scholarly journals Review article: Existing and potential evidence for Holocene grounding-line retreat and readvance in Antarctica

2021 ◽  
Author(s):  
Joanne S. Johnson ◽  
Ryan A. Venturelli ◽  
Greg Balco ◽  
Claire S. Allen ◽  
Scott Braddock ◽  
...  
Keyword(s):  
Direct Evidence ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Ice Cores ◽  
Radar Data ◽  
Oceanic Circulation ◽  
Surface Mass ◽  
The Holocene ◽  
Grounding Line ◽  
The Antarctic

Abstract. Widespread existing geological records from above the modern ice-sheet surface and outboard of the current ice margin show that the Antarctic Ice Sheet (AIS) was much more extensive at the Last Glacial Maximum (~20 ka) than at present. However, whether it was ever smaller than present during the last few millennia, and (if so) by how much, is known only for a few locations because direct evidence lies within or beneath the ice sheet, which is challenging to access. Here, we describe how retreat and readvance (henceforth “readvance”) of AIS grounding lines during the Holocene could be detected and quantified using subglacial bedrock, subglacial sediments, marine sediment cores, relative sea-level (RSL) records, radar data, and ice cores. Of these, only subglacial bedrock and subglacial sediments can provide direct evidence for readvance. Marine archives are of limited utility because readvance commonly covers evidence of earlier retreat. Nevertheless, stratigraphic transitions documenting change in environment may provide support for direct evidence from subglacial records, as can the presence of transgressions in RSL records. With independent age control, past changes in ice structure and flow patterns revealed by radar can be used to infer ice volume changes commensurate with readvance. Since ice cores capture changes in surface mass balance, elevation, and changes in atmospheric and oceanic circulation that are known to drive grounding-line migration, they also have potential for identifying readvance. A multidisciplinary approach is likely to provide the strongest evidence for or against a smaller-than-present AIS in the Holocene.

scholarly journals Mass balance of the Sør Rondane glacial system, East Antarctica

2015 ◽  
Vol 56 (70) ◽  
pp. 63-69 ◽  
Author(s):  
Denis Callens ◽  
Nicolas Thonnard ◽  
Jan T.M. Lenaerts ◽  
Jan M. Van Wessem ◽  
Willem Jan Van de Berg ◽  
...  
Keyword(s):  
Mass Balance ◽  
Drainage Basin ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Antarctic Ice Sheet ◽  
Outlet Glacier ◽  
Surface Mass ◽  
Mass Budget ◽  
Grounding Line ◽  
The Antarctic

AbstractMass changes of polar ice sheets have an important societal impact, because they affect global sea level. Estimating the current mass budget of ice sheets is equivalent to determining the balance between surface mass gain through precipitation and outflow across the grounding line. For the Antarctic ice sheet, grounding line outflow is governed by oceanic processes and outlet glacier dynamics. In this study, we compute the mass budget of major outlet glaciers in the eastern Dronning Maud Land sector of the Antarctic ice sheet using the input/output method. Input is given by recent surface accumulation estimates (SMB) of the whole drainage basin. The outflow at the grounding line is determined from the radar data of a recent airborne survey and satellite-based velocities using a flow model of combined plug flow and simple shear. This approach is an improvement on previous studies, as the ice thickness is measured, rather than being estimated from hydrostatic equilibrium. In line with the general thickening of the ice sheet over this sector, we estimate the regional mass balance in this area at 3.15 ± 8.23 Gt a−1 according to the most recent SMB model results.

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

2021 ◽  
Vol 13 (6) ◽  
pp. 3057-3074
Author(s):  
Yetang Wang ◽  
Minghu Ding ◽  
Carleen H. Reijmer ◽  
Paul C. J. P. Smeets ◽  
Shugui Hou ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Mass Balance ◽  
Ice Sheet ◽  
Ice Cores ◽  
Surface Mass Balance ◽  
Surface Mass ◽  
Temporal And Spatial Variability ◽  
Temporal And Spatial ◽  
The Antarctic ◽  
Comprehensive Compilation

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.

scholarly journals A comparison of automated approaches to extracting englacial-layer geometry from radar data across ice sheets

