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Equilibrium-Line Altitudes and Paleoenvironment in the Merchants Bay Area, Baffin Island, N.W.T., Canada

  • Fred F. Hawkins (a1)

Abstract

The fiordlands south of Merchants Bay contain an extensive, well-preserved moraine record of a late Foxe advance of local valley glaciers. This has allowed accurate reconstruction of former glacier margins and computation of former equilibrium-line altitudes (ELAs) by a variety of methods. Statistical comparison of three methods (maximum lateral-moraine elevation, median elevation, and accumulation area ratio (AAR)) shows that different techniques can give different results for the same glaciers. Lateral moraines gave estimates that were too low, probably due to post-glacial erosion or to non-deposition. Median elevations and the AAR method produced statistically similar results but only for glaciers of simple geometry. The median-elevation method fails to take into account variations in valley morphology and glaciological parameters, and so is not reliable in all situations. The AAR method is supported by empirical evidence and is the best of the three methods for estimating former ELAs.

Analysis of trend surfaces of present and late Foxe ELAs shows changes in elevation and orientation through time due to changing environmental factors. Present ELAs are strongly influenced by local factors, southerly storm tracks, and warm maritime conditions. Paleo-ELAs do not show this influence, suggesting that Davis Strait may have been ice-covered during the late Foxe stade and that storm tracks were from the north.

Résumé

Les fiords au sud de la Baie des Marchands présentent une longue moraine bien préservée qui témoigne de la dernière avancée du Foxe pour les glaciers de vallée du lieu. Ceci a permis une reconstitution précise des anciennes limites des glaciers et un calcul des altitudes de la ligne d’équilibre (ELAs) par différentes méthodes. Une comparaison statistique des trois méthodes (hauteur maximale des moraines latérales, altitude moyenne, et proportion de la surface d’accumulation (AAR)) montre que des techniques différentes conduisent à des résultats différents pour les mêmes glaciers. Les moraines latérales ont donné des estimations trop basses, probablement dues à l’érosion post-glaciaire ou au manque de dépôt. Les altitudes moyennes et la méthode de l’AAR donnent des altitudes statistiquement semblables pour des glaciers de géométrie simple. L’altitude moyenne ne prend pas en compte les changements de morphologie de la vallée ni les paramètres glaciologiques et pour cela elle n’est pas fiable dans toutes les situations. La méthode de l’AAR est confirmée par des preuves empiriques et elle est la meilleure des trois méthodes pour estimer les ELAs passées.

Des analyses des tendances de surface entre les ELAs présentes et du Foxe montrent des changements en altitude et orientation dans le temps dus aux variations des facteurs d’environnement. Les ELAs actuelles sont fortement influencées par des facteurs locaux, les trajets des précipitations du Sud, et les conditions maritimes tempérées. Les Paléo-ELAs ne révèlent pas cette influence, ce qui suggère que le détroit de Davis a pu être couvert de glace pendant le stade de Foxe et qu’alors les trajets des précipitations ont pu venir du Nord.

Zusammenfassung

Die Fjordküsten südlich der Merchants Bay vermitteln einen ausgedehnten, gut erhaltenedn Nachweis von Moränen eines späten Foxe-Vorstosses lokaler Talgletscher. Dies ermöglichte eine genaue Rekonstruktion früherer Gletscherstände und eine Berechnung der Höhen früherer Gleichgewichtslinien (ELA) mit mehreren Methoden. Der statistische Vergleich von drei Methoden (maximale Höhe der Seitenmoräne, mittlere Höhe, relativer Flächenanteil des Akkumulationsgebietes (AAR)) zeigt, dass verschiedenes Vorgehen zu verschiedenen Ergebnissen für dieselben Gletscher führen kann. Seitenmoränen ergeben zu niedrige Abschätzungen, vermutlich infolge postglazialer Erosion oder wegen fehlender Ablagerung. Mittlere Höhen und die AAR-Methode lieferten statistisch ähnliche Ergebnisse, jedoch für Gletscher mit einfacher Geometrie. Die Methode der mittleren Höhe ist nicht in der Lage, Änderungen in ler Talgestalt und bei glaziologischen Parametern zu berücksichtigen, weshalb sie nicht in allen Fällen zuverlässig ist. Die AAR-Methode wird durch Erfahrungswerte gestützt und ist deshalb das beste von den drei Verfahren zur Abschätzung früherer Höhen der Gleichgewichtslinie.

Die Analyse tendenzieller Oberflächen gegenwärtiger und später Foxe-Stadien zeigt zeitliche Änderungen in Höhe und Orientierung infolge wechselnder Umweltverhältnisse. Gegenwärtige Höhen der Gleichgewichtslinie sind stark durch lokale Verhältnisse, Sturmbahnen aus dem Süden und warme maritime Bedingungen beeinflusst. Ältere Höhen zeigen diesen Einfluss nicht; dies führt zu der Annahme, dass die Davis Strait im späten Foxe-Stadium eisbedeckt war und die Sturmbahnen vom Norden Kamen.

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References

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Equilibrium-Line Altitudes and Paleoenvironment in the Merchants Bay Area, Baffin Island, N.W.T., Canada

  • Fred F. Hawkins (a1)

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