East Antarctica Ice Sheet Research Articles

East Antarctica ice sheet in Schirmacher Oasis, Central Dronning Maud Land, during the past 158 ka

Varied geomorphic landforms along the coast of eastern Antarctica suggest that the most recent phase of ice retreat was spatially heterogeneous. Ice retreat here comprised; a thinning of the East Antarctic Ice Sheet (EAIS) by up to 500 m and the recession of the ice wall in kilometre. This retreat deposited moraines over the Schirmacher Oasis (SO) in central Dronning Maud Land with minimal reworking. The present study used optical dating of the recessional moraines to determine the timing of their final emplacement. Three phases of moraine deposition, during 158–125 ka; 76–50 ka and 22 ka to present, were inferred. It is suggested that decreased sea surface temperatures and increased sea ice cover of the surrounding oceans limited the moisture supply and led to the retreat of ice. By ~ 35 ka the SO became ice-free and has remained so, ever since. The inference that the ice sheet in this region was moisture limited, implies that in a global warming context, this region may not contribute to an increase in sea-level. Instead, a warming-induced increase in moisture supply may even add to ice cover in the region.

Detection of Surface Crevasses over Antarctic Ice Shelves Using SAR Imagery and Deep Learning Method

Crevasses are formed by glacier movement and the stresses within glacier ice. Knowledge of the crevasses’ distribution is critical for understanding the glacier and ice shelf stability. In this study, we propose an automated crevasse extraction framework based on Sentinel-1 SAR imagery and an improved U-Net network. The spatial distribution of crevasses on Antarctic ice shelves in 2020 was mapped with a spatial resolution of ~40 m, and the characteristics of crevasses on the Nickerson Ice Shelf, Jelbart Ice Shelf, Amery Ice Shelf, Thwaites Glacier, and Shackleton Ice Shelf were analyzed. The results indicated the extraction accuracy of our method was 84.2% and the F1 score was 72.5%. Compared with previous published studies, the identification of the crevasse areas had good visual consistency. However, in some scenes, the recall rate was relatively lower due to the quality of the SAR image, terrain surrounding the crevasses, and observation geometry. The crevasses on different ice shelves had different characteristics in terms of length, density, type, and spatial pattern, implying the different stress structures of ice shelves. The Thwaites Glacier and the Nickerson Ice Shelf in the West Antarctica Ice Sheet (WAIS) had shorter ice crevasses, whereas the lengths of ice crevasses on the Jelbart Ice Shelf and the Amery Ice Shelf in the East Antarctica Ice Sheet (EAIS) were relatively long. Nevertheless, there are more closely spaced crevasses on the ice shelf in WAIS compared to that in the EAIS. For the distribution of crevasse types, the Nickerson Ice Shelf and the Shackleton Ice Shelf had various forms of crevasses. There were mainly transverse crevasses developed on the Jelbart Ice Shelf and the Amery Ice Shelf. This study provides a helpful reference and guidance for automated crevasse extraction. The method proposed by this study manifests great application potential and the efficacy of producing a time-series crevasse data set with higher spatial resolution and larger coverage. In the future, more Sentinel-1 SAR imagery will be applied and the effect of temporal and spatial variations in crevasses on the stability of ice shelves will be investigated, which will contribute to project the ice shelf stability and explore the sea level rise implications of recent and future cryosphere changes.

Physically-constrained data-driven inversions to infer the bed topography beneath glaciers flows. Application to East Antarctica

