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δD – δ18O Relationships in Ice Formed by Subglacial Freezing: Paleoclimatic Implications

  • R. A. Souchez (a1) and J. M. de Groote (a1)

Abstract

A freezing slope, distinct from that of precipitation, is displayed on a δD–δ18O diagram by basal ice in different circumstances. However, if the subglacial reservoir allowed to freeze is mixed in the course of time with an input having a lighter isotopic composition, basal ice cannot be distinguished from glacier ice in terms of slope. Such a situation is encountered at the base of Grubengletscher and is indicated by a computer simulation using the open-system model of Souchez and Jouzel (1984). Suggested implications for the paleoclimatic interpretation of deep ice cores recovered from the bottom part of polar ice sheets are given.

Résumé

Les échantillons de glace basale de glacier sont souvent alignés, dans un diagramme δD–δ18O, sur une pente de gel différente de celle des précipitations. Cependant, si le réservoir sous-glaciaire en cours de congélation est mélangé à un apport de composition isotopique plus négative, la glace basale ne montre plus cette différence de pente par rapport à la glace de glacier. Une telle situation se présente à la base du Grubengletscher et est simulée par ordinateur en utilisant le modèle en système ouvert de Souchez et Jouzel (1984). Les conséquences pour l’interprétation paléoclimatique des sondages profonds des calottes glaciaires polaires sont indiquées.

Zusammenfassung

Eis vom Untergrund eines Gletschers weist unter verschiedenen Umständen in einem δD–δ18O-Diagramm ein Gefriergefälle auf, das sich von dem des Niederschlages unterscheidet. Wenn jedoch das subglaziale Reservoir, das dem Gefrieren ausgesetzt ist, im Laufe der Zeit mit einem Zustrom von leichterer Isotopenzusammensetzung gemischt wird, kann Grundeis von Gletschereis nicht aus dem Gefriergefälle unterschieden werden. In dieser Lage befindet sich der Untergrund des Grubengletschers; sie wird mit einer Rechnersimulierung nachgeahmt, die auf dem Modell des offenen Systems von Souchez und Jouzel (1984) beruht. Folgerungen für die paläoklimatische Interpretation tiefer Eiskerne aus dem Unterteil polarer Eisschilde werden vorgeschlagen.

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Copyright

References

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δD – δ18O Relationships in Ice Formed by Subglacial Freezing: Paleoclimatic Implications

  • R. A. Souchez (a1) and J. M. de Groote (a1)

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