2002-2003 Science Planning Summary

Oceans & Climate

Dr. Bernhard Lettau
Program Manager

OO-253-O

NSF/OPP 0126007
Station: McMurdo Station
RPSC POC: Howie Tobin
Research Site(s): McMurdo Station, McMurdo Sound

Measurements and improved parameterizations of the thermal conductivity and heat flow through first-year sea ice
Dr. Hajo Eicken
University of Alaska Fairbanks
Geophysical Institute
hajo.eicken@gi.alaska.edu
Dr. Martin Jeffries
University of Alaska, Fairbanks

Deploying Team Members: Lars G Backstrom . Hajo Eicken . Margaret E Smith
Research Objectives: The sea-ice cover in the polar oceans strongly modifies ocean-atmosphere heat transfer. Most important, the ice cover thermally insulates the ocean, with sea-ice thermal conductivity determining the magnitude of the heat flow for a given ice-temperature gradient. Despite its importance (second only to ice albedo), knowledge of sea-ice thermal conductivity is limited to highly idealized models developed several decades ago. General circulation models (GCMs) and large-scale sea-ice models currently include overly simplistic parameterizations of ice thermal conductivity that are likely to contribute significantly to errors in estimating ice production rates.

Researchers will carry out a set of field measurements from which the thermal conductivity of first-year sea ice will be derived as a function of ice microstructure, temperature, salinity, and other parameters. Measurements will be carried out by letting thermistor arrays freeze into the McMurdo Sound fast ice, which represents an ideal natural laboratory for this type of measurement. To minimize errors and identify the most robust technique, the research team will collaborate with colleagues from New Zealand and compare different methodologies for measurement and analysis. They will also assess the impact of ice microstructure (spatial distribution of brine, crystal sizes) and convective processes on the effective rate of heat transfer.

Antarctic data will be compared with arctic thermal conductivity data sets to assess regional contrasts and the impact of different physical processes on heat flow and to arrive at a comprehensive, improved parameterization of ice thermal conductivity for large-scale simulations and GCMs. This component of the work will involve ice-growth modeling and collaboration with the Sea-Ice Model Intercomparison Project Team established under the auspices of the World Climate Research Program. This research will advance and improve

- The understanding of the processes and parameters controlling heat transfer and the thermal conductivity of first-year sea ice

- Techniques for deriving thermal conductivity and heat flow data from thermistor arrays

- The understanding of sea-ice processes and heat flow through the ice cover in McMurdo Sound

- Parameterizations of thermal conductivity for use in large-scale and high-resolution one-dimensional simulations

- The representation of first-year ice thermal properties (both antarctic and arctic) in GCMs.


Field Season Overview:
In collaboration with New Zealand researchers, project team members plan to visit a set of thermistor strings frozen into the ice about 5 km off Arrival Heights near Scott Base. They will conduct in-situ measurements of sea ice parameters -- temperature, thermal properties and microstructure. Researchers will also take ice samples back to McMurdo Station for preparation of thick and thin sections in a cold room and measurements on melted ice samples. These measurements will be augmented by surveys of ice properties and heat transfer at other locations in the McMurdo fast-ice cover.

Researchers will work from a temporary sea ice camp that the New Zealand team will erect on the fast ice. Facilities at McMurdo Station will only be used for processing of ice core samples.