Trends in Antarctic Ice Sheet Elevation and Mass

Shepherd, Andrew; Gilbert, Lin; Muir, Alan; Konrad, Hannes; McMillan, Malcolm; Slater, Thomas; Briggs, K.; Sundal, A. V.; Hogg, Anna E.; Engdahl, Marcus

doi:10.1029/2019gl082182

Cited by 179 publications

(221 citation statements)

References 68 publications

(114 reference statements)

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“…Colours denote the SSMB in mm w.e. per year for all grounded ice sheet basins as well as the ice shelves these drain into, defined in Shepherd et al (2019). The numbers included in the basins denote the basin integrated SMB in Gt year −1 for the grounded ice sheet for the period 1980 to 2010 with the exception of COSMO-CLM 2 where the time series starts in 1987.…”

Section: Assessing the Surface Mass Balance Of Antarcticamentioning

confidence: 99%

What is the Surface Mass Balance of Antarctica? An Intercomparison of Regional Climate Model Estimates

Mottram¹,

Hansen²,

Kittel³

et al. 2020

Preprint

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Abstract. Antarctic ice sheet mass loss is currently equivalent to around 1 mm year−1 of global mean sea level rise. Most mass is lost due to sub-ice shelf melting and calving of icebergs. Ice sheet models of the Antarctic ice sheet have thus largely concentrated on parameterising sub-shelf and calving processes. However, surface mass balance (SMB) is also of crucial importance in controlling the stability and evolution of the vast Antarctic ice sheet. In this paper we compare the performance of five different regional climate models (COSMO-CLM2, HIRHAM5, MAR3.10, MetUM and RACMO2.3p2) in simulating the near surface climate and SMB of Antarctica. Our results show that, when regional climate models (RCMs) are forced by the ERA-Interim reanalysis, the integrated Antarctic ice sheet ensemble mean annual SMB is 2329 ± 94 Gigatonnes (Gt) year−1 over the common 1987 to 2015 period. However, individual model estimates vary from 1961 ± 70 to 2519 ± 118 Gt year−1. The large differences are mostly explained by different SMB estimates in West Antarctica and the peninsula as well as around the Transantarctic mountains. The calculated annual average SMB is very sensitive to the period chosen but over the climatological mean period of 1980 to 2010 the ensemble mean is 2486 Gt year−1. The interannual variability in SMB is consistent between the models and dominated by variability in the driving ERA-Interim reanalysis. The declining trend in Antarctic SMB reported in other studies is also very sensitive to period chosen and models disagree on the sign and magnitude of the trend in Antarctic SMB over the ERA-Interim period. Evaluation of models shows that they simulate Antarctic climate well when compared with daily observed temperature (Pearson correlation of 0.85 and higher) and pressure (bias ranges from −0.39 hPa in HIRHAM5 to −6.01 hPa in MAR with a mean of −3.49 hPa over all models) and nudged models, constrained within the domain as well as at lateral boundaries, perform better than un-nudged models. We compare modelled surface mass balance with a large dataset of observations which, though biased by undersampling in some regions, indicates that many of the biases in modelled SMB are common between models. The inclusion of drifting snow schemes improves modelled SMB on ice sheet slopes between 1000 and 2000 m where strong katabatic winds form but other regions where precipitation rates are high lack observations needed for the evaluation of different SMB estimates. Different ice masks have a substantial impact on the integrated total SMB and along with model resolution is therefore factored into our analysis. The majority of the different values for continental SMB are due to differences in modelled precipitation at relatively few grid points in coastal areas. Our analysis suggests that targeting coastal areas for observational campaigns will be key to improving and refining estimates of the total surface mass balance of Antarctica.

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Section: Assessing the Surface Mass Balance Of Antarcticamentioning

confidence: 99%

What is the Surface Mass Balance of Antarctica? An Intercomparison of Regional Climate Model Estimates

Mottram¹,

Hansen²,

Kittel³

et al. 2020

Preprint

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“…These additional 2 years of data added by our study to the long altimetry record already available show that the surface elevation lowering on Pine Island and Thwaites Glacier has continued at a similar pace compared to the 2013–2017 period. However, compared to surface elevation change estimates recorded during the 2000's from a combination of ERS‐2 and ENVISAT (Shepherd et al, ), the rate of elevation change over the fast‐flowing section of Thwaites Glacier has increased by 43 % and decreased by 9 % over Pine Island Glacier compared to the AltiKa record from 2013 to 2019. Overall, our study highlights the capability of AltiKa, the first space‐borne Ka‐band altimeter, for measuring surface elevation change in West Antarctica.…”

Section: Discussionmentioning

confidence: 88%

Ice Sheet Elevation Change in West Antarctica From Ka‐Band Satellite Radar Altimetry

Otosaka

Shepherd

McMillan

2019

Geophysical Research Letters

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Satellite altimetry has been used to track changes in ice sheet elevation using a series of Ku‐band radars in orbit since the late 1970s. Here, we produce an assessment of higher‐frequency Ka‐band satellite radar altimetry for the same purpose, using SARAL/AltiKa measurements recorded over West Antarctica. AltiKa elevations are 3.8 ± 0.5 and 2.5 ± 0.1 m higher than those determined from airborne laser altimetry and CryoSat‐2, respectively, likely due to the instruments' coarser footprint in the sloping coastal margins. However, AltiKa rates of elevation change computed between 2013 and 2019 are within 0.6 ± 2.4 and 0.1 ± 0.1 cm/year of airborne laser and CryoSat‐2, respectively, indicating that trends in radar penetration are negligible. The fast‐flowing trunks of the Pine Island and Thwaites Glaciers thinned by 117 ± 10 and 100 ± 20 cm/year, respectively, amounting to a 9% reduction and a 43% increase relative to the 2000s.

