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| Titel |
Laboratory study of initial sea-ice growth: properties of grease ice and nilas |
| VerfasserIn |
A. K. Naumann, D. Notz, L. Håvik, A. Sirevaag |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 6, no. 4 ; Nr. 6, no. 4 (2012-07-10), S.729-741 |
| Datensatznummer |
250003688
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| Publikation (Nr.) |
 copernicus.org/tc-6-729-2012.pdf |
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| Zusammenfassung |
We investigate initial sea-ice growth in an ice-tank study by freezing an NaCl
solution of about 29 g kg−1 in three different setups:
grease ice grew in
experiments with waves and in experiments with a current and wind,
while nilas formed in a quiescent experimental setup. In this paper we
focus on the differences in bulk salinity, solid fraction and
thickness between these two ice types.
The bulk salinity of the grease-ice layer in our experiments remained almost
constant until the ice began to consolidate.
In contrast, the initial bulk-salinity evolution of the nilas is
well described by a linear decrease of about 2.1 g kg−1 h−1
independent of air temperature. This rapid decrease can be
qualitatively understood by considering a Rayleigh number
that became maximum while the nilas was still less than 1 cm thick.
Comparing three different methods to measure solid fraction in grease
ice based on (a) salt conservation, (b) mass conservation and (c) energy conservation, we find that the method based on salt
conservation does not give reliable results if the salinity of the
interstitial water is approximated as being equal to the salinity of
the underlying water. Instead the increase in salinity of the
interstitial water during grease-ice formation must be taken into
account. In our experiments, the solid fraction of grease ice was relatively
constant with values of 0.25, whereas it increased to values as high
as 0.50 as soon as the grease ice consolidated at its surface. In
contrast, the solid fraction of the nilas increased continuously in the
first hours of ice formation and reached an average value of 0.55
after 4.5 h.
The spatially averaged ice thickness was twice as large in the first 24 h of
ice formation in the setup with a current and wind compared to the
other two setups, since the wind kept parts of the water surface ice
free and therefore allowed for a higher heat loss from the water. The development of the ice thickness can be reproduced well with
simple, one dimensional models that only require air temperature or ice surface temperature as input. |
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