Future surface mass balance and surface melt in the Amundsen sector of the West Antarctic Ice Sheet

Abstract. We present projections of West Antarctic surface mass balance (SMB) and surface melt to 2080–2100 under the RCP8.5 scenario and based on a regional model at 10 km resolution. Our projections are built by adding a CMIP5 (Coupled Model Intercomparison Project Phase 5) multi-model-mean seasonal climate-change anomaly to the present-day model boundary conditions. Using an anomaly has the advantage to reduce CMIP5 model biases, and a perfect-model test reveals that our approach captures most characteristics of future changes despite a 16 %–17 % underestimation of projected SMB and melt rates. SMB over the grounded ice sheet in the sector between Getz and Abbot increases from 336 Gt yr−1 in 1989–2009 to 455 Gt yr−1 in 2080–2100, which would reduce the global sea level changing rate by 0.33 mm yr−1. Snowfall indeed increases by 7.4 % ∘C−1 to 8.9 % ∘C−1 of near-surface warming due to increasing saturation water vapour pressure in warmer conditions, reduced sea-ice concentrations, and more marine air intrusion. Ice-shelf surface melt rates increase by an order of magnitude in the 21st century mostly due to higher downward radiation from increased humidity and to reduced albedo in the presence of melting. There is a net production of surface liquid water over eastern ice shelves (Abbot, Cosgrove, and Pine Island) but not over western ice shelves (Thwaites, Crosson, Dotson, and Getz). This is explained by the evolution of the melt-to-snowfall ratio: below a threshold of 0.60 to 0.85 in our simulations, firn air is not entirely depleted by melt water, while entire depletion and net production of surface liquid water occur for higher ratios. This suggests that western ice shelves might remain unaffected by hydrofracturing for more than a century under RCP8.5, while eastern ice shelves have a high potential for hydrofracturing before the end of this century.

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Climate and surface mass balance of coastal West Antarctica resolved by regional climate modelling

Annals of Glaciology ◽

10.1017/aog.2017.42 ◽

2017 ◽

Vol 59 (76pt1) ◽

pp. 29-41 ◽

Cited By ~ 16

Author(s):

Jan T. M. Lenaerts ◽

Stefan R. M. Ligtenberg ◽

Brooke Medley ◽

Willem Jan Van de Berg ◽

Hannes Konrad ◽

...

Keyword(s):

High Resolution ◽

Mass Balance ◽

Ice Sheet ◽

Small Scale ◽

Climate Modelling ◽

Surface Mass Balance ◽

West Antarctica ◽

Surface Mass ◽

West Antarctic ◽

Surface Melt

ABSTRACTWest Antarctic climate and surface mass balance (SMB) records are sparse. To fill this gap, regional atmospheric climate modelling is useful, providing that such models are employed at sufficiently high horizontal resolution and coupled with a snow model. Here we present the results of a high-resolution (5.5 km) regional atmospheric climate model (RACMO2) simulation of coastal West Antarctica for the period 1979–2015. We evaluate the results with available in situ weather observations, remote-sensing estimates of surface melt, and SMB estimates derived from radar and firn cores. Moreover, results are compared with those from a lower-resolution version, to assess the added value of the resolution. The high-resolution model resolves small-scale climate variability invoked by topography, such as the relatively warm conditions over ice-shelf grounding zones, and local wind speed accelerations. Surface melt and SMB are well reproduced by RACMO2. This dataset will prove useful for picking ice core locations, converting elevation changes to mass changes, for driving ocean, ice-sheet and coupled models, and for attributing changes in the West Antarctic Ice Sheet and shelves to changes in atmospheric forcing.

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Future ice-sheet surface mass balance and melting in the Amundsen region, West Antarctica

10.5194/tc-2020-113 ◽

2020 ◽

Author(s):

Marion Donat-Magnin ◽

Nicolas C. Jourdain ◽

Christoph Kittel ◽

Cécile Agosta ◽

Charles Amory ◽

...