2020 ◽  
Vol 61 (81) ◽  
pp. 234-241 ◽  
Author(s):  
Richard Delf ◽  
Dustin M. Schroeder ◽  
Andrew Curtis ◽  
Antonios Giannopoulos ◽  
Robert G. Bingham
Keyword(s):  
Ice Core ◽  
Accurate Determination ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Ice Cores ◽  
Radar Data ◽  
Test Case ◽  
Estimation Algorithms ◽  
Ice Sheet Dynamics ◽  
The Antarctic

AbstractRadar surveys across ice sheets typically measure numerous englacial layers that can often be regarded as isochrones. Such layers are valuable for extrapolating age–depth relationships away from ice-core locations, reconstructing palaeoaccumulation variability, and investigating past ice-sheet dynamics. However, the use of englacial layers in Antarctica has been hampered by underdeveloped techniques for characterising layer continuity and geometry over large distances, with techniques developed independently and little opportunity for inter-comparison of results. In this paper, we present a methodology to assess the performance of automated layer-tracking and layer-dip-estimation algorithms through their ability to propagate a correct age–depth model. We use this to assess isochrone-tracking techniques applied to two test case datasets, selected from CreSIS MCoRDS data over Antarctica from a range of environments including low-dip, continuous layers and layers with terminations. We find that dip-estimation techniques are generally successful in tracking englacial dip but break down in the upper and lower regions of the ice sheet. The results of testing two previously published layer-tracking algorithms show that further development is required to attain a good constraint of age–depth relationships away from dated ice cores. We recommend that auto-tracking techniques focus on improved linking of picked stratigraphy across signal disruptions to enable accurate determination of the Antarctic-wide age–depth structure.

scholarly journals Snowfall versus sub-shelf melt: response of an idealized 3D ice-sheet-shelf system to mass redistribution

2018 ◽  
Author(s):  
Johannes Feldmann ◽  
Ronja Reese ◽  
Ricarda Winkelmann ◽  
Anders Levermann
Keyword(s):  
Ice Sheet ◽  
Length Change ◽  
Ice Shelf ◽  
Thickness Change ◽  
Surface Mass ◽  
Ice Shelves ◽  
Mass Redistribution ◽  
Grounding Line ◽  
Future Warming ◽  
The Antarctic

Abstract. Surface accumulation and sub-ice-shelf melting are key drivers for the flow dynamics of the Antarctic Ice Sheet and are most likely to change under future warming which leads to 1) higher snowfall and 2) stronger melting below ice shelves. Here we carry out conceptual simulations in which an equilibrium ice-sheet-shelf system is perturbed such that the increased sub-shelf melting is compensated by enhanced snowfall. Although the net surface mass balance of the whole system remains unchanged, the redistribution of mass leads to a dynamic response of the ice sheet due to changes in ice thickness, surface slope, ice-shelf backstress and ice discharge. In particular, we show that such forcing can lead to the counter-intuitive situation of a retreating ice sheet which gains mass, thus having a negative sea-level contribution but smaller ice-sheet extent. The ice-sheet evolution and the corresponding steady states are investigated varying relevant parameters that affect ice properties and bed geometry as well as for different magnitudes of mass redistribution. Furthermore, the ice-sheet response is analyzed with respect to the pattern of applied melting, i.e., the area over which melting is distributed and the location where it is applied. We find throughout the ensemble of simulations that after two decades, melting at the lateral ice-shelf margins induces more ice-shelf thinning, resulting in stronger grounding line retreat and transient ice discharge compared to melting adjacent to the central grounding-line section. Analyzing changes in ice-shelf backstress with respect to changes in the ice-shelf length and mean thickness, respectively, we show that a thickness change has up to four times more influence on the backstress of the ice shelf than a length change.

