Ice Mass Research Articles

Subglacial tills: a process model based on microsedimentological clues

Abstract Subglacial sediments are subject to erosion, transport, and deposition in active, ephemeral, and spatially localized glacial environments. It is critical to determine how these mobilized sediments become immobilized in a time-transgressive process and can be frequently remobilized and reimmobilized. Microscopic sedimentary structural signatures provide invaluable information on subglacial processes and contribute to understanding till formation. Data were obtained from a series of field sites in Canada and Austria investigating the microsedimentological aspects of both alpine and continental glaciation tills to construct a conceptual model of subglacial deformation. Microstructures in these tills indicate rheological behaviors that can be summarized into a potential model for soft deforming subglacial sediments. Most microstructures noted in these subglacial till examples highlight the development of subglacial interface kinematics providing clues to till deposition mechanics, subglacial bedform development, and the processes involved in till provenance distributions. A conceptual process model of subglacial interface conditions in soft mobile sediments is developed that uses microsedimentological evidence and highlights how an active ice mass integrates with ongoing substrate deformation. In the model, interaction occurs between the ice and its sediment bed with internal sediment microstructures evolving where multiple transient shear deformation processes cause localized deformation linked to pervasive and nonpervasive sediment deformation.

Modelling the historical and future evolution of six ice masses in the Tien Shan, Central Asia, using a 3D ice-flow model

Abstract. In the Tien Shan, few modelling studies exist that examine in detail how individual ice bodies are responding to climate change. Nonetheless, earlier research demonstrated that the glacier response to climate change in this mountain range is heterogeneous. Here, we use several measurements and reconstructions of the ice thickness, surface elevation, surface mass balance, and ice temperature to model in depth six different ice bodies in the Kyrgyz Tien Shan: five valley glaciers and one ice cap. The selected ice masses are located in different sub-regions of the Tien Shan with different climatic and topographic settings, and they are all characterized by detailed recent glaciological measurements. A three-dimensional higher-order thermomechanical ice-flow model is calibrated and applied to simulate the evolution of the ice masses since the end of the Little Ice Age (1850) and to make a prognosis of the future evolution up to 2100 under different Coupled Model Intercomparison Project Phase 6 (CMIP6) shared socioeconomic pathway (SSP) climate scenarios. The results reveal a strong retreat of most of the ice masses under all climate scenarios, albeit with notable variations in both timing and magnitude. These can be related to the specific climate regime of each of the ice bodies and their geometry. Under a moderate warming scenario, the ice masses characterized by a limited elevation range undergo complete disappearance, whereas the glaciers with a larger elevation range manage to preserve some ice at the highest altitudes. Additionally, our findings indicate that glaciers that primarily receive precipitation during the late spring and summer months exhibit a more rapid retreat in response to climate change, while the glaciers experiencing higher precipitation levels or more winter precipitation remain for a longer duration. Projections concerning the overall glacier runoff reveal that the maximum water discharge from the ice masses is expected to occur around or prior to the middle of the 21st century and that the magnitude of this peak is contingent upon the climate scenario, with a higher warming scenario resulting in a higher peak.

West Antarctica’s contribution to sea level rise as Earth’s climate warms

West Antarctica’s contribution to sea level rise as Earth’s climate warms Dr Dan Lubin, Researcher at the Scripps Institution of Oceanography, explores the contribution of West Antarctica to sea level rise as Earth’s climate warms. Sea level rise (SLR) is one of the most pressing concerns with greenhouse gas-induced climate warming. Over one-third of the human population, including nearly two-thirds of the global urban population, lives within 100 km of the sea. SLR increases flooding from storm surges and high tides, deterioration of infrastructure, shoreline erosion, contamination of agriculture, and numerous other hardships. Climate warming causes SLR in two primary ways: the melting of polar ice sheets and glaciers and the thermal expansion of the ocean as it warms. The two largest contributors to SLR from the steadily warming polar regions are the Greenland Ice Sheet (GIS) and the West Antarctic Ice Sheet (WAIS), at approximately 280 and 160 gigatons of ice per year, respectively. The GIS and WAIS have contrasts in the details of their ice mass loss.