A method for infering bed topography beneath glaciers from surface measurements (elevation from altimetry and velocity from InSAR) and sparse thickness measurements is developed and evaluated. The method is based on an original non-isothermal Reduced Uncertainty (RU) version of the Shallow Ice Approximation (SIA) equation that natively incorporates the surface measurements. The flow model has a single dimensionless multi-physics parameter γ. This parameter takes into account the basal slipperiness and the variable vertical rate factor profiles, thus the vertical thermal variations. The inversions are based on three steps involving: an Artificial Neural Network (ANN) and two Variational Data Assimilation (VDA) processes. The ANN-based stage aims at estimating the multi-physics number γ from the thickness measurements; the resulting estimator is remarkably robust. The full inversion method is valid for half-sheared flows (presenting a moderate basal slipperiness): it can be applied to inland ice-sheets areas. Also these estimates connect continuously with estimates from mass conservation only, i.e. with areas of sliding flows. Numerical results are presented for areas of the East Antarctica Ice Sheet where bed elevation can be very uncertain (Bedmap2 values). Estimates are valid for wavelengths longer than \(\sim 10 \bar h\) (due to the long wave assumption, shallow flow model) with resolution at \(\sim \bar h\) (\(\bar h\) a characteristic thickness value).

Stable isotopic composition in snowpack along the traverse from a coastal location to Dome A (East Antarctica): Results from observations and numerical modeling

Stable isotopic composition (δ18O and δD) in Antarctic snow/ice cores serves as the proxy of past temperature. However, the accuracy of temperature reconstruction is largely dependent on the relationship between water isotopes and local temperature (δ-T) derived from present conditions. Thus, it is crucial to quantitatively understand the spatial δ-T relationship and the influencing factors of δ18O and δD in surface snow besides temperature. In this work, we characterized the spatial and temporal variation of stable isotopes in surface snow using a comprehensive assessment of observations and simulations on the traverse from the coast to Dome A, the summit of East Antarctica ice sheet. The δ18O and δD from surface snow and snow pit samples show an insignificant variation at interannual scale, possibly suggesting that interannual changes in controlling factors are not remarkable during the investigation period. Along the traverse, the spatial δ18O-T slope is 0.91‰·oC−1 based on averages of δ18O measurements for snow pits and annual mean temperature at the sampling site. Results from the mixed cloud isotope model (MCIM) suggest that the effects of evaporative conditions and transportation paths of moisture on water isotopes for specific sites are insignificant. Therefore, it is more important to consider other effects on water isotopes (e.g. post-depositional processes) when interpreting ice core records, particularly in interior Antarctica.

Fe variation characteristics and sources in snow samples along a traverse from Zhongshan Station to Dome A, East Antarctica

Iron concentrations in the Southern Ocean are thought to act as a driver of the regular glacial–interglacial cycles in atmospheric carbon dioxide (CO2). This study presents the concentrations of bioavailable Fe (dissolved Fe (DFe) and total dissolved Fe (TDFe)), major ions (Na+, K+, Mg2+, Ca2+, Cl−,NO3‐,SO42‐ and methanesulfonic acid (MSA)), heavy metal elements (Sr, Pb, V, Ti and Cd), and rare earth elements (REEs; specifically, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) and the oxygen and hydrogen isotopic compositions (δ18O and δD) from a series of surface snow samples collected during from January 22 to February 5, 2017 along a traverse from Zhongshan Station to Dome A in East Antarctica. The results reflect the Antarctic surface snow Fe and the other trace element concentrations on the East Antarctica ice sheet. In particular, the DFe and TDFe concentrations were measured using inductively coupled plasma sector field mass spectrometry (SF-ICP-MS). The concentration patterns of DFe and TDFe show three different stages along this transect. First, there is an abrupt decrease with distance inland from the coast and then a slight decreasing trend with increasing elevation. The maximum concentrations were observed at distances of 450–600 km from the coast, indicating that there are different potential sources and/or transporting air masses. The variations show that the sources and processes that deliver bioavailable Fe differ along this transect. These data are useful for assessing bioavailable Fe release from the Antarctic ice sheet.

