Data Set ID:
NSIDC-0550

Temperature Profile of the West Antarctic Ice Sheet Divide Deep Borehole, Version 1

This data set reports depth versus temperatures in the fluid-filled portion of the West Antarctic Ice Sheet Divide (WAIS–D) deep borehole (70 to 3328 meters depth). Data were acquired on December 5, 2011 and have been post-processed to convert resistance to temperature.

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Geographic Coverage

Parameter(s):
  • Sea Ice > Ice Depth/Thickness > Depth
  • Paleoclimate Reconstructions > Air Temperature Reconstruction > Temperature
Spatial Coverage:
  • N: -79.4676, S: -79.4676, E: -112.0865, W: -112.0865

Spatial Resolution: Not Specified
Temporal Coverage:
  • 5 December 2011
Temporal Resolution: Not specified
Data Format(s):
  • ASCII Text
Platform(s) GROUND-BASED OBSERVATIONS
Sensor(s): THERMISTORS
Version: V1
Data Contributor(s): Kurt Cuffey, Gary D. Clow
Please contact the data provider for the correct Data Citation for this data set.

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This data set reports depth versus temperatures in the fluid-filled portion of the West Antarctic Ice Sheet Divide (WAIS–D) deep borehole (70 to 3328 meters depth). Data were acquired on December 5, 2011 and have been post-processed to convert resistance to temperature.

Detailed Data Description

The data are in a two–column matrix. The first column is depth in meters, second column is Temperature in degrees Centigrade.

Format

Data are provided in Space–delimited ASCII text (.dat) file format.

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File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/AGDC/nsidc0550_cuffey/ directory. Within this directory, there is one .dat space–delimited ASCII text file: WAISDivide_borehole_Temperatures_dec2011.dat.

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File Size

The data file is 896 KB.

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Volume

The data volume is 896 KB.

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Spatial Coverage

West Antarctic Ice Sheet Divide (WAIS–D), central West Antarctica. WAIS–D is situated 24 km west of the Ross–Amundsen ice flow divide and 160 km east of the Byrd ice core site.

79.4676° South, 112.0865° West

Spatial Resolution

Single point data at site of bore hole. This data set reports depth versus temperatures in the fluid–filled portion of the West Antarctic Ice Sheet Divide (WAIS–D) deep borehole (70 to 3328 meters depth).

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Temporal Coverage

05 December 2011

Temporal Resolution

Single day of measurement.

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Parameter or Variable

Parameter Description

The parameters in this data include Depth in meters and Temperature in degrees Centigrade.

Sample Data Record

The following is a sample from the WAISDivide_borehole_Temperatures_dec2011.dat data file. The first column contains depth measurements and the second column contains temperature measurements.

sample data
Figure 1. Sample Data Record

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Software and Tools

Software and Tools

The data file can be opened using any software capable of reading space–delimited ASCII.

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Quality Assessment

Comparison of calibration data for both the probe and the resistance-readout with past calibrations indicated these components were operating normally. Interconductor leakage and other system checks just prior to the WAIS–D logging experiments also confirmed the system was operating normally. The acquired data were inspected for instrumental noise levels, the relationship between the magnitude of the convective temperature fluctuations and the temperature gradient, and other characteristics. Based on past experience and a comprehensive uncertainty analysis (Clow 2008), nothing unusual was seen in the data. As a further check, two complete temperature logs were acquired in the WAIS–D borehole during December 2011. These two logs compare with each other quite well.

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Data Acquisition and Processing

Data Acquisition Methods

Data were acquired with the USGS borehole logging system described in Clow et al 1996 and Clow 2008 . A thermistor string is lowered down the borehole on a cable and resistance recorded continuously. Resistances are later converted to temperature via a calibration relation and deconvolution for sensor response time.

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Derivation Techniques and Algorithms

Processing Steps

Several sources of systematic error exist for the resistance measurements, including: leakage currents between the conductors of the measuring circuit, capacitance effects, self-heating of the sensor due to the passage of the test current, and thermal EMFs (thermoelectric voltages). Resistance corrections are made for these systematic errors to obtain an estimate of the sensor's true resistance Rs. Expressed in terms of temperature, these corrections are generally limited to 0.1–0.2 mK. The sensor's true resistance Rs is then converted to temperature T using a 4–term calibration function similar to the often used 3–term Steinhart–Hart equation. Inclusion of a fourth term offers a more precise fit to the calibration data, particularly below 0°C. The calibration constants in this function are determined for the sensor just prior to the Antarctic field season at the USGS temperature calibration facility in Lakewood, Colorado, USA. Because the time constant of the temperature sensor (7–15 s) is greater than the sampling rate (2 s), a temperature measurement T represents an average of what the probe experiences over 3–4 time constants. The actual temperatures in the borehole are determined from the temperature measurements T using a digital deconvolution with the logging system's impulse response function. Details of these procedures are discussed in Clow 2008 and Clow 2014.