Conceptual model for the formation of bedforms along subglacial meltwater corridors (SMCs) by variable ice‐water‐bed interactions

AbstractSubglacial meltwater landforms found on palaeo‐ice sheet beds allow the properties of meltwater drainage to be reconstructed, informing our understanding of modern‐day subglacial hydrological processes. In northern Canada and Fennoscandia, subglacial meltwater landforms are largely organized into continental‐scale networks of subglacial meltwater corridors (SMCs), interpreted as the relics of subglacial drainage systems undergoing variations in meltwater input, effective pressure and drainage efficiency. We review the current state of knowledge of bedforms (hummocks, ridges, murtoos, ribbed bedforms) and associated landforms (channels, eskers) described along SMCs and use selected high‐resolution DEMs in Canada and Fennoscandia to complete the bedform catalogue and categorize their characteristics, patterning and spatial distributions. We synthesize the diversity of bedform and formation processes occurring along subglacial drainage routes in a conceptual model invoking spatiotemporal changes in hydraulic connectivity, basal meltwater pressure and ice‐bed coupling, which influences the evolution of subglacial processes (bed deformation, erosion, deposition) along subglacial drainage systems. When the hydraulic capacity of the subglacial drainage system is overwhelmed glaciofluvial erosion and deposition will dominate in the SMC, resulting in tracts of hummocks and ridges arising from both fragmentation of underlying pre‐existing bedforms and downstream deposition of sediments in basal cavities and crevasses. Re‐coupling of ice with the bed, when meltwater supply decreases, facilitates deformation, transforming existing and producing new bedforms concomitant with the wider subglacial bedform imprint. We finally establish a range of future research perspectives to improve understanding of subglacial hydrology, geomorphic processes and bedform diversity along SMCs. These perspectives include the new acquisition of remote‐sensing and field‐based sedimentological and geomorphological data, a better connection between the interpreted subglacial drainage configurations down corridors and the mathematical treatments studying their stability, and the quantification of the scaling, distribution and evolution of the hydraulically connected drainage system beneath present‐day ice masses to test our bedform‐related conceptual model.

Monitoring glacier calving using underwater sound

Abstract. Climate shifts are particularly conspicuous in glaciated areas. Satellite and terrestrial observations show significant increases in the melting and breakup of tidewater glaciers and their influence on sea level rise and ocean mixing. Increasing melt rates are creating an urgency to better understand the link between atmospheric and oceanic conditions and glacier frontal ablation through iceberg calving and melting. Elucidating this link requires a combination of short- and long-timescale measurements of terminus activity. Recent work has demonstrated the potential of using underwater sound to quantify the time and scale of calving events to yield integrated estimates of ice mass loss (Glowacki and Deane, 2020). Here, we present estimates of subaerial calving flux using underwater sound recorded at Hansbreen, Svalbard, in September 2013 combined with an algorithm for the automatic detection of calving events. The method is compared with ice calving volumes estimated from geodetic measurements of the movement of the glacier terminus and an analysis of satellite images. The total volume of above-water calving during the 26 d of acoustical observation is estimated to be 1.7±0.7×107 m3, whereas the subaerial calving flux estimated by traditional methods is 7±2×106 m3. The results suggest that passive cryoacoustics is a viable technique for long-term monitoring of mass loss from marine-terminating glaciers.

Increasing Antarctic Ice Mass to Help Offset Sea Level Rise

Global sea level is predicted to rise for centuries even if greenhouse gas emissions are greatly reduced. Sea level rise (SLR) threatens coastal communities where a large fraction of the human population lives. A possible mitigation effort is to increase the ice mass in Antarctica. Coastal Antarctic radiosonde profiles are supersaturated with respect to ice on average 47% of the time. If all of this excess water vapor and supercooled liquid cloud water were removed from the atmosphere and deposited on the Antarctic landmass, it would offset 11 cm of SLR by 2100, or about 15 (8–17) percent of the predicted SLR. This strategy could be used to supplement other efforts to reduce climate change impacts, such as carbon dioxide removal or solar climate intervention.

