Ice-thickness Patterns and the Dynamics of the Ross Ice Shelf, Antarctica

Abstract

ABSTRACT. As part of the Ross Ice Shelf G eophysical and Glaciological Survey, a detailed IJIap of ice thickness has been produced from airborne ra dar m easurements closely tied to the network of survey stations on the ice-shelf surface. The map, drawn with a 2 0 m contour interval, reveals a highly complex pattern of thickness variations reflecting presumably, at least in part, complex ice-shelf dynamics. Many features of the thickness variation pattern appear to be associated with zones of grounded ice, but not all. Features of interest include many ice thickness minima, with closures up to 120 m; a narrow, greatly elongated ridgetrough system 450 km or more in length ; a few ice thickness maxima; steep regional gradients of IQ m /km in freely floating ice ; highly contorted contours suggesting a large-scale " turbulence"; and at least two remarka ble step-like changes in ice thickness. The irregula rity of many of these features suggests dynamic non-equilibrium, i.e. the existence of transients in the dynamic system, so that the ice shelf as a whole suggests a state of rather rapid change. Flow-bands constructed on the basis of the strengths of the echo from the ice-wa ter interface clearly delineate the outflow from the main East Antarctic outlet glaciers in the grid eastern p a rt of the shelf. A discontinuous fl ow ba nd originating in a sm a ll mountain glacier (Robb Glacier ) suggests a va riable mesoclima te in the vicinity of the glacier within the last thousand years. Strong refl ections near the ice front suggest bottom melting of saline ice previously froz en on to the underside of the ice. Several rifts or incipient rifts in the ice shelf characteristically show two lateral bands of strong reflections with a non-reflecting zone in between.R ESUME. La repartitian des ipaisseurs de glace et la dy namique du Rass Ice Shelf, Antarctique. Comme une participa tion a R oss I ce Shelf G eophysical a nd Glaciological Survey, un e carte detaillee d e l'epaisseur d e la glace a ete etablie par mesures aeriennes au rad a r, en liaison etroite a vec le reseau des stations d' observations sur la cou verture de glace elle-meme. Dessinee a vec des courbes d e niveau equidistantes d e 20 m, la carte revele un d essin tres complique d es variations d 'epaisseur de la glace, qui refl ete proba blem ent au moins en partie, la complexite de la dyn a mique de la couverture de glace. Beau coup de caracteristiques du dessin d es variatio ns d 'epaisseur de glace paraissent associees avec des zones d e glaces de terre m a is pas toutes. L es caracteristiques interessantes comportent beau coup de minimum d' ep a isseur de glace qui vont jusqu'a 120 m ; un system e etroit et tres a llonge de rides et d e creux de 450 km et plus de longueur ; un petit nombre d e maximum d'epaisseur d e glace; un gradient regional eleve de 10 m /km dans la glace fiottant librement; des lignes de niveau tres sinueuses suggera nt une " turbulence" a gra nde echelle ; et au moins deux rema rqua bles ch angem ents en marche d'escalier d e l'epais...

The Recent Advance of the Ross Ice Shelf Antarctica

“…The volume of ice that remains since its advance beyond the 1962 ice-front position can be roughly estimated by referring to ice-thickness maps by the Scott Polar Research Institute (unpublished [a]) and by Bentley and others (1979). The thickness patterns in Figure 7a and b differ most near the ice front in the east longitudes near Ross Island.…”

The Effects of Basal Melting on the Present Flow of the Ross Ice Shelf, Antarctica

“…Local surveys are possible (Clough and Hansen, 1979;Shabtaie and Bentley, 1979) but they are most useful for verification of precisely defined regions of basal melting. The second method is attempted in this study using observations made during the Ross Ice Shelf Glaciological and Geophysical Survey (RIGGS) and other field programs (Zumberge, 1964;Bentley and others, 1979;Thomas and others, 1984).…”

“…H is the observed ice thickness (Bentley and others, 1979) (Fig. I), and 11 is the horizontal velocity calculated by the numerical model.…”

“…This constitutive relation is derived from laboratory measurements of the deformation of isotropic ice samples u.nder ap~lied.loads (Glen, 1955;Hooke, 1981) and is consIstent wIth fIeld observations of unconfined ice-shelf flow (Thomas, 1973 ( Bentley and others , 1979 Bentley and others ( 1979) …”

Snow accumulation and compaction derived from GPR data near Ross Island, Antarctica

“…Radar has been utilised for glaciological analysis of ice thickness and the detection of internal layers for many years, e.g., Bentley et al (1979), Bogorodsky et al (1985), Arcone et al (1995), Eisen et al (2003), and Rotschky et al (2006). Reflections seen in radar recordings can sometimes be associated with distinct accumulation or melt events, or depth hoar layers (Eisen et al, 2004;Arcone et al, 2005;Helm et al, 2007;Dunse et al, 2008).…”