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Site U1315

ODP Site 642 (Site U1315) is located on the Vøring Plateau in a water depth of ~1280 mbsl. The primary objective at this site is to document the bottom water temperature and salinity variations with instrumentation that sits in the water column attached to an elevated reentry cone. Hole U1315A was drilled to 179 mbsf and cased. The installed borehole observatory consists of a circulation obviation retrofit kit (CORK) to seal the borehole from the overlying ocean and instruments to monitor and document subbottom temperature variations. The instrumentation in Hole U1315A includes two pressure cases and a thermistor string. This configuration allows high-precision temperature measurements as a function of both depth and time. By analyzing subbottom temperature perturbations we expect to reconstruct, for the first time, a temperature record of bottom water during at least the last 100 y (i.e., going back in time far beyond the directly measured temperature records available up to now). This record will contribute significantly to the ongoing discussion about causes and consequences of oceanographic and climatic changes observed in the North Atlantic over the last few decades. After setting the CORK in the newly drilled Hole U1315A (Harris et al., 2006), temperature measurements were made in Hole 642E to compare with those acquired 20 y ago when the hole was drilled (see Eldholm et al., 1987). The comparison indicates fluid flowing from the basement, up the hole, and into the ocean at an estimated rate of 6–11 m/h and yields an estimated permeability of 10–13 m2, reflecting relatively impermeable sediments overlying a relatively permeable basement (Harris and Higgins, 2008).