Estimation of present-day glacial isostatic adjustment, ice mass change and elastic vertical crustal deformation over the Antarctic ice sheet

ABSTRACTThis study explores an iterative method for simultaneously estimating the present-day glacial isostatic adjustment (GIA), ice mass change and elastic vertical crustal deformation of the Antarctic ice sheet (AIS) for the period October 2003–October 2009. The estimations are derived by combining mass measurements of the GRACE mission and surface height observations of the ICESat mission under the constraint of GPS vertical crustal deformation rates in the spatial domain. The influence of active subglacial lakes on GIA estimates are mitigated for the first time through additional processing of ICESat data. The inferred GIA shows that the strongest uplift is found in the Amundsen Sea Embayment (ASE) sector and subsidence mostly occurs in Adelie Terre and the East Antarctica inland. The total GIA-related mass change estimates for the entire AIS, West Antarctica Ice Sheet (WAIS), East Antarctica Ice Sheet (EAIS), and Antarctic Peninsula Ice Sheet (APIS) are 43 ± 38, 53 ± 24, −23 ± 29 and 13 ± 6 Gt a−1, respectively. The overall ice mass change of the AIS is −46 ± 43 Gt a−1 (WAIS: −104 ± 25, EAIS: 77 ± 35, APIS: −20 ± 6). The most significant ice mass loss and most significant elastic vertical crustal deformations are concentrated in the ASE and northern Antarctic Peninsula.

Paleoceanographic changes in the Northeast Indian Ocean during middle Miocene inferred from carbon and oxygen isotopes of foraminiferal fossil shells

The middle Miocene transition witnessed rapid fluctuations in oceanographic and climatic systems. However, very limited work has been attempted in Miocene sediments of the Northern Indian Ocean to identify these changes. Here we present the first detailed δ13C and δ18O records of surface and deep dwelling foraminifera from ODP site 758 in the Northeast Indian Ocean, located atop the Ninetyeast Ridge. Carbon and oxygen isotopic data on Globigerinoides quadrilobatus (planktonic) and Cibicidoides wuellerstorfi (benthic foraminifera) indicated various global and local successions of oceanographic and climatic importance. The climatic events recorded at ODP 758 are; (a) Mid Miocene climatic Optimum (17–15 Ma), (b) Monterey excursion (17–14 Ma), (c) East Antarctica Ice sheet formation (13.8 Ma), (d) Initiation of Indian Summer Monsoon with waning of Antarctica Ice sheet (12.3–10.4 Ma), and (e) evidence of a cooling event (10.2–9.6Ma).Our benthic foraminifera δ18O record showed almost identical deep water evolution to that of the Indo Pacific for 13.9–11.5 Ma interval. A significant decrease in δ13Cben at ~10.2 Ma was indicative of a complete re-adjustment of the carbon cycle after the Monterey excursion and export of the North Atlantic Deep Water (NADW) towards the southern Ocean to give rise to the Circumpolar Deep Water (CDW), with a δ13C value of ~0.4‰. The formation of the NADW had given rise to modern deep water like conditions at ~10 Ma ago. A comparison of our record with previously published isotopic records from other regions suggested a good correlation between the South Pacific, Indo Pacific and Northeast Indian Ocean during the studied time interval. It appears that a strong westerly Indian Ocean current (MIOjet) may have linked these Oceans from 14 to 9 Ma.

Despite extensive ice melt elsewhere, East Antarctica ice sheet is growing

Despite extensive ice melt elsewhere, East Antarctica ice sheet is growing

Initiation of the West Antarctic Ice Sheet and estimates of total Antarctic ice volume in the earliest Oligocene

AbstractReconstructions of Antarctic paleotopography for the late Eocene suggest that glacial erosion and thermal subsidence have lowered West Antarctic elevations considerably since then, with Antarctic land area having decreased ~20%. A new climate‐ice sheet model based on these reconstructions shows that the West Antarctic Ice Sheet first formed at the Eocene‐Oligocene transition (33.8–33.5 Ma, E‐O) in concert with the continental‐scale expansion of the East Antarctica Ice Sheet and that the total volume of East and West Antarctic ice (33.4–35.9 × 106 km3) was >1.4 times greater than previously assumed. This larger modeled ice volume is consistent with a modest cooling of 1–2°C in the deep ocean during the E‐O transition, lower than other estimates of ~3°C cooling, and suggests the possibility of substantial ice in the Antarctic interior before the Eocene‐Oligocene boundary.

