scholarly journals Detecting high spatial variability of ice-shelf basal mass balance (Roi Baudouin ice shelf, Antarctica)

2017 ◽  
Author(s):  
Sophie Berger ◽  
Reinhard Drews ◽  
Veit Helm ◽  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Spatial Variability ◽  
Mass Balance ◽  
Mass Conservation ◽  
Atmospheric Model ◽  
Small Scale ◽  
Ice Shelf ◽  
Surface Mass ◽  
Ice Shelves ◽  
Shelf Slope ◽  
Grounding Line

Abstract. Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e., the difference between refreezing and melting. Here, we present a novel technique – based on satellite observations – to capture the small-scale variability in the BMB of ice-shelves. As a case study we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica and derive its yearly-averaged BMB at 10 m horizontal gridding. We use mass conservation within a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which avoids spatial averaging hence loss of spatial resolution. Our BMB field exhibits high detail and ranges from −14.8 to 8.6 m a−1 ice equivalent. Highest melt rates are found close to the grounding line where the basal ice-shelf slope is the steepest. The BMB field agrees well with on-site measurements from phase-sensitive radar, although unresolved spatial variations in firn density determined from profiling radar occur. We show that the surface expression of an englacial lake (0.7 × 1.3 km2 wide and 30 m deep) lowers by 0.5 to 1.4 m a−1, which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice-shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice-shelf channels advect passively toward the ice-shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.

scholarly journals Detecting high spatial variability of ice shelf basal mass balance, Roi Baudouin Ice Shelf, Antarctica

2017 ◽  
Vol 11 (6) ◽  
pp. 2675-2690 ◽  
Author(s):  
Sophie Berger ◽  
Reinhard Drews ◽  
Veit Helm ◽  
Sainan Sun ◽  
Frank Pattyn
Keyword(s):  
Spatial Variability ◽  
Mass Balance ◽  
Mass Conservation ◽  
Atmospheric Model ◽  
Small Scale ◽  
Ice Shelf ◽  
Surface Mass ◽  
Ice Shelves ◽  
Shelf Slope ◽  
Grounding Line

Abstract. Ice shelves control the dynamic mass loss of ice sheets through buttressing and their integrity depends on the spatial variability of their basal mass balance (BMB), i.e. the difference between refreezing and melting. Here, we present an improved technique – based on satellite observations – to capture the small-scale variability in the BMB of ice shelves. As a case study, we apply the methodology to the Roi Baudouin Ice Shelf, Dronning Maud Land, East Antarctica, and derive its yearly averaged BMB at 10 m horizontal gridding. We use mass conservation in a Lagrangian framework based on high-resolution surface velocities, atmospheric-model surface mass balance and hydrostatic ice-thickness fields (derived from TanDEM-X surface elevation). Spatial derivatives are implemented using the total-variation differentiation, which preserves abrupt changes in flow velocities and their spatial gradients. Such changes may reflect a dynamic response to localized basal melting and should be included in the mass budget. Our BMB field exhibits much spatial detail and ranges from −14.7 to 8.6 m a−1 ice equivalent. Highest melt rates are found close to the grounding line where the pressure melting point is high, and the ice shelf slope is steep. The BMB field agrees well with on-site measurements from phase-sensitive radar, although independent radar profiling indicates unresolved spatial variations in firn density. We show that an elliptical surface depression (10 m deep and with an extent of 0.7 km × 1.3 km) lowers by 0.5 to 1.4 m a−1, which we tentatively attribute to a transient adaptation to hydrostatic equilibrium. We find evidence for elevated melting beneath ice shelf channels (with melting being concentrated on the channel's flanks). However, farther downstream from the grounding line, the majority of ice shelf channels advect passively (i.e. no melting nor refreezing) toward the ice shelf front. Although the absolute, satellite-based BMB values remain uncertain, we have high confidence in the spatial variability on sub-kilometre scales. This study highlights expected challenges for a full coupling between ice and ocean models.

scholarly journals Characteristics of ice rises and ice rumples in Dronning Maud Land and Enderby Land, Antarctica

