The internal origin of the west-east asymmetry of Antarctic climate change

Recent Antarctic surface climate change has been characterized by greater warming trends in West Antarctica than in East Antarctica. Although this asymmetric feature is well recognized, its origin remains poorly understood. Here, by analyzing observation data and multimodel results, we show that a west-east asymmetric internal mode amplified in austral winter originates from the harmony of the atmosphere-ocean coupled feedback off West Antarctica and the Antarctic terrain. The warmer ocean temperature over the West Antarctic sector has positive feedback, with an anomalous upper-tropospheric anticyclonic circulation response centered over West Antarctica, in which the strength of the feedback is controlled by the Antarctic topographic layout and the annual cycle. The current west-east asymmetry of Antarctic surface climate change is undoubtedly of natural origin because no external factors (e.g., orbital or anthropogenic factors) contribute to the asymmetric mode.

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Simultaneous solution for mass trends on the West Antarctic Ice Sheet

The Cryosphere Discussions ◽

10.5194/tcd-8-2995-2014 ◽

2014 ◽

Vol 8 (3) ◽

pp. 2995-3035 ◽

Cited By ~ 1

Author(s):

N. Schön ◽

A. Zammit-Mangion ◽

J. L. Bamber ◽

J. Rougier ◽

T. Flament ◽

...

Keyword(s):

Mass Loss ◽

Antarctic Peninsula ◽

Ice Sheet ◽

The West ◽

Spatial Error ◽

Antarctic Ice Sheet ◽

Forward Models ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

The Antarctic

Abstract. The Antarctic Ice Sheet is the largest potential source of future sea-level rise. Mass loss has been increasing over the last two decades in the West Antarctic Ice Sheet (WAIS), but with significant discrepancies between estimates, especially for the Antarctic Peninsula. Most of these estimates utilise geophysical models to explicitly correct the observations for (unobserved) processes. Systematic errors in these models introduce biases in the results which are difficult to quantify. In this study, we provide a statistically rigorous, error-bounded trend estimate of ice mass loss over the WAIS from 2003–2009 which is almost entirely data-driven. Using altimetry, gravimetry, and GPS data in a hierarchical Bayesian framework, we derive spatial fields for ice mass change, surface mass balance, and glacial isostatic adjustment (GIA) without relying explicitly on forward models. The approach we use separates mass and height change contributions from different processes, reproducing spatial features found in, for example, regional climate and GIA forward models, and provides an independent estimate, which can be used to validate and test the models. In addition, full spatial error estimates are derived for each field. The mass loss estimates we obtain are smaller than some recent results, with a time-averaged mean rate of −76 ± 15 GT yr−1 for the WAIS and Antarctic Peninsula (AP), including the major Antarctic Islands. The GIA estimate compares very well with results obtained from recent forward models (IJ05-R2) and inversion methods (AGE-1). Due to its computational efficiency, the method is sufficiently scalable to include the whole of Antarctica, can be adapted for other ice sheets and can easily be adapted to assimilate data from other sources such as ice cores, accumulation radar data and other measurements that contain information about any of the processes that are solved for.

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Monitoring changes of the Antarctic Ice sheet by GRACE, ICESat and GNSS

Contributions to Geophysics and Geodesy ◽

10.2478/congeo-2019-0021 ◽

2019 ◽

Vol 49 (4) ◽

pp. 403-424

Author(s):

Fang Zou ◽

Robert Tenzer ◽

Samurdhika Rathnayake

Keyword(s):

Mass Loss ◽

Ice Sheet ◽

The West ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

Ice Volume ◽

West Antarctic ◽

Elevation Changes ◽

A Minor ◽

The Antarctic

Abstract In this study, we estimate the ice mass changes, the ice elevation changes and the vertical displacements in Antarctica based on analysis of multi-geodetic datasets that involve the satellite gravimetry (GRACE), the satellite altimetry (ICESat) and the global navigation satellite systems (GNSS). According to our estimates, the total mass change of the Antarctic ice sheet from GRACE data is −162.91 Gt/yr over the investigated period between April 2002 and June 2017. This value was obtained after applying the GIA correction of −98.12 Gt/yr derived from the ICE-5G model of the glacial iso-static adjustment. A more detailed analysis of mass balance changes for three individual drainage regions in Antarctica reveal that the mass loss of the West Antarctic ice sheet was at a rate of −143.11 Gt/yr. The mass loss of the Antarctic Peninsula ice sheet was at a rate of −24.31 Gt/yr. The mass of the East Antarctic ice sheet increased at a rate of 5.29 Gt/yr during the investigated period. When integrated over the entire Antarctic ice sheet, average rates of ice elevation changes over the period from March 2003 to October 2009 derived from ICESat data represent the loss of total ice volume of −155.6 km3.The most prominent features in ice volume changes in Antarctica are characterized by a strong dynamic thinning and ice mass loss in the Amundsen Sea Embayment that is part of the West Antarctic ice sheet. In contrast, coastal regions between Dronning Maud Land and Enderby Land exhibit a minor ice increase, while a minor ice mass loss is observed in Wilkes Land. The vertical load displacement rates estimated from GRACE and GPS data relatively closely agree with the GIA model derived based on the ice-load history and the viscosity profile. For most sites, the GRACE signal appears to be in phase and has the same amplitude as that obtained from the GPS vertical motions while other sites exhibit some substantial differences possibly attributed to thermo-elastic deformations associated with surface temperature.

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Radar studies at the mouths of ice streams D and E, Antarctica

Annals of Glaciology ◽

10.3189/s0260305500012945 ◽

1993 ◽

Vol 17 ◽

pp. 262-268 ◽

Cited By ~ 3

Author(s):

Robert W. Jacobel ◽

Robert Bindschadler

Keyword(s):

Climate Change ◽

Surface Topography ◽

Satellite Imagery ◽

Ice Thickness ◽

West Antarctica ◽

Ice Streams ◽

The West ◽

Mass Balance Calculation ◽

Grounding Line ◽

Thickness Measurements

Ice thickness measurements have been carried out at the mouths of ice streams D and E, West Antarctica using a surface-based impulse radar. These studies have been undertaken as a part of the continuing effort to understand the state of the West Antarctica ice sheet and its response to climate change. Thickness measurements will be used in the mass balance calculation currently in progress and to better understand features in the surface topography seen at low angle sun illumination in the satellite imagery. Results show that the discharge areas of ice streams D and E are thickening by approximately 1 m per year, and thus that these ice streams are probably loosing mass. Aperiodic wavelike features in the surface topography are described which pose interesting questions about migration of the grounding line and ice-stream dynamics.

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Seismic anisotropy of the lithospheric mantle beneath Marie Byrd Land, West Antarctica: Constraints from peridotite xenoliths

10.5194/egusphere-egu2020-11597 ◽

2020 ◽

Author(s):

Seth Kruckenberg ◽

Vasileios Chatzaras

Keyword(s):