The Climate of the Apes

Climate Science The middle Miocene, around 15 million years ago, was a crucial time in the evolution of apes and eventually humans. Apes had recently evolved, and as climate warmed, their range expanded greatly, across most of Eurasia, leading to further diversification. One view is that some of these Eurasian apes eventually recolonized Africa as climate later cooled, although the fossil record remains sparse from this period. Hamon et al. explored the climatic conditions that led to this period of warmth in the Miocene and particularly that were favorable for the expansion of subtropical forests that the apes depended on. Using a global climate model, they concluded that the range of forests would be greatest when atmospheric CO2 levels were between about 560 and 700 ppmv. The East Antarctica Ice Sheet, which is thought to have begun to form by the middle Miocene as the overall Cenozoic climate was cooling, but not uniformly, was about 25% of its modern extent. Both conditions are needed to increase precipitation in Europe at that time. Further decreases in atmospheric CO2 levels and the expansion of ice led to the reduction of forests later in the Miocene. Geology 10.1130/G32990.1 (2012).

Antarctica ice sheet mass balance

The mass balance of the Antarctica ice sheet is one of the sources of uncertainty about the sea-level rise. However it is not easy to determine the mass balance due to a lack of knowledge of the physical processes affecting both the ice dynamics and the polar climate. Other limitations are the long time lag between a perturbation and its effect, but also the lack of reliable data, the size of the continent and finally the huge range of variability involved. This article examines the results given by three different ways of estimating mass balance, first by measuring the difference between mass input and output, second by monitoring the changing geometry of the continent and third by modelling both the dynamic and climatic evolution of the continent. The concluding synthesis suggests that the East Antarctica ice sheet is more or less in balance, except for a slight signature of Holocene warming, which is still active at the current time. On the contrary, the West Antarctica ice sheet seems to be more sensitive to current warming. To cite this article: F. Rémy, M. Frezzotti, C. R. Geoscience 338 (2006).

Geological evidence for changes in the East Antarctica ice sheet (60°–120°E) during the last glaciation

AbstractThe East Antarctica ice sheet advanced onto the continental shelf during the last glaciation but appears to have been thinner (<300 m) than previously hypothesised and probably did not everywhere extend to the edge of the continental shelf. Where the shelf is wide, the ice probably terminated against shallow banks on its outer edge. There may not have been time for the sheet to develop the maximum profile form and thickness predicted by Hollin (1962) and Hughes and others (1981) of about 1000–500 moverthe shelf. Large outlet glaciers occupied deep troughs that conveyed most of the ice towards the edge of the shelf: intervening areas were less intensely glaciated. Much of Prince Charles Mountains and Amery Oasis were not ice-covered: Vestfold, Bunger and Casey oases were glaciated. Vestfold and Bunger oases became ice-free after 10 ka BP under the influence of the Holocene marine transgression, which was complete by about 6 ka BP. During at least the last 5–6 ka these oases have been approximately their present size. Since then the margins of the Antarctic continental ice sheet have maintained almost steady state conditions against the landward edges of the hill masses.

Miocene isotope reference section, Deep Sea Drilling Project Site 608: An evaluation of isotope and biostratigraphic resolution