Cliff collapse on Comet 67P/Churyumov–Gerasimenko – I. Aswan

ABSTRACT The Aswan cliff on Comet 67P/Churyumov–Gerasimenko collapsed on 2015 July 10. Thereby, relatively pristine comet material from a depth of $\sim 12\, \mathrm{m}$ was exposed at the surface. Observations of the collapse site by the microwave instrument Rosetta/Microwave Instrument for Rosetta Orbiter (MIRO) have been retrieved from 8 months prior to collapse, as well as from 5, 7, and 11 months post-collapse. The MIRO data are analysed with thermophysical and radiative transfer models. The pre-collapse observations are consistent with a 30 MKS thermal inertia dust mantle with a thickness of at least $3\, \mathrm{cm}$. The post-collapse data are consistent with (1) a dust/water–ice mass ratio of 0.9 ± 0.5 and a molar CO2 abundance of ∼30 per cent relative to water; (2) formation of a dust mantle after ∼7 months, having a thickness of a few millimetres or a fraction thereof; (3) a CO2 ice sublimation front at 0.4 cm that withdrew to 2.0 cm and later to $20\pm 6\, \mathrm{cm}$; (4) a thermal inertia ranging 10–45 MKS; (5) a gas diffusivity that decreased from $0.1$ to $0.001\, \mathrm{m^2\, s^{-1}}$; and (6) presence of a solid-state greenhouse effect parts of the time. The data and the analysis provide a first empirical glimpse of how ice-rich cometary material ages and evolves when exposed to solar heating.

Late Cenozoic sea-surface-temperature evolution of the South Atlantic Ocean

Abstract. At present, a strong latitudinal sea-surface-temperature (SST) gradient of ∼ 16 ∘C exists across the Southern Ocean, maintained by the Antarctic Circumpolar Current (ACC) and a set of complex frontal systems. Together with the Antarctic ice masses, this system has formed one of the most important global climate regulators. The timing of the onset of the ACC system, its development towards modern-day strength and the consequences for the latitudinal SST gradient around the southern Atlantic Ocean are still uncertain. Here we present new TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms)-derived SST records from two sites located east of Drake Passage (south-western South Atlantic) to assist in better understanding two critical time intervals of prominent climate transitions during the Cenozoic: the late Eocene–early Oligocene (Ocean Drilling Program, ODP, Site 696) and Middle–Late Miocene (IODP Site U1536) transitions. Our results show temperate conditions (20–11 ∘C) during the first time interval, with a weaker latitudinal SST gradient (∼ 8 ∘C) across the Atlantic sector of the Southern Ocean compared to present day. We ascribe the similarity in SSTs between Sites 696 and 511 in the late Eocene–early Oligocene South Atlantic to a persistent, strong subpolar gyre circulation connecting the sites, which can only exist in the absence of a strong throughflow across the Drake Passage. Surprisingly, the southern South Atlantic record Site 696 shows comparable SSTs (∼ 12–14 ∘C) during both the earliest Oligocene oxygen isotope step (EOIS, ∼ 33.65 Ma) and the Miocene Climatic Optimum (MCO, ∼ 16.5 Ma). Apparently, maximum Oligocene Antarctic ice volume could coexist with warm ice-proximal surface ocean conditions, while at similar ocean temperatures, the Middle Miocene Antarctic ice sheet was likely reduced. Only a few Middle–Late Miocene (discontinuous) high-latitude records exist due to ice advances causing unconformities. Our low-resolution Site U1536 record of southern South Atlantic SSTs cooled to ∼ 5 ∘C during the Middle Miocene Climate Transition (MMCT, 14 Ma), making it the coldest oceanic region in the poorly recorded Antarctic realm and likely the main location for deep-water formation. The already-cold south-western South Atlantic conditions at the MMCT with relatively moderate additional cooling during the Late Miocene contrasts with the profound cooling in the lower latitudes and other sectors of the Southern Ocean due to northward expansion of the Southern Ocean frontal systems.