2020 ◽  
Vol 66 (260) ◽  
pp. 1064-1078
Author(s):  
Vikram Goel ◽  
Kenichi Matsuoka ◽  
Cesar Deschamps Berger ◽  
Ian Lee ◽  
Jørgen Dall ◽  
...  
Keyword(s):  
Mass Balance ◽  
Ice Cores ◽  
Ice Thickness ◽  
Ice Shelf ◽  
Ice Dynamics ◽  
Surface Mass ◽  
Ice Shelves ◽  
The Past ◽  
Dronning Maud Land ◽  
The Antarctic

AbstractIce rises and rumples, locally grounded features adjacent to ice shelves, are relatively small yet play significant roles in Antarctic ice dynamics. Their roles generally depend upon their location within the ice shelf and the stage of the ice-sheet retreat or advance. Large, long-stable ice rises can be excellent sites for deep ice coring and paleoclimate study of the Antarctic coast and the Southern Ocean, while small ice rises tend to respond more promptly and can be used to reveal recent changes in regional mass balance. The coasts of Dronning Maud Land (DML) and Enderby Land in East Antarctica are abundant with these features. Here we review existing knowledge, presenting an up-to-date status of research in these regions with focus on ice rises and rumples. We use regional datasets (satellite imagery, surface mass balance and ice thickness) to analyze the extent and surface morphology of ice shelves and characteristic timescales of ice rises. We find that large parts of DML have been changing over the past several millennia. Based on our findings, we highlight ice rises suitable for drilling ice cores for paleoclimate studies as well as ice rises suitable for deciphering ice dynamics and evolution in the region.

scholarly journals Constraining variable density of ice shelves using wide-angle radar measurements

2016 ◽  
Vol 10 (2) ◽  
pp. 811-823 ◽  
Author(s):  
Reinhard Drews ◽  
Joel Brown ◽  
Kenichi Matsuoka ◽  
Emmanuel Witrant ◽  
Morgane Philippe ◽  
...  
Keyword(s):  
Mass Balance ◽  
Propagation Speed ◽  
Radar Data ◽  
Temporal Variations ◽  
Variable Density ◽  
Ice Thickness ◽  
Wide Angle ◽  
Ice Shelf ◽  
Surface Mass ◽  
Ice Shelves

Abstract. The thickness of ice shelves, a basic parameter for mass balance estimates, is typically inferred using hydrostatic equilibrium, for which knowledge of the depth-averaged density is essential. The densification from snow to ice depends on a number of local factors (e.g., temperature and surface mass balance) causing spatial and temporal variations in density–depth profiles. However, direct measurements of firn density are sparse, requiring substantial logistical effort. Here, we infer density from radio-wave propagation speed using ground-based wide-angle radar data sets (10 MHz) collected at five sites on Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, Antarctica. We reconstruct depth to internal reflectors, local ice thickness, and firn-air content using a novel algorithm that includes traveltime inversion and ray tracing with a prescribed shape of the depth–density relationship. For the particular case of an ice-shelf channel, where ice thickness and surface slope change substantially over a few kilometers, the radar data suggest that firn inside the channel is about 5 % denser than outside the channel. Although this density difference is at the detection limit of the radar, it is consistent with a similar density anomaly reconstructed from optical televiewing, which reveals that the firn inside the channel is 4.7 % denser than that outside the channel. Hydrostatic ice thickness calculations used for determining basal melt rates should account for the denser firn in ice-shelf channels. The radar method presented here is robust and can easily be adapted to different radar frequencies and data-acquisition geometries.

scholarly journals Mass balance of East Antarctic glaciers and ice shelves from satellite data

2002 ◽  
Vol 34 ◽  
pp. 217-227 ◽  
Author(s):  
Eric Rignot
Keyword(s):  
Mass Balance ◽  
Snow Accumulation ◽  
Glacier Mass Balance ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Mass Fluxes ◽  
Grounding Line ◽  
Ice Velocity ◽  
Flux Gate ◽  
Mass Discharge

