The East Antarctic Ice Sheet is the largest, highest, coldest, driest, and windiest ice sheet on Earth. Understanding of the surface mass balance (SMB) of Antarctica is necessary to determine the present state of the ice sheet, to make predictions of its potential contribution to sea level rise, and to determine its past history for paleoclimatic reconstructions. However, SMB values are poorly known because of logistic constraints in extreme polar environments, and they represent one of the biggest challenges of Antarctic science. Snow accumulation is the most important parameter for the SMB of ice sheets. SMB varies on a number of scales, from small-scale features (sastrugi) to ice-sheet-scale SMB patterns determined mainly by temperature, elevation, distance from the coast, and wind-driven processes. In situ measurements of SMB are performed at single points by stakes, ultrasonic sounders, snow pits, and firn and ice cores and laterally by continuous measurements using ground-penetrating radar. SMB for large regions can only be achieved practically by using remote sensing and/or numerical climate modeling. However, these techniques rely on ground truthing to improve the resolution and accuracy. The separation of spatial and temporal variations of SMB in transient regimes is necessary for accurate interpretation of ice core records. In this review we provide an overview of the various measurement techniques, related difficulties, and limitations of data interpretation; describe spatial characteristics of East Antarctic SMB and issues related to the spatial and temporal representativity of measurements; and provide recommendations on how to perform in situ measurements.

/pdf/ground-based-measurements-of-spatial-and-temporal-he9zzbslph.pdf

Ground‐based measurements of spatial and temporal variability of snow accumulation in East Antarctica

A database of surface Antarctic snow isotopic composition is constructed using available measurements, with an estimate of data quality and local variability. Although more than 1000 locations are documented, the spatial coverage remains uneven with a majority of sites located in specific areas of East Antarctica. The database is used to analyze the spatial variations in snow isotopic composition with respect to geographical characteristics (elevation, distance to the coast) and climatic features (temperature, accumulation) and with a focus on deuterium excess. The capacity of theoretical isotopic, regional, and general circulation atmospheric models (including “isotopic” models) to reproduce the observed features and assess the role of moisture advection in spatial deuterium excess fluctuations is analyzed.

/pdf/a-review-of-antarctic-surface-snow-isotopic-composition-1eanqllt52.pdf

A Review of Antarctic Surface Snow Isotopic Composition : Observations, Atmospheric Circulation, and Isotopic Modeling

[1] During the 1996 Programma Nazionale di Ricerche in Antartide-International Trans-Antarctic Scientific Expedition traverse, two firn cores were retrieved from the Talos Dome area (East Antarctica) at elevations of 2316 m (TD, 89 m long) and 2246 m (ST556, 19 m long). Cores were dated by using seasonal variations in non-sea-salt (nss) SO42− concentrations coupled with the recognition of tritium marker level (1965–1966) and nss SO42− spikes due to the most important volcanic events in the past (Pinatubo 1991, Agung 1963, Krakatoa 1883, Tambora 1815, Kuwae 1452, Unknown 1259). The number of annual layers recognized in the TD and ST556 cores was 779 and 97, respectively. The δD record obtained from the TD core has been compared with other East Antarctic isotope ice core records (Dome C EPICA, South Pole, Taylor Dome). These records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries, which might be related to the Little Ice Age (LIA) cold period. Because of the high degree of geographical variability, the strongest LIA cooling was not temporally synchronous over East Antarctica, and the analyzed records do not provide a coherent picture for East Antarctica. The accumulation rate record presented for the TD core shows a decrease during part of the LIA followed by an increment of about 11% in accumulation during the 20th century. At the ST556 site, the accumulation rate observed during the 20th century was quite stable.

/pdf/eight-centuries-of-volcanic-signal-and-climate-change-at-13sq1t2cgm.pdf

Eight centuries of volcanic signal and climate change at Talos Dome (East Antarctica)

