At Site 1229, the downhole tools employed were the Adara temperature shoe, DVTP, DVTP-P, WSTP, APC-M tool, FPC, and PCS. The results of the temperature and pressure measurements at Site 1229 are described in the two sections below. A short summary of the other tool deployments is provided in the third section.
One good downhole temperature determination was made in Hole 1229A using the DVTP. An Adara temperature shoe deployment before Core 201-1229A-1H yielded a value for the bottom-water temperature of 14.9°C. The WSTP deployment successfully recorded a value of 15.1°C for water temperature 10 m above the seafloor. Figure F22 shows the data from the successful DVTP deployment at 164.9 mbsf. Four other deployments at 33.4, 68.4, 83.5, and 107.9 mbsf resulted in records that could not be used. Table T9 summarizes Site 1229 temperature measurements together with the Site 681 data.
The results of the DVTP and Adara temperature measurements are displayed in Figure F23. Because we obtained only one good downhole temperature value at Site 1229, the results from Site 681 were included in the thermal gradient estimate. Because of a variety of problems documented by the Leg 112 Shipboard Scientific Party (1988), each of the estimates for Site 681 is denoted as either an upper or lower bound on the true formation temperature. In the combined plot in Figure F23, four of the data points are nearly collinear. These four points yield a linear gradient of 0.0346°C/m in the upper 187 m of the sediment column (Fig. F23). Extrapolating this gradient upward to the seafloor yields a bottom-water temperature of 13.5°C, which is 1.4°C lower than the measured value at Site 681. Although 4°C seasonal temperature variations are possible at 100- to 200-m depths in upwelling systems (e.g., Smith et al., 1991), specific data were not available on board the ship to verify whether 13.5°C is a reasonable mean bottom-water temperature for Site 1229. The extrapolated temperature at the bottom of Hole 1229A, at 192.9 mbsf, is 20.2°C. Multiplying the gradient by an average thermal conductivity of 0.87 W/(m·K) (Fig. F20A) gives a conductive heat flow estimate of 30 mW/m2 at Site 1229. This result is equal to the 30 mW/m2 value estimated as a lower bound for Site 681 by the Leg 112 Shipboard Scientific Party (1988). It is also close to our estimates of 32 mW/m2 for Site 1228 and 37 mW/m2 for Site 1227. Figure F23B shows a theoretical steady-state conductive temperature profile calculated using a constant heat flow of 35.5 mW/m2, a seafloor temperature of 13°C, and the measured thermal conductivities from the Hole 1229A cores. The theoretical profile is noticeably curved because of the factor of 1.7 downhole increase in thermal conductivity (see Fig. F20A).
The failure rate for DVTP measurements attributed to formation and sea conditions increased at Site 1229 to a high of 80% compared to 50% at Sites 1227 and 1228 and 0% at Sites 1225 and 1226. The one successful measurement at Site 1229 was the deepest deployment attempted at 164.9 mbsf. It was located in lithostratigraphic Unit II, composed of alternating sand and silt (Fig. F1), and the subsequent core had the lowest recovery compared to the other four deployments (recovery = 43%). The four unsuccessful deployments were located at shallower depths in silt, clay, or diatom ooze. These results indicate that deployments of the DVTP in shallow water (<200 m) may be more likely to succeed at depths below 150 mbsf.
The DVTP-P was deployed once at Site 1229 at a depth of 79.4 mbsf (after Core 201-1229A-9H). The lithology for this depth was composed of diatom-rich ooze with an average porosity of 75%. The record displayed in Figure F24 exhibits 5-min stops at the seafloor and the base of the hole both before and after the tool was pushed into the sediments. A stepped pressure increase occurred when the tool entered the formation, followed by a sharp drop within 1 min to ~2.42 MPa, which equals the predicted hydrostatic value for the hole depth and measured salinity gradient. For the remainder of the 30-min deployment, the pressure oscillated at 2.42 ± 0.02 MPa. The amplitude of the oscillation corresponds to ~4 m of head, which was comparable to the oscillations at Site 1228. An investigation into the cause of the oscillations is needed.
After a failed deployment of the WSTP above Hole 1229A, a sample of bottom water was successfully collected from 10 m above the seafloor at Hole 1229C. Chlorinity data showed that this sample deviated <2% from International Association of Physical Sciences of the Ocean standard seawater (see "Interstitial Water" in "Biogeochemistry"). The APC-M tool was run continuously from Cores 201-1229A-2H through 13H. The tool appeared to function correctly, and the data will be analyzed postcruise. The FPC was tested twice at Site 1229 at 24.4 and 174.4 mbsf (Cores 201-1229B-4M and 201-1229A-20M, respectively). Because of a number of mechanical problems, the FPC failed to retrieve pressurized cores on either deployment. The single deployment of the PCS (Core 201-1229D-10P) successfully recovered 0.86 m of sediment from the 2-m cored interval.