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Coupled Model ◽

Water Vapour Pressure ◽

Surface Mass Balance ◽

Near Surface ◽

Surface Mass ◽

Ice Shelves ◽

Surface Warming ◽

West Antarctic

Abstract. We present projections of West-Antarctic surface mass balance (SMB) and surface melting to 2080–2100, under the RCP8.5 scenario and based on a regional model at 10 km resolution. Our projections are built by adding a CMIP5 (5th Coupled Model Intercomparison Project) multi-model-mean seasonal climate-change anomaly to the present-day model boundary conditions. Using an anomaly has the advantage to reduce CMIP5 model biases, and a perfect-model test reveals that our approach captures most characteristics of future changes, despite a 16–17 % underestimation of projected SMB and melt rates. SMB over the grounded ice sheet in the sector between Getz and Abbot increases from 336 Gt yr−1 in 1989–2009 to 455 Gt yr−1 in 2080–2100, which would reduce the global sea level changing rate by 0.33 mm yr−1. Snowfall indeed increases by 7.4 to 8.9 % per °C of near-surface warming, due to increasing saturation water vapour pressure in warmer conditions, reduced sea-ice concentrations, and more marine air intrusion. Ice-shelf surface melt rates increase by an order of magnitude along the 21st century, mostly due to higher downward radiation from increased humidity, and to reduced albedo in the presence of melting. Eastern ice shelves (Abbot, Cosgrove and Pine Island) experience significant runoff in the future, while western ice shelves (Thwaites, Crosson, Dotson and Getz) remain without runoff. This is explained by the evolution of the melt-to-snowfall ratio: below a threshold of 0.60 to 0.85, firn air is not entirely depleted by melt water, while entire depletion and runoff occur for higher ratios. This suggests that western ice shelves might remain unaffected by hydrofracturing for more than a century under RCP8.5, while eastern ice shelves have a high potential for hydrofracturing before the end of this century.

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Small impact of surrounding oceanic conditions on 2007–2012 Greenland Ice Sheet surface mass balance

The Cryosphere Discussions ◽

10.5194/tcd-8-1453-2014 ◽

2014 ◽

Vol 8 (2) ◽

pp. 1453-1477 ◽

Cited By ~ 2

Author(s):

B. Noël ◽

X. Fettweis ◽

W. J. van de Berg ◽

M. R. van den Broeke ◽

M. Erpicum

Keyword(s):

Mass Balance ◽

North Atlantic ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Mass Balance ◽

Katabatic Winds ◽

Surface Mass ◽

The North ◽

The North Atlantic ◽

Surface Melt

Abstract. During recent summers (2007–2012), several surface melt records were broken over the Greenland Ice Sheet (GrIS). The extreme summer melt resulted in part from a persistent negative phase of the North-Atlantic Oscillation (NAO), favouring warmer than normal conditions over the GrIS. In addition, it has been suggested that significant anomalies in sea ice cover (SIC) and sea surface temperature (SST) may partially explain recent anomalous GrIS surface melt. To assess the impact of 2007–2012 SIC and SST anomalies on GrIS surface mass balance (SMB), a set of sensitivity experiments was carried out with the regional climate model MAR. These simulations suggest that changes in SST and SIC in the seas surrounding Greenland do not significantly impact GrIS SMB, due to the katabatic winds blocking effect. These winds are strong enough to prevent oceanic near-surface air, influenced by SIC and SST variability, from penetrating far inland. Therefore, the ice sheet SMB response is restricted to coastal regions, where katabatic winds are weaker. However, anomalies in SIC and SST could have indirectly affected the surface melt by changing the general circulation in the North Atlantic region, favouring more frequent warm air advection to the GrIS.

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Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet

The Cryosphere ◽

10.5194/tc-15-1215-2021 ◽

2021 ◽

Vol 15 (3) ◽

pp. 1215-1236

Author(s):

Christoph Kittel ◽

Charles Amory ◽

Cécile Agosta ◽

Nicolas C. Jourdain ◽

Stefan Hofer ◽

...

