Thermal regime and dynamics of the West Antarctic ice sheet

Abstract

The temperature-depth profiles measured in 22 boreholes drilled on the West Antarctic ice sheet exhibit two distinctly different thermal states of its basal ice. The warm state shows on Siple Dome and on Whillans Ice Stream. A relatively colder state, found at the Unicorn, Kamb Ice Stream (former Ice Stream C) and Bindschadler Ice Stream (former Ice Stream D), has basal temperature gradients greater than 50 K km -1 . A large block of cold ice stranded and frozen to the bed at the Unicorn and simultaneously much warmer ice existing only a few kilometers across the Dragon shear margin in fastmoving Alley Ice Stream (former Ice Stream B2) poses a paradox. The relatively cold ice at the Unicorn must have come from a source different from the present Whillans Ice Stream catchment area. It is hypothesized that the Unicorn paradox was created by a super-surge. Also, the stagnant Siple Ice Stream, many relict shear margins, cold patches of ice at the Crary Ice Rise, ice rafts embedded in the Ross Ice Shelf, all point to a major event triggered either by an internal instability or by a subareal volcanic eruption. Most of these features appeared to have been formed about 500 years ago. Subsequent freeze-on of a 10-20 m thick basal layer of debris-laden ice and water loss caused a slowdown of ice streams and, in the case of Kamb Ice Stream, an almost complete stoppage.

Monitoring the temperature-dependent elastic and anelastic properties in isotropic polycrystalline ice using resonant ultrasound spectroscopy

“…While near-surface temperatures are typically below −20 • C, basal temperatures can exceed the bulk melting point (Pattyn, 2010;Cuffey and Paterson, 2010;Engelhardt, 2004;Joughin et al, 2004;Iken et al, 1993). It follows that a significant temperature-induced flow viscosity gradient must exist within large ice masses, on top of other contributing factors such as crystalline fabrics, which induce mechanical anisotropy.…”

“…Ice can undergo pre-melting where water (or some modified form of water) exists on ice grain boundaries at temperatures potentially as low as −30 • C (Hobbs, 1974). Ice-sheet thermal structures at ice divides (Engelhardt, 2004) show that the upper ice sheet is below pre-melt temperatures and the base is above pre-melt temperatures, imparting a strong mechanical contrast.…”

Parameter and state estimation with a time-dependent adjoint marine ice sheet model

“…Ice internal temperature, while difficult to observe on large scales, can play an important role in ice flow and in the controls on basal melting and freezing of grounded ice. Many parameter estimation studies assume temperature is steady (Joughin et al, 2009;Morlighem et al, 2010), but there is evidence in certain locations that there is ongoing thermal adjustment due to unsteady transport (Engelhardt, 2004), and complex thermomechanical coupling in shear margins (Schoof, 2012). Using the existing tracer transport framework of MITgcm, we plan to implement thermal advection/diffusion in our ice model.…”

Basal melt rates beneath Whillans Ice Stream, West Antarctica

“…The inferred presence of a hydrologic pressure ridge that runs parallel to the shear margin (Fricker and others, 2007) may act to further concentrate heat by keeping basal water proximal. Furthermore, the borehole investigations of Engelhardt (2004b) discovered under-pressured channelized water downstream of areas of high melt production beneath Kamb Ice Stream. Also, basal-water routing models (Le Brocq and others, 2009) suggest a concentration of basal water along the northern margin of WIS.…”