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Surface mass balance (SMB) over the Antarctic Ice Sheet must be better understood to document current Antarctic contribution to sea-level rise. Field 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 validate 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 terrains. 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 has the advantage of being spatially extensive with a temporal resolution that varies between annual and sub-decadal resolution from which we can derive a SMB record over the entire radar survey. This comparison allows us therefore 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 for most ice rises a plateau ~1–2 km away from the ice crest 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 it is limited to a surface areas 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.

Ice cores remain the highest resolution proxy for measuring past surface mass balance (SMB) that can be used for model-data comparison. However, there is a clear difference in the spatial resolution of the ice cores, with a surface sample on the order of cm2, and the spatial resolution of models, with at best a surface footprint on the order of a few km2. Comparing ice core SMB records and model SMB outputs directly is therefore not a one-to-one comparison. In addition, it is well known that ice cores, as point measurements, sample very local SMB conditions which can be affected by local wind redistribution of the SMB at the surface.We set out to answer the question: how representative are ice-cores of regional SMB? For this, we use several ground-penetrating radar (GPR) surveys in East Antarctica, which have co-located ice core drill sites. Most of our sites share a relatively similar climatology, as they are all coastal ice promontories/rises along the Dronning Maud Land coast, with the exception of the Dome Fuji survey on the high plateau in the interior of the continent.We will show that the comparison of the SMB signals of the GPR and the ice core records allows us to estimate the spatial footprint of the ice cores, and that this spatial footprint varies widely from site to site. We will provide a summary of the spatial and temporal characteristics for each location.

Promontory ice rises are locally grounded features adjacent to ice shelves that are still connected to the ice sheet. Ice rises are an archive for the atmospheric and ice dynamic history of the respective outflow regions where the presence, absence, or migration of Raymond arches in radar stratigraphy represents a memory of the ice-rise evolution. However, ice rises and their inferred dynamic history are not yet used to constrain large-scale ice flow model spin-ups because matching the arch amplitudes includes many unknown parameters, e.g., those pertaining to ice rheology. In particular, anisotropic ice flow models predict gradients in ice fabric anisotropy on either side of an ice divide. However, this has thus far not been validated with observations. The ground-based phase-sensitive Radio Echo Sounder (pRES) has previously been used to infer ice fabric types for various flow regimes using the co-polarized polarimetric coherence phase as a metric to extract information from the birefringent radar backscatter. Here, we apply this technique using quad-polarimetric radar data along a 5 km transect across a ridge near the triple junction of Hammarryggen Ice Rise at the Princess Ragnhild Coast. A comparison with ice core data collected at the dome shows that the magnitude of ice fabric anisotropy can reliably be reconstructed from the quad-polarimetric data. We use the combined dataset also to infer the spatial variation of ice fabric orientations in the vicinity of the triple junction. The observations are integrated with airborne radar profiles and strain rates based on the shallow ice approximation. We then discuss whether estimated anisotropy from radar polarimetry on ice rises, in general, can be another observational constraint to better ice rises as an archive of ice dynamics.

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 (km 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 cores records has been increasing these last 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), ions concentrations (Na+, K+, Mg+, Ca+, 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 derived data 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 of deuterium excess (d-excess) and a long-term increase of δ18O, although less pronounced. In terms of chemical proxies, the non-sea-salt sulfate (nssSO42-) concentrations of FK17 are twice the ones of TIR18 and display an increasing trend on the long-term while 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 sea water 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 and 0.56 m i.e. a-1 respectively), but the annual records are very different: since the 1950’s, 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 km scale) in East Antarctica. The “Mass2Ant IceCores” datasets are available on Zenodo (https://doi.org/10.5281/zenodo.7848435; Wauthy et al., 2023).

Changes in sea ice conditions and atmospheric circulation over the Southern Ocean play an important role in modulating Antarctic climate. However, observations of both sea ice and wind conditions are limited in Antarctica and the Southern Ocean, both temporally and spatially. Ice core chemistry data can be used to reconstruct changes over annual, decadal, and millennial timescales. To facilitate sea ice and wind reconstructions, the CLIVASH2k working group has compiled a database of two species, sodium [Na+] and sulphate [SO42-], commonly measured ionic species. The database contains records from 105 Antarctic ice cores, containing records with a maximum age duration of 2000 years. An initial filter has been applied, based on evaluation against climate observations, to identify sites suitable for reconstructing past sea ice conditions, wind strength, or atmospheric circulation.

