Surface Mass Balance Variability Research Articles

Spatial and temporal variability of environmental proxies from the top 120 m of two ice cores in Dronning Maud Land (East Antarctica)

Abstract. The Antarctic ice sheet's future contribution to sea level rise is difficult to predict, mostly because of the uncertainty and variability of the surface mass balance (SMB). Ice cores are used to locally (kilometer scale) reconstruct SMB with a very good temporal resolution (up to sub-annual), especially in coastal areas where accumulation rates are high. The number of ice core records has been increasing in recent years, revealing an important spatial variability and different trends of SMB, highlighting the crucial need for greater spatial and temporal representativeness. We present records of density, water stable isotopes (δ18O, δD, and deuterium excess), major ions concentrations (Na+, K+, Mg2+, Ca2+, MSA, Cl−, SO42-, and NO3-), and continuous electrical conductivity measurement (ECM), as well as age models and resulting surface mass balance from the top 120 m of two ice cores (FK17 and TIR18) drilled on two adjacent ice rises located in coastal Dronning Maud Land and dating back to the end of the 18th century. Both environmental proxies and SMB show contrasting behaviors, suggesting strong spatial and temporal variability at the regional scale. In terms of precipitation proxies, both ice cores show a long-term decrease in deuterium excess (d-excess) and a long-term increase in δ18O, although less pronounced. In terms of chemical proxies, the non-sea-salt sulfate (nssSO42-) concentrations of FK17 are twice those of TIR18 and display an increasing trend on the long-term, whereas there is only a small increase after 1950 in TIR18. The SO42-/Na+ ratios show a similar contrast between FK17 and TIR18 and are consistently higher than the seawater ratio, indicating a dominant impact of the nssSO42- on the SO42- signature. The mean long-term SMB is similar for FK17 and TIR18 (0.57 ± 0.05 and 0.56 ± 0.05 mi.e.yr-1, respectively), but the annual records are very different: since the 1950s, TIR18 shows a continuous decrease while FK17 has shown an increasing trend until 1995 followed by a recent decrease. The datasets presented here offer numerous development possibilities for the interpretation of the different paleo-profiles and for addressing the mechanisms behind the spatial and temporal variability observed at the regional scale (tens of kilometers) in East Antarctica. The “Mass2Ant IceCores” datasets are available on Zenodo (https://doi.org/10.5281/zenodo.7848435; Wauthy et al., 2023).

Investigating the spatial representativeness of East Antarctic ice cores: a comparison of ice core and radar-derived surface mass balance over coastal ice rises and Dome Fuji

Abstract. Surface mass balance (SMB) of the Antarctic Ice Sheet must be better understood to document the current Antarctic contribution to sea-level rise. In situ point data using snow stakes and ice cores are often used to evaluate the state of the ice sheet's mass balance, as well as to assess SMB derived from regional climate models, which are then used to produce future climate projections. However, spatial representativeness of individual point data remains largely unknown, particularly in the coastal regions of Antarctica with highly variable terrain. Here, we compare ice core data collected at the summit of eight ice rises along the coast of Dronning Maud Land, as well as at the Dome Fuji site, and shallow ice-penetrating radar data over these regions. Shallow radar data have the advantage of being spatially extensive, with a temporal resolution that varies between a yearly and multi-year resolution, from which we can derive a SMB record over the entire radar survey. This comparison therefore allows us to evaluate the spatial variability of SMB and the spatial representativeness of ice-core-derived SMB. We found that ice core mean SMB is very local, and the difference with radar-derived SMB increases in a logarithmic fashion as the surface covered by the radar data increases, with a plateau ∼ 1–2 km away from the ice crest for most ice rises, where there are strong wind–topography interactions, and ∼ 10 km where the ice shelves begin. The relative uncertainty in measuring SMB also increases rapidly as we move away from the ice core sites. Five of our ice rise sites show a strong spatial representativeness in terms of temporal variability, while the other three sites show that it is limited to a surface area between 20–120 km2. The Dome Fuji site, on the other hand, shows a small difference between pointwise and area mean SMB, as well as a strong spatial representativeness in terms of temporal variability. We found no simple parameterization that could represent the spatial variability observed at all the sites. However, these data clearly indicate that local spatial SMB variability must be considered when assessing mass balance, as well as comparing modeled SMB values to point field data, and therefore must be included in the estimate of the uncertainty of the observations.

