USGS T-3 Original Thermal Gradient, Thermal Conductivity, and Heat Flow Data from T-3 Ice Island, 1963-73

This process step gives an overview of the acquisition of the original data. Details about the operations to acquire the data are given in Lachenbruch and others (2019)--see cross-reference. Summary information about procedures is also provided in the other cross-referenced publications, , particularly the Journal of Geophysical Research paper by Ruppel and others (2019). The heat flow measurements were made once a day or once every several days (occasionally two per day) during USGS occupation of the T-3 ice island. The measurements were made through a permanent hole in the ice (moonpool) maintained under the protection of a hut near the Colby Bay portion of the T-3 ice island. The apparatus consisted of a corer with attached thermistors (four thermistors during the first few years of the operation and then five thermistors on a slightly longer core barrel during subsequent years). The thermistor closest to the bottom of the core barrel was designated as #1. Thermistor accuracy was 0.001 degrees Celsius based on Lachenbruch and others(2019).
The corer with attached thermistors was lowered to the seafloor on a winch system. The probe remained in the bottom sediments long enough for the frictional heat pulse associated with sediment penetration to decay to the conductive part of the curve so that an equilibrium temperature could be determined for each thermistor during post-analysis. Thermal conductivity was not measured in situ in the seafloor. The probe was recovered with sediments in the corer. Far more sediment cores were recovered than heat flow measurements taken (for example, refer to the information in the University of Wisconsin NCEI dataset at https://doi.org/10.7289/v51834g7 for selected information about USGS T-3 sediment cores). It is unknown whether heat flow measurements were not attempted on every coring run or whether the heat flow probe or recording instrumentation suffered frequent problems. The consistent recovery of sediment cores indicates that the probe penetrated the sediments at many locations, meaning that a heat flow measurement was in theory possible at those locations as well.
After completion of a measurement, data would have been analyzed to determine an equilibrium temperature for each thermistor. These equilibrium temperature data have been lost, as have the bottom water temperature data recorded during the surveys and information about the penetration depth of the probe. For Ruppel and others (2019)--see cross-reference, attempts were made to use the lengths of recovered cores as an indicator of the probe's penetration depth to assist in determination of equilibrium thermal gradients, but this analysis was unsuccessful. The reported data from the heat flow measurements are thermal gradients between adjacent thermistors. For a 4-thermistor penetration with all 4 thermistors operational, the dataset provides thermal gradient values between thermistors 1 and 2, 2 and 3, and 3 and 4. If one thermistor were not functioning (for example, thermistor #2), the reported gradients would be between thermistors 1 and 3 and 3 and 4.
Thermal conductivity values were measured on the laboratory benchtop on recovered sediment cores using needle probes. The reported values correspond to core sections between each of the working thermistors. For example, if a gradient is reported for the interval between thermistors 2 and 3, then the dataset gives a corresponding thermal conductivity determination in that interval from the corresponding core. The original thermal conductivity data have been lost, but it is suspected that far more thermal conductivity measurements were completed than are compiled or averaged to generate the values in the dataset. Ruppel and others (2019)--see cross-reference-- analyzes some of the thermal conductivity data in this dataset. Heat flow was calculated by multiplying average thermal gradient and average thermal conductivity. Uncertainties are reported on a subset of the values as a percentage of the heat flow. A maximum heat flow uncertainty is also provided by for heat flow values to which a percentage deviation was assigned. Process date likely spanned the duration of the experiment and is reported below as the last day of 1974, which is the approximate date of the USGS report provided in Lachenbruch and others (2019)--see cross-reference

This process step details how the original table was digitized and quality checked. The original table was available only as a PDF scan of Table 2 from Lachenbruch and others (2019). In 2016, Carolyn Ruppel manually keyed most of this table. Subsequently, technical staff (B. Clark and M. Arsenault) at the USGS Woods Hole Coastal and Marine Science Center conducted optical character recognition on parts of the scanned file. The two inputs were combined, and then Deborah Hutchinson conducted quality control on the resulting table. This process identified entries that were partially illegible in the original PDF scan of the report, positions that had been improperly keyed, and one position (station FL-532) that did not plot on the T-3 navigation track obtained through independent means and released with this dataset as "T-3 Ice Island One Hour Navigation: May 14, 1962 to September 15, 1974." Values were corrected in the table based on this analysis. It is expected that some errors likely remain in the transfer of the original PDF scan to the digital data file. It is not believed that any of the possible errors affect the subsequent outcome or analysis in any significant way. The initial digital files and the accompanying scanned portions of the original data table are provided in the following images included in this dataset: Table2_2to66.jpg, Table2_71to146.jpg, Table2_147to231.jpg, Table2_233to287.jpg, Table2_288to340.jpg, Table2_341to386.jpg, Table2_387to441.jpg, Table2_442to552.jpg, Table2_556to584.jpgj. The range of numbers in the title of each plot refer to heat flow stations. Also provided is a file to explain error checking: digitizationoftable.txt

The Excel 2013 XLSX file was written in CSV format using "save as".

Added keywords section with USGS persistent identifier as theme keyword.