The future contributions of the Antarctic Ice Sheet to sea level rise will be highly dependent on the evolution of its surface mass balance (SMB), which can offset increased ice discharge at the grounding line. In-situ SMB constraints over annual to multi-decadal timescales come mostly from firn and ice cores. However, although they have a high temporal resolution, ice cores are local measurements of SMB with a surface footprint on the order of cm2. Post depositional processes (e.g. wind driven redistribution) can change the initial snowfall record locally and therefore affect our interpretation of the SMB signal recovered. On the other hand, regional climate models have a high temporal resolution but may miss some of the processes at work as a result of their large spatial footprint, on the order of km2. Comparisons of ice core and model SMB records often show large discrepancies in terms of trends and variability.We investigate the representativeness of a single shallow core record of SMB of the area surrounding it. For this, we use ice-penetrating radar data, co-located with the ice core records examined, to obtain a multi-annual to decadal radar-derived SMB record. We then compare the radar-derived SMB records to the ice core SMB records to determine the surface area that the ice core record is representative of, in terms of mean SMB as well as SMB temporal variability on historical timescales. We examine ice core records situated over the coastal ice rises of East Antarctica, where SMB is high and spatially heterogeneous, as well as over the interior of the West Antarctic Ice Sheet, where SMB is more uniform spatially. By comparing these two contrasting regions in terms of SMB, we will determine whether a general rule of thumb can be obtained to determine the spatial representativeness of an ice core SMB record.

This work presents the results of physical and biological investigations at 27 biogeochemical stations of early winter sea ice in the Ross Sea during the 2017 PIPERS cruise. Only two similar cruises occurred in the past, in 1995 and 1998. The year 2017 was a specific year, in that ice growth in the Central Ross Sea was considerably delayed, compared to previous years. These conditions resulted in lower ice thicknesses and Chl- a burdens, as compared to those observed during the previous cruises. It also resulted in a different structure of the sympagic algal community, unusually dominated by Phaeocystis rather than diatoms. Compared to autumn-winter sea ice in the Weddell Sea (AWECS cruise), the 2017 Ross Sea pack ice displayed similar thickness distribution, but much lower snow cover and therefore nearly no flooding conditions. It is shown that contrasted dynamics of autumnal-winter sea-ice growth between the Weddell Sea and the Ross Sea impacted the development of the sympagic community. Mean/median ice Chl- a concentrations were 3–5 times lower at PIPERS, and the community status there appeared to be more mature (decaying?), based on Phaeopigments/Chl- a ratios. These contrasts are discussed in the light of temporal and spatial differences between the two cruises., info:eu-repo/semantics/published

Several studies have shown that there is often a poor match between surface mass balance (SMB, mass gain at the surface of the ice sheet) simulated by regional climate models and the one locally measured from ice cores in Antarctica. Models’ representation of the physical processes that affect SMB is known to be imperfect, while ice core records may be strongly influenced by local processes such as post-depositional wind redistribution and precipitation intermittency. These two sources of uncertainty likely both have a role to play in the discrepancy identified between modeled and observed ice core SMB estimates over the past centuries.The goal here is to estimate the uncertainties associated with the difference between a point-wise measurement of SMB as provided by the ice core and the SMB averages over a grid of several square kilometers of the models. To do so, we use ground-penetrating radar (GPR) data, collected over several ice rises, located along the high accumulation Princess Ragnhild Coast (East Antarctica), to obtain a multi-year resolution record that goes back ∼30-40 years, representing SMB spatial and temporal variability at the scale of a few km2 for each ice rise. Ice cores were collected during each radar field campaign, which allows us to place age constraints on the radar stratigraphy obtained and compare the GPR SMB estimates with the ice core SMB estimate.Therefore, we are able to calculate an error of representativeness for each ice core SMB, estimated as the difference between the average GPR SMB over a few km2 and the ice core SMB. This representativeness error can be split into two components: a systematic error (on the order of ∼0.1 m w.e. yr-1) and a random error (on the order of ±1 cm w.e. yr-1). Finally, we then compare our corrected ice core SMB records to regional SMB derived from a state-of-the-art polar-oriented regional climate model to quantify the impact of ice core uncertainties on the modeled-observed SMB discrepancy.

International audience; Winter to summer CO2 dynamics within landfast sea ice in McMurdo Sound (Antarctica) were investigated using bulk ice pCO2 measurements, air‐snow‐ice CO2 fluxes, dissolved inorganic carbon (DIC), total alkalinity (TA), and ikaite saturation state. Our results suggest depth‐dependent biotic and abiotic controls that led us to discriminate the ice column in three layers. At the surface, winter pCO2 supersaturation drove CO2 release to the atmosphere while spring‐summer pCO2 undersaturation led to CO2 uptake most of the time. CO2 fluxes showed a diel pattern superimposed upon this seasonal pattern which was potentially assigned to either ice skin freeze‐thaw cycles or diel changes in net community production. In the ice interior, the pCO2 decrease across the season was driven by physical processes, mainly independent of the autotrophic and heterotrophic phases. Bottom sea ice was characterized by a massive biomass build‐up counterintuitively associated with transient heterotrophic activity and nitrate plus nitrite accumulation. This inconsistency is likely related to the formation of a biofilm. This biofilm hosts both autotrophic and heterotrophic activities at the bottom of the ice during spring and may promote calcium carbonate precipitation.