THERMAL CONDUCTIVITY

Thermal conductivity is a measure of the rate that heat flows through material. In marine geophysics, thermal conductivity profiles of sediment and rock sections are used with temperature measurements to determine heat flow. Heat flow is not only characteristic of the material, but is an indicator of type and age of ocean crust and fluid circulation processes at shallow and great depths.

Thermal conductivity can be measured by heating a material with a known heating source and measuring the temperature change with time. Conductivity values are reported in watts per meter degrees Kelvin (W/[m·K]). Prior to Leg 109, conductivity was reported in cal·10–3/cm-sec-deg but was converted to W/(m·K) before entry into the S1032 database. During ODP, ~37,000 individual measurements were collected during 104 of the 110 legs.

Data Acquisition

TCON measurements were done on both whole cores and split cores. Soft and semi-indurated sediments were usually analyzed as whole cores. Hard rocks were often measured after splitting. The sections were allowed to equilibrate after they were brought to the laboratory. TCON measurements were made after the sections were run through the MST. Small holes were drilled through the core liner to allow the full-space probes to be inserted. If the sediment was semiconsolidated, the hole was drilled into the sediment with thermal joint compound applied to ensure good contact between the probe and the sediments. For hard rock measurements, a smooth surface was prepared on a split-core specimen at least 5 cm long.

The first system used for TCON measurements was the Thermcon-85 built by Woods Hole Oceanographic Institution (WHOI). Initially, data were collected using a DEC PRO-350. As many as five needles could be connected to the system at one time: one needle was inserted into a standard material for a control measurement and the other needles were inserted into the cored material. The processed results were logged on log sheets and entered into the S1032 database. A new personal computer–based program was deployed during Leg 129 that allowed the operator to control the measurements, process the raw data, and write the results to a file. The needles had to be calibrated periodically using standard materials of known thermal conductivity. The calibration data were analyzed by linear least squares, and the coefficients were stored in a file that the program accessed during analysis. The Thermcon-85 was operational for all of ODP, though it was not used much after Leg 168, when the Teka TK04 system was deployed.

The Teka TK04 system was more automated than the Thermcon-85 system. It provided automated calibration, drift and measurement features, full-space and half-space needle configurations, and processing and graphing of results. Multiple measurements could be taken under identical conditions. Optional files could be created in addition to the file with the results. The optional files contained the measurement parameters, raw data (temperature–time series), evaluation parameters, and all valid calculated thermal conductivity values.

Additional information about ODP thermal conductivity measurements can be found in Chapter 8 of Technical Note 26 (Blum, 1997).

Archive

Pre-Janus Archive

Early during ODP, TCON data were collected on log sheets which were sent back to ODP/TAMU at the end of each cruise. The data were entered into the S1032 database and the log sheets were microfilmed for archival storage. TCON data were stored in the S1032 database through Leg 128. A new personal computer–based program was deployed on Leg 129 which created files that were brought back and archived on the ODP/TAMU servers.

Migration of Thermal Conductivity Data to Janus

The data model for TCON data can be found in "Janus TCON Data Model" in "Appendix O." Included are the relational diagram and the list of the tables that contain data pertinent to TCON analyses, the column names, and the definition of each column attribute. ODP Information Services Database Group was responsible for the migration of pre-Leg 171 data to Janus.

The thermal conductivity tables were yet not finalized when Janus became operational on Leg 171. After discussions about how to implement the TCON part of the database, it was decided to save only the calculated thermal conductivity measurements. Because the raw data collected on the two systems were different, the implementation of storing raw data in the database was deferred and not completed during ODP. Raw data are still archived on IODP/TAMU servers and can be requested through the IODP/TAMU Data Librarian.

Janus Thermal Conductivity Data Format

TCON analyses can be retrieved from Janus Web using a predefined query. The thermal conductivity query Web page allows the user to extract data using the following variables to restrict the amount of data retrieved: leg, site, hole, core, section, probe number, depth, or latitude and longitude ranges. TCON analyses made with the TK04 system often produce multiple measurements at the same interval. It became common practice to put the individual measurement values in the Comments field and the average was stored in the Thermcon_value field.

Table T33 contains the data fields retrieved from the Janus database using the Janus Web predefined query. The first column contains the data item, the second column indicates the Janus table or tables in which the data were stored, and the third column is the Janus column name or the calculations used to produce the value. "Description of Data Items from TCON Query" in "Appendix O" contains additional information about the fields retrieved using the Janus Web thermal conductivity query, and the data format for the archived ASCII files.

Data Quality

The TCON data set is one of the more complete data sets collected during ODP. A common error found during migration falls in the generic category of operator error. Analytical results were written on log sheets. These data were then typed into the S1032 database. The data acquisition programs required manual entry, and mistakes in logging intervals, logging data, typing data into the database, an so on, occasionally happened and were not always identified. Often, the Scientific Party found errors and corrected them for the data included in the Initial Reports volume, but data sent back to ODP/TAMU were not corrected.

Most data collected after the Janus database was operational on Leg 171 were verified as part of the Janus data management and verification procedures (see "Janus Data Management and Verification"). Some verification was done on the pre-Leg 171 data; however, if there is a discrepancy between the database and data in the Initial Reports volumes, the published data should be considered more reliable.

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