Meteoric and marine ice crystal orientation fabrics from the Amery Ice Shelf, East Antarctica

Abstract

ABSTRACT. The northwestern sector of the Amery Ice Shelf, East Antarctica, has a layered structure, due to the presence of both meteoric ice and a marine ice layer resulting from sub-shelf freezing processes. Crystal orientation fabric and grain-size data are presented for ice cores obtained from two boreholes $70 km apart on approximately the same flowline. Multiple-maxima crystal orientation fabrics and large mean grain sizes in the meteoric ice are indicative of stress relaxation and subsequent grain growth in ice that has flowed into the Amery Ice Shelf. Strongly anisotropic single-maximum crystal orientation fabrics and rectangular textures near the base of the $200 m thick marine ice layer suggest accretion occurs by the accumulation of frazil ice platelets. Crystal orientation fabrics in older marine ice exhibit vertical large circle girdle patterns, influenced by the complex stress configurations that exist towards the margins of the ice shelf. Post-accumulation grain growth and fabric development in the marine ice layer are restricted by a high concentration of brine and insoluble particulate inclusions. Differences in the meteoric and marine ice crystallography are indicative of the contrasting rheological properties of these layers, which must be considered in relation to large-scale ice-shelf dynamics.

Marine ice deformation experiments: an empirical validation of creep parameters

“…These excursions are worth considering further in terms of potential other drivers. A wide range of solid and soluble impurity contents has been described in the marine or meteoric ice literature [e.g., Jones and Glen, 1969;Oerter et al, 1992;Tison et al, 1993;Moore et al, 1994;Trickett et al, 2000;Khazendar et al, 2001;Treverrow et al, 2010], and these can also potentially affect the E * value. Even though our samples covered a relatively large salinity range, no significant systematic deviation could be isolated in the studied range of temperature and stresses.…”

“…By nature, and regardless of its rheology, marine ice is therefore a good candidate for stabilizing the ice shelf flow. Several studies have described marine ice properties and compared it to the meteoric ice formed through snow metamorphism on the continent [ Moore et al ., ; Oerter et al ., ; Souchez et al ., ; Tison et al ., ; Khazendar et al ., ; Treverrow et al ., , and references therein]. The sample properties differ significantly: marine ice is 2 orders of magnitude more saline than meteoric ice (but also 2 orders of magnitude less saline than sea ice), shows a positive δ 18 O signature because it is formed from the freezing of sea water, is devoid of bubbles, and can contain solid inclusions of marine or detritic origin.…”

“…In recent work where they study grain size, texture, and ice fabrics of marine ice in the Amery Ice Shelf, Treverrow et al . [] suggested that compression experiments be performed on marine ice to characterize its rheological properties. Preliminary tests have already been initiated by Samyn et al .…”

“…[3] Using inverse modeling, Khazendar et al [2009] has concluded that potential locations of marine ice accretion show lower inferred viscosities, suggesting marine ice deforms faster than meteoric ice. In recent work where they study grain size, texture, and ice fabrics of marine ice in the Amery Ice Shelf, Treverrow et al [2010] suggested that compression experiments be performed on marine ice to characterize its rheological properties. Preliminary tests have already been initiated by Samyn et al [2007] and Dierckx et al [2010] in that respect, but a detailed experimental study is still lacking.…”

Marine ice formation in a suture zone on the Larsen C Ice Shelf and its influence on ice shelf dynamics

“…The missing reflections from the marine ice‐ocean interface can be explained by the high dielectric absorption of the saline ice [ Thyssen , ]. The transition from marine ice to ocean water may be on a spectrum spanning water containing frazil ice, slushy ice, and fully consolidated ice, as observed in ice cores on the Ronne Ice Shelf and Amery Ice Shelf [ Treverrow et al ., ; Craven et al ., ; Oerter et al ., ]. Although the extent and relative proportion of mass of the marine ice bodies in LCIS are smaller than those in the Ronne or Amery Ice Shelf, these elongated zones play an important role for ice shelf stability, as they appear to prevent the propagation of lateral rifts [visible in Figure ; Holland et al ., ; Glasser et al ., ].…”