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

Mathieu Morlighem,Aleah Sommers,Harihar Rajaram

doi:10.5194/gmd-11-2955-2018

Mathieu Morlighem, Aleah Sommers + Show 1 more

Open Access

https://doi.org/10.5194/gmd-11-2955-2018

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Abstract

Abstract. Subglacial hydrology has a strong influence on glacier and ice sheet dynamics, particularly through the dependence of sliding velocity on subglacial water pressure. Significant challenges are involved in modeling subglacial hydrology, as the drainage geometry and flow mechanics are constantly changing, with complex feedbacks that play out between water and ice. A clear tradition has been established in the subglacial hydrology modeling literature of distinguishing between channelized (efficient) and sheetlike (inefficient or distributed) drainage systems or components and using slightly different forms of the governing equations in each subsystem to represent the dominant physics. Specifically, many previous subglacial hydrology models disregard opening by melt in the sheetlike system or redistribute it to adjacent channel elements in order to avoid runaway growth that occurs when it is included in the sheetlike system. We present a new subglacial hydrology model, SHAKTI (Subglacial Hydrology and Kinetic, Transient Interactions), in which a single set of governing equations is used everywhere, including opening by melt in the entire domain. SHAKTI employs a generalized relationship between the subglacial water flux and the hydraulic gradient that allows for the representation of laminar, turbulent, and transitional regimes depending on the local Reynolds number. This formulation allows for the coexistence of these flow regimes in different regions, and the configuration and geometry of the subglacial system evolves naturally to represent sheetlike drainage as well as systematic channelized drainage under appropriate conditions. We present steady and transient example simulations to illustrate the features and capabilities of the model and to examine sensitivity to mesh size and time step size. The model is implemented as part of the Ice Sheet System Model (ISSM).

Highlights

One of the significant consequences of contemporary climate change is rising sea level
We describe the model formulation of SHAKTI (Subglacial Hydrology and Kinetic, Transient Interactions), which allows for flexible evolution of the subglacial drainage system configuration and flow regimes using a single set of governing equations over the entire domain
We presented the SHAKTI model formulation with simple illustrative simulations to highlight some of the model features under different conditions

Summary

Introduction

One of the significant consequences of contemporary climate change is rising sea level. Future ice dynamics remain a major uncertainty in sea level rise predictions involving many uncertain factors, including basal lubrication and effects on sliding velocities from subglacial drainage (e.g., Church et al, 2013; Shannon et al, 2013). Massive outlet glaciers of West Antarctica may be on the verge of irreversible collapse in the 200 to 1000 years (Joughin et al, 2014; DeConto and Pollard, 2016), the Greenland ice sheet is currently the single largest contributor to sea level rise (Shepherd et al, 2012). Since 1990, many Greenland outlet glaciers have displayed dramatic accelerations and frontal retreats, yielding substantial changes on the rapid timescale of decades or years (Joughin et al, 2010). The recent accelerations observed in marineterminating outlet glaciers, which exhibit some of the great-

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