SHAKTI: Subglacial Hydrology and Kinetic, Transient Interactions v1.0

Sommers, Aleah; Rajaram, Harihar; Morlighem, Mathieu

doi:10.5194/gmd-11-2955-2018

Cited by 39 publications

(49 citation statements)

References 72 publications

(100 reference statements)

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“…Our observations support some of the features shown by recent subglacial drainage models [Schoof, 2010a, Hewitt, 2011, Hewitt, 2013, Werder et al, 2013, Bueler and van Pelt, 2015, Downs et al, 2018, Sommers et al, 2018, such as the existence of a distributed drainage system that exists year-round and during the melt season it evolves into a progressively more channelized and focused system. However, the most notable differences are the extremely heterogeneous distribution of diffusivity that our results suggest, the importance of normal stress transfers, and the existence of disconnected areas.…”

Section: Resultssupporting

confidence: 84%

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Supplementary material to "Subglacial drainage characterization from eight years of continuous borehole data on a small glacier in the Yukon Territory, Canada"

Rada¹,

Schoof²

2018

Preprint

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Understanding the physical processes that control the growth and decline of glaciers is vital to create models capable of forecasting how changing glaciers will affect the geography, biosphere and climate. This PhD thesis investigates basal sliding, which corresponds to the increase in speed a glacier experience by sliding downhill over the underlying terrain. We have studied a glacier in the Yukon Territory, Canada, installing over 300 pressure sensors at the base of the glacier to understand how water can create there a subglacial drainage system and accelerate or slowdown the glacier. Contrary to the predictions of current subglacial hydrology models, we found that different regions of the bed are typically either hydraulically well-connected or disconnected, and the transition between these two regimes is generally abrupt. Also, we found that the extent of areas hydraulically disconnected from the surface seems to have a very significant role in controlling basal sliding. v Preface This PhD thesis is based on multiple datasets acquired over nine consecutive years starting on 2008 by a group from the University of British Columbia led by Professor Christian Schoof, and a group from Simon Fraser University led by professor Gwen Flowers. I actively participated in fieldwork preparation, design, and execution between the years 2012 and 2016. During this period, I collaborated in the drilling of boreholes, and the installation and maintenance of pressure sensors, data loggers, GPS towers, and repeat photography cameras. I designed and built the repeat photography cameras, the digital sensors, and their associated data loggers. I conducted all of the borehole data analysis and wrote the manuscript with the close collaboration of my supervisor Christian Schoof, who provided numerous corrections and suggestions. A version of Chapter 2 has been published: Camilo Rada & Christian Schoof "Channelised, distributed, and disconnected: subglacial drainage under a valley glacier in the Yukon", The

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Section: Resultssupporting

confidence: 84%

“…Current subglacial drainage models [Schoof, 2010a, Hewitt, 2011, Hewitt, 2013, Werder et al, 2013, Bueler and van Pelt, 2015, Downs et al, 2018, Sommers et al, 2018 [Hewitt, 2013, Werder et al, 2013. However, these models still fail to reproduce direct borehole observations [Flowers, 2015].…”

Section: Introductionmentioning

confidence: 99%

Supplementary material to "Subglacial drainage characterization from eight years of continuous borehole data on a small glacier in the Yukon Territory, Canada"

Rada¹,

Schoof²

2018

Preprint

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“…Subglacial hydrology model have shown the localised effect on N , which is likely having consequences on the spread between the employed grid resolutions (e.g. Werder et al, 2013;de Fleurian et al, 2016;Sommers et al, 2018;Beyer et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the AWI contribution to ISMIP6-Greenland using ISSM

Rückamp

Goelzer

Humbert

2020

Preprint

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Abstract. Projections of the contribution of the Greenland ice sheet to future sea-level rise include uncertainties primarily due to the imposed climate forcing and the initial state of the ice sheet model. Several state-of-the-art ice flow models are currently being employed on various grid resolutions to estimate future mass changes in the framework of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). Here we investigate the sensitivity to grid resolution on centennial sea-level contributions from the Greenland ice sheet and study the mechanism at play. To this end, we employ the finite-element higher-order ice flow model ISSM and conduct experiments with four different horizontal resolutions, namely 4, 2, 1 and 0.75 km. We run the simulation based on the ISMIP6 core GCM MIROC5 under the high emission scenario RCP8.5 and consider both atmospheric and oceanic forcing in full and separate scenarios. Under the full scenarios, finer simulations unveil up to ~5 % more sea-level rise compared to the coarser resolution. The sensitivity depends on the magnitude of outlet glacier retreat, which is implemented as a series of retreat masks following the ISMIP6 protocol. Without imposed retreat under atmosphere-only forcing, the resolution dependency exhibits an opposite behaviour with about ~ 5 % more sea-level contribution in the coarser resolution. The sea-level contribution indicates a converging behaviour