We developed an isotope (87Sr/86Sr, δ18O) reference section for the uppermost Oligocene to lower upper Miocene (ca. 25–8 Ma) at Site 608 in the northeastern North Atlantic. This site contains the least ambiguous magnetostratigraphic record of Miocene polarity changes available, providing direct correlations to the Geomagnetic Polarity Time Scale (GPTS). We integrate biostratigraphic, magnetostratigraphic, Sr isotope, and stable isotope data to provide a reference section for Miocene isotope fluctuations. The direct correlation of isotopes and biostratigraphy to the Geomagnetic Polarity Time Scale (GPTS) provides relatively precise age estimates. We use these age estimates to evaluate the timing of first and last occurrences of planktonic foraminifera, and conclude that many of these are synchronous within a 0.5 m.y. resolution between subtropical Site 563 (33°N) and high‐latitude Site 608 (43°N). In addition, we use this chronology to estimate the ages of previously established Miocene oxygen isotope Zones Mi 1 through Mi 7 and to compare the Sr isotope record at Site 608 with previously published87Sr/86Sr records. We approximate latest Oligocene to early late Miocene (25–8 Ma) Sr isotope changes with two linear regressions. The rate of increase of87Sr/86Sr was high from the latest Oligocene (∼25 Ma) to earliest middle Miocene (∼15 Ma), with an estimated rate of 0.000059/m.y. Our ability to reproduce Sr isotope measurements is ±0.000030 or better, yielding a stratigraphic resolution of as good as ±0.5 m.y. for this interval. The rate of change was much lower from about 15 to 8 Ma (on average, 0.000013/m.y.), yielding Sr isotope stratigraphic resolution of worse than ±2.3 m.y. The causes of the late Eocene to Miocene87Sr/86Sr increases are not known. We speculate that a moderate87Sr/86Sr increase (0.000030/m.y) which occurred during the late Eocene‐latest Oligocene can be explained by intermittent glaciations and deglaciations of the Antarctic continent. These pulse‐like changes in the input of glacial weathering products yield what appears to be a monotonic, linear increase. The increase in the frequency of glaciations during the latest Oligocene‐early Miocene can explain the higher rate of change of87Sr/86Sr at this time. We speculate that by the middle Miocene, the development of a permanent east Antarctica ice sheet resulted in decreased input of glacial weathering products and a lower rate of87Sr/86Sr change.Appendix 1 is available with entire article on microfiche.Order from American Geophysical Union, 2000 FloridaAvenue N.W., Washington, D.C. 20009. Document P90‐001;$2.50. Payment must accompany order.

The morphology and meteorology of southern hemisphere spring total ozone mini‐holes

Rapid ozone decreases near the base of the Antarctic Penninsula have recently been observed in total ozone maps produced from the Total Ozone Mapping Spectrometer (TOMS). These rapid decreases have been labeled mini‐holes because of their relatively small horizontal scales (1000‐3000 km) with respect to the larger scale ozone hole. The mini‐holes do not show a preferential genesis region, but they do tend to intensify most strongly over the Antarctic Penninsula and the East Antarctica ice sheet. Typical time scales are on the order of 1‐5 days. The mini‐holes have been analyzed using a digital filter. Two mini‐holes case studies from 1987 show: 1) a strong correlation of the total ozone mini‐hole with a temperature mini‐hole (i.e. a negative temperature perturbation), 2) a westward tilt with altitude of the temperature mini‐hole. 3) the mini‐hole in ozone is phase shifted slightly to the east of a high in the geopotential height field, and 4) the mini‐hole is phase shifted slightly to the west of a local low in the Ertel's potential vorticity (Epv) field (note that an Epv low is generally associated with cyclonic flow in the southern hemisphere).

Response of the East Antarctica ice sheet to sea‐level rise

A nonsteady ice‐flow model that explicitly includes longitudinal stresses is used to study the effects of marginal changes on the interior portions of an ice sheet. Sea‐level rise is found to cause a wave of thinning to propagate upglacier, and this wave is slowed, diffused, and damped. At the ice divide at dome C in central East Antarctica, post‐Wisconsinan sea‐level rise is modeled as having caused 110 m thinning, with response now 70% complete. If accumulation rates increased by 10% at the same time, then calculated net thinning has been only 75 m. Ice‐sheet response to changes in sea level and accumulation rate is relatively rapid; response to temperature changes is an order of magnitude slower. Response times are shorter if the marginal position of an ice sheet is controlled.