Unraveling contributions of Greenland's seasonal and transient crustal deformation during the past two decades

Contemporary research on Greenland surface mass balance (SMB) is largely focused on the characteristics of decadal or longer trends, periodic oscillations, and acceleration. However, the specific components of the SMB such as snowfall (SF), rainfall (RF) and runoff (RU), and their corresponding temporal and spatial variability remain poorly understood. Here, we explore the respective contributions of SF, RF, and RU to the seasonal and transient crustal deformations of Greenland during the past two decades using GPS network and satellite gravimetry (GRACE) datasets, and regional climate model output. Our study unraveled that the largest annual vertical displacement caused by precipitations is in southeastern Greenland, reaching 7.27 mm. The largest surface displacement caused by RU is in western Greenland, reaching 19.82 mm. Ice mass gain/loss in Greenland shows a clear correlation between latitude and temperature, with greater variations in the south compared to the north. The transient deformation signals in Greenland mainly manifested in terms of abrupt subsidence in 2010, followed by uplift in 2014. The 2014 uplift can mainly be attributable to the combined effect of SF, RF, and RU. The largest transient signal occurs in the southeast subregions, with peak-to-peak amplitude exceeding 10 mm. Transient crustal deformation is mainly caused by precipitation in southeastern Greenland, while the contribution of RU dominates most of the time and in most subregions. We find that even though RF is increasing due to an increasingly warmer climate, its effect on SMB is still negligible, when compared with SF and RU. In some subregions and some periods, SF could become the primary contributor to transient SMB variations in Greenland.

Mass balance of the Greenland and Antarctic ice sheets from 1992 to 2020

Abstract. Ice losses from the Greenland and Antarctic ice sheets have accelerated since the 1990s, accounting for a significant increase in the global mean sea level. Here, we present a new 29-year record of ice sheet mass balance from 1992 to 2020 from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE). We compare and combine 50 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, in ice sheet volume, and in Earth's gravity field. Between 1992 and 2020, the ice sheets contributed 21.0±1.9 mm to global mean sea level, with the rate of mass loss rising from 105 Gt yr−1 between 1992 and 1996 to 372 Gt yr−1 between 2016 and 2020. In Greenland, the rate of mass loss is 169±9 Gt yr−1 between 1992 and 2020, but there are large inter-annual variations in mass balance, with mass loss ranging from 86 Gt yr−1 in 2017 to 444 Gt yr−1 in 2019 due to large variability in surface mass balance. In Antarctica, ice losses continue to be dominated by mass loss from West Antarctica (82±9 Gt yr−1) and, to a lesser extent, from the Antarctic Peninsula (13±5 Gt yr−1). East Antarctica remains close to a state of balance, with a small gain of 3±15 Gt yr−1, but is the most uncertain component of Antarctica's mass balance. The dataset is publicly available at https://doi.org/10.5285/77B64C55-7166-4A06-9DEF-2E400398E452 (IMBIE Team, 2021).