Keyword(s):

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Surface Mass Balance ◽

Near Surface ◽

Surface Mass ◽

Ice Shelves ◽

Run Off ◽

The Antarctic

Abstract. The future surface mass balance (SMB) will influence the ice dynamics and the contribution of the Antarctic ice sheet (AIS) to the sea level rise. Most of recent Antarctic SMB projections were based on the fifth phase of the Coupled Model Intercomparison Project (CMIP5). However, new CMIP6 results have revealed a +1.3 ∘C higher mean Antarctic near-surface temperature than in CMIP5 at the end of the 21st century, enabling estimations of future SMB in warmer climates. Here, we investigate the AIS sensitivity to different warmings with an ensemble of four simulations performed with the polar regional climate model Modèle Atmosphérique Régional (MAR) forced by two CMIP5 and two CMIP6 models over 1981–2100. Statistical extrapolation enables us to expand our results to the whole CMIP5 and CMIP6 ensembles. Our results highlight a contrasting effect on the future grounded ice sheet and the ice shelves. The SMB over grounded ice is projected to increase as a response to stronger snowfall, only partly offset by enhanced meltwater run-off. This leads to a cumulated sea-level-rise mitigation (i.e. an increase in surface mass) of the grounded Antarctic surface by 5.1 ± 1.9 cm sea level equivalent (SLE) in CMIP5-RCP8.5 (Relative Concentration Pathway 8.5) and 6.3 ± 2.0 cm SLE in CMIP6-ssp585 (Shared Socioeconomic Pathways 585). Additionally, the CMIP6 low-emission ssp126 and intermediate-emission ssp245 scenarios project a stabilized surface mass gain, resulting in a lower mitigation to sea level rise than in ssp585. Over the ice shelves, the strong run-off increase associated with higher temperature is projected to decrease the SMB (more strongly in CMIP6-ssp585 compared to CMIP5-RCP8.5). Ice shelves are however predicted to have a close-to-present-equilibrium stable SMB under CMIP6 ssp126 and ssp245 scenarios. Future uncertainties are mainly due to the sensitivity to anthropogenic forcing and the timing of the projected warming. While ice shelves should remain at a close-to-equilibrium stable SMB under the Paris Agreement, MAR projects strong SMB decrease for an Antarctic near-surface warming above +2.5 ∘C compared to 1981–2010 mean temperature, limiting the warming range before potential irreversible damages on the ice shelves. Finally, our results reveal the existence of a potential threshold (+7.5 ∘C) that leads to a lower grounded-SMB increase. This however has to be confirmed in following studies using more extreme or longer future scenarios.

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Supplementary material to "Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet"

10.5194/tc-2020-291-supplement ◽

2020 ◽

Author(s):

Christoph Kittel ◽

Charles Amory ◽

Cécile Agosta ◽

Nicolas C. Jourdain ◽

Stefan Hofer ◽

...

Keyword(s):

Mass Balance ◽

Ice Sheet ◽

Surface Mass Balance ◽

Surface Mass ◽

Ice Shelves ◽

Supplementary Material ◽

The Antarctic

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

10.5194/egusphere-egu2020-17355 ◽

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

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 compensates 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&#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&#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.

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The surface albedo of the Greenland Ice Sheet between 1982 and 2015 from the CLARA-A2 dataset and its relationship to the ice sheet's surface mass balance

The Cryosphere ◽

10.5194/tc-13-2597-2019 ◽

2019 ◽

Vol 13 (10) ◽

pp. 2597-2614 ◽

Cited By ~ 2

Author(s):

Aku Riihelä ◽

Michalea D. King ◽

Kati Anttila

Keyword(s):

Time Series ◽

Mass Balance ◽

Surface Runoff ◽

Surface Albedo ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Early Summer ◽

