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SUMMARY:In situ detection of fluid movement in Antarctic land-fast sea ice
  - Pat Langhorne (University of Otago)
DTSTART:20171003T123000Z
DTEND:20171003T131500Z
UID:TALK83541@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:<span>Co-authors: Pat Wongpan		(University of Otago)\, Ken Hug
 hes		(University of Otago & University of Victoria)\, Inga J\, Smith		(Uni
 versity of Otago)        <br></span><span><br>Vertical temperature strings
  are used in sea ice research to study heat flow\, ice growth &#x2028\;rat
 e\, and ocean-ice-atmosphere interaction. We demonstrate the feasibility o
 f using temperature fluctuations as a proxy for fluid movement\, a key pro
 cess to resupply nutrients to &#x2028\;Antarctic land-fast sea ice algal c
 ommunities. Four thermistor arrays (including two mid-winter records) were
  deployed in the land-fast sea ice of McMurdo Sound\, Antarctica. By &#x20
 28\;smoothing temperature data with the robust LOESS method\, we obtain te
 mperature fluctuations that cannot be explained by insolation or heat loss
  to the atmosphere. Statistical &#x2028\;distributions of these temperatur
 e fluctuations are investigated with sensitivities to the distance from th
 e ice-ocean interface\, average ice temperature\, and sea ice structure. T
 emperature fluctu&#x2028\;ations are discrete events that have greatest ma
 gnitude close to the ice-ocean interface (< 50 mm) at temperatures > &minu
 s\;3 &# x25E6\;C. At temperatures > &minus\;3 &#x25E6\;C fluctuations occu
 r for 43% of the time\, when the ice is colder (&minus\;3 to &minus\;5 &#x
 25E6\;C) this active period is reduced to 11%. Assuming temperature fluctu
 ations occur at a critical Rayleigh number derived from mushy layer theory
 \, we parameterise a measure of permeability of this thick (>1 m) &#x2028\
 ;Antarctic land-fast sea ice in terms of average ice temperature. &#x2028\
 ;This permeability decreases by three orders of magnitude between the ice-
 ocean interface &#x2028\;and &sim\;70 mm above it\, as the sea ice tempera
 ture changes from the freezing point to &minus\;5 &#x25E6\;C. &#x2028\; Th
 e same permeability parameterisation is independent of whether the sea ice
  has a columnar crystal structure or has a more disordered platelet ice st
 ructure\, characteristic of proximity to an ice shelf.&nbsp\;</span>
LOCATION:Seminar Room 1\, Newton Institute
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