AbstractThe velocity and mass discharge of nine major East Antarctic glaciers not draining into the Ross or Filchner–Ronne Ice Shelves is investigated using interferometric synthetic aperture radar (InSAR) data from the European Remote-sensing Satellite 1and 2 (ERS-1/2) andRADARSAT-1. The glaciers are: David,Ninnis, Mertz, Totten, Scott, Denman, Lambert, Shirase and Stancomb-Wills. InSAR is used to locate their grounding line with precision. Ice velocity is measured with either InSAR or a speckle-tracking technique. Ice thickness is deduced from prior-determined ice-shelf elevation assuming hydrostatic equilibrium. Mass fluxes are calculated both at the grounding line and at a flux gate located downstream. The grounding-line flux is compared to a mass input calculated from snow accumulation to deduce the glacier mass balance. The calculation is repeated at the flux gate downstream of the grounding line to estimate the average bottom melt rate of the ice shelf under steady-state conditions. The main results are: (1) Grounding lines are found several tens of km upstream of prior-identified positions, not because of a recent ice-sheet retreat but because of the inadequacy of prior-determined grounding-line positions. (2) No gross imbalance between outflow and inflow is detected on the nine glaciers being investigated, with an uncertainty of 10–20%. Prior-determined, largely positive mass imbalances were due to an incorrect localization of the grounding line. (3) High rates of bottom melting (24±7 mice a–1) are inferred near grounding zones, where ice reaches the deepest draft. A few glaciers exhibit lower bottom melt rates (4±7 mice a–1). Bottom melting, however, appears to be a major source of mass loss on Antarctic ice shelves.

scholarly journals Kinematic response of ice-rise divides to changes in oceanic and atmospheric forcing

2019 ◽  
Author(s):  
Clemens Schannwell ◽  
Reinhard Drews ◽  
Todd A. Ehlers ◽  
Olaf Eisen ◽  
Christoph Mayer ◽  
...  
Keyword(s):  
Quantitative Interpretation ◽  
Ice Shelf ◽  
Catchment Scale ◽  
Local Flow ◽  
Surface Mass ◽  
Ice Shelves ◽  
Modelling Framework ◽  
Grounding Line ◽  
Flow Information ◽  
Mesh Resolution

Abstract. The majority of Antarctic ice shelves are bounded by grounded ice rises. These ice rises exhibit local flow regimes that partially oppose the flow of the surrounding ice shelves. Formation of such ice rises is accompanied by a characteristic upward arching internal stratigraphy (Raymond arches), archiving potential past divide migration and the onset of divide flow. Information about past ice-sheet conditions can therefore be retrieved in areas where other archives are missing. However, the quantitative interpretation of the stratigraphy requires modelling and radar observations. Hitherto, ice-rise modelling has been restricted to 2D and excluded the coupling between ice shelf and ice rise. This presents a major limitation for the interpretation of ice rises as ice-dynamic archive. Here we present an improved modelling framework to study ice-rise evolution using a calibrated, isothermal, and isotropic 3D Full-Stokes model including grounding-line dynamics at the required mesh resolution (<500 m). We apply the model to the Ekström Ice Shelf catchment containing two ice rises. Our results show that changes in the surface mass balance result in immediate and sustained divide migration (>2.0 m/yr) of up to 3.5 km. In contrast, instantaneous ice-shelf disintegration causes a short-lived and delayed (by 60–100 years) response of smaller magnitude (<0.75 m/yr). The model tracks migration of a triple junction and synchronous ice-divide migration in both ice rises with similar magnitude but differing rates. The model is suitable for glacial/interglacial simulations on the catchment scale, providing the next step forward to unravel the ice-dynamic history stored in ice rises all around Antarctica.

Decreasing Antarctic surface mass balance due to runoff-dominated ablation by 2100

2020 ◽  
Author(s):  
Christoph Kittel ◽  
Charles Amory ◽  
Cécile Agosta ◽  
Nicolas Jourdain ◽  
Stefan Hofer ◽  
...  
Keyword(s):  
Mass Balance ◽  
Sea Level Rise ◽  
Sea Level ◽  
Ice Sheet ◽  
Surface Mass Balance ◽  
Ice Shelf ◽  
Antarctic Ice Sheet ◽  
Surface Mass ◽  
Ice Shelves ◽  
The Antarctic