Brief communication: Measuring and modelling the ice thickness of the Grigoriev ice cap (Kyrgyzstan) and comparison with global datasets

Abstract. An accurate ice thickness distribution is crucial for correct projections of the future state of an ice mass. However, measuring the ice thickness with an in situ system is time-consuming and not scalable. Therefore, models have been developed to estimate the ice thickness without direct measurements. In this study, we reconstruct the ice thickness of the Grigoriev ice cap, Kyrgyzstan, from in situ observations and the yield stress method. We compare the results with data from six global ice thickness datasets composed without the use of our local measurements. The results highlight the limitations of these generic datasets primarily stemming from the subdivision of ice caps into distinct glaciers, the adoption of a (calibrated) creep parameter value, assumptions regarding ice mass flux, and errors regarding surface velocity observations. These shortcomings emphasize the importance of integrating local observations to calibrate models to achieve precise representations of ice thickness, particularly when dealing with smaller or slow-flowing cold ice caps, such as the Grigoriev ice cap.

Linking timescale-dependent Antarctic sea ice kinematic observations to ice thickness

Sea ice kinematics impacts the global ocean–atmosphere system in numerous ways: modification of albedo, ice cover, and ice mass; heat transmission between atmosphere and ocean; and ice thickness distribution. Such research is often conducted using in situ and remotely-sensed observations of ice motion. In recent work, an ice motion product generated from overlapping sections of multiple individual swath pairs – the so-called swath-to-swath (S2S) approach – has been favourably evaluated by buoys in the Arctic. This new product is better able to represent drifting buoy trajectories, however, it has yet to be applied to ice kinematics research. In this study, we investigate the Antarctic sea ice differential kinematic parameters (DKPs) represented by divergence and maximum shear rate computed from the new S2S ice motion product, and compare these with the daily-map (DM)-derived DKP magnitudes. Results indicate that S2S-derived DKP magnitudes are highly timescale-dependent and well represented by an exponential relationship. Furthermore, the exponential DKP curve parameters in this work are shown to correspond well to ice thickness, thus enabling a new class of Antarctic ice thickness proxy observations. This technique lays the groundwork for the possibility of new proxy measurement of ice thickness back to at least 1991, when the high-accuracy S2S measurements of ice motion become available.

The chance of freezing – a conceptional study to parameterize temperature-dependent freezing by including randomness of ice-nucleating particle concentrations

Abstract. Ice-nucleating particle concentrations (INPCs) can spread over several orders of magnitude at any given temperature. However, this variability is rarely accounted for in heterogeneous ice-nucleation parameterizations. In this paper, we present an approach to incorporate the random variation in the INPC into the parameterization of immersion freezing and analyze this novel concept with various sensitivity tests. In the new scheme, the INPC is drawn from a relative frequency distribution of cumulative INPCs. At each temperature, this distribution describing the INPCs is expressed as a lognormal frequency distribution. The new parameterization scheme does not require aerosol information from the driving model to represent the heterogeneity of INPCs. The scheme's performance is tested in a large-eddy simulation of a relatively warm Arctic mixed-phase stratocumulus. We find that it leads to reasonable ice masses in the cloud, especially when compared to immersion freezing schemes that yield one fixed INPC per temperature and lead to almost no ice production in the simulated cloud. The scheme is sensitive to the median of the frequency distribution and highly sensitive to the standard deviation of the distribution, as well as to the frequency of drawing a new INPC and the resolution of the model. Generally, a higher probability of drawing large INPCs leads to substantially more ice in the simulated cloud. We expose inherent challenges to introducing such a parameterization and explore possible solutions and potential developments.

Climate Variability and Glacier Evolution at Selected Sites Across the World: Past Trends and Future Projections