Recent snow accumulation rate is a key quantity for ice-core and mass-balance studies. Several accumulation measurement methods (stake farm, fin core, snow-radar profiling, surface morphology, remote sensing) were used, compared and integrated at eight sites along a transect from Terra Nova Bay to Dome C, East Antarctica, to provide information about the spatial and temporal variability of snow accumulation. Thirty-nine cores were dated by identifying tritium/b marker levels (1965-66) and non-sea-salt (nss) SO4 2- spikes of the Tambora (Indonesia) volcanic event (1816) in order to provide information on temporal variability. Cores were linked by snow radar and global positioning system surveys to provide detailed information on spatial variability in snow accumulation. Stake-farm and ice-core accumulation rates are observed to differ significantly, but isochrones (snow radar) correlate well with ice-core derived accumulation. The accumulation/ablation pattern from stake measurements suggests that the annual local noise (metre scale) in snow accumulation can approach 2 years of ablation and more than four times the average annual accumulation, with no accumulation or ablation for a 5 year period in up to 40% of cases. The spatial variability of snow accumulation at the kilometre scale is one order of magnitude higher than temporal variability at the multi-decadal/secular scale. Stake measurements and firn cores at Dome C confirm an approximate 30% increase in accumulation over the last two centuries, with respect to the average over the last 5000 years.

/pdf/spatial-and-temporal-variability-of-snow-accumulation-in-245v5ljaj6.pdf

Spatial and temporal variability of snow accumulation in East Antarctica from traverse data

. Here we present Antarctic snow accumulation variability at the regional scale over the past 1000 years. A total of 79 ice core snow accumulation records were gathered and assigned to seven geographical regions, separating the high-accumulation coastal zones below 2000 m of elevation from the dry central Antarctic Plateau. The regional composites of annual snow accumulation were evaluated against modelled surface mass balance (SMB) from RACMO2.3p2 and precipitation from ERA-Interim reanalysis. With the exception of the Weddell Sea coast, the low-elevation composites capture the regional precipitation and SMB variability as defined by the models. The central Antarctic sites lack coherency and either do not represent regional precipitation or indicate the model inability to capture relevant precipitation processes in the cold, dry central plateau. Our results show that SMB for the total Antarctic Ice Sheet (including ice shelves) has increased at a rate of 7 ± 0.13 Gt decade−1 since 1800 AD, representing a net reduction in sea level of ∼ 0.02 mm decade−1 since 1800 and ∼ 0.04 mm decade−1 since 1900 AD. The largest contribution is from the Antarctic Peninsula (∼ 75 %) where the annual average SMB during the most recent decade (2001–2010) is 123 ± 44 Gt yr−1 higher than the annual average during the first decade of the 19th century. Only four ice core records cover the full 1000 years, and they suggest a decrease in snow accumulation during this period. However, our study emphasizes the importance of low-elevation coastal zones, which have been under-represented in previous investigations of temporal snow accumulation.

/pdf/regional-antarctic-snow-accumulation-over-the-past-1000-10jd0nhtsr.pdf

Regional Antarctic snow accumulation over the past 1000 years

A 42.2 m firn core was collected at the Hercules Neve plateau (100 km inland and 2960 m a.s.L), northern Victoria Land, during the 1994-95 Italian Antarctic Expedition. Chemical (Cl–, NO3 –, SO4 2–’; δ18O δ18O δ18O; m-2a-1) and isotope (5180) analyses were performed to evaluate the snow-accumulation rate at this site. Tritium measurements were performed in the upper part of the core to narrow down the dating of the core. High nssSO4 2- concentrations seem to be related to some explosive volcanic eruptions, such as Tambora (AD 1815) and the preceding event called "Unknown" (AD 1809), Coseguina (AD 1835), Makjan (AD 1861), Krakatoa (AD 1883) and Tarawera (AD 1886). A comparison between the seasonal variations observed in the isotope and chemical profiles was carried out in order to reduce the dating uncertainty, using the tritium and the volcanic markers as time constraints. A deposition period of 222 years was determined. The 3 year smoothed «5180 profile shows more negative values from the bottom of the core (dated AD 1770) throughout the 19th century, suggesting "cooler" conditions, in agreement with other East Antarctic ice-core records! Subsequently, a general increase in δ180-values is observed. The calculated average snow-accumulation rates between the above-mentioned time markers are 111-129 kg m-2a-1.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/F3AF3A4D40D6B2B7CF728E32537D06B7/S0260305500267487a.pdf/div-class-title-200-years-of-isotope-and-chemical-records-in-a-firn-core-from-hercules-neve-northern-victoria-land-antarctica-div.pdf

R. Gragnani

Papers

200 years of isotope and chemical records in a firn core from Hercules Névé, northern Victoria Land, Antarctica