&lt;p&gt;&lt;span&gt;The surface mass balance (SMB) of the Antarctic ice sheet is often considered as a negative contributor to the sea level rise as present snowfall accumulation largely compensate&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; for ablation through wind erosion, sublimation and runoff. The latter is even almost negligible since current Antarctic surface melting is limited to relatively scarce events over generally peripheral areas and refreezes almost entirely into the snowpack. However, melting can significantly affect the stability of ice shelves through hydrofracturing, potentially leading to their disintegration, acceleration of grounded ice and increased sea level rise. Although a large increase in snowfall is expected in a warmer climate, more numerous and stronger melting events could conversely lead to a larger risk of ice shelf collapse. In this study, we provide an estimation of the SMB of the Antarctic ice sheet for the end of the 21st&amp;#160;century by forcing the state-of-the-art regional climate model MAR with three different global climate models. We chose the models (from both the Coupled Model Intercomparison Project Phase 5 and 6 - CMIP5 and CMIP6) providing the best metrics for representing the current Antarctic climate. While the increase in snowfall largely compensates snow ablation through runoff in CMIP5-forced projections, CMIP6-forced simulations reveal that runoff cannot be neglected in the future as it accounts for a maximum of 50% of snowfall and becomes the main ablation component over the ice sheet. Furthermore, we identify a tipping point (ie., a warming of 4&amp;#176;C) at which the Antarctic SMB starts to decrease as a result of enhanced runoff particularly over ice shelves. Our results highlight the importance of taking into account meltwater production and runoff and indicate that previous model studies neglecting these processes yield overestimated SMB estimates, ultimately leading to underestimated Antarctic contribution to sea level rise. Finally, melt rates over each ice shelf are higher than those that led to the collapse of the Larsen A and B ice shelves, suggesting a high probability of ice shelf collapses all over peripheral Antarctica by 2100.&lt;/span&gt;&lt;/p&gt;

scholarly journals Kinematic response of ice-rise divides to changes in ocean and atmosphere forcing

2019 ◽  
Vol 13 (10) ◽  
pp. 2673-2691 ◽  
Author(s):  
Clemens Schannwell ◽  
Reinhard Drews ◽  
Todd A. Ehlers ◽  
Olaf Eisen ◽  
Christoph Mayer ◽  
...  
Keyword(s):  
Mass Balance ◽  
Surface Mass Balance ◽  
Ice Shelf ◽  
Catchment Scale ◽  
Rock Outcrops ◽  
Local Flow ◽  
Surface Mass ◽  
Ice Shelves ◽  
Modelling Framework ◽  
Mesh Resolution

Abstract. The majority of Antarctic ice shelves are bounded by grounded ice rises. These ice rises exhibit local flow fields that partially oppose the flow of the surrounding ice shelves. Formation of ice rises is accompanied by a characteristic upward-arching internal stratigraphy (“Raymond arches”), whose geometry can be analysed to infer information about past ice-sheet changes in areas where other archives such as rock outcrops are missing. Here we present an improved modelling framework to study ice-rise evolution using a satellite-velocity calibrated, isothermal, and isotropic 3-D full-Stokes model including grounding-line dynamics at the required mesh resolution (<500 m). This overcomes limitations of previous studies where ice-rise modelling has been restricted to 2-D and excluded the coupling between the ice shelf and ice rise. We apply the model to the Ekström Ice Shelf, Antarctica, containing two ice rises. Our simulations investigate the effect of surface mass balance and ocean perturbations onto ice-rise divide position and interpret possible resulting unique Raymond arch geometries. Our results show that changes in the surface mass balance result in immediate and sustained divide migration (>2.0 m yr−1) of up to 3.5 km. In contrast, instantaneous ice-shelf disintegration causes a short-lived and delayed (by 60–100 years) response of smaller magnitude (<0.75 m yr−1). The model tracks migration of a triple junction and synchronous ice-divide migration in both ice rises with similar magnitude but differing rates. The model is suitable for glacial/interglacial simulations on the catchment scale, providing the next step forward to unravel the ice-dynamic history stored in ice rises all around Antarctica.

scholarly journals <i>In-situ</i> GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica

2017 ◽  
Author(s):  
David E. Shean ◽  
Knut Christianson ◽  
Kristine M. Larson ◽  
Stefan R.M. Ligtenberg ◽  
Ian R. Joughin ◽  
...  
Keyword(s):  
Time Series ◽  
Strain Rate ◽  
Mass Balance ◽  
Surface Elevation ◽  
Surface Mass Balance ◽  
Elevation Change ◽  
Ice Shelf ◽  
Surface Mass ◽  
Grounding Line

