Abstract
Abstract. Subglacial hydrology plays an important role in ice sheet dynamics as it determines the sliding velocity. It also drives freshwater into the ocean, leading to undercutting of calving fronts by plumes. Modeling subglacial water has been a challenge for decades. Only recently have new approaches been developed such as representing subglacial channels and thin water sheets by separate layers of variable hydraulic conductivity. We extend this concept by modeling a confined–unconfined aquifer system (CUAS) in a single layer of an equivalent porous medium (EPM). The advantage of this formulation is that it prevents unphysical values of pressure at reasonable computational cost. We performed sensitivity tests to investigate the effect of different model parameters. The strongest influence of model parameters was detected in terms of governing the opening and closure of the system. Furthermore, we applied the model to the Northeast Greenland Ice Stream, where an efficient system independent of seasonal input was identified about 500 km downstream from the ice divide. Using the effective pressure from the hydrology model, the Ice Sheet System Model (ISSM) showed considerable improvements in modeled velocities in the coastal region.
Highlights
Subglacial water has been identified as a key component in glacial processes; it is fundamental in driving large ice flow variations over short time periods
Observations and measurements of subglacial processes are in general difficult to obtain and sparse. We address this by testing the model with some of the benchmark experiments of the Subglacial Hydrology Model Inter-comparison Project (SHMIP; de Fleurian et al, 2018)
Since the ice is slow in the Parallel Ice Sheet Model (PISM) results in that area, basal melt rates are low, and, since we use these as input in our hydrology model, it is expected that our model computes low water pressure here
Summary
Subglacial water has been identified as a key component in glacial processes; it is fundamental in driving large ice flow variations over short time periods. The layer representing the channels has its parameters (namely the hydraulic conductivity and the storage) adjusted to exhibit the behavior of an effective system We take this idea even further and apply Darcy flow to only a single layer of an equivalent porous medium (EPM), accounting for both drainage mechanisms (efficient and inefficient) by locally adjusting the effective hydraulic transmissivity. This means that we approximate the channel flow as a fast diffusion process to work in de Fleurian et al (2014). A short conclusions and outlook section wraps up the present study
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