Sublimation of ice through sediment in beacon valley, antarctica

Abstract

The time-dependent physics of ice sublimation through thin layers of till is considered, to determine whether sublimation could be sufficiently slow to permit the preservation of ice for 8 Ma in the Dry Valleys, Antarctica. This could only happen if the ice had been very thick, but other evidence (crystal size, dating of other ice-cored moraines) is not consistent with this possibility. Steady-state models suggest that sublimation is rate-controlled by vapor transport. A time-dependent model coupling vapor concentration, air pressure, temperature and ice concentration is formulated, and the resulting equations solved non-linearly. No transient coupling between vapor concentration, air temperature and pressure that substantially slows down sublimation was found in the numerical experiments. This means either that vapor transport is being slowed down by some unconsidered physical process or that the ice is much younger than 8 Ma.

Ground ice recharge via brine transport in frozen soils of Victoria Valley, Antarctica: Insights from modeling δ18O and δD profiles

“…This value is in good agreement with modeled ice sublimation rates of the order of 0.1 mm a À1 in various regions in the McMurdo Dry Valleys (e.g. Beacon Valley and Linneaus Terrace, Hindmarsh et al, 1998;McKay et al, 1998;Schorghofer, 2005). A much lower sublimation rate, 0.017 mm a À1 , was found for Beacon Valley by Kowalewski (2006), but this may well be an underestimate because it is based on climate data that do not include January, the period of most rapid sublimation as inferred from data in Victoria Valley (Hagedorn et al, 2007).…”

Geomorphological applications of cosmogenic isotope analysis

“…The significance of this buried ice is that if it is of Miocene age (minimum 8.1 Ma BP) -as has been inferred from stratigraphic relationships to overlying tills dated by 40 Ar/ 39 Ar analyses of presumed in situ volcanic ash -it confirms the persistence of a cold, hyper-arid climate in the area throughout the Pliocene and refutes the notion of an unstable East Antarctic Ice Sheet during this period (Sugden et al, 1995). The ability of ice in the near subsurface to survive sublimation over the time spans proposed has been questioned (Hindmarsh et al, 1998), as has the interpretation that the volcanic ash deposits are undisturbed and thus provide a chronological constraint on the age of the ice. Through an analysis of the concentrations of cosmogenic 3 He and 21 Ne in two surface dolerite erratics and one shielded erratic from within the ice, Schäfer et al (2000) demonstrated that sublimation rates could not have exceed more than a few metres per million years and that the ice must be at least several million years old.…”

Degradation of glacial deposits quantified with cosmogenic nuclides, Quartermain Mountains, Antarctica

“…Sublimation and erosion rates are probably not steady on yearly timescales, and are likely punctuated by extreme events and periods of stability, but over ~10 5 years, these variations are indistinguishable from steady degradation. The development of a sublimation till over dirty ice is thought to shield the underlying ice from sublimation, and as the till layer thickens, sublimation rates should lower (Hindmarsh et al, 1998;Schorghofer, 2005;Kowalewski et al, 2006). The results of this study suggest that erosion of the overlying sublimation till may act to thin the till such that sublimation rates remain constant on a ~10 5 year timescale.…”

“…The results of this study suggest that erosion of the overlying sublimation till may act to thin the till such that sublimation rates remain constant on a ~10 5 year timescale. The age and stability of the relict glacier ice in Beacon Valley has been the subject of much debate and research (Sugden et al, 1995;van der Wateren and Hindmarsh, 1995;Hindmarsh et al, 1998;Marchant et al, 2002;Ng et al, 2005;Kowalewski et al, 2006). The results of this study only record what has happened at the study sites for the past 0·4-2 Ma, and therefore do not directly address the preservation of ice that is 8·1 Ma.…”

“…Presently, sublimation rates of bare ice in the MDV are on the order of 10 4 to 10 5 m Ma −1 (Clow et al, 1988) and many authors have modeled and measured sublimation rates of ice through a soil layer in various parts of the MDV. Most of the measurements and models suggest that ground ice in the MDV should be actively subliming, and that the upper few meters of soil in the MDV should be ice-free on the order of 10 3 to 10 5 years (Hindmarsh et al, 1998;McKay et al, 1998;Campbell and Claridge, 2006;Bockheim et al, 2007;Hagedorn et al, 2007), but recent models have shown that small variations in cloud cover, relative humidity, and snow cover can cause near equilibrium conditions and allow for the long term stability of ground ice (Schorghofer, 2005;Kowalewski et al, 2006;McKay, 2009). Although these models disagree as to whether or not ice in soils in the MDV should be actively subliming or are near equilibrium and stable, the observation remains that ground ice persists near the surface within Miocene-aged soils in the Quartermain Mountains (Bockheim, 2007).…”