AbstractThe availability of freshwater from glaciers and snowmelt is of vital importance for people and ecosystems in the context of global climate change. Here, we focus on 25 glaciers located in different climates and latitudes and investigate their recent (1958–2020) and future projected trends (2020–2050 and 2070–2100) in monthly precipitation (Pr), maximum and minimum temperatures, ice mass loss, and their relationships with cloud properties. The study sites are located in Temperate Europe (France), the Inner (Ecuador, Venezuela, and Colombia) and Outer Tropics (Bolivia and Peru), Central America (Mexico), tropical Southeast Asia (Indonesia), Equatorial Africa (Uganda), and the Southern dry and Patagonian Andes (Chile and Argentina). The climate analyses are based on TerraClimate data (Monthly Climate and Climatic Water Balance for Global Terrestrial Surfaces) and 28 CORDEX (Coordinated Regional Climate Downscaling Experiment) climate simulations. Our findings reveal that, extrapolating current glacier volume change trends, almost half of the studied glaciers are likely to vanish (95%–100% volume loss) by 2050, with widespread warming and drying trends since 1958. A shift toward wetter conditions at Pico Humboldt (Venezuela) and Martial Este (Argentina) identifiable in the CORDEX simulation will very likely not have a limiting impact on glacier mass loss owing to increasing temperatures, which will raise the elevation of the rain/snow limit. Our results provide useful new information to better understand glacier‐climate relationships and future scenarios dominated by ice mass loss trends across the globe. These findings suggest serious consequences for future water availability, which exacerbate the vulnerability of local populations and ecosystems.

Rainy Days in the Arctic

Abstract The Arctic is warming faster than anywhere on Earth, and with these warming temperatures, there is likely to be more precipitation falling as rain. This precipitation phase change will have profound impacts on the hydrologic cycle, energy balance, and snow and sea ice mass budgets. Here, we examine the number of rainfall days in the Arctic from three reanalyses, ERA-Interim, ERA5, and MERRA-2, over 1980–2016. We show that the number of rainfall days has increased over this period, predominantly in the autumn and in the North Atlantic and peripheral seas, and the length of the rain season has increased in all reanalyses. This is positively correlated to the number of days with above freezing air temperatures and a lengthening of the warm season. ERA-Interim produces significantly more rainfall days than other reanalyses and CloudSat observations, as well as significantly more rainfall when temperatures are below freezing. Investigation into the cloud microphysics schemes revealed that the scheme employed by ERA-Interim allowed for mixed-phase clouds to form rain at temperatures below freezing following a temperature-dependent phase partitioning function between 250 and 273 K. This simple diagnostic treatment erroneously overestimates rain at temperatures below 273 K and produces unrealistic rainfall compared to ERA5 and MERRA-2. This work highlights the importance of having accurate physics and improving microphysical schemes in models for simulating precipitation in the Arctic and the caution that is warranted for interpreting reanalysis trends.

Local Ice Mass Balance Rates via Bayesian Analysis of Mars Polar Trough Migration

AbstractWith the aim of better understanding the past depositional environment of the north polar region of Mars, we infer local ice accumulation and retreat rates in the area between 86° and 87°N and 16°–20°E. We follow a novel approach utilizing a Bayesian framework with observations of bounding surfaces associated with the migration of two polar spiral troughs. Over time, spiral troughs have migrated toward the north pole due to ice accumulation, sublimation, and wind transport. We relate the record of trough migration with local ice accumulation and retreat rates using a phenomenological migration model and explore the climate parameters that affect these rates using a Markov chain Monte Carlo algorithm. Using this data‐driven approach, we find best fit mean accumulation rates of 0.11–0.18 mm/yr in the upper 500 m of the stratigraphy of our study region. These mean accumulation rates correspond to trough ages of over 4 Myr, which implies that the north polar cap is older than most current assumptions. We also find that the relationship between accumulation rates and the obliquity of Mars is complex, with periods of positive correlation occurring in the last several Myr. Future work extending this analysis to all troughs in the cap will further constrain these relationships and ages.