Climatic control of the surface mass balance of the Patagonian Icefields

Abstract. The Patagonian Icefields (Northern and Southern Patagonian Icefield) are the largest ice masses in the Andes Cordillera. Despite its importance, little is known about the main mechanisms that underpin the interaction between these ice masses and climate. Furthermore, the nature of large-scale climatic control over the surface mass variations of the Patagonian Icefields still remains unclear. The main aim of this study is to understand the present-day climatic control of the surface mass balance (SMB) of the Patagonian Icefields at interannual timescales, especially considering large-scale processes. We modeled the present-day (1980–2015) glacioclimatic surface conditions for the southern Andes Cordillera by statistically downscaling the output from a regional climate model (RegCMv4) from a 10 km spatial resolution to a 450 m resolution grid and then using the downscaled fields as input for a simplified SMB model. Series of spatially averaged modeled fields over the Patagonian Icefields were used to derive regression and correlation maps against fields of climate variables from the ERA-Interim reanalysis. Years of relatively high SMB are associated with the establishment of an anomalous low-pressure center near the Drake Passage, the Drake low, that induces an anomalous cyclonic circulation accompanied with enhanced westerlies impinging on the Patagonian Icefields, which in turn leads to increases in the precipitation and the accumulation over the icefields. Also, the Drake low is thermodynamically maintained by a core of cold air that tends to reduce the ablation. Years of relatively low SMB are associated with the opposite conditions. We found low dependence of the SMB on main atmospheric modes of variability (El Niño–Southern Oscillation, Southern Annular Mode), revealing a poor ability of the associated indices to reproduce the interannual variability of the SMB. Instead, this study highlights the Drake Passage as a key region that has the potential to influence the SMB variability of the Patagonian Icefields.

Spatiotemporal variations of extreme events in surface mass balance over Greenland during 1958–2019

AbstractGreenland surface mass balance (SMB) is undergoing dramatic change due to the amplified Arctic warming, with more frequent record‐breaking melt events. To comprehensively understand the behaviour of the Greenland ice sheet, we develop a suite of indices to examine the spatiotemporal variations of extreme events in SMB over Greenland during 1958–2019 based on the RACMO2.3p2 model outputs. We illustrate that the climatological distributions of extreme ablation‐dominated events (i.e., extremes with SMB < 0) share large similarity with the mean SMB in terms of intensity and frequency, showing a coastal‐to‐inland decreasing pattern. This pattern holds for the intensity of the extreme accumulation‐dominated events (i.e., extremes with SMB > 0), but not for the frequency which increases from the coastal to inland Greenland. Regarding the temporal evolution, the intensity and frequency of extreme ablation‐dominated events show a decreasing trend over Greenland during 1958–1978, whereas the trend increases afterwards, especially during the last two decades (2001–2019). However, these trends fluctuate regionally across the GrIS both in terms of magnitude and sign, with the most pronounced variations occurring in southwest Greenland. In contrast, extreme accumulation‐dominated events show, on average, a long‐term increasing trend from 1958 to 2019 in terms of intensity and frequency. However, obvious spatial fluctuations exist across the GrIS during 1958–2019, especially between the southwest and northeast Greenland where an opposite trend is observed. Additionally, the variations of SMB extremes in boreal summer are linked with the changes in regional temperature and precipitation and the associated atmospheric circulations, and the dominating factor varies with different extreme indices and time intervals. Our results may advance our understanding on SMB variability over Greenland and contribute to the design of future Greenland observational networks.

Climate Controls on the Interseasonal and Interannual Variability of the Surface Mass and Energy Balances of a Tropical Glacier (Zongo Glacier, Bolivia, 16°S): New Insights From the Multi‐Year Application of a Distributed Energy Balance Model

AbstractThe application of a distributed energy balance model over nine years at an hourly time step to a 20 × 20 m grid cell over Glacier Zongo (Bolivia, 16°S) enabled assessment of the climate factors that control the interseasonal and interannual variability of its surface mass balance. The model was validated by comparing the measured and simulated discharge at the outlet, albedo at the Automatic Weather Station, surface state and annual mass balance both glacier‐wide and as a function of altitude. Analysis of the mean monthly energy fluxes highlighted the importance of the meteorological conditions over October and November on the variability of the annual surface mass balance. Two sensitivity analyses are presented, one of the distribution of precipitation over time which maintains a physical coherence between the different meteorological variables and one of the impact of prolonged periods of intense cloud radiative forcing on the surface mass balance. The distribution of precipitation events over time and their associated amounts are the main drivers of the interannual variability of the surface mass balance via an albedo feedback effect. Additionally, prolonged periods of negative cloud radiative forcing, specifically over the month of November, notably reduce the melt rate.