Abstract. In the last two decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to ice-shelf basal melt and marine ice-sheet instability. To better understand these processes, we analyzed 2008–2010 and 2012–2014 in-situ GPS records for PIG to constrain surface mass balance, firn compaction, and basal melt. We computed time series of horizontal velocity, strain rate, antenna height, surface elevation, and Lagrangian elevation change (Dh/Dt). The antenna height time series show a surface elevation increase of ~ 0.7–1.0 m/yr, which is consistent with model estimates for surface mass balance (SMB) of ~ 0.7–0.9 mwe/yr and ~ 0.7–0.8 m/yr downward velocity due to firn compaction. An abrupt ~ 0.2–0.3 m surface elevation decrease, likely due to surface melt, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dh/Dt for all PIG shelf sites is highly linear, with trends of −1 to −4 m/yr and residuals of

scholarly journals High variability of climate and surface mass balance induced by Antarctic ice rises

2014 ◽  
Vol 60 (224) ◽  
pp. 1101-1110 ◽  
Author(s):  
Jan T.M. Lenaerts ◽  
Joel Brown ◽  
Michiel R. Van Den Broeke ◽  
Kenichi Matsuoka ◽  
Reinhard Drews ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Ice Cores ◽  
Horizontal Resolution ◽  
Surface Mass Balance ◽  
Ice Shelf ◽  
Local Climate ◽  
Surface Mass ◽  
Ice Shelves ◽  
Drifting Snow

AbstractIce rises play key roles in buttressing the neighbouring ice shelves and potentially provide palaeoclimate proxies from ice cores drilled near their divides. Little is known, however, about their influence on local climate and surface mass balance (SMB). Here we combine 12 years (2001–12) of regional atmospheric climate model (RACMO2) output at high horizontal resolution (5.5 km) with recent observations from weather stations, ground-penetrating radar and firn cores in coastal Dronning Maud Land, East Antarctica, to describe climate and SMB variations around ice rises. We demonstrate strong spatial variability of climate and SMB in the vicinity of ice rises, in contrast to flat ice shelves, where they are relatively homogeneous. Despite their higher elevation, ice rises are characterized by higher winter temperatures compared with the flat ice shelf. Ice rises strongly influence SMB patterns, mainly through orographic uplift of moist air on the upwind slopes. Besides precipitation, drifting snow contributes significantly to the ice-rise SMB. The findings reported here may aid in selecting a representative location for ice coring on ice rises, and allow better constraint of local ice-rise as well as regional ice-shelf mass balance.

scholarly journals Three-decade spatial patterns in surface mass balance of the Nivlisen Ice Shelf, central Dronning Maud Land, East Antarctica

2021 ◽  
pp. 1-13
Author(s):  
Bhanu Pratap ◽  
Rahul Dey ◽  
Kenichi Matsuoka ◽  
Geir Moholdt ◽  
Katrin Lindbäck ◽  
...  
Keyword(s):  
Mass Balance ◽  
Climate Model ◽  
Regional Scale ◽  
Ice Cores ◽  
East Antarctica ◽  
Surface Mass Balance ◽  
Ice Shelf ◽  
Grid Pattern ◽  
Surface Mass ◽  
Ice Shelves

Abstract The coastal Droning Maud Land in East Antarctica is characterized by small ice shelves with numbers of promontories and locally grounded isles, both called ice rises. These ice rises are typically dome-shaped and surface elevations are hundreds of meters above the surrounding ice shelves, which cause strong orographic effects on surface mass balance (SMB). We conducted shallow ice-penetrating radar sounding to visualize firn stratigraphy in the top 35 m over ~400 km of profiles across the Nivlisen Ice Shelf, and in a grid pattern over two adjacent ice rises (Djupranen and Leningradkollen). We tracked six reflectors (isochrones) and dated them using two ice cores taken at the ice rise summits, from which SMB over six periods in the past three decades was retrieved. The overall SMB pattern across the ice shelf remained similar for all periods; however, the eastwest contrast in SMB varies by a factor of 1.5–2 between the Leningradkollen and Djupranen grounding lines. The SMB patterns over the ice rises are more varied owing to complex interactions between topography, snowfall and wind. We use our results to evaluate the regional climate model RACMO2.3p2 in terms of the spatial SMB distribution and temporal changes over the ice shelf and ice rises at regional scale.

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