2012, more solar heat was deposited into the ice‐ocean system than in 2013. Summer 2013 was characterized by later melt onset, intermittent freezing events and an earlier fall freeze‐up, resulting in considerably fewer effective days of surface melt and a higher average albedo. Calculations for idealized seasonal albedo evolution show that moving the melt onset just 1 week earlier in mid‐June increases the total absorbed solar radiation by nearly 14% for the summer season. Therefore, the earlier melt onset may have been one of the most important factors driving the more dramatic melt season in 2012 than 2013, though atmospheric circulation patterns, e.g., cyclone in early August 2012, likely contributed as well.

Glaciers of the northern massif of the Suntar-Khayata Mountains: current state and dynamics since the end of 1950s

The estimation of glaciers of the Suntar-Khayata Mountains (the Northeastern Siberia) in the context of previously published data is presented. Under the background of current warming the glaciers in this region retreat enough quickly, they decrease not only in a real size, but also by the ice thickness. In this paper the mean summer temperature and solid precipitation of the key factors for glaciation, which indicate unfavorable conditions for the glacier existence at present time are presented as spatial distribution of trends (for 45 years, until 2012). The glaciers of the northern massif of the Suntar-Khayata have a negative ice mass balance as their entire surface is below the equilibrium line altitude. Mean thickness of superimposed ice on the glaciers of this massif was about 17 cm. Based on the assumption of climate variation in the Northern Pacific data it is suggested about the beginning of more favorable climatic conditions for the Suntar-Khayata glaciers.

Influence of wet conditions on snow temperature diurnal variations: An East Antarctic sea–ice case study

A one-dimensional snow–sea–ice model is used to simulate the evolution of temperature profiles in dry and wet snow over a diurnal cycle, at locations where associated observations collected during the Sea Ice Physics and Ecosystem eXperiment (SIPEX-II) are available. The model is used at two sites, corresponding to two of the field campaign׳s sea–ice stations (2 and 6), and under two configurations: dry and wet snow conditions. In the wet snow model setups, liquid water may refreeze internally into the snow. At station 6, this releases latent heat to the snow and results in temperature changes at the base of the snow pack of a magnitude comparing to the model-observation difference (1–2°C). As the temperature gradient across the snow is in turn weakened, the associated conductive heat flux through snow decreases. At station 2, internal refreezing also occurs but colder air temperatures and the competing process of strengthened heat conduction in snow concurrent to snow densification maintain a steady temperature profile. However, both situations share a common feature and show that the conductive heat flux through the snow may significantly be affected (by 10–20% in our simulations) as a result of the liquid water refreezing in snow, either through thermal conductivity enhancement or direct temperature gradient alteration. This ultimately gives motivation for further investigating the impacts of these processes on the sea–ice mass balance in the framework of global scale model simulations.

Observations of the summer breakup of an Arctic sea ice cover

AbstractThe Arctic sea ice cover evolves dramatically through the summer melt season. Floe size distribution (FSD) is a critical parameter used to examine this change as the ice cover transitions from large rectilinear plates in spring to an ensemble of discrete rounded floes by midsummer. The FSD at a given time impacts the dynamic and thermodynamic behavior of the ice cover. Focusing on the seasonal marginal ice zone in the Beaufort and Chukchi Seas from May to September 2014, we present qualitative and quantitative results derived from National Technical Means high‐resolution imagery and supported by ice mass balance buoy data. Results indicate that as melt accelerates, floe breaking pattern, and therefore FSD, is heavily influenced by the distribution of melt ponds. Discrete element model results using morphological conditions derived from analyzed satellite imagery confirmed that breaking occurs along ponds and perpendicular to applied stress.

Decadal and quadratic variations of Earth's oblateness and polar ice mass balance from 1979 to 2010

Decadal and quadratic variations of Earth's oblateness and polar ice mass balance from 1979 to 2010

Melt pond fraction and spectral sea ice albedo retrieval from MERIS data – Part 1: Validation against in situ, aerial, and ship cruise data

Abstract. The presence of melt ponds on the Arctic sea ice strongly affects the energy balance of the Arctic Ocean in summer. It affects albedo as well as transmittance through the sea ice, which has consequences for the heat balance and mass balance of sea ice. An algorithm to retrieve melt pond fraction and sea ice albedo from Medium Resolution Imaging Spectrometer (MERIS) data is validated against aerial, shipborne and in situ campaign data. The results show the best correlation for landfast and multiyear ice of high ice concentrations. For broadband albedo, R2 is equal to 0.85, with the RMS (root mean square) being equal to 0.068; for the melt pond fraction, R2 is equal to 0.36, with the RMS being equal to 0.065. The correlation for lower ice concentrations, subpixel ice floes, blue ice and wet ice is lower due to ice drift and challenging for the retrieval surface conditions. Combining all aerial observations gives a mean albedo RMS of 0.089 and a mean melt pond fraction RMS of 0.22. The in situ melt pond fraction correlation is R2 = 0.52 with an RMS = 0.14. Ship cruise data might be affected by documentation of varying accuracy within the Antarctic Sea Ice Processes and Climate (ASPeCt) protocol, which may contribute to the discrepancy between the satellite value and the observed value: mean R2 = 0.044, mean RMS = 0.16. An additional dynamic spatial cloud filter for MERIS over snow and ice has been developed to assist with the validation on swath data.