Surface Mass Balance ◽

Surface Mass ◽

Surface Melt

Abstract. The Greenland Ice Sheet is losing mass at a significant rate, driven in part by increasing surface-melt-induced runoff. Because the ice sheet's surface melt is closely connected to changes in the surface albedo, studying multidecadal changes in the ice sheet's albedo offers insight into surface melt and associated changes in its surface mass balance. Here, we first analyse the CM SAF Cloud, Albedo and Surface Radiation dataset from AVHRR data second edition (CLARA-A2) Surface Albedo (SAL), covering 1982–2015, to obtain decadal albedo trends for each summer month. We also examine the rates of albedo change during the early summer, supported with atmospheric reanalysis data from MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2), to discern changes in the intensity of early summer melt, and their likely drivers. We find that rates of albedo decrease during summer melt have accelerated during the 2000s relative to the early 1980s and that the surface albedos now often decrease to values typical of bare ice at elevations 50–100 m higher on the ice sheet. The southern margins exhibit the opposite behaviour, though, and we suggest this is due to increasing snowfall over the area. We then subtract ice discharge from the mass balance estimates observed by the Gravity Recovery and Climate Experiment (GRACE) satellite mission to estimate surface mass balance. The CLARA-A2 albedo changes are regressed with these data to obtain a summer-aggregated proxy surface mass balance time series for the summer periods 1982–2015. This proxy time series is compared with latest regional climate model estimates from the MAR model to perform an observation-based test on the dominance of surface runoff in the magnitude and variability of the summer surface mass balance. We show that the proxy time series agrees with MAR through the analysed period within the associated uncertainties of the data and methods, demonstrating and confirming that surface runoff has dominated the rapid surface mass loss period between the 1990s and 2010s. Finally, we extend the analysis to the drainage basin scale to examine discharge–albedo relationships. We find little evidence of surface-melt-induced ice flow acceleration at annual timescales.

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Reconstruction of the 1979–2006 Greenland ice sheet surface mass balance using the regional climate model MAR

The Cryosphere Discussions ◽

10.5194/tcd-1-123-2007 ◽

2007 ◽

Vol 1 (1) ◽

pp. 123-168 ◽

Cited By ~ 9

Author(s):

X. Fettweis

Keyword(s):

Heat Flux ◽

Mass Balance ◽

Sensible Heat Flux ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Surface Mass Balance ◽

Outlet Glacier ◽

Surface Mass ◽

Melt Water ◽

Surface Melt

Abstract. Results from a 28-year simulation (1979–2006) over the Greenland ice sheet (GIS) reveal an increase of the solid precipitation (+0.4±2.5 km3 yr−2) and the run-off (+7.9±3.3 km3 yr−2) of surface melt water. The net effect of these competing factors leads to a significant Surface Mass Balance (SMB) loss rate of −7.2±5.1 km3 yr−2. The contribution of changes in the net water vapour fluxes (+0.02±0.09 km3 yr−2) and rainfall (+0.2±0.2 km3 yr−2) to the SMB variability is negligible. The melt water supply has increased because the GIS surface has been warming up +2.4°C since 1979. Latent heat flux, sensible heat flux and net solar radiation have not varied significantly over the last three decades. However, the simulated downward infra-red flux has increased by 9.3 W m−2 since 1979. The natural climate variability (e.g. the North Atlantic Oscillation) does not explain these changes on the GIS. The recent global warming, due to the greenhouse gas concentration increase induced by the human activities, could be a cause of these changes. The doubling of the surface melt water flux into the ocean over the period 1979–2006 suggests that the overall ice sheet mass balance has been increasingly negative, given the probable meltwater-induced outlet glacier acceleration. This study suggests that an increased melting dominates over an increased accumulation in a warming scenario and that the GIS would likely continue to loose mass in the future. A GIS melting would have an effect on the stability of the thermohaline circulation (THC) and the global sea level rise.

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Diverging future surface mass balance between the Antarctic ice shelves and grounded ice sheet

10.5194/tc-2020-291 ◽

2020 ◽

Author(s):

Christoph Kittel ◽

Charles Amory ◽

Cécile Agosta ◽

Nicolas C. Jourdain ◽

Stefan Hofer ◽

...