GPS‐Observed Elastic Deformation Due to Surface Mass Balance Variability in the Southern Antarctic Peninsula

AbstractIn Antarctica, Global Positioning System (GPS) vertical time series exhibit non‐linear signals over a wide range of temporal scales. To explain these non‐linearities, a number of hypotheses have been proposed, among them the short‐term rapid solid Earth response to contemporaneous ice mass change. Here we use GPS vertical time series to reveal the solid Earth response to variations in surface mass balance (SMB) in the Southern Antarctic Peninsula (SAP). At four locations in the SAP we show that interannual variations of SMB anomalies cause measurable elastic deformation. We use regional climate model SMB products to calculate the induced displacement assuming a perfectly elastic Earth. Our results show a reduction of the misfit when fitting a linear trend to GPS time series corrected for the elastic response to SMB variations. Our results imply that, for a better understanding of the glacial isostatic adjustment signal in Antarctica, SMB variability must be considered.

Modeling the Greenland englacial stratigraphy

Abstract. Radar reflections from the interior of the Greenland ice sheet contain a comprehensive archive of past accumulation rates, ice dynamics, and basal melting. Combining these data with dynamic ice sheet models may greatly aid model calibration, improve past and future sea level estimates, and enable insights into past ice sheet dynamics that neither models nor data could achieve alone. Unfortunately, simulating the continental-scale ice sheet stratigraphy represents a major challenge for current ice sheet models. In this study, we present the first three-dimensional ice sheet model that explicitly simulates the Greenland englacial stratigraphy. Individual layers of accumulation are represented on a grid whose vertical axis is time so that they do not exchange mass with each other as the flow of ice deforms them. This isochronal advection scheme does not influence the ice dynamics and only requires modest input data from a host thermomechanical ice sheet model, making it easy to transfer to a range of models. Using an ensemble of simulations, we show that direct comparison with the dated radiostratigraphy data yields notably more accurate results than calibrating simulations based on total ice thickness. We show that the isochronal scheme produces a more reliable simulation of the englacial age profile than traditional age tracers. The interpretation of ice dynamics at different times is possible but limited by uncertainties in the upper and lower boundary conditions, namely temporal variations in surface mass balance and basal friction.

The AntSMB dataset: a comprehensive compilation of surface mass balance field observations over the Antarctic Ice Sheet

Abstract. A comprehensive compilation of observed records is needed for accurate quantification of surface mass balance (SMB) over Antarctica, which is a key challenge for calculation of Antarctic contribution to global sea level change. Here, we present the AntSMB dataset: a new quality-controlled dataset of a variety of published field measurements of the Antarctic Ice Sheet SMB by means of stakes, snow pits, ice cores, ultrasonic sounders, and ground-penetrating radar (GPR). The dataset collects 3579 individual multi-year-averaged observations, 687 annually resolved time series from 675 sites extending back over the past 1000 years, and daily resolved records covering 245 years from 32 sites across the whole ice sheet. These records are derived from ice cores, snow pits, stakes/stake farms, and ultrasonic sounders. Furthermore, GPR multi-year-averaged measurements are included in the dataset, covering an area of 22 025 km2. This is the first ice-sheet-scale compilation of SMB records at different temporal (daily, annual, and multi-year) resolutions from multiple types of measurement and is available at https://doi.org/10.11888/Glacio.tpdc.271148 (Wang et al., 2021). The database has potentially wide applications such as the investigation of temporal and spatial variability in SMB, model validation, assessment of remote sensing retrievals, and data assimilation. As a case of model estimation, records of the AntSMB dataset are used to assess the performance of ERA5 for temporal and spatial variability in SMB over Antarctica.

Performance of MAR (v3.11) in simulating the drifting-snow climate and surface mass balance of Adélie Land, East Antarctica

Abstract. Drifting snow, or the wind-driven transport of snow particles originating from clouds and the surface below and above 2 m above ground and their concurrent sublimation, is a poorly documented process on the Antarctic ice sheet, which is inherently lacking in most climate models. Since drifting snow mostly results from erosion of surface particles, a comprehensive evaluation of this process in climate models requires a concurrent assessment of simulated drifting-snow transport and the surface mass balance (SMB). In this paper a new version of the drifting-snow scheme currently embedded in the regional climate model MAR (v3.11) is extensively described. Several important modifications relative to previous version have been implemented and include notably a parameterization for drifting-snow compaction of the uppermost snowpack layer, differentiated snow density at deposition between precipitation and drifting snow, and a rewrite of the threshold friction velocity above which snow erosion initiates. Model results at high resolution (10 km) over Adélie Land, East Antarctica, for the period 2004–2018 are presented and evaluated against available near-surface meteorological observations at half-hourly resolution and annual SMB estimates. The evaluation demonstrates that MAR resolves the local drifting-snow frequency and transport up to the scale of the drifting-snow event and captures the resulting observed climate and SMB variability, suggesting that this model version can be used for continent-wide applications.

