Fulfilling the Promise of the DSDP/ODP Legacy with Multiparameter Logging of Archive Cores

Since 1968, the Deep-Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) have been storing their recovered sediment and rock cores in purpose-built, refrigerated repositories. Approximately 300 km of core was recovered by DSDP and ODP at an estimated average cost of $2,000,000/km. Half of every core recovered is kept as an archive half, normally only available for viewing (subsampling requires special permissions). Sound archiving policies and storage techniques over the years have ensured that these half cores have remained well preserved for analyses that were not made, or were not technically possible, at the time of recovery. The archive half-cores are well suited for automated non-destructive geophysical measurements ("core logging"), including many of those that provide essential data for reconstructing Earth's climatic history, such as high-resolution magnetic susceptibility, natural gamma spectroscopy, and UV/VIS/IR spectrophotometry. Most of the cores have either not been logged for all the relevant parameters or have not been logged at the spatial intervals necessary for high resolution climatic studies. Consequently, a very large, untapped reservoir of paleoclimatic and other data awaits extraction from these well-preserved archive half-cores. Recently we used a new Geotek MSCL-XYZ core logger at the IODP West Coast Repository to log archive core halves recovered by D/V Glomar Challenger in 1983. We wished to obtain a high-resolution paleoclimate record for DSDP Site 594, east of New Zealand, Southwest Pacific, to complement the record obtained more recently from nearby ODP Site 1119, cored in 1998. The new MSCL-XYZ system is specifically designed to allow multiparameter, non-destructive geophysical data to be collected easily at high spatial resolutions from archive core halves. Because the data acquisition from archive cores can be slow, either because of the measurement itself or the frequency at which the data is required, the system holds multiple 1.5 m-long core sections (currently up to 9) and can be left to run unattended for hours or days at a time. We obtained complete data sets of natural gamma, magnetic susceptibility, spectral color and RGB digital line scan images for the top 150m of the sediment column at Site 594 . No useful core log data was previously available for this site. The data set of primary interest was natural gamma, which will be compared with the downhole natural gamma record from Site 1119. To our knowledge this is the first time that a high-resolution natural gamma data log has been recovered from an archive core half. Detailed magnetic susceptibility records were also obtained despite low signal levels, using 10 sec sampling time throughout. The excellent quality of the spectral color and RGB image data, despite the partially ephemeral nature of these properties, is a testament to the core storage techniques employed over 21 years. As core working halves become depleted, pressure is mounting to allow subsampling from the archive core-halves. The community now has the tools necessary to take advantage of what could be a final opportunity to collect continuous geophysical data on ocean cores drilled over the past three decades.