Basic organic geochemical analyses were performed to support the general scientific objectives of ODP. Elemental carbon data obtained from samples contributed to a wide range of studies. Carbonate contents of cores were used for sedimentological and lithostratigraphic classification purposes. Organic carbon content (from organic matter) provided valuable evidence for ocean paleoenvironmental studies and depositional environment classification. Carbon/nitrogen ratios were used to infer the nature of the organic matter (e.g., land or aquatic plant material) preserved in cores. Molecular organic geochemical analyses such as alkenone unsaturation can be used to infer marine paleotemperature information.
One of the reasons for performing carbon analyses was to monitor for hydrocarbons. Although much of the carbon in sediments was in the form of inorganic carbon or carbonate, most of the interest was in the organic carbon—that carbon derived from marine phytoplankton, bacteria, algae, and other organic material. The JOIDES Resolution was not designed to drill into pressurized reservoirs of oil or gas, so constant monitoring for hydrocarbons was required. Maturation of organic material in undersea environments may result in hydrocarbon generation, so sediments were monitored for increasing amounts of organic carbon.
Many diagenetic changes occur in the uppermost 150 m of the sediment column, which was one of the reasons for higher density sampling of the uppermost 10–15 cores in a hole. During the first part of ODP, 25- to 30-cm whole-core OG samples were taken every 30 m and immediately frozen to preserve the core because of the volatile nature of organic matter. Not all analyses could be done in the shipboard chemistry laboratory, and freezing these samples slowed deterioration of the organic matter and minimized chances of contamination. Shipboard scientists stopped taking OG samples after Leg 134, probably because they were able to collect the information they needed and there were few requests for OG samples for shore-based studies.
Analyses of samples produced data as weight percentages of total carbon, inorganic carbon, and organic carbon directly or by difference. Although other carbonates may be present, all acid-soluble (i.e., inorganic) carbon was reported as calcium carbonate. In addition, analyses sometimes included data for elemental concentrations of sulfur, nitrogen, and hydrogen. These data were used to characterize the nature of the organic carbon.
Samples taken for carbon analysis were freeze-dried, crushed, and carefully weighed. If the sample was to be analyzed for carbonate, the sample was mixed with acid to convert the carbonate to CO2 before analysis in the coulometer. Samples to be analyzed using a CHNS analyzer for total carbon, nitrogen, and sulfur were mixed with an oxidizer and combusted at 1000°C. Table T2 briefly outlines the variety of instruments used to collect organic and inorganic carbon data during ODP.
Additional information about carbon measurements can be found in Technical Note 30 (Pimmel and Claypool, 2001).
Early in ODP, carbonate data were collected on log sheets which were sent back to ODP/TAMU at the end of each cruise. The data were entered into an S1032 database, and the log sheets were microfilmed for archival storage. Data entry routines were implemented so that data entry could be done on the ship. Carbonate data were stored in the S1032 database until the Janus database became operational for Leg 171.
The data model for carbonate data can be found in "Janus Carbonate Chemistry Data Model" in "Appendix A." Included are the relational diagram and list of tables that contain data pertinent to carbonates, column names, and definitions of each column attribute. ODP Information Services Database Group was responsible for the migration of pre-Leg 171 data to Janus.
Carbonate analyses can be retrieved from Janus Web using a predefined query. The carbonate 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, depth ranges, or latitude and longitude ranges.
Table T3 lists the data fields retrieved from the Janus database for the carbonates 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 calculation used to produce the value. "Description of Data Items from Carbonates Query" in "Appendix A" has additional information about the fields retrieved using the Janus Web carbonates query and the data format for the archived ASCII files.
The carbonate data in Janus represent an extensive collection of inorganic and organic carbon in sediments from ocean basins throughout Earth. More than 66,000 samples were analyzed for inorganic and organic carbon. There are few known instances where there was any major problem with data collection. Anything written or typed was a potential source of errors. Analytical results were written on log sheets. These data were then typed into S1032. Data entry programs were implemented to add the data to S1032, but these programs still required manual data entry. Data acquisition programs were later implemented to collect carbon data, but the operator manually entered the sample information. Writing or typing incorrect information occasionally happened, and some mistakes were not 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 was not corrected.
Another error found during the migration of carbon data was that samples were missing from the database. In those instances, a sample was entered into the database so that the data could be migrated. The verification of those samples and of the entire carbonate data set were not completed because of time constraints. Most data collected after the Janus database was operational for 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.
Janus does not contain any calibration information for carbonates. Procedures for storing calibration information were not implemented during ODP.