Multi-Scale Polar Object Detection Based on Computer Vision

When ships navigate in polar regions, they may collide with ice masses, which may cause structural damage and endanger the safety of their occupants. Therefore, it is essential to promptly detect sea ice, icebergs, and passing ships. However, individual data sources have limits and should be combined and integrated to obtain more thorough information. A polar multi-target local-scale dataset with five categories was constructed. Sea ice, icebergs, ice melt ponds, icebreakers, and inter-ice channels were identified by a single-shot detector (SSD), with a final mAP value of 70.19%. A remote sensing sea ice dataset with 15,948 labels was constructed. The You Only Look Once (YOLOv5) model was improved with Squeeze-and-Excitation Networks (SE), Funnel Activation (FReLU), Fast Spatial Pyramid Pooling, and Cross Stage Partial Network (SPPCSPC-F). In the detection stage, a slicing operation was performed on remote sensing images to detect small targets. Simulated sea ice data were included to verify the model’s generalization ability. Then, the improved model was trained and evaluated in an ablation experiment. The mAP, recall (R), and precision (P) values of the improved YOLOv5 were 75.3%, 70.3, and 75.4%, with value increases of 3.5%, 3.4%, and 1.9%, respectively, compared to the original model. The improved YOLOv5 was also compared with other models such as YOLOv3, Faster-RCNN, and YOLOv4-tiny. The results indicated that the performance of the proposed model surpassed those of the other conventional models. This study achieved the detection of multiple targets on different scales in a polar region and realized data fusion, avoiding the limitations of using a single data source, and provides a method to support polar ship path planning.

Effects of ice content on compression characteristics of frozen sandstone by in-situ NMR technology

In cold regions, the freezing of pore water in rock affects the mechanical behavior of the rock. This paper studied the ice content of frozen sandstone at different temperatures and its effects on the mechanical properties of sandstone. First, the progressive freezing treatment (from 25.0 to − 30.0 °C) and in-situ nuclear magnetic resonance test were conducted to study the evolution of the ice content of sandstone with temperature. This evolution was quantitatively described by the frozen ratio defined as the percentage of the mass of ice and the total mass of water. Then, the mechanical properties of frozen sandstone at different temperatures (25.0 °C, 0.0 °C, − 5.0 °C, − 10.0 °C, − 20.0 °C and − 30.0 °C, respectively) were tested, such as P-wave velocity, uniaxial compressive strength (UCS), peak strain and elastic modulus. Finally, the effects of the frozen ratio on these properties were discussed. The results show that the pore water in sandstone shows three stages as the temperature decreases: stable liquid (from 25.0 to 0.0 °C), sharp phase transition (from 0.0 to − 2.5 °C) and slow phase transition (from − 2.5 to − 30.0 °C). Especially, the capillary and bulk water in sandstone is almost completely frozen in the sharp phase transition stage. As the temperature decreases, the frozen ratio first remains constant, then increases rapidly and finally increases slowly. Moreover, as the frozen ratio increases, the P-wave velocity, UCS and peak strain increase while the elastic modulus decreases. Interestingly, the compressive failure mode of sandstone changes from brittle to ductile as the frozen ratio increases.

Cross-Polarized SfM Photogrammetry for the Spatial Reconstruction of Challenging Surfaces, the Case Study of Dobšiná Ice Cave (Slovakia)

Geodetic methods are integral to mapping surface and subsurface objects and phenomena. Modern geodetic technologies such as laser scanning and digital photogrammetry have also become a standard part of the mapping and documentation of cave spaces. In some cases, these technologies cannot accurately capture the measured surface and thus provide reliable data. One such example is the ice with specific surface characteristics in caves with ice deposits. One of the world’s most studied ice caves is the Dobšiná Ice Cave (Slovakia), which has undergone significant changes in the ice-filling area and volume in recent years. To monitor and analyze all these changes properly, we need to know the surface and volume of this ice mass and monitor it regularly. Where modern geodetic methods such as terrestrial laser scanning (TLS) or digital photogrammetry may fail due to the ice’s physical properties, we propose using cross-polarized Structure-from-Motion (SfM) photogrammetry. As a case study, this method was used in a 28 m long ice tunnel in this cave. Two polarizing filters (on the flash as a light source and on the camera lens) were used in 90° rotation to each other to achieve the cross-polarization effect and remove surface reflections. This removed the surface reflections, giving us a compact and accurate point cloud of the entire tunnel. The dense cloud from cross-polarized (CP) photogrammetry is denser and more compact and does not contain as many outliers and noise points when compared to non-cross-polarized (non-CP) photogrammetry. The TLS point cloud covers the entire surface of the tunnel without significant holes; however, the penetration of the beam through the ice makes such a cloud unusable. Only the cloud from CP photogrammetry covers the entire surface of the tunnel densely enough without additional noise. This methodology can then be used in other parts of the cave or other geomorphological applications to suppress reflections so high-quality results for further processing and analysis can be obtained.