Error Sources

The resistance of the downhole sensor is made using a high–quality resistance readout which is recalibrated just prior to each logging experiment using a set of 'standard' resistors. The subsequent drift of the readout is controlled by maintaining the readout in a Faraday cage maintained at 23±0.5°C for the duration of the logging experiment. Several sources of noise potentially perturb the resistance measurements. These include: electrostatic coupling between charged objects (e.g. snow particles) and the Kelvin measuring circuit, electromagnetic EMFs generated when an alternating magnetic field passes through the Kelvin circuit, triboelectric currents generated within the logging cable as it flexes over the sheave wheels or vibrates in the wind, and switching effects within the electromechanical slip–ring assembly. Several noise-reduction strategies were incorporated in the design of the USGS polar temperature logging system (Clow 2008). As a result, the dominant source of noise is generally limited to switching effects in the slip–ring assembly. However, both of the 2011 WAIS–D temperature logs were acquired during Condition 2 weather with high winds and dry blowing snow. With the increased electrostatic coupling and triboelectric currents, the standard deviation of all noise sources for these two logs was higher than normal, 0.25 mK. Combining the errors due to measurement–circuit drift and noise, the standard uncertainty of the ITS-90 temperature measurements is less than 3.3 mK.

Two environmental factors introduce errors in the WAIS-D measurements.

  1. The fluid filling the borehole has a relatively low viscosity and hence tends to convect when subjected to even a small positive temperature gradient. Temperature fluctuations associated with the convection cells constitutes a natural source of noise. In the WAIS-D borehole, the fluid begins to convect about 1850 m below the surface. The convection becomes increasingly intense with depth as the temperature gradient increases. The standard deviation of the convection–induced temperature fluctuations ranges from 0 mK at 1850 m to 1.25 mK at 3320 m.
  2. Several processes disturb the temperatures in the ice surrounding a borehole as it is drilled, most notably the addition of relatively warm fluid to the hole as it is deepened. While an additional set of temperature logs will be required to quantify the magnitude of this disturbance, modeling to date suggests the drilling disturbance around the WAIS–D borehole was less than 4 mK at the time of the 2011 temperature logs except for two zones: (a) in the upper 200 meters of the borehole the drilling disturbance may have been as large as 5–15 mK, and (b) in the 2300–3200 m depth range the disturbance is predicted to have been large and negative, peaking at about −8 mK.
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Sensor or Instrument Description

Measurements were made with the United States Geological Survey Polar Temperature Logging System, a custom designed and built combination of temperature sensor, cable, winch, and electronics (see Clow 2008 for complete description). The System employs a 4–wire circuit to eliminate resistance effects of the long wires required for measurements in kilometers–deep boreholes. The temperature sensor comprises a parallel–series package of 15 thermistors. With the set of calibrations used in this project, the uncertainty of measured temperatures is smaller than 3.3 mK compared to absolute standards, and less than 2 mK for temperature differences along the borehole. The uncertainty of depth measurements is less than 250 ppm. Total uncertainty of the temperature measurement as an indicator of ice temperature is larger than uncertainty of the sensor due to convective mixing of borehole fluid and incomplete dissipation of heat introduced by the drilling process. The magnitudes of these additional uncertainties are still being assessed but are generally less than 10 mK.

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References and Related Publications

Contacts and Acknowledgments

Kurt M. Cuffey
University of California, Berkeley
Department of Geography
507 McCone Hall
Berkeley, CA 94720-4740

Gary D. Clow
United States Geological Survey
Geosciences and Environmental Change Science Center
Lakewood, Colorado

Acknowledgments: 

This research was funded by the National Science Foundation (NSF) Division of Polar Programs, Antarctic Research, Glaciology grant number 0539232, Collaborative Research: Physical Properties of the WAIS Divide Deep Ice Core.

Document Information

Document Creation Date

30 April 2014

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