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“…Together, Thwaites and Pine Island glaciers were responsible for >30 % of the annual ice discharge from the West Antarctic Ice Sheet (WAIS) between 2009 and 2017 (compared with 25 % for 1979-1989Rignot et al, 2019), and TG alone accounted for ca. 55% of the annual mass balance from the WAIS between 1992 and 2017 (Shepherd et al, 2019). Recent observations and mass balance calculations show that TG is experiencing some of the highest rates of flow acceleration (Mouginot et al, 2014), discharge (Rignot et al, 2019), thinning (McMillan et al, 2014;Milillo et al, 2019;Shepherd et al, 2019), and grounding-line retreat (Rignot et al, 2014;Milillo et al, 2019) across the entire ice sheet.…”

Section: Introductionmentioning

confidence: 99%

“…55% of the annual mass balance from the WAIS between 1992 and 2017 (Shepherd et al, 2019). Recent observations and mass balance calculations show that TG is experiencing some of the highest rates of flow acceleration (Mouginot et al, 2014), discharge (Rignot et al, 2019), thinning (McMillan et al, 2014;Milillo et al, 2019;Shepherd et al, 2019), and grounding-line retreat (Rignot et al, 2014;Milillo et al, 2019) across the entire ice sheet. For example, over the past three decades net mass loss from TG is calculated to have increased from 12±1 https://doi.org/10.5194/tc-2020-25 Preprint.…”

Section: Introductionmentioning

confidence: 99%

“…Gt yr -1 during the period 1992-1997 to 76±6 Gt yr -1 from 2012 to 2016 (Shepherd et al, 2019). Its configuration, on a reversebed slope with direct connectivity to the deep WAIS interior (Holt et al, 2006) and its wide marine-terminating ice front (>120 km) with only small, unconfined frontal ice shelves, implies that TG is particularly susceptible to retreat via marine ice sheet instability (Weertman, 1974;Hughes, 1981;Vaughan & Arthern, 2007;Schoof, 2012).…”

Section: Introductionmentioning

confidence: 99%

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Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

Hogan

Larter

Graham

et al. 2020

Preprint

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Abstract. The geometry of the sea floor beyond Thwaites Glacier (TG) is a major control on the routing of warm ocean waters towards the ice stream’s grounding zone, which has led to increased mass loss through sub-ice-shelf melting and resulting accelerated ice flow. Nearshore topographic highs act as pinning points for the Thwaites Ice Shelf and potentially provide barriers to warm water incursions. To date, few vessels have been able to access this area due to persistent sea-ice and iceberg cover. This critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project, with more than 2000 km2 of new multibeam echo-sounder data (MBES) were acquired offshore TG. Here, these data along with legacy MBES datasets are compiled to produce a set of standalone bathymetric grids for the inner Amundsen Sea shelf beyond both Pine Island and Thwaites glaciers. At TG, the bathymetry is dominated by a > 1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some parts having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf, suggesting a positive feedback mechanism for ice-shelf ungrounding. Knowing that this offshore area is a former bed for TG, we applied a novel spectral approach to investigate bed roughness and find that derived power spectra can be approximated using an inverse-square law, a result that is consistent with spectra for bed profiles from the modern TG. Using existing ice-flow theory, we also make a first assessment of the form drag (basal drag contribution) for ice flow over this topography. Ice flowing over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting in the grounding zone today. We show that the sea-floor bathymetry is an analogue for extant bed areas of TG and that more can be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. Comparisons with existing regional bathymetric compilations for the area show that high-frequency (finer than 5 km) bathymetric variability beyond Antarctic ice shelves can only be resolved by observations such as MBES and that without these data calculations of the capacity of bathymetric troughs, and thus oceanic heat flux, may be significantly underestimated. This work meets the requirements of recent numerical ice-sheet and ocean modelling studies that have recognised the need for accurate and high-resolution bathymetry to determine warm water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.

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Trends in Antarctic Ice Sheet Elevation and Mass

Cited by 179 publications

References 68 publications

What is the Surface Mass Balance of Antarctica? An Intercomparison of Regional Climate Model Estimates

What is the Surface Mass Balance of Antarctica? An Intercomparison of Regional Climate Model Estimates

Ice Sheet Elevation Change in West Antarctica From Ka‐Band Satellite Radar Altimetry

Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

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