A thicker Antarctic ice stream during the mid-Pliocene warm period

Ice streams regulate most ice mass loss in Antarctica. Determining ice stream response to warmer conditions during the Pliocene could provide insights into their future behaviour, but this is hindered by a poor representation of subglacial topography in ice-sheet models. We address this limitation using a high-resolution model for Dronning Maud Land (East Antarctica). We show that contrary to dynamic thinning of the region’s ice streams following ice-shelf collapse, the largest ice stream, Jutulstraumen, thickens by 700 m despite lying on a retrograde bed slope. We attribute this counterintuitive thickening to a shallower Pliocene subglacial topography and inherent high lateral stresses at its flux gate. These conditions constrict ice drainage and, combined with increased snowfall, allow ice accumulation upstream. Similar stress balances and increased precipitation projections occur across 27% of present-day East Antarctica, and understanding how lateral stresses regulate ice-stream discharge is necessary for accurately assessing Antarctica’s future sea-level rise contribution.

Quantified mass loss of the Laohugou ice core and its precipitation signal during 1961–2005 at high elevation in the northeastern Tibetan Plateau

Abstract Ice records provide a qualitative rather than a quantitative indication of the trend of climate change. Using the bulk aerodynamic method and degree day model, this study quantified ice mass loss attributable to sublimation/evaporation (S/E) and meltwater on the basis of integrated observations (1960–2006) of glacier-related and atmospheric variables in the northeastern Tibetan Plateau. During 1961–2005, the average annual mass loss in the ice core was 95.33 ± 20.56 mm w.e. (minimum: 78.97 mm w.e. in 1967, maximum: 146.67 mm w.e. in 2001), while the average ratio of the revised annual ice accumulation was 21.2 ± 7.7% (minimum: 11.0% in 1992, maximum 44.8% in 2000). A quantitative formula expressing the relationship between S/E and air temperature at the monthly scale was established, which could be extended to estimation of S/E changes of other glaciers in other regions. The elevation effect on alpine precipitation determined using revised ice accumulation and instrumental data was found remarkable. This work established a method for quantitative assessment of the temporal variation in ice core mass loss, and advanced the reconstruction of long-term precipitation at high elevations. Importantly, the formula established for reconstruction of S/E from temperature time series data could be used in other regions.

Assimilating CryoSat-2 freeboard to improve Arctic sea ice thickness estimates

Abstract. In this study, a new method to assimilate freeboard (FB) derived from satellite radar altimetry is presented with the goal of improving the initial state of sea ice thickness predictions in the Arctic. In order to quantify the improvement in sea ice thickness gained by assimilating FB, we compare three different model runs: one reference run (refRun), one that assimilates only sea ice concentration (SIC) (sicRun), and one that assimilates both SIC and FB (fbRun). It is shown that estimates for both SIC and FB can be improved by assimilation, but only fbRun improved the FB. The resulting sea ice thickness is evaluated by comparing sea ice draft measurements from the Beaufort Gyre Exploration Project (BGEP) and sea ice thickness measurements from 19 ice mass balance (IMB) buoys deployed during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The sea ice thickness of fbRun compares better than refRun and sicRun to the longer BGEP observations more poorly to the shorter MOSAiC observations. Further, the three model runs are compared to the Alfred Wegener Institute (AWI) weekly CryoSat-2 sea ice thickness, which is based on the same FB observations as those that were assimilated in this study. It is shown that the FB and sea ice thickness from fbRun are closer to the AWI CryoSat-2 values than the ones from refRun or sicRun. Finally, comparisons of the abovementioned observations and both the fbRun sea ice thickness and the AWI weekly CryoSat-2 sea ice thickness were performed. At the BGEP locations, both fbRun and the AWI CryoSat-2 sea ice thickness perform equally. The total root-mean-square error (RMSE) at the BGEP locations equals 30 cm for both sea ice thickness products. At the MOSAiC locations, fbRun's sea ice thickness performs significantly better, with a total 11 cm lower RMSE.