Lithospheric Mantle ◽

Seismic Anisotropy ◽

P Wave ◽

Spinel Peridotite ◽

Seismic Structure ◽

West Antarctica ◽

The West ◽

West Antarctic ◽

Peridotite Xenoliths ◽

Static Conditions

Constraining the seismic structure of the West Antarctic mantle is important for understanding its viscosity structure, and thus for accurately predicting the evolution of the West Antarctic Ice Sheet.&#160; Seismic anisotropy, which is the dependence of seismic velocities on the propagation and polarization direction of seismic waves, is a valuable tool for understanding mantle deformation and flow. &#160;We provide petrological and microstructural data from a suite of 44 spinel peridotite xenoliths entrained in Cenozoic (1.4 Ma) basalts of 7 volcanic centers located in Marie Byrd Land, West Antarctica.&#160; Equilibration temperatures obtained from three different calibrations of the two-pyroxene geothermometer and the olivine-spinel Fe-Mg exchange geothermometer range from 780&#176;C to 1200&#176;C, calculated at a pressure of 1500 MPa.&#160; This range of temperatures corresponds to extraction depths between 39 and 72 km, constraining the source of the xenoliths within the lithospheric mantle above the low velocity zone modelled by seismic studies.The Marie Byrd Land xenoliths are fertile with average clinopyroxene mode that ranges between 15 and 24%.&#160; Based on their modal composition, xenoliths are predominantly classified as lherzolites (n=30), with lesser occurrences of harzburgite (n=4), wehrlite (n=3), dunite (n=3), olivine websterite (n=1), websterite (n=1), and clinopyroxenite (n=2).&#160; Petrological data suggest that the xenoliths have been affected by various degrees of partial melting as well as by reaction with silicate melts or fluids.&#160; For example, clinopyroxenes in the more fertile lherzolites and wehrlites show a constant TiO2 concentration at 0.65 wt% and 0.8 wt% over a range of olivine Mg# values, while TiO2 decreases rapidly with increasing Mg#, down to 0.01 wt% in the more refractory harzburgites and dunites.&#160; The observed trend is interpreted to indicate a refertilization process.&#160; Microstructures also indicate multiple episodes of reactive melt percolation under either static conditions or during the late stages of deformation.&#160; Pyroxenes may enclose rounded olivine grains in crystallographic continuity with neighbouring grains, cross-cut the subgrain boundaries of olivine grains, or show an interstitial habit, either forming cuspate-shaped grains in olivine triple junctions or films along olivine-olivine grain boundaries.&#160; Olivine shows a range of crystallographic preferred orientation (CPO) patterns, including the A-type, axial-[010], axial-[100], and B-type.&#160; Pyroxenes have weaker but not random CPOs with [001] axes having similar orientation to olivine [100] axes in the majority of the xenoliths.&#160; Calculated P and S waves anisotropy is variable (2&#8211;12%) and increases with olivine fraction but decreases with both increasing ortho- or clinopyroxene content. &#160;P-wave anisotropy is correlated with the strength of olivine CPO expressed with the M-index and increases with increasing strength of the orthopyroxene CPO, but seems to be less correlated with the strength of the clinopyroxene CPO.

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Active subglacial volcanism in West Antarctica as assessed by airborne geophysics: Distribution and context

10.5194/egusphere-egu2020-21391 ◽

2020 ◽

Author(s):

Donald Blankenship ◽

Enrica Quatini ◽

Duncan Young

Keyword(s):

Ice Sheet ◽

Ice Cores ◽

Rift System ◽

West Antarctica ◽

The West ◽

Amundsen Sea ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Subglacial Volcanism

A combination of aerogeophysics, seismic observations and direct observation from ice cores and subglacial sampling has revealed at least 21 sites under the West Antarctic Ice sheet consistent with active volcanism (where active is defined as volcanism that has interacted with the current manifestation of the West Antarctic Ice Sheet). Coverage of these datasets is heterogenous, potentially biasing the apparent distribution of these features. Also, the products of volcanic activity under thinner ice characterized by relatively fast flow are more prone to erosion and removal by the ice sheet, and therefore potentially underrepresented. Unsurprisingly, the sites of active subglacial volcanism we have identified often overlap with areas of relatively thick ice and slow ice surface flow, both of which are critical conditions for the preservation of volcanic records. Overall, we find the majority of active subglacial volcanic sites in West Antarctica concentrate strongly along the crustal thickness gradients bounding the central West Antarctic Rift System, complemented by intra-rift sites associated with the Amundsen Sea to Siple Coast lithospheric transition.

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Crustal density structure of the Antarctic continent from constrained 3-D gravity inversion

10.5194/egusphere-egu2020-4427 ◽

2020 ◽

Author(s):

Fei Ji ◽

Qiao Zhang

Keyword(s):

Gravity Inversion ◽

Inversion Method ◽

Rift System ◽

Low Density ◽

Density Structure ◽

West Antarctica ◽

The West ◽

Antarctic Continent ◽

Crustal Density ◽

The Antarctic

Crustal density is a fundamental physical parameter that helps to reveal its composition and structure, and is also significantly related to the tectonic evolution and geodynamics. Based on the latest Bouguer gravity anomalies and the constrains of 3-D shear velocity model and surface heat flow data, the 3-D gravity inversion method, incorporating deep weight function, has been used to obtain the refined density structure over the Antarctic continent. Our results show that the density anomalies changes from -0.25 g/cm3 to 0.20 g/cm3. Due to the multi-phase extensional tectonics in Mesozoic and Cenozoic, the low density anomalies dominates in the West Antarctica, while the East Antarctica is characterized by high values of density anomalies. By comparing with the variations of effective elastic thickness, the inverted density structure correlates well with the lithospheric integrated strength. According to the mechanical strength and inverted density structure in the West Antarctic Rift System (WARS), our analysis found that except for the local area affected by the Cenozoic extension and magmatic activity, the crustal thermal structure in the WARS tends to be normal under the effect of heat dissipation. Finally, the low density anomalies features in West Antarctica extend to beneath the Transantarcitc Mountains (TAMs), however, we hypothesize that a single rift mechanism seems not be used to explain the entire TAMs range.

