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Geothermal measurements provide important constraints on dynamic Earth processes; therefore, temperature was among the first downhole properties to be measured during the Deep Sea Drilling Project (DSDP) (Von Herzen and Maxwell, 1964). New tools were developed and modified during DSDP (Horai, 1985; Uyeda and Horai, 1982) and throughout the Ocean Drilling Program (ODP) (Davis et al., 1997; Fisher and Becker, 1993; Shipboard Scientific Party, 1992). Temperature measurements made during marine scientific drilling have been used to investigate heat transfer from the interior of Earth, oceanic lithosphere evolution, continental margin formation and subduction, and hotspot volcanism. In addition, these data have been used to examine processes associated with fluid flow and gas hydrate formation (e.g., Erikson et al., 1975; Hyndman et al., 1987; Pribnow et al., 2000). Undoubtedly, measurements of formation and fluid temperature will remain a high priority for downhole tool operations in the Integrated Ocean Drilling Program (IODP).
During a 2004 IODP downhole tools workshop (Flemings et al., 2004), all participants agreed that precise downhole temperature measurements are essential for fulfilling the goals of the IODP Initial Science Plan (ISP) (Kappel and Adams, 2001) in all three of the primary research themes:
With these goals in mind, researchers began developing the next generation of tools to measure subseafloor temperatures during routine piston coring operations. This data report summarizes results of the first in situ deployments of a new instrument that will help to achieve high-priority IODP goals.
Soon after development of the advanced piston corer (APC) during the late stages of DSDP, researchers developed a miniature sensor and logger package designed to fit in the APC cutting shoe to measure sediment temperatures as a core was taken (Horai and Von Herzen, 1985); the Advanced Piston Corer Temperature (APCT) tool. This tool allowed DSDP (and later, ODP) personnel to determine in situ temperatures within the undisturbed formation well ahead of the drilling bit without making a dedicated tool run. The APCT tool was first deployed during DSDP Leg 86 in 1984, and its use almost immediately became a routine part of drilling operations. Eight of these first-generation APCT tools were purchased by ODP at the start of the new program, but these tools became damaged over the years until none was left by the time of ODP Leg 117. It took several years to develop a replacement tool, but this was finally accomplished in time for ODP Leg 139 in 1991 (Shipboard Scientific Party, 1992). Ten of the second-generation APCT tools were purchased for ODP use and were deployed successfully during numerous expeditions over the next 12 y, through the end of ODP at-sea operations.
By the end of ODP operations in 2003, most of the second-generation APCT tools had been lost or damaged, and several of the remaining tools had been serviced one or more times to repair damage. In addition, evaluation and comparison of in situ temperatures determined with the APCT tool and with other downhole tools (e.g., Shipboard Scientific Party, 1997) suggested that there was a need to reevaluate tool design, performance, calibration, and analysis procedures and to develop a third generation of APCT instrumentation. Funds for the development of a third-generation APCT system were secured by a joint German and U.S. team led by H. Villinger (University of Bremen) and A. Fisher (University of California, Santa Cruz). In order to produce instruments with greater stability, accuracy, measurement frequency, and robustness than were available in the past, and in order to minimize development time and cost, the research team worked cooperatively on design of the new instruments with Fa. Antares (Stuhr, Germany), who had recently developed a miniaturized temperature data logger (MTL), also in cooperation with the University of Bremen (Pfender and Villinger, 2002; Jannasch et al., 2003). The design team consulted extensively with personnel from the U.S. operator for IODP to evaluate the design of the existing APCT coring shoe and related hardware in order to retain compatibility of system components with conventional coring operations. Work on the new system progressed during 2004–2005, and a prototype was made available in time for testing at sea during IODP Expedition 311. This third-generation APCT system is herein referred to as the APCT-3 tool.
The prototype APCT-3 tool was calibrated immediately before Expedition 311, as described below, and deployed nine times during the expedition. The calibrated APCT-3 prototype was also used to cross-check calibration of previous generation APCT tools that were also used during the expedition. The primary scientific objective of Expedition 311 was to understand processes that control the distribution and amount of gas hydrate in the shallow sediments of the accretionary margin offshore Vancouver Island, northeastern Pacific Ocean (see the "Expedition 311 summary" chapter). Determination of subseafloor temperature is particularly important for achieving this objective because thermal conditions fundamentally control gas hydrate stability. Comparison of in situ temperatures, gas hydrate stability, and the depth of bottom-simulating reflectors (BSRs) determined with seismic reflection surveys will help to determine whether the gas hydrates found in the Expedition 311 region are in thermodynamic equilibrium. Thermal data collected during Expedition 311 are reported in individual site chapters along with preliminary determinations of in situ temperatures, thermal gradients, and heat flow derived from the data.