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The following operations were successfully accomplished during Expedition 301T:

• Successfully "fished" OsmoSampler string and miscellaneous hardware left at Site 1253. The OsmoSampler string was dropped to the seabed during the recovery operation.
• Removed the OsmoSampler string from Hole 1255A and replaced it with a new 3.5 y OsmoSampler string.
• Reentered Hole 1253A, confirmed removal of the OsmoSampler string, and reinstalled a new 3.5 y OsmoSampler string.
• Successfully located the OsmoSampler string from Hole 1253A on the seabed and "fished" the upper OsmoSampler and associated hardware. The lower OsmoSampler was lost to either the hole or the seabed.

The prime objective of this operation was to retrieve and replace the OsmoSamplers from Sites 1253 and 1255, which were installed during ODP Leg 205. Operations during the cruise were successful, and the instrument strings were retrieved and replaced; only the lower OsmoSampler package from Site 1253 was lost. Due to close proximity of the two Site 1253 Osmosampler packages, this loss will have minimal impact on the data. Operations for this transit cruise required 3.8 days, concluding 8 September 2004.

After retrieval, the Teflon coils of the OsmoSamplers were subdivided in preparation for shorebased analyses. A subset of the fluids was analyzed for ephemeral properties shipboard (alkalinity, pH, and ammonium). The alkalinity and ammonium concentrations at the two sites are distinct. They are considerably higher in the décollement fluid at Site 1255, with maximum values of 17.1 mM and 1828 µM, respectively. At Site 1253, in the igneous complex formation fluid, maximum concentrations of alkalinity and ammonium are 0.8 mM and 170 µM respectively. Bacterially mediated diagenesis of organic matter is responsible for the high alkalinity and ammonium observed at Site 1255.

Postcruise analyses will provide 2 y high-resolution time series of fluid chemistry and temperature and at Site 1255 also of fluid flow rates and relative flow directions, with implications for seismogenic zone activity, chemistry of the arc volcanoes, and solute fluxes into the ocean.

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