Geometric properties of platelet ice crystals
Details of Research
TitleGeometric properties of platelet ice crystalsAbstractSea ice that forms in McMurdo Sound, Antarctica, which is adjacent to the McMurdo and Ross Ice Shelves, exhibits the uncommon ice fabric, incorporated platelet ice. This ice fabric is the subject of a high resolution thin sectioning study, consisting of ten closely spaced horizontal sections bounded above and below by vertical sections. From these we investigate the crystallographic and geometric properties of the ice grains and find a relationship between c-axis orientation and the minor axis of an ellipse fitted to a crystalÅ› grain boundary. Although accuracy is dependent upon the size and shape of the crystal, the technique provides a means of extracting crystallographic information from historical datasets for which only thin section photographs remain. Identification of common grains in multiple, 2-D sections allows us to reconstruct an approximation of the original 3-D crystal structures. These structures exhibit a variety of growth interactions, including upward directed crystal growth and intertwining crystals. We also construct hypothetical crystal grain boundaries that might be observed for a variety of vertical thin section orientations. These indicate that grain shape can depend on thin section orientation and illustrates some of the limitations of 2-D representations of 3-D crystals. Serrated grain boundaries are identified between neighboring crystals in several vertical sections. Geometric arguments and crystallographic observations lead us to propose a mechanism of layer nucleation within grain boundary grooves that occurs as supercooling exceeds a threshold value. Copyright 2012 Elsevier B.V.AcknowledgementsThis work was funded by the Foundation for Research, Science and Technology, New Zealand, a New Zealand Post Antarctic Scholarship and a University of Otago Postgraduate Award. Logistical support in the field was provided by Antarctica New Zealand and Johno Leitch. The authors wish to thank Alex Gough for a review of an early draft of this manuscript; Dr. Craig Stevens, NIWA, for photos in Figs. 3 and 5; and Mike Williams, Craig Stevens, Natalie Robinson and Brett Grant of NIWA for assistance in the field. Comments from two anonymous reviewers improved the quality of this manuscript.
1st AuthorDempsey, D.AuthorDempsey, D.Langhorne, P.Year2012JournalCold Regions Science and TechnologyVolume78Pages1/13/17DOI10.1016/j.coldregions.2012.03.002URLhttps://www.scopus.com/inward/recor.....91b0a761f89eb91adaba45f75KeywordsAntarcticaC-axis orientationsCrystallographic informationData setsGeometric argumentsGeometric propertiesGrain boundary groovesGrain shapesHigh resolutionHorizontal sectionIce crystalsIce grainsIce shelvesMinor axisRoss ice shelvesSize and shapeThin sectionVertical section, Crystal growthCrystalsGeometryGrain boundariesPhotographyPlateletsSea iceThree dimensional, Crystal orientation, crystal structurecrystallographydata setgeometrygrain boundaryice crystalice shelfsea ice, AntarcticaEast AntarcticaMcMurdo SoundRoss Ice ShelfWest Antarctica, rank5Author KeywordsCrystalGrain boundaryIce shelfPlatelet iceSea iceThin sectionProgrammeK131 - Sea Ice and Southern Ocean Processes
TypeArticleCitationDempsey, D. and Langhorne, P. (2012). Geometric properties of platelet ice crystals. Cold Regions Science and Technology, 78: 1-13
Antarctica NZ (26th Nov 2018). Geometric properties of platelet ice crystals. In Website Antarctica NZ. Retrieved 29th Sep 2020 08:23, from https://adam.antarcticanz.govt.nz/nodes/view/63469