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The Equilibrium State of the Eastern Half of the Ross Ice Shelf*

  • Robert H. Thomas (a1) and Charles R. Bentley (a2)

Abstract

Measurements of ice thickness, velocity, snow accumulation rates, and surface strain-rates are used to examine the state of equilibrium of three flow bands of the Ross Ice Shelf. The analysis gives the rate of thickening of the ice shelf in terms of the basal freezing rate, which is unknown. However, indirect evidence suggests that the basal flux ranges from a small value of freezing in the south to a melting rate of about one meter of ice per year at the ice front. If these values are correct then the flow band in the south-east corner of the ice shelf appears to be thickening at an average value of (34 ± 15) cm of ice per year. Persistent thickening at this rate must lead to grounding of large areas of the ice shelf. This would restrict drainage from West Antarctic ice streams which feed this part of the ice shelf and these would tend to thicken and advance their grounding lines into the ice shelf. Further north, near the RISP bore-hole site, the ice shelf is probably in equilibrium. The largest flow band is to the south and east of Roosevelt Island, and this also may be in equilibrium if there is significant bottom melting from ice shelf that is more than 100 km from the ice front.

Résumé

Par des mesures d'épaisseur de glace, de vitesse, d'accumulation de neige, et de vitesse de déformation en surface, on examine l'état d'équilibre de trois bandes d'écoulement du Ross Ice Shelf. L'analyse donne la vitesse d'épaississement de la glace en fonction de la vitesse de congélation à la base qui est inconnue. Cependant, des indices indirects suggèrent que le flux basal varie depuis une faible valeur de congélation dans te sud jusqu'à une vitesse de fusion d'environ un mètre de glace par au sur le front du glacier. Si ces estimations sont correctes, alors le courant de glace du coin Sud-Est de la banquise semble s'épaissir au rythme moyen de (34 ± 15) cm de glace par an. Un épaississeinent persistant à cette vitesse devrait conduire à appuyer sur le sol de larges zones de la banquise. Ceci restreindrait le drainage par les courants de glace de l'Ouest de l'Antarctique qui nourrissent cette partie de la banquise; ces courants tendent à s'épaissir et à avancer leur ligne de décollement du fond vers l'intérieur de la banquise. Plus loin au Nord, prés du site de forage du RISP, la glace est probablement en équilibre. Les plus grands courants d'écoulement sont vers le Sud et l'Est de Roosevelt Island et peuvent aussi être en équilibre s'il y a une fusion au fond significative à partir de la banquise à plus de ion km du front glaciaire.

Zusammenfassung

Zur Untersuchung des Gleichgewichtszusiandes dreier Ströme des Ross-Schelfeises werden Messungen der Eisdicke, der Geschwindigkeit, der Schneeakkumulation und der Deformation an der Oberfläche herangezogen. Die Analyse liefert die Zunahmerate der Schelfeisdicke in Abhängigkeit von Auffrierrate an der Unterseite, die jedoch unbekannt ist. Indirekte Schlüsse lassen jedoch vermuten, dass der Massenfluss an der Unterseite zwischen einem geringen Auffrieren im Süden und einem Schmelzbetrag von etwa 1 m Eis pro Jahr an der Eisfront liegt. Wenn diese Werte richtig sind, dann scheint der Eisstrom am Südost-Eck des Schelfeises um einen Mittelwert von (34 ± 15) cm pro.Jahr an Dicke zuzunehmen. Eine anhaltende Dickenzunahme in diescm Ausmass muss zum Aufsitzen weiter Gebiete des Schelfeises am Untergrund führen. Damit würde die Transportleistung der Eisströme aus der West-Antarktis, welche diesen Teil des Schelfeises ernähren, drosseln; sie würden an Dicke zunehmen und ihre Aufsitzlinie gegen das Schelfeis vorschieben. Weiter nördlich, an der Stelle des RISP-Bohrloches, befindet sich das Eis vermutlich im Gleichgewicht. Der stärkste Eisstrom liegt im Süden und Osten von Roosevelt Island; er dünfte sich ebenfalls im Gleichgewichtszustand befinden, sofern dort beträchtliches Abschmelzen an der Unterseite des Schelfeises bis zu mehr als 100 km Frontabstand stattfindet.

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Copyright

Footnotes

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*

Geophysical and Polar Research Center Contribution No. 347.

Footnotes

References

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