At Site 1228, the downhole tools employed were the Adara temperature shoe, DVTP, DVTP-P, WSTP, APC-Methane (APC-M) tool, FPC, and the PCS. The results of the temperature and pressure measurements at Site 1228 are described in the two sections below. A short summary of the other tool deployments is provided in the third section.
Two reasonably good downhole temperature determinations were made in Hole 1228A using the DVTP. An Adara temperature shoe deployment before Core 201-1228A-1H yielded a value for the bottom-water temperature of 13.7°C. The WSTP deployments did not successfully record a value for bottom-water temperature. Figure F20 shows the data from the two successful DVTP deployments at 80.9 and 194.6 mbsf. Two other deployments at 42 and 137.9 mbsf resulted in records that could not be used. Table T9 summarizes all the temperature measurements and the observed problems.
The results of the DVTP temperature estimates are displayed in Figure F21. In situ temperatures were estimated by extrapolation of the station data using thermal conductivities measured on adjacent cores to correct for the frictional heating on penetration as described in "Downhole Tools" in the "Explanatory Notes" chapter. For both of the successful Site 1228 deployments, the data from the lower thermistor were used to extrapolate the in situ temperature. Because we obtained only two good downhole temperature estimates at Site 1228, the results from Leg 112 Site 680 are given in the summary table and were included in the thermal gradient estimate.
The combined downhole temperatures of Sites 1228 and 680 define a gradient of 0.0336°C/m in the upper 196 m of the sediment column (Fig. F21). Extrapolating this gradient upward to the seafloor yields a bottom-water temperature 1.2°C lower than the measured value of 13.7°C. Specific data were not available on board the ship to verify whether 12.5°C is a reasonable value for the mean bottom-water temperature at Site 1228. The extrapolated temperature at the bottom of Hole 1228A, at 200.9 mbsf, is 19.3°C. Multiplying the gradient by an average thermal conductivity of 0.96 W/(m·K) (Fig. F18A) gives a conductive heat flow estimate of 32 mW/m2 at Site 1228. This result is significantly lower than the 46-mW/m2 estimate obtained for Site 680 by the Leg 112 Shipboard Scientific Party (1988b) but is closer to the estimates of 31 mW/m2 obtained for Site 684 and 37 mW/m2 for Site 1227. These lower values appear more reliable than the Site 680 estimate because they are based on measurements spanning a greater depth below seafloor.
Figure F21B shows a theoretical steady-state conductive temperature profile calculated using a constant heat flow of 31 mW/m2 and the measured thermal conductivities from the Hole 1228A cores. The theoretical profile is noticeably curved because of the factor of 1.6 downhole increase in thermal conductivity (see Fig. F18). It is also worth noting that the measured temperature at 194.9 mbsf is 0.5°C higher than expected for a conductive trend.
Comparing lithology and depth from locations that produced good and bad temperature data showed some differences that may be used to optimize future DVTP deployments. The two successful deployments were located at 80.9 and 194.9 mbsf. The sediments surrounding the first location were composed of diatom-rich silty clay, and recoveries averaged 70% (Cores 201-1228A-9H and 10H). The second location, near the base of the hole, was overlain by clay-bearing quartz feldspar sand, and recovery was 41% (Core 201-1228A-22H). Two failed deployments were located at 42.9 and 137.9 mbsf. The first interval was composed of silt, ash, and diatom ooze, and the recoveries for the surrounding cores (Cores 201-1228A-5H and 6H) were 80% and 98%. However, for sediments cored in Hole 1228B over this same interval, recovery dropped to 60% (Core 201-1228B-5H). The worst deployment was at 137.9 mbsf in sandy clay, where no sediments were recovered in the subsequent core (Core 201-1228A-17H). Site 1228 was located in shallow water at a depth of 261 m. These observations indicate that at shallow-water sites where recoveries can be poor, deployments may be more successful deeper in the hole and in intervals with higher recoveries.
The DVTP-P was deployed once at Site 1228 at a depth of 196.9 mbsf (after Core 201-1228A-22H). The record displayed in Figure F22 shows only a small pressure increase when the tool was pushed into the sediments. The pressure dropped within 3 min to ~4.74 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 4.76 ± 0.02 MPa. The amplitude of the oscillation corresponds to ~4 m of head, making it larger than the recorded ~1-m heave of the ship during the deployment. However, periodic displacement of the drill pipe in the borehole could amplify the oscillations caused by heave.
After two failed deployments of the WSTP above Hole 1228A, a sample of bottom water was successfully collected from 10 m above the seafloor at Hole 1228C. Chlorinity data showed that this sample deviated <7% from International Association of the Physical Sciences of the Ocean standard seawater (see "Interstitial Water" in "Biogeochemistry"). The APC-M tool was successfully run continuously from Cores 201-1228A-9H through 12H and on Core 14H. The tool appeared to function correctly, and the data will be analyzed postcruise. The FPC was tested three times at Site 1228 at 7.3, 54.3, and 109.4 mbsf (Cores 201-1228E-2M, 201-1228B-7M, and 201-1228A-13M, respectively). Because of a number of mechanical problems, the FPC failed to retrieve pressurized cores on any of the deployments. The one attempted use of the PCS (Core 201-1228A-23P) resulted in only 7 cm of recovery from the 2-m cored interval. This core released ~60 mL of air when it was opened to atmospheric pressure.