Surface Mass Balance Models Vs. Stake Observations: A Comparison in the Lake Vostok Region, Central East Antarctica

The surface mass balance (SMB) is very low over the vast East Antarctic Plateau, for example in the Vostok region, where the mean SMB is on the order of 20–35 kg m-2 a-1. The observation and modeling of spatio-temporal SMB variations are equally challenging in this environment. Stake measurements carried out in the Vostok region provide SMB observations over half a century (1970–2019). This unique data set is compared with SMB estimations of the regional climate models RACMO2.3p2 (RACMO) and MAR3.11 (MAR). We focus on the SMB variations over time scales from months to decades. The comparison requires a rigorous assessment of the uncertainty in the stake observations and the spatial scale dependence of the temporal SMB variations. Our results show that RACMO estimates of annual and multi-year SMB agree well with the observations. The regression slope between modelled and observed temporal variations is close to 1.0 for this model. SMB simulations by MAR are affected by a positive bias which amounts to 6 kg m-2 a-1 at Vostok station and 2 kg m-2 a-1 along two stake profiles between Lake Vostok and Ridge B. None of the models is capable to reproduce the seasonal distributions of SMB and precipitation. Model SMB estimates are used in assessing the ice-mass balance and sea-level contribution of the Antarctic Ice Sheet by the input-output method. Our results provide insights into the uncertainty contribution of the SMB models to such assessments.

Analysis of the surface mass balance for deglacial climate simulations

Abstract. A realistic simulation of the surface mass balance (SMB) is essential for simulating past and future ice-sheet changes. As most state-of-the-art Earth system models (ESMs) are not capable of realistically representing processes determining the SMB, most studies of the SMB are limited to observations and regional climate models and cover the last century and near future only. Using transient simulations with the Max Planck Institute ESM in combination with an energy balance model (EBM), we extend previous research and study changes in the SMB and equilibrium line altitude (ELA) for the Northern Hemisphere ice sheets throughout the last deglaciation. The EBM is used to calculate and downscale the SMB onto a higher spatial resolution than the native ESM grid and allows for the resolution of SMB variations due to topographic gradients not resolved by the ESM. An evaluation for historical climate conditions (1980–2010) shows that derived SMBs compare well with SMBs from regional modeling. Throughout the deglaciation, changes in insolation dominate the Greenland SMB. The increase in insolation and associated warming early in the deglaciation result in an ELA and SMB increase. The SMB increase is caused by compensating effects of melt and accumulation: the warming of the atmosphere leads to an increase in melt at low elevations along the ice-sheet margins, while it results in an increase in accumulation at higher levels as a warmer atmosphere precipitates more. After 13 ka, the increase in melt begins to dominate, and the SMB decreases. The decline in Northern Hemisphere summer insolation after 9 ka leads to an increasing SMB and decreasing ELA. Superimposed on these long-term changes are centennial-scale episodes of abrupt SMB and ELA decreases related to slowdowns of the Atlantic meridional overturning circulation (AMOC) that lead to a cooling over most of the Northern Hemisphere.

