Skip to main content Accessibility help
×
Home

On the Origin of Stratified Debris in Ice Cores from the Bottom of the Antarctic Ice Sheet

  • A. J. Gow (a1), S. Epstein (a2) and W. Sheehy (a1)

Abstract

Cores from the bottom 4.83 m of the Antarctic ice sheet at Byrd Station contain abundant stratified debris ranging from silt-sized particles to cobbles. The nature and disposition of the debris, together with measurements of the physical properties of the inclosing ice, indicate that this zone of dirt-laden ice originated by “freezing-in” at the base of the ice sheet. The transition from air-rich glacial ice to ice practically devoid of air coincided precisely with the first appearance of debris in the ice at 4.83 m above the bed. Stable-isotope studies made in conjunction with gas-content measurements also confirm the idea of incorporation of basal debris by adfreezing of melt water at the ice―rock interface. It is suggested that the absence of air from basal ice may well constitute the most diagnostic test for discriminating between debris incorporated in a melt―refreeze process and debris entrapped by purely mechanical means, e.g. shearing. We conclude from our observations on bottom cores from Byrd Station that “freezing-in” of basal debris is the major mechanism by which sediment is incorporated into polar ice sheets.

Résumé

Sur l’origine des sédiments stratifiés dans les carottes de glace provenant du fond de la calotte glaciaire Antarctique. Des carottes provenant des 4,83 derniers mètres avant le fond de la calotte Antarctique à la station Byrd contiennent une grande quantité de matériaux solides par couches stratifiées allant de la taille des grains de limon à celle de galets. La nature et la disposition de ces sédiments, ainsi que la mesure des propriétiés physiques de la glace qui les emballe, indiquent que cette zone de glace sale a pour origine le gel au fond à la base de la calotte. La transition entre la glace de glacier riche en air à la glace pratiquement dépourvue d’air coïncide précisément avec la première apparition de sédiment dans la glace à 4,83 m au dessus du lit. Les études d’isotope stables faites en liaison avec les mesures de teneur en gaz confirment l’idée d’une incorporation des débris du fond par regel de l’eau de fusion à l’interface glace–roche. On suggère que l’absence d’air dans la glace de fond peut bien constituer le meilleur test pour distinguer entre les sédiments incorporés dans un processus fusion-regel et ceux qui sont captés par des moyens purement mécaniques par exemple par cisaillement. Nous concluons de nos observations sur les carottes du fond issues de la station Byrd que le gel au fond des sédiments est le mécanisme principal d’incorporation des sédiments dans les calottes glaciaires polaires.

Zusammenfassung

Über den Ursprung geschichteten Schuttes in Eiskernen vom Untergrund des antarktischen Eisschildes. Kerne aus den untersten 4,83 m des antarktischen Eisschildes bei der Byrd-Station enthalten reichlichen, geschichteten Schutt von der Grösse verschlämmter Partikel bis zu der von Steinen. Die Art und Anordnung des Schuttes lassen zusammen mit Messungen der physikalischen Eigenschaften des einschliessenden Eises darauf schliessen, dass diese Zone verschmutzten Eises durch Einfrieren am Grunde des Eisschildes entstanden ist. Der Übergang von luftreichem zu praktisch luftleerem Eis fällt genau mit dem ersten Auftreten von Schutt im Eis, 4,83 m über dem Bett, zusammen. Studien mit stabilen Isotopen, die in Verbindung mit Gasgehaltsmessungen angestellt wurden bestätigen ebenfalls die Vorstellung von der Aufnahme des Untergrundschuttes durch Anfrieren von Schmelzwasser an der Grenzfläche zwischen Eis und Fels. Es wird vermutet, dass das Fehlen von Luft im Eis das sicherste Kriterium für die Unterscheidung zwischen Schutt, der durch einen Schmelz- und Regelationsprozess ins Eis gelangte, und solchem, der durch rein mechanische Vorgänge, z.B. Scherung, aufgenommen wurde, darstellt. Die Beobachtungen an Tiefkernen von der Byrd-Station lassen darauf schliessen, dass das Einfrieren von Schutt der wichtigste Mechanismus ist, durch den Sedimente in polare Eisschilde gelangen.

  • View HTML
    • Send article to Kindle

      To send this article to your Kindle, first ensure no-reply@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about sending to your Kindle. Find out more about sending to your Kindle.

      Note you can select to send to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

      Find out more about the Kindle Personal Document Service.

      On the Origin of Stratified Debris in Ice Cores from the Bottom of the Antarctic Ice Sheet
      Available formats
      ×

      Send article to Dropbox

      To send this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Dropbox.

      On the Origin of Stratified Debris in Ice Cores from the Bottom of the Antarctic Ice Sheet
      Available formats
      ×

      Send article to Google Drive

      To send this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your <service> account. Find out more about sending content to Google Drive.

      On the Origin of Stratified Debris in Ice Cores from the Bottom of the Antarctic Ice Sheet
      Available formats
      ×

Copyright

References

Hide All
Boulton, G. S. 1970. On the origin and transport of englacial debris in Svalbard glaciers. Journal of Glaciology, Vol. 9, No. 56, p. 21329.
Epstein, S. and Mayeda, T. K. 1953. Variation of O18 content of waters from natural sources. Geochimica et Cosmochimica Acta, Vol. 4, No. 5, p. 21324.
Epstein, S. and others. 1970. Antarctic ice sheet: stable isotope analysis of Byrd Station cores and interhemispheric climatic implications, by Epstein, S. Sharp, R. P. and Gow, A. J.. Science, Vol. 168, No. 3939, p. 157072.
Gow, A. J. and Williamson, T. C.. 1975. Gas inclusions in the Antarctic ice sheet and their glaciological significance. Journal of Geophysical Research, Vol. 80, No. 36, p. 510108.
Gow, A. J. and others. 1968. Antarctic ice sheet: preliminary results of first core hole to bedrock, by Gow, A. J. Ueda, H. T. and Garfield, D. E.. Science, Vol. 161, No. 3845, p. 101113.
Langway, C. C. jr. 1958. Bubble pressures in Greenland glacier ice. Union Géodésique et Géophysique Internationale. Association Internationale d’Hydrologie Scientifique. Symposium de Chamonix, 16–24 sept. 1958, P. 33649. (Publication No. 47 de l’Association Internationale d’Hydrologie Scientifique.)
Lorius, C. and others. 1968. Densité de la glace et étude des gaz en profondeur dans un glacier antarctique, [par] Lorius, C. Raynaud, D. et Dolle, L.. Tellus, Vol. 20, No. 3, p. 44960.
O’Neil, J. R. 1968. Hydrogen and oxygen isotope fractionation between ice and water. Journal of Physical Chemistry, Vol. 72, No. 10, p. 368384.
Rainwater, F. H. and Guy, H. P. 1961. Some observations of the hydrochemistry and sedimentation of the Chamberlin Glacier area, Alaska. U.S. Geological Survey. Professional Paper 441–C.
Weertman, J. 1961. Mechanism for the formation of inner moraines found near the edge of cold ice caps and ice sheets. Journal of Glaciology, Vol. 3, No. 30, p. 96578.
Weertman, J. 1966. Effect of a basal water layer on the dimensions of ice sheets. Journal of Glaciology, Vol. 6, No. 44, p. 191207.

Metrics

Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed