Atmosphere-driven ice sheet mass loss paced by topography: Insights from modelling the south-western Scandinavian Ice Sheet

Åkesson, Henning; Morlighem, Mathieu; Nisancioglu, Kerim H.; Svendsen, John‐Inge; Mangerud, Jan

doi:10.1016/j.quascirev.2018.07.004

Cited by 18 publications

(16 citation statements)

References 116 publications

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“…Given this ice‐sheet geometry, the revised deglacial chronology supports recent modelling suggesting that air temperature (i.e. surface melt) was the dominant factor driving widespread, millennial‐scale ice sheet mass loss during deglaciation in south‐west Norway (Åkesson et al ., ).…”

Section: Discussionmentioning

confidence: 97%

“…Such deposits are critical, however, for improving knowledge of the timing of glacier readvances (i.e. maximum-limiting ages), for better understanding local palaeoclimatic trends, and for identifying asynchronous vs. synchronous behaviour of ice margins during deglaciation (Andersen et al, 1995;Briner et al, 2014;Åkesson et al, 2018). These gaps in knowledge due to missing or obscured geological archives are highlighted by recent compilations of ice age palaeogeography in Scandinavia Stroeven et al, 2016), which have relatively few constraints for Bølling-Allerød ice sheet margins.…”

Section: Introductionmentioning

confidence: 99%

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Coastal lake records add constraints to the age and magnitude of the Younger Dryas ice‐front oscillation along the Skagerrak coastline in southern Norway

Romundset

Lakeman

Høgaas

2019

J Quaternary Science

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Basal records from nine lake basins, located within a small area inside the Younger Dryas Ra moraine in southern Norway, were analysed and radiocarbon dated. Six reworked shell fragments from the lowermost facies in five different basins date to the Bølling–Allerød chronozone and are interpreted to represent an ice‐free coastline before a Younger Dryas ice sheet readvance of at least 8 km. The widespread shell fragments within the Younger Dryas ice margin but pre‐dating the Younger Dryas are demonstrated using a systematic survey of the lowermost strata in a collection of lake basins. A further 13 dated samples, mostly in situ articulated bivalves found in clayey silt overlying the basal facies, yielded overlapping ages close to the Younger Dryas–Holocene boundary. The 13 shell dates, along with two additional similar ages obtained on terrestrial plant macrofossils from basal strata in two basins near the marine limit, provide a minimum‐limiting age of 11.6k cal a BP for ice sheet retreat from the Ra moraine. This suggests that the ice sheet in south‐east Norway retreated from its Younger Dryas maximum position nearly a thousand years later than previously assumed. Similar systematic approaches may lead to improved ice sheet reconstructions from other formerly glaciated coastlines.

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Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Coastal lake records add constraints to the age and magnitude of the Younger Dryas ice‐front oscillation along the Skagerrak coastline in southern Norway

Romundset

Lakeman

Høgaas

2019

J Quaternary Science

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“…To understand why high upstream velocities are not reproduced in models, one must look into how the ice stream is initiated. The origin of NEGIS has been explained by a geothermal heat flux (GHF) anomaly left behind by the passage of the Icelandic plume (Fahnestock et al, 2001;Rogozhina et al, 2016;Martos et al, 2018;Alley et al, 2019). Interpretation of radar data points to unusually high basal melt rates at the head of the ice stream, corresponding to an exceptionally high GHF of 970 mW m −2 (Fahnestock et al, 2001;Macgregor et al, 2016;Alley et al, 2019;Keisling et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…These large uncertainties in the estimates of the GHF have been shown to dominate the uncertainty on the ice flux in this region (Smith-Johnsen et al, 2019). In addition, the GHF maps are coarse and may not capture local anomalies like the one suggested to exist at the head of NEGIS (Fahnestock et al, 2001;Macgregor et al, 2016;Alley et al, 2019). Accurately capturing such a feature and explicitly representing the effect of high melt rates on basal sliding are key to reproduce the distinct velocity pattern of NEGIS in ice sheet models.…”

Section: Introductionmentioning

confidence: 99%

Exceptionally high heat flux needed to sustain the Northeast Greenland Ice Stream

et al. 2020

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Abstract. The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting heat flux anomalies with various locations and intensities. In our model experiment, a minimum heat flux value of 970 mW m−2 located close to the East Greenland Ice-core Project (EGRIP) is required locally to reproduce the observed NEGIS velocities, giving basal melt rates consistent with previous estimates. The value cannot be attributed to geothermal heat flux alone and we suggest hydrothermal circulation as a potential explanation for the high local heat flux. By including high heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation.

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“…As the cryosphere community continues to make strides in understanding processes that govern variability of the present-day ice sheets, geologic proxies constraining past ice sheet change provide important clues as to how ice sheets may have responded to past climate change (Alley et al, 2010). Decades of research have led to the development of high-resolution geologic reconstructions that detail the spatial pattern and rate of retreat of the Greenland ice sheet (GrIS) over the last deglaciation as it evolved towards its present-day geometry (Weidick, 1968;Bennike and Bjorck, 2002;Young and Briner, 2015).…”

Section: Introductionmentioning

confidence: 99%

The impact of model resolution on the simulated Holocene retreat of the southwestern Greenland ice sheet using the Ice Sheet System Model (ISSM)

et al. 2019

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Abstract. Geologic archives constraining the variability of the Greenland ice sheet (GrIS) during the Holocene provide targets for ice sheet models to test sensitivities to variations in past climate and model formulation. Even as data–model comparisons are becoming more common, many models simulating the behavior of the GrIS during the past rely on meshes with coarse horizontal resolutions (≥10 km). In this study, we explore the impact of model resolution on the simulated nature of retreat across southwestern Greenland during the Holocene. Four simulations are performed using the Ice Sheet System Model (ISSM): three that use a uniform mesh and horizontal mesh resolutions of 20, 10, and 5 km, and one that uses a nonuniform mesh with a resolution ranging from 2 to 15 km. We find that the simulated retreat can vary significantly between models with different horizontal resolutions based on how well the bed topography is resolved. In areas of low topographic relief, the horizontal resolution plays a negligible role in simulated differences in retreat, with each model instead responding similarly to retreat driven by surface mass balance (SMB). Conversely, in areas where the bed topography is complex and high in relief, such as fjords, the lower-resolution models (10 and 20 km) simulate unrealistic retreat that occurs as ice surface lowering intersects bumps in the bed topography that would otherwise be resolved as troughs using the higher-resolution grids. Our results highlight the important role that high-resolution grids play in simulating retreat in areas of complex bed topography, but also suggest that models using nonuniform grids can save computational resources through coarsening the mesh in areas of noncomplex bed topography where the SMB predominantly drives retreat. Additionally, these results emphasize that care must be taken with ice sheet models when tuning model parameters to match reconstructed margins, particularly for lower-resolution models in regions where complex bed topography is poorly resolved.

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Atmosphere-driven ice sheet mass loss paced by topography: Insights from modelling the south-western Scandinavian Ice Sheet

Cited by 18 publications

References 116 publications

Coastal lake records add constraints to the age and magnitude of the Younger Dryas ice‐front oscillation along the Skagerrak coastline in southern Norway

Coastal lake records add constraints to the age and magnitude of the Younger Dryas ice‐front oscillation along the Skagerrak coastline in southern Norway

Exceptionally high heat flux needed to sustain the Northeast Greenland Ice Stream

The impact of model resolution on the simulated Holocene retreat of the southwestern Greenland ice sheet using the Ice Sheet System Model (ISSM)

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