Abstract

Co-authors: Pat Wongpan (University of Otago), Ken Hughes (University of Otago & University of Victoria), Inga J, Smith (University of Otago)

Vertical temperature strings are used in sea ice research to study heat flow, ice growth 
rate, and ocean-ice-atmosphere interaction. We demonstrate the feasibility of using temperature fluctuations as a proxy for fluid movement, a key process to resupply nutrients to 
Antarctic land-fast sea ice algal communities. Four thermistor arrays (including two mid-winter records) were deployed in the land-fast sea ice of McMurdo Sound, Antarctica. By 
smoothing temperature data with the robust LOESS method, we obtain temperature fluctuations that cannot be explained by insolation or heat loss to the atmosphere. Statistical 
distributions of these temperature fluctuations are investigated with sensitivities to the distance from the ice-ocean interface, average ice temperature, and sea ice structure. Temperature fluctu
ations are discrete events that have greatest magnitude close to the ice-ocean interface (< 50 mm) at temperatures > −3 &# x25E6;C. At temperatures > −3 ◦C fluctuations occur for 43% of the time, when the ice is colder (−3 to −5 ◦C) this active period is reduced to 11%. Assuming temperature fluctuations occur at a critical Rayleigh number derived from mushy layer theory, we parameterise a measure of permeability of this thick (>1 m) 
Antarctic land-fast sea ice in terms of average ice temperature. 
This permeability decreases by three orders of magnitude between the ice-ocean interface 
and ∼70 mm above it, as the sea ice temperature changes from the freezing point to −5 ◦C. 
 The same permeability parameterisation is independent of whether the sea ice has a columnar crystal structure or has a more disordered platelet ice structure, characteristic of proximity to an ice shelf.