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Contrasting response of West and East Antarctic ice sheets to Glacial Isostatic Adjustment

10.5194/egusphere-egu2020-6974 ◽

2020 ◽

Author(s):

Violaine Coulon ◽

Kevin Bulthuis ◽

Sainan Sun ◽

Konstanze Haubner ◽

Frank Pattyn

Keyword(s):

Solid Earth ◽

Sea Level ◽

Ice Sheet ◽

East Antarctica ◽

Climate Forcing ◽

West Antarctica ◽

Antarctic Ice Sheet ◽

West Antarctic ◽

Earth Structures ◽

The Antarctic

The Antarctic ice sheet (AIS) lies on a solid Earth that displays large spatial variations in rheological properties, with a thin lithosphere and low-viscosity upper mantle (weak Earth structure) beneath West Antarctica and an opposing structure beneath East Antarctica. This contrast is known to have a significant impact on ice-sheet grounding-line stability. Here, we embedded a modified glacial-isostatic ELRA model within an Antarctic ice sheet model that considers a weak Earth structure for West Antarctica supplemented with an approximation of gravitationally-consistent local sea-level changes. By taking advantage of the computational efficiency of this elementary GIA model, we assess in a probabilistic way the impact of uncertainties in the Antarctic viscoelastic properties on the response of the Antarctic ice sheet to future warming by using an ensemble of 2000 Monte Carlo simulations that span a range of plausible solid Earth structures for both West and East Antarctica. We show that on multicentennial-to-millennial timescales, model projections that do not consider the dichotomy between East and West Antarctic solid Earth structures systematically overestimate the sea-level contribution from the Antarctic ice sheet because regional solid-Earth deformation plays a significant role in promoting the stability of the West Antarctic ice sheet (WAIS). However, WAIS collapse cannot be prevented under high-emissions climate scenarios. At longer timescales and under unabated climate forcing, future mass loss may be underestimated because in East Antarctica, GIA feedbacks have the potential to re-enforce the influence of the climate forcing as compared with a spatially-uniform GIA model. In this context, the AIS response might be an even larger source of uncertainty in projecting sea-level rise than previously thought, with the highest uncertainty arising from the East Antarctic ice sheet where the Aurora Basin is very GIA-dependent.

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Uncertainty quantification of the multi-centennial response of the Antarctic Ice Sheet to climate change

10.5194/tc-2018-220 ◽

2018 ◽

Author(s):

Kevin Bulthuis ◽

Maarten Arnst ◽

Sainan Sun ◽

Frank Pattyn

Keyword(s):

Climate Change ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Parametric Uncertainty ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

Sources Of Uncertainty ◽

West Antarctic ◽

The Antarctic

Abstract. Ice loss from the Antarctic ice sheet (AIS) is expected to become the major contributor to sea-level rise in the next centuries. Projections of the AIS response to climate change based on numerical ice-sheet models remain challenging to establish due to the complexity of physical processes involved in ice-sheet dynamics, including instability mechanisms that can destabilise marine sectors with retrograde slopes. Moreover, uncertainties in ice-sheet models limit the ability to provide accurate sea-level rise projections. Here, we apply probabilistic methods to a hybrid ice-sheet model to investigate the influence of several sources of uncertainty, namely sources of uncertainty in atmospheric forcing, basal sliding, grounding-line flux parameterisation, calving, sub-shelf melting, ice-shelf rheology and bedrock relaxation, on the continental response of the Antarctic ice sheet to climate change over the next millennium. We provide probabilistic projections of sea-level rise and grounding-line retreat and we carry out stochastic sensitivity analyses to determine the most influential sources of uncertainty. We find that all sources of uncertainty, except perhaps the bedrock relaxation times, contribute to the uncertainty in the projections. We show that the sensitivity of the projections to uncertainties increases and the contribution of the uncertainty in sub-shelf melting to the uncertainty in the projections becomes more and more dominant as the scenario gets warmer. We show that the significance of the AIS contribution to sea-level rise is controlled by marine ice-sheet instability (MISI) in marine basins, with the biggest contribution stemming from the more vulnerable West Antarctic ice sheet. We find that, irrespectively of parametric uncertainty, the strongly mitigated RCP 2.6 scenario prevents the collapse of the West Antarctic ice sheet, that in both RCP 4.5 and RCP 6.0 scenarios the occurrence of MISI in marine basins is more sensitive to parametric uncertainty and that, almost irrespectively of parametric uncertainty, RCP 8.5 triggers the collapse of the West Antarctic ice sheet.

