Estimates of the refreezing rate in an ice-shelf borehole

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TitleEstimates of the refreezing rate in an ice-shelf boreholeAbstractThe refreezing rate of a borehole drilled through a 252m thick region of the Ross Ice Shelf, Antarctica, is determined using oceanographic measurements over two periods of a day. We first use a method based on the conservation of salt in the supercooled salt water of the borehole. This is compared to a model using a numerical solution of the heat equation to find the temperature distribution in the host ice, allowing ice growth to be calculated from the balance of heat fluxes at the ice/water interface. This second method broadly confirms the refreezing rates deduced from salinity measurements, giving confidence in the generalization of this simple heat-flux model to predict refreezing rates of other boreholes. Predictions from both are subject to uncertainty due to the poorly defined value of the solid fraction of ice that freezes in a supercooled volume of sea water. This is taken to be 0.5-0.1 throughout this study. The predicted rates are also strongly dependent on the initial and boundary conditions chosen, but results show the initial diameter of 600mm decreases at a rate of-3-5mmh-1 in an ice shelf with a minimum temperature of -228C.AcknowledgementsWe are grateful to the ANDRILL team at Coulman High for making and maintaining the boreholes and assistance with data collection. We particularly thank Tamsin Falconer for providing the hot-water drilling records, Craig Stewart for measuring heights in the ice shelf, Craig Stevens and the three anonymous reviewers for comments on this paper, and Angelika Humbert for comments regarding Ross Ice Shelf temperatures. We are grateful for logistical support from Antarctica New Zealand and the United States Antarctic Program. The data collection was funded by the New Zealand Ministry of Business, Innovation, and Employment (contract No. C05X1001), and NIWA core funding under the National Climate Centre Research Programme 2 (2011--12 and 2012--13), and support was provided by a University of Otago Research Grant to write this paper.

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1st AuthorHughes, K.AuthorHughes, K.Langhorne, P.Williams, M.Year2013JournalJournal of GlaciologyVolume59Number217Pages938-948DOI10.3189/2013JoG12J117URLhttps://www.scopus.com/inward/recor.....c1ee1b8042997a4f0d436f547Keywordsborehole loggingboundary conditionestimation methodfreeze-thaw cycleglaciologyheat fluxice shelfice thicknessinstrumentationmeasurement methodsalinity, AntarcticaRoss Ice ShelfWest Antarctica, rank5ProgrammeK131 - Sea Ice and Southern Ocean Processes

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TypeArticleCitationHughes, K., Langhorne, P. and Williams, M. (2013). Estimates of the refreezing rate in an ice-shelf borehole. Journal of Glaciology, 59(217): 938-948