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Bottom Melting under George VI Ice Shelf, Antarctica

  • J. F. Bishop and J. L. W. Walton (a1)

Abstract

Bottom melting rates have been calculated for a large number of sites on George VI Ice Shelf from measurements of its kinematic behaviour. No simple explanation for the melt-rate pattern was found in terms of ice-shelf parameters, assuming steady-state conditions. Values of apparent melt rates varied from 1 to 8 m a−1 of ice. Along different flow lines the melt rate would sometimes increase with distance from the grounding line and sometimes the melt rate would decrease with distance. Large melt rates were found both where ice flowed off Palmer Land and where the ice shelf butted against Alexander Island. Although oceanographic conditions probably control bottom melting rates the complex pattern with large spatial variation seems to indicate that some areas of ice shelf are changing in thickness.

Résumé

Les taux de fusion à la base ont été calculés dans un grand nombre d’emplacements de la George VI Ice Shelf à partir de mesures de comportements cinématiques. On n’a pas trouvé d’explication simple des variations du taux de fusion à partir des paramètres propres à la plateforme de glace en supposant un état d’équilibre stable. Les valeurs du taux apparent de fusion varient de 1 à 8 m de glace par an. Le long de différentes lignes de courant, la vitesse de fusion pourrait parfois croître avec la distance à la ligne de décollement et parfois décroître avec cette distance. De grandes vitesses de fusion ont été trouvées aussi bien au point où la glace s’éloigne de Palmer Land et à celui où la plateforme butte contre Alexander Island. Bien que ce soient probablement les conditions océanographiques qui contrôlent les vitesses de fusion le long du lit, la complexité et les fortes variations dans l’espace du système des vitesses de fusion semblent indiquer que certaines zones de la plateforme sont en train de changer d’épaisseur.

Zusammenfassung

Aus Messungen des kinematischen Verhaltens wurden Schmelzraten am Untergrund für eine grosse Zahl von Stellen auf dem George VI Ice Shelf berechnet. Für die Verteilung der Schmelzraten bei stationärem Zustand konnte keine einfache Erklärung mit Hilfe der Parameter des Schelfeises gefunden werden. Die Werte der scheinbaren Schmelzraten schwankten von 1 bis 8 m Eis pro Jahr. Längs verschiedener Stromlinien können die Schmelzraten mit wachsendem Abstand von der Aufsetzlinic sowohl zu- wie abnehmen. Grosse Schmelzraten wurden sowohl beim Eiszustrom aus Palmer Land wie an der Berührungsstelle des Schelfeises mit Alexander Island gefunden. Obwohl das Schmelzen an der Unterseite vermutlich von ozeanographischen Faktoren abhängt, scheint das komplizierte Muster der räumlichen Schwankungen darauf hinzuweisen, dass sich die Dicke des Schelfeises in manchen Gebieten ändert.

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Copyright

References

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