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Antarctic Peninsula warming triggers enhanced basal melt rates throughout West Antarctica

10.5194/egusphere-egu21-10418 ◽

2021 ◽

Author(s):

Andrew Thompson ◽

Mar Flexas ◽

Michael Schodlok ◽

Kevin Speer

Keyword(s):

Antarctic Peninsula ◽

Ocean Circulation ◽

Heat Fluxes ◽

Coastal Current ◽

West Antarctica ◽

Ice Shelf ◽

West Antarctic ◽

Freshwater Forcing ◽

Run Off ◽

The Antarctic

The acceleration of ice-shelf basal melt rates throughout West Antarctica, as well as their potential to destabilize the ice sheets they buttress, is well documented. &#160;Yet, the mechanisms that determine both trends and variability of these melt rates remain uncertain. &#160;Explanations for the intensification of melting have largely focused on local processes in seas surrounding the ice shelves, including variations in wind stress over the continental slope and shelf. &#160;Here, we show that non-local freshwater forcing, propagated between shelf seas by the Antarctic Coastal Current (AACC), can have a significant impact on ice-shelf melt rates. &#160;We present results from a suite of high-resolution (~3-km) numerical simulations of the ocean circulation in West Antarctica that includes a dynamic sea-ice field, ice-shelf cavities and forcing from ice shelf-ocean interactions. &#160;Motivated by persistent warming at the northern Antarctic Peninsula since the 1950&#8217;s, freshwater perturbations are applied to the West Antarctic Peninsula. &#160;This leads to a strengthening of the AACC and a westward propagation of the freshwater signal. &#160;Critically, basal melt rates increase throughout the WAP, Bellingshausen and Amundsen Seas in response to this perturbation. &#160;The freshwater anomalies stratify the ocean surface near the coast, enhancing lateral heat fluxes that lead to greater ice-shelf melt rates. &#160;A suite of sensitivity studies show that changes in meltrates are linearly proportional to the magnitude of the freshwater anomaly, changing by as much as 30% for realistic perturbations, but are relatively insensitive to the distribution of the perturbation across the WAP shelf. &#160;These results indicate that glacial run-off on the Antarctic Peninsula, one of the first signatures of a warming climate in Antarctica, could be a key trigger for increased melt rates in the Amundsen and Bellingshausen Seas.

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Chapter 7.5 Active subglacial volcanism in West Antarctica

Geological Society London Memoirs ◽

10.1144/m55-2019-3 ◽

2021 ◽

pp. M55-2019-3

Author(s):

Enrica Quartini ◽

Donald D. Blankenship ◽

Duncan A. Young

Keyword(s):

Ice Sheet ◽

Ice Cores ◽

Rift System ◽

West Antarctica ◽

The West ◽

Amundsen Sea ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Subglacial Volcanism

AbstractA combination of aerogeophysics, seismic observations and direct observation from ice cores, and subglacial sampling, has revealed at least 21 sites under the West Antarctic Ice Sheet consistent with active volcanism (where active is defined as volcanism that has interacted with the current manifestation of the West Antarctic Ice Sheet). Coverage of these datasets is heterogeneous, potentially biasing the apparent distribution of these features. Also, the products of volcanic activity under thinner ice characterized by relatively fast flow are more prone to erosion and removal by the ice sheet, and therefore potentially under-represented. Unsurprisingly, the sites of active subglacial volcanism that we have identified often overlap with areas of relatively thick ice and slow ice surface flow, both of which are critical conditions for the preservation of volcanic records. Overall, we find the majority of active subglacial volcanic sites in West Antarctica concentrate strongly along the crustal-thickness gradients bounding the central West Antarctic Rift System, complemented by intra-rift sites associated with the Amundsen Sea–Siple Coast lithospheric transition.

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