measurements of permeability of sea ice - Clarkson University

Proceedings oh the 18th IAHR InternationalSymposium on Ice (2006)MEASUREMENTS OF PERMEABILITY OF SEA ICEToshiyuki Kawamura 1 , Masao Ishikawa 1 , Toru Takatsuka 1 ,Shinsuke Kojima 2 and Kunio Shirasawa 11Institute of Low Temperature Science, Hokkaido University2Department of Civil Engineering, Kitami Institute of TechnologyABSTRACTRecently contribution of snow cover to sea ice growth has become of major interest. Thecontribution is partly due to snow-ice formation, which needs to infiltrate seawater throughsea ice. Measurements on such an index, i.e. permeability, have scarcely been done in spite ofa quite important factor. We measured the permeability of sea ice in both field and laboratoryexperiments. In the field studies, we obtained the values of the orders of -11 to -10. Definiterelations between the permeability and the ice properties, e.g. temperature, salinity andstructure, were not found. In the laboratory experiments, especially, we aimed to clarifydifference of the permeability between ice types, i.e. granular and columnar ice. We obtainedthe values of the permeability of the same order of the magnitude as those in the field studies.The values were compared with those of the previous studies.KEY WORDS: Sea ice; Permeability; Ice Types; Ice properties.INTRODUCTIONThe role of snow is usually perceived as negative during ice formation because of its low heatconductivity, which reduces bottom growth rates. Following recent studies conducted in theAntarctic Oceans, however, the positive contribution of snow cover to sea ice growth hasbecome of major interest (e.g., Lange and others, 1990; Lange and Eicken, 1991; Jeffries andothers, 1994). The contribution is due to two specific types of sea ice growth processes, i.e.,snow-ice (e.g., Lange and others, 1990; Eicken and others, 1995; Worby and others, 1998)and superimposed-ice growth (Jeffries and others, 1994, 1997; Kawamura and others, 1997;Eicken, 1998; Haas and others, 2001). Snow ice is formed from a mixture of surface snowand infiltrating seawater (e.g., Lange and others, 1990; Jeffries and others, 1997).Superimposed ice is formed by the refreezing of fresh melt water that percolates through thesurface snow cover onto the ice (Koerner, 1970). Both growth processes provide upward icegrowth in contrast with ordinary downward congelation growth at the bottom. The processescan be very effective mechanisms for thickening, because the freezing interface is close to thecooling source.Snow ice is created through a process of soaking of seawater into snow cover through sea ice-105-

Proceedings oh the 18th IAHR InternationalSymposium on Ice (2006)1.0E-10Permeability (m 2 )8.0E-116.0E-114.0E-112.0E-11c. iceg. ice0.0E+00-5.0 -4.0 -3.0 -2.0 -1.0 0.0Temperature (°C)Figure 6: Relation of the permeability to temperature ofthe ice in the laboratory study.All the permeability measured in the laboratory experiment has values of the orders of -11with 1.16 to 7.95 x 10 -11 m 2 . Unfortunately, since no salinity data were measured, a relationbetween the permeability and the ice brine volume was not obtained. Figure 6 illustrates arelation between the ice permeability and temperature. The values of permeability are similarto those of the laboratory study although the ice temperature is in a very narrow range andslightly lower than those. The columnar ice might have the lower values than granular ice inspite of very limited data.Freitag and Eicken (2003) carried out in situ permeability measurements in Arctic during thesummers. Their data showed the value of a range from 10 -11 to 10 -8 m 2 . The mean and modalvalues were the orders of -9 in 1995 and -10 in 1996, depending melting rates, which wereone or two orders magnitude higher than ours. Such high permeability is probably explainedby the fact that their measurements were done in a melting season, when the evolution andwidening of the brine channeling system as a result of brine drainage and internal meltingprocesses. The values from laboratory studies on artificial sea ice at temperatures of –5 to –20°C by Saeki and others (1986) were in the order of –12, being one order of magnitude smallerthan our values probably because of lower temperature.SUMMARYMeasurements of the permeability of sea ice were conducted in both field and laboratoryexperiments. One of the objectives of this study is to obtain difference of the permeabilitybetween ice types, i.e. granular and columnar ice. The difference and comparison with theprevious studies were described. However, definite difference and relations between thepermeability and ice properties could not be found. The reason is caused by the limited data ofthe narrow regions of the ice properties. Therefore, further study of the wide range of theproperties is required to clarify the relations.REFERENCESBennett, A.S. (1976), “Conversion of in situ measurements of conductivity to salinity,”Deep-Sea Res., Vol.23, pp.157-165.Crocker, G.B., and Wadhams, P. (1989), “Modelling Arctic fast ice growth,” J. Glaciol.,-111-

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