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

2021 ◽  
Author(s):  
Yetang Wang ◽  
Minghu Ding ◽  
Carleen H. Reijmer ◽  
Paul C. J. P. Smeets ◽  
Shugui Hou ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ice Sheet ◽  
Ice Cores ◽  
Field Measurements ◽  
Surface Mass Balance ◽  
Antarctic Ice Sheet ◽  
Surface Mass ◽  
Ground Penetrating ◽  
The Antarctic ◽  
Comprehensive Compilation

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 radars. The dataset collects 268 913 individual multi-year averaged observations, 687 annual resolved time series from 675 sites extending back the past 1000 years, and 78 968 records at daily resolution from 32 sites across the whole ice sheet. These records are derived from ice core, snow pits, stakes/stake farms, ultrasonic sounders and ground-penetrating radar measurements. This is the first ice-sheet-scale compilation of SMB records at different temporal (daily, annual and multi-year) resolutions from multiple types of measurements, which 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.

scholarly journals A study of different‑scale relationship between changes of the surface air temperature and the СО2 concentration in the atmosphere

2016 ◽  
Vol 56 (4) ◽  
pp. 533-544 ◽  
Author(s):  
N. V. Vakulenko ◽  
V. M. Kotlyakov ◽  
F. Parrenin ◽  
D. M. Sonechkin
Keyword(s):  
Carbon Dioxide ◽  
Time Series ◽  
Carbon Dioxide Concentration ◽  
Ice Cores ◽  
Glacial Maximum ◽  
Temperature Variations ◽  
The Holocene ◽  
The Antarctic ◽  
The Last Glacial Maximum ◽  
The Last Glacial

A concept of the anthropogenic origin of the current global climate warming assumes that growth of concentration of the atmospheric carbon dioxide and other greenhouse gases is of great concern in this process. However, all earlier performed analyses of the Antarctic ice cores, covering the time interval of several glacial cycles for about 1 000 000 years, have demonstrated that the carbon dioxide concentration changes had a certain lag relative to the air temperature changes by several hundred years during every beginning of the glacial terminations as well as at endings of interglacials. In contrast to these findings, a recently published careful analysis of Antarctic ice cores (Parrenin et al., 2013) had shown that both, the carbon dioxide concentration and global temperature, varied almost synchronously during the transition from the last glacial maximum to the Holocene. To resolve this dilemma, a special technique for analysis of the paleoclimatic time series, based on the wavelets, had been developed and applied to the same carbon dioxide concentration and temperature time series which were used in the above paper of Parrenin et al., 2013. Specifically, a stack of the Antarctic δ18O time series (designated as ATS) and the deuterium Dome C – EPICA ones (dD) were compared to one another in order to: firstly, to quantitatively estimate differences between time scales of these series; and, secondly, to clear up the lead–lag relationships between different scales variations within these time series. It was found that accuracy of the mutual ATS and dD time series dating lay within the range of 80–160 years. Perhaps, the mutual dating of the temperature and carbon dioxide concentration series was even worse due to the assumed displacement of air bubbles within the ice. It made us to limit our analysis by the time scales of approximately from 800 to 6000 years. But it should be taken into account that any air bubble movement changes the time scale of the carbon dioxide series as a whole. Therefore, if a difference between variations in any temperature and the carbon dioxide time series is found to be longer than 80–160 years, and if these variations are timescale‑dependent, it means that the bubble displacements are not essential, and so these advancing and delays are characteristic of the time series being compared. Our wavelet‑based comparative and different‑scale analysis confirms that the relationships between the carbon dioxide concentration and temperature variations were essentially timescale‑dependent during the transition from the last glacial maximum to the Holocene. The carbon dioxide concentration variations were ahead of the temperature ones during transition from the glacial maximum to the Boelling – Alleroud warming as well as from the Young Drias cooling to the Holocene optimum. However, the temperature variations were ahead during the transition from the Boelling – Alleroud warming to the Young Drias cooling and during the transition from the Holocene optimum to the present‑day climate.

scholarly journals Last Glacial Maximum-Holocene Glacial and Depositional History From Sediment Cores at Coulman High Beneath the Ross Ice Shelf, Antarctica

2021 ◽  
Author(s):  
◽  
Sanne M Maas
Keyword(s):  
Last Glacial Maximum ◽  
Ross Sea ◽  
Sediment Cores ◽  
Ice Sheet ◽  
Open Water ◽  
Glacial Maximum ◽  
Ice Shelf ◽  
Last Glacial ◽  
Ross Ice Shelf ◽  
Grounding Line