Keyword(s):

Mass Balance ◽

Sea Level Rise ◽

Sea Level ◽

Ice Sheet ◽

Surface Mass Balance ◽

Near Surface ◽

Surface Mass ◽

Ice Shelves ◽

The Future ◽

The Antarctic

Abstract. The future surface mass balance (SMB) will influence the ice dynamics and the contribution of the Antarctic ice sheet (AIS) to the sea-level rise. Most of recent Antarctic SMB projections were based on the 5th phase of the Coupled Model Intercomparison Project (CMIP5). However, new CMIP6 results have revealed a +1.3 °C higher mean Antarctic near-surface temperature than in CMIP5 at the end of the 21st century enabling estimations of future SMB in warmer climates. Here, we investigate the AIS sensitivity to different warmings with an ensemble of four simulations performed with the polar regional climate model MAR forced by two CMIP5 and two CMIP6 models over 1981–2100. Statistical extrapolation allows us to expand our results to the whole CMIP5 and CMIP6 ensembles. Our results highlight a contrasting effect on the future grounded ice sheet and the ice shelves. The SMB over grounded ice is projected to increase as a response to stronger snowfall, only partly offset by enhanced meltwater runoff. This leads to a cumulated sea-level rise mitigation (i.e. an increase in surface mass) of the grounded Antarctic surface by 5.1 ± 1.9 cm sea-level equivalent (SLE) in CMIP5-RCP8.5 and 6.3 ± 2.0 cm SLE in CMIP6-ssp585. Additionally, the CMIP6 low-emission ssp126 and intermediate-emission ssp245 scenarios project a stabilised surface mass gain resulting in a lower mitigation to sea-level rise than in ssp585. Over the ice shelves, the strong runoff increase associated with higher temperature is projected to lower the SMB with a stronger decrease in CMIP6-ssp585 compared to CMIP5-RCP8.5. Ice shelves are however predict to have a close-to-present-equilibrium stable SMB under CMIP6 ssp126 and ssp245 scenarios. Future uncertainties are mainly due to the sensitivity to anthropogenic forcing and the timing of the projected warming. While ice shelves should remain at a close-to-equilibrium stable SMB under the Paris Agreements, MAR projects strong SMB decrease for an Antarctic near-surface warming above +2.5 °C limiting the warming range before potential irreversible damages on the ice-shelves. Finally, our results reveal the existence of a potential threshold (+7.5 °C) that leads to a lower grounded SMB increase. This however has to be confirmed in following studies using more extreme or longer future scenarios.

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Surface mass balance and melting projections over the Amundsen coastal region, West Antarctica

10.5194/egusphere-egu2020-16488 ◽

2020 ◽

Author(s):

Nicolas Jourdain ◽

Marion Donat-Magnin ◽

Christoph Kittel ◽

Cécile Agosta ◽

Charles Amory ◽

...

Keyword(s):

Mass Balance ◽

Projection Method ◽

Surface Mass Balance ◽

West Antarctica ◽

Ice Shelf ◽

Near Surface ◽

Surface Mass ◽

Ice Shelves ◽

The Future ◽

Surface Melt

We present Surface Mass Balance (SMB) and surface melt rates projections in West Antarctica for the end of the 21st century using the MAR regional atmosphere and firn model (Gall&#233;e 1994; Agosta et al. 2019) forced by a CMIP5-rcp85 multi-model-mean seasonal anomaly added to the ERA-Interim 6-hourly reanalysis.&#160;First of all, we assess the validity of our projection method, following a perfect-model approach, with MAR constrained by the ACCESS-1.3 present-day and future climates. Changes in large-scale variables are well captured by our anomaly-based projection method, and errors on surface melting and SMB projections are typically 10%.&#160;Based on the CMIP5-rcp85 multi-model mean, SMB over the grounded ice sheet in the Amundsen sector is projected to increase by 35% over the 21st century. This corresponds to a SMB sensitivity to near-surface warming of 8.3%.&#176;C-1. Increased humidity, resulting from both higher water vapour saturation in warmer conditions and decreased sea-ice concentrations, are shown to favour increased SMB in the future scenario.&#160;Ice-shelf surface melt rates at the end of the 21st century are projected to become 6 to 15 times larger than presently, depending on the ice shelf under consideration. This is due to enhanced downward longwave radiative fluxes related to increased humidity, and to an albedo feedback leading to more absorption of shortwave radiation. Interestingly, only three ice shelves produce runoff (Abbot, Cosgrove and Pine Island) in the future climate. For the other ice shelves (Thwaites, Crosson, Dotson, Getz), the future melt-to-snowfall ratio remains too low to produce firn air depletion and subsequent runoff.&#160;

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