Brief communication: CMIP6 does not suggest any atmospheric blocking increase in summer over Greenland by 2100

AbstractThe Greenland blocking index (GBI), an indicator of the synoptic‐scale circulation over Greenland, has been anomalously positive during most summers since the late 1990s. Such changes in atmospheric circulation, favouring anticyclonic conditions, have led to an increase in Greenland summer temperatures, a decrease in cloud cover and larger surface melt. The GBI is therefore a key indicator of melting and surface mass balance variability over the Greenland ice sheet. However, the models of fifth phase of the Coupled Model Intercomparison Project (CMIP5) do not represent the increase in GBI that is suggested by recent observations, and do not project any significant increase in GBI until 2100. In this study, the new generation of CMIP6 Earth‐system models is evaluated in order to analyse the evolution of the future GBI. All CMIP5 and CMIP6 projections reveal the same trend towards a decrease of the GBI until 2100 and no model reproduces the strong increase in the persistence of summer blocking events observed over the last few decades. Significant melting events related to a highly positive GBI, as observed in summer 2019, are still not considered by CMIP6 models and therefore the projected surface melt increase of the ice sheet could be underestimated if such summer circulation changes persist in the next decades.

Scoring Antarctic surface mass balance in climate models to refine future projections

Abstract. An increase in Antarctic Ice Sheet (AIS) surface mass balance (SMB) has the potential to mitigate future sea level rise that is driven by enhanced solid ice discharge from the ice sheet. For climate models, AIS SMB provides a difficult challenge, as it is highly susceptible to spatial, seasonal, and interannual variability. Here we use a reconstructed data set of AIS snow accumulation as “true” observational data, to evaluate the ability of the CMIP5 and CMIP6 suites of models in capturing the mean, trends, temporal variability, and spatial variability in SMB over the historical period (1850–2000). This gives insight into which models are most reliable for predicting SMB into the future. We found that the best scoring models included the National Aeronautics and Space Administration (NASA) GISS model and the Max Planck Institute (MPI) for Meteorology's model for CMIP5, as well as one of the Community Earth System Model v2 (CESM2) models and one MPI model for CMIP6. Using a scoring system based on SMB mean value, trend, and temporal variability across the AIS, as well as spatial SMB variability, we selected a subset of the top 10th percentile of models to refine 21st century (2000–2100) AIS-integrated SMB projections to 2274 ± 282 Gt yr−1, 2358 ± 286 Gt yr−1, and 2495 ± 291 Gt yr−1 for Representative Concentration Pathways (RCPs) 2.6, 4.5, and 8.5, respectively. We also reduced the spread in AIS-integrated mean SMB by 79 %, 79 %, and 74 % in RCPs 2.6, 4.5, and 8.5, respectively. Notably, we find that there is no improvement from CMIP5 to CMIP6 in overall score. In fact, CMIP6 performed slightly worse on average compared to CMIP5 at capturing the aforementioned SMB criteria. Our results also indicate that model performance scoring is affected by internal climate variability (particularly the spatial variability), which is illustrated by the fact that the range in overall score between ensemble members within the CESM1 Large Ensemble is comparable to the range in overall score between CESM1 model simulations within the CMIP5 model suite. We also find that a higher horizontal resolution does not yield to a conclusive improvement in score.

Spatio-temporal variability of surface mass balance in the accumulation zone of the Mer de Glace, French Alps, from multitemporal terrestrial LiDAR measurements

AbstractSpatio-temporal variability of the winter surface mass balance is a major uncertainty in the modelling of annual surface mass balance. Moreover, its measurement at high spatio-temporal resolution (sub-200 m) is very useful to force, calibrate or validate models. This study presents the results of year-round field campaigns to study the evolution of the surface mass balance in a ~2 km2 portion of the accumulation zone of the Mer de Glace (France). It is based on repeated LiDAR acquisitions, submergence-velocity measurements and meteorological records. The two methods used to quantify submergence velocities show good agreement. They present a linear temporal evolution without significant seasonal changes but display significant spatial variability. We conclude that a dense network of submergence velocity measurements is required to reduce the uncertainties when computing winter and annual surface mass balance from digital elevation model differencing. Finally, a hight spatio-temporal variability of the winter surface mass balance is highlighted (e.g., a std dev. of 0.92 m in April) even though the topography is homogeneous (std dev. of 25 m). Attempts to relate this variability to different morpho-topographic variables and wind-related indexes show the need for studies conducted at the snowfall event scale to obtain a better understanding of the variability in mass balance at the glacier scale.

