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doi:10.2204/iodp.proc.301.206.2009

Introduction

Integrated Ocean Drilling Program (IODP) Expedition 301 was part of a series of expeditions and experiments to quantify hydrogeologic, lithologic, biogeochemical, and microbiological properties, processes, and linkages on the eastern flank of the Juan de Fuca Ridge. This effort included site surveys to map bathymetric relief, seismic reflection profiles to delineate sediment thickness, sediment cores to allow analysis of pore fluids, and heat flow measurements to determine patterns of lithospheric and hydrothermal heat loss. Operations during Expedition 301 included replacing one existing subseafloor borehole observatory (CORK), drilling two basement holes and installing two new long-term observatories, coring the upper ~300 m of basement and shallow sediments above basement, and collecting in situ hydrogeologic and geophysical data from basement. Subsequent remotely operated vehicle (ROV) and submersible expeditions have serviced IODP observatories, collecting pressure and temperature data and fluid and microbiological samples and replacing components as needed to maintain these systems for future use. Another drilling expedition is planned to emplace three more borehole observatories (one in an existing basement hole and two in new holes) and initiate crosshole tests, and additional ROV and submersible expeditions will conduct long-term experiments and recover subseafloor data and samples. Proposals and planning for work that eventually led to Expedition 301 began in 1998, and completion of long-term experiments will require 3–4 y after the second drilling expedition. Thus Expedition 301 was part of a long-term effort, likely to last 15–16 y in total.

This paper summarizes operations and scientific studies related to Expedition 301 and having an emphasis on the hydrogeology of upper ocean crust. These studies have helped to advance high-priority goals that motivated Expedition 301, although completion of the main crosshole experiments will occur during and after the next drilling expedition. Other research papers published since the end of Expedition 301 include studies of sedimentology (Kiyoka and Yokoyama, submitted), physical properties (Goto and Matsubayashi, 2008), fluid geochemistry (Wheat and McManus, 2008), sedimentary microbiology (Engelen et al., 2008; Lipp et al., 2008; Nakagawa et al., 2006), contamination during coring (Lever et al., 2006), and methods in organic geochemistry (Heuer et al., 2006). A comprehensive listing of publications associated with Expedition 301 can be found at publications.iodp.org/proceedings/301/301bib.htm.

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