Under-ice eddy covariance flux measurements of heat, salt, momentum, and dissolved oxygen in an artificial sea ice pool

Turbulent exchanges under sea ice play a controlling role in ice mass balance, ice drift, biogeochemistry, and mixed layer modification. In this study, we examined the potential to measure under-ice turbulent exchanges of heat, salt, momentum, and dissolved oxygen using eddy covariance in an experimental sea ice facility. Over a 15-day period in January 2013, an underwater eddy covariance system was deployed in a large (500m3) in-ground concrete pool, which was filled with artificial seawater and exposed to the ambient (−5 to −30°C) atmosphere. Turbulent exchanges were measured continuously as ice grew from 5 to 25cm thick. Heat, momentum, and dissolved oxygen fluxes were all successfully derived. Quantification of salt fluxes was unsuccessful due to noise in the conductivity sensor, a problem which appears to be resolved in a subsequent version of the instrument. Heat fluxes during initial ice growth were directed upward at 10 to 25Wm−2. Dissolved oxygen fluxes were directed downward at rates of 5 to 50mmolm−2 d−1 throughout the experiment, at times exceeding the expected amount of oxygen rejected with the brine during ice growth. Bubble formation and dissolution was identified as one possible cause of the high fluxes. Momentum fluxes showed interesting correlations with ice growth and melt but were generally higher than expected. We concluded that with the exception of the conductivity sensor, the eddy covariance system worked well, and that useful information about turbulent exchanges under thin ice can be obtained from an experimental sea ice facility of this size.

Evaluation of a Coupled Snow and Energy Balance Model for Zhadang Glacier, Tibetan Plateau, Using Glaciological Measurements and Time-Lapse Photography

We present a new open-source, collaborative “COupled Snowpack and Ice surface energy and MAss balance model” (COSIMA) that is evaluated for Zhadang glacier, Tibetan Plateau. The model is calibrated, run, and validated based on in situ measurements and atmospheric model data from the High Asia Refined analysis (HAR) over the period April 2009 to June 2012. Results for the model runs forced by both in situ measurements and HAR agree well with observations of various atmospheric, glaciological, surface, and subsurface parameters on the glacier. A time-lapse camera system next to the glacier provides a 3-year image time series of the mean transient snow line altitude and the snow cover pattern, which is used for the spatial and temporal validation of the model. The model output corresponds very well to the observed temporal and spatial snow cover variability. The model is then run for a 10-year period of October 2001 to September 2011 forced with HAR data. In general, the radiation components dominate the overall energy turnover (65%), followed by the turbulent fluxes (31%). The generally dry atmosphere on the Tibetan Plateau causes sublimation to be responsible for 26% of the total mass loss. A proportion of 11% of the surface and subsurface melt refreezes within the snowpack.

Correction of inconsistencies in ECMWF's operational analysis data during de-aliasing of GRACE gravity models

SUMMARY The main objective of the Gravity Recovery and Climate Experiment (GRACE) Atmospheric and Oceanic De-Aliasing Level-1B product (AOD1B) is the removal of high-frequency nontidal mass variations due to sub-monthly mass transport in the atmosphere and oceans. Application of AOD1B shall avoid aliasing of these high-frequency signals into monthly gravity models derived from modern gravity missions and shall help to derive consistent orbit solutions for altimetry and Satellite Laser Ranging missions. The AOD1B 6-h series of spherical harmonic coefficients up to degree and order 100 are routinely generated at the German Research Centre for Geoscience and distributed to the GRACE Science Data System and the user community. Inputs for this product are acquired from numerical weather prediction models which are regularly revised and consequently not stable in time. The latest AOD1B release 5 (RL05) is based, as all other releases, on input from ECMWF and does not resolve this problem of discontinuities present in the surface pressure and surface geopotential input data. This might contaminate the gravity field variations derived from atmospheric mass variations. In this paper we present a method to overcome this problem during future AOD1B product generation,aswellastwonewLevel-2products(GAEandGAF)that,overland,fixaposteriori the two jumps present in the already distributed Level-2 RL05 monthly gravity models which were based on AOD1B RL05. The impact of the proposed correction on the variations and long-term trend of the total mass of the atmosphere and on the ice mass balance over Antarctica and over Greenland is also illustrated. We found that the GAE/GAF-corrected trend of the global atmospheric mass over the GRACE mission lifetime significantly decreased from −0.05 to −0.02 mm yr −1 in terms of geoid height. A considerable effect (33 per cent) was also found in the quadratic term of ice mass loss over Antarctica which results in an acceleration of 3.2 Gt yr −1 yr −1 smaller than without applying this correction.

Regional variability in sea ice melt in a changing Arctic.

In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover.

Glacier surface motion pattern in the Eastern part of West Kunlun Shan estimation using pixel-tracking with PALSAR imagery

Mountain glacier is considered as one of the most sensitive natural indicators of climate change. Glacier surface motion distribution in West Kunlun Shan (WKS) has been attracting considerable attention and represents a fundamental glacier parameter for better understanding glacier dynamics, ice mass balance, and even for the climate change. This paper would present the accurate ice motion observation of mountain glacier in eastern part of WKS by the refined pixel-tracking method with phased array type L-band synthetic aperture radar images acquired on December 13, 2008 and January 28, 2009. The standard deviation values in nonglacial area before/after topographic effect compensation are 0.61 and 0.43 m, respectively, during 46-day temporal interval. In addition, the terrain almost is a determining factor of ice velocity distribution in study area because the elevation of topography is generally shown to be positive correlated with glacier surface velocity along the central line. Furthermore, with estimated detailed glacier surface movement distribution pattern, we found that the continental glaciers were actively moving with spatially variable ice motion, while the icecaps maintain the stable status without apparent motion on most part of surface. Therefore, the refined SAR-based pixel-tracking method, including topographic effect compensation operation, provides a useful and robust tool to map and measure the glacier motion in mountain area with complex terrain.