Greenland Ice Sheet Elevation Change: Direct Observation of Process and Attribution at Summit

AbstractGreenland Ice Sheet surface elevation is changing as mass loss accelerates. In understanding elevation change, the magnitudes of physical processes involved are important for interpretation of altimetry and assessing changes in these processes. The four key processes are surface mass balance (SMB), firn densification, ice dynamics, and isostatic adjustment. We quantified these processes at Summit, Greenland, where monthly Global Navigation Satellite System (GNSS) snowmobile traverses measured elevation change from 2008 to 2018. We find an elevation increase of 0.019 m a−1. The sum of the effects of the four processes reproduces the measured elevation time series, in linear trend and in intra‐annual variability. The short‐term variability in elevation is primarily explained by the variability in SMB. Since SMB has not changed significantly over the last century, and the other processes change over longer time scales, the elevation change likely has been ongoing for at least the last 100 years.

Temporal and spatial variabilities in surface mass balance at the EGRIP site, Greenland from 2009 to 2017

Temporal variability in surface mass balance (SMB) on the Greenland ice sheet is important for understanding the mass balance of the ice sheet. Additionally, knowledge of the spatial variability in SMB at ice core drilling sites helps to interpret the spatial representativeness of SMB data obtained from a single ice core. In this study, to investigate the spatiotemporal variability in recent SMB in the East Greenland Ice Core Project (EGRIP) area in the northeastern Greenland ice sheet, pit observations were made at six sites in the summers of 2016–2018. In all pits, depth profiles of water isotope ratios showed clear seasonal variations. The annual SMB differed from site to site, which is probably due to post-depositional redistribution of snow caused by wind erosion and snowdrift. However, the multiple-site averages of annual SMBs, which ranged from 134 to 157 mm w. e. yr−1 (average 146 mm w. e. yr−1) during 2009–2017, were very similar. This indicates that annual SMBs in the EGRIP area were nearly constant in this period. The seasonal SMBs in the EGRIP area tended to be larger in the summer–winter period than in the winter–summer period.

Historical surface mass balance from a frequency-modulated continuous-wave (FMCW) radar survey from Zhongshan station to Dome A

AbstractUsing frequency-modulated continuous wave radar data from the 32nd Chinese Antarctic Research Expedition in 2015/16, subsurface profiles were obtained along an East Antarctic inland traverse from Zhongshan station to Dome A, and four distinct regions were selected to analyze the spatiotemporal variability in historical surface mass balance (SMB). Based on depth, density, and age data from ice cores along the traverse, the radar data were calibrated to yield average SMB data. The zone 49–195 km from the coast has the highest SMB (235 kg m−2a−1). The 780–892 km zone was most affected by the Medieval Warm Period and the Little Ice Age, and the SMB duringad1454–1836 (71 kg m−2a−1) was only one-quarter of that in the 20th century. The SMB in the 1080–1157 km zone fluctuates the most, possibly due to erosion or irregular deposition of snow by katabatic winds in low SMB areas with surface elevation fluctuations. Dome A (1157–1236 km) has the lowest SMB (29 kg m−2a−1) and did not decrease during Little Ice Age. Understanding the spatiotemporal variability of SMB in a larger space can help us understand the complex climate history of Antarctica.

Antarctic Surface Mass Balance: Natural Variability, Noise, and Detecting New Trends

AbstractThe emergence of new, statistically robust trends in Antarctic surface mass balance (SMB) requires an understanding of the underlying SMB variability (noise). We show that simple white or AR[1] noise models do not adequately represent the variability of SMB in both the RACMO2.3p2 SMB model output (1979–2017) and composite ice core records (1800–2010), underestimating low‐frequency variability. By testing a range of noise models, we find that a Generalized Gauss Markov (GGM) model better approximates the noise around a linear trend. The general preference for GGM noise applies over spatial scales from the total ice sheet down to individual drainage basins. Over the longest timescales considered, trend uncertainties are 1.3–2.3 times larger using a GGM model compared to using an AR1 model at the ice sheet scale. Overall, our results suggest that larger trends or longer periods are required before new SMB trends can be robustly separated from background noise.