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“…It is crucial to couple surface meltwater routing models with subglacial hydrological models to build a complete understanding of surface-to-bed meltwater connections. One path forward would be to use SUH, SRLF, and/or RWF to calculate moulin hydrographs using DEMs of different sources and spatial resolutions, then coupling this output to the Subglacial Hydrology and Kinetic, Transient Interactions (SHAKTI) subglacial hydrology model (Sommers et al, 2018). Doing so would allow derivation of hourly changes in subglacial water pressure in response to different moulin discharge inputs.…”

Section: Future Research Directionsmentioning

confidence: 99%

A new surface meltwater routing model for use on the Greenland Ice Sheet surface

et al. 2018

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Large volumes of surface meltwater are routed through supraglacial internally drained catchments (IDCs) on the Greenland Ice Sheet surface each summer. Because surface routing impacts the timing and discharge of meltwater entering the ice sheet through moulins, accurately modeling moulin hydrographs is crucial for correctly coupling surface energy and mass balance models with subglacial hydrology and ice dynamics. Yet surface routing of meltwater on ice sheets remains a poorly understood physical process. We use high-resolution (0.5 m) satellite imagery and a derivative high-resolution (3.0 m) digital elevation model to partition the runoff-contributing area of the Rio Behar catchment, a moderately sized ( ∼ 63 km 2 ) midelevation (1207-1381 m) IDC in the southwestern Greenland ablation zone, into open meltwater channels (supraglacial streams and rivers) and interfluves (small upland areas draining to surface channels, also called "hillslopes" in terrestrial geomorphology). A simultaneous in situ moulin discharge hydrograph was previously acquired for this catchment in July 2015. By combining the in situ discharge measurements with remote sensing and classic hydrological theory, we determine mean meltwater routing velocities through open channels and interfluves within the catchment. Two traditional terrestrial hydrology surface routing models, the unit hydrograph and rescaled width function, are applied and also compared with a surface routing and lake-filling model. We conclude that (1) surface meltwater is routed by slow interfluve flow (∼ 10 −3 -10 −4 m s −1 ) and fast open-channel flow (∼ 10 −1 m s −1 ); (2) the slow interfluve velocities are physically consistent with shallow, unsaturated subsurface porous media flow (∼ 10 −4 -10 −5 m s −1 ) more than overland sheet flow (∼ 10 −2 m s −1 ); (3) the open-channel velocities yield mean Manning's roughness coefficient (n) values of ∼ 0.03-0.05 averaged across the Rio Behar supraglacial stream-river network; (4) interfluve and open-channel flow travel distances have mean length scales of ∼ 10 0 -10 1 m and ∼ 10 3 m, respectively; and (5) seasonal evolution of supraglacial drainage density will alter these length scales and the proportion of interfluves vs. open channels and thus the magnitude and timing of meltwater discharge received at the outlet moulin. This phenomenon may explain seasonal subglacial water pressure variations measured in a borehole ∼ 20 km away. In general, we conclude that in addition to fast open-channel transport through supraglacial streams and rivers, slow interfluve processes must also be considered in ice sheet surface meltwater routing models. Interfluves are characterized by slow overland and/or shallow subsurface flow, and it appears that shallow unsaturated porous-mediaPublished by Copernicus Publications on behalf of the European Geosciences Union. 3792 K. Yang et al.: A new surface meltwater routing model flow occurs even in the bare-ice ablation zone. Together, bothinterfluves and open channels combine to modulate the timing and ...

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SHAKTI: Subglacial Hydrology and Kinetic, Transient Interactions v1.0

Cited by 39 publications

References 72 publications

Supplementary material to "Subglacial drainage characterization from eight years of continuous borehole data on a small glacier in the Yukon Territory, Canada"

Supplementary material to "Subglacial drainage characterization from eight years of continuous borehole data on a small glacier in the Yukon Territory, Canada"

Sensitivity of Greenland ice sheet projections to spatial resolution in higher-order simulations: the AWI contribution to ISMIP6-Greenland using ISSM

A new surface meltwater routing model for use on the Greenland Ice Sheet surface

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