<p>Sediment Cores collected from the shallow sub-sea floor beneath the Ross Ice Shelf at Coulman High have been analysed using sedimentological techniques to constrain the retreat history of the Last Glacial Maximum (LGM) ice sheet in the Ross Embayment, and to determine when the modern-day calving line location of the Ross Ice Shelf was established. A characteristic vertical succession of facies was identified in these cores, that can be linked to ice sheet and ice shelf extent in the Ross Embayment. The base of this succession consists of unconsolidated, clast rich muddy diamicts, and is interpreted to be deposited subglacially or in a grounding line proximal environment on account of a distinct provenance in the clast content which can only be attributed to subglacial transport from the Byrd Glacier 400 km to the south of the drill site. This is overlain by a mud with abundant clasts, similar in character to a granulated facies that has been documented previously in the Ross Sea, and is interpreted as being a characteristic grounding line lift-o facies in a sub-ice shelf setting. These glacial proximal facies pass upward into a mud, which comprises three distinctive units. i) Muds with sub-mm scale laminae resulting from traction currents occurring near the grounding line in a sub-ice shelf environment overlain by, ii) muds with sub-mm scale laminae and elevated biogenic content (diatoms and foraminifera) and sand/gravel clasts, interpreted as being deposited in open water conditions, passing up into a iii) bioturbated mud, interpreted as being deposited in sub-ice shelf environment, proximal to the calving line. The uppermost facies consists of a 20 cm thick diatom ooze with abundant clasts and pervasive bioturbation, indicative of a condensed section deposited during periodically open marine conditions. During post-LGM retreat of the ice sheet margin in western Ross Sea, and prior to the first open marine conditions at Coulman High, it is hypothesized that the grounding and calving line were in relative close proximity to each other. As the calving line became "pinned" in the Ross Island region, the grounding line likely continued its retreat toward its present day location. New corrected radiocarbon ages on the foraminifera shells in the interval of laminated muds with clasts, provide some of the first inorganic ages from the Ross Sea, and strengthen inferences from previous studies, that the first open marine conditions in the vicinity of Ross Island were 7,600 14C yr BP. While retreat of the calving line south of its present day position is implied during this period of mid-Holocene warmth prior to its re-advance, at present it is not possible to constrain the magnitude of retreat or attribute this to climate change rather than normal calving dynamics.</p>

scholarly journals A high-resolution synthetic bed elevation grid of the Antarctic continent

2016 ◽  
Author(s):  
Felicity S. Graham ◽  
Jason L. Roberts ◽  
Ben K. Galton-Fenzi ◽  
Duncan Young ◽  
Donald Blankenship ◽  
...  
Keyword(s):  
High Resolution ◽  
Ice Sheet ◽  
Radar Data ◽  
Detailed Knowledge ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Bed Elevation ◽  
Antarctic Continent ◽  
Ice Sheet Dynamics ◽  
The Antarctic

Abstract. Digital elevation models of Antarctic bed topography are heavily smoothed and interpolated onto low-resolution (> 1 km) grids as our current observed topography data are generally sparsely and unevenly sampled. This issue has potential implications for numerical simulations of ice-sheet dynamics, especially in regions prone to instability where detailed knowledge of the topography, including fine-scale roughness, is required. Here, we present a high-resolution (100 m) synthetic bed elevation terrain for the whole Antarctic continent. The synthetic bed surface preserves topographic roughness characteristics of airborne and ground-based ice-penetrating radar data from the Bedmap1 compilation and the ICECAP consortium. Broad-scale features of the Antarctic landscape are incorporated using a low-pass filter of the Bedmap2 bed-elevation data. Although not intended as a substitute for Bedmap2, the simulated bed elevation terrain has applicability in high-resolution ice-sheet modelling studies, including investigations of the interaction between topography, ice-sheet dynamics, and hydrology, where processes are highly sensitive to bed elevations. The data are available for download at the Australian Antarctic Data Centre (doi:10.4225/15/57464ADE22F50).

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