Expedition 393 (South Atlantic Transect 2) is the last in a series of 4 expeditions in the middle of the South Atlantic. Occupying 4 of the 7 total sites, this expedition also provided an opportunity for repeated downhole activities that potentially captured temporal variations. This is on top of the rare site layout that transect the western flank of the Atlantic mid-oceanic ridge. Given this rare chance for a spatio-temporal coverage, a list of downhole activities were conducted during this expedition: the normal wireline logging, APCT-3 runs, CTD profiling and Niskin bottom water bottle sampling for microbiology.
Activities
Wireline Logging
A new Schlumberger Logging Engineer, Kirby Garrett, sailed aboard the JR this expedition, with Giles Guerrin (LDEO-RG) as the logging scientist.
| Hole | Runs | Comments |
|---|---|---|
| U1559B | Cancelled | Coring discontinued due to very slow advance. Given the shallow hole, TC, FMS and UBI runs were cancelled. |
| U1558D | Cancelled | Lost re-entry funnel and casing. |
| U1583F | TC (no MSS, no source) | MSS was removed to shorten TC to 35.93 m and maximize span of borehole that can be logged/reached by the various sensors. Run-in 7/16/2022 ~20:40. After reaching 500mbrf, return to surface due to electrical short/power loss that was traced to the HRLA. A back-up tool was used to solve the problem.Complete downlog; repeat log turned into a main pass as the tool cannot descend past 4390 mbrf. |
| FMS-sonic, | 7/17/2022. Completed downlog to 4390 and Pass1, but could not descend past 4333 for a second pass, neither could the FMS enter back into the pipe. The FMS arm was opened and closed, the toolstring moved up and down across the EOP, all the time pumping surface water into the drillstring in an effort to dislodge whatever debris that might be stuck in the FMS arms, which was reading 2 ", for a 3" diameter tool. Finally, it was suggested that the drillstring be rotated a quarter turn using the Rotary Table, which allowed the winch operator to ease the toolstring up into the pipe, reaching the rig floor at about 22:40. The FMS arrived topside with all arms damaged and one pad missing. | |
| UBI | Cancelled. | |
| U1560 | TC | Ran with MSS and source. Successful runs, tagging bottom at 4051 mbrf (316.2 mbsf). |
| FMS-sonic | Successful 2 passes; went for 3rd pass but got momentarily stuck in casing. | |
| UBI | Successful 2 passes. |
APCT-3
| Hole | Cores | Comments |
|---|---|---|
| U1558F | 3H, 7H, 10H | Supplementary measurements to those collected from 390C-U1558A. Temperature and geothermal gradient are very low. |
| U1583C | 4H, 7H, 10H | Heat flow about 34 to 35 mW/m2 as calculated using the Pribnow et al. (2000) spreadsheet: very low considering proximity to MOR. Reported heat flow are (a) 28 mW/m2, calculated as a product of the thermal gradient and average conductivity or (b) 30mW/m2 using the Bullard plot (393PP Site Report) |
| U1583D | 5H, 8H | |
| U1560C | 5H, 8H, 11H | Using TC from holes A (sediment) and B (basalt unit), and the APCT3 data from holes A and C, the heat flow is between 16 to 18 mW/m2 as calculated using the Pribnow et al. (2000) spreadsheet. |
All run sheets are scanned and copied to :\data1\14.1 Formation Temperature APCT-3_ SET_ WINTEMP_ TPFIT
CTD
In all four sites occupied during Expedition 393, we had a total of 9 deployments of the CTD. Only one set of sensors were used for all runs, and will be sent back to AML Oceanographics for re-calibration at the end of the expedition: CT.Xchange 450735 and P.Xchange 306526
| Hole | Log Files C:\MinosX_31067\Logs\393\saved | Exported depth and pressure1 C:\MinosX_31067\Exports\393\393_depth or \393_dBar | Date | Comments | Niskin sample |
|---|---|---|---|---|---|
| U1559B | u1559b_20220619.log | 393-U1559B 2 2022-06-19 21-55-17 Down.csv 393-U1559B 2 2022-06-19 21-55-17 Up.csv | 2022 June 19 21:55:17 | Deployed during re-entry to U1558B. Immersed in freshwater to equilibrate to ambient conditions before deployment. | No |
| U1558D | u1558d _20220628.log | 393-U1558D 51 2022-06-28 11-51-51 Up.csv 393-U1558D 51 2022-06-28 11-51-51 Down.csv | 2022 June 28 11:51:51 | Deployed during re-entry to U1559D. Immersed in freshwater to equilibrate to ambient conditions before deployment. | Yes |
| u1558d_7_20220704.log | 393-U1558D 30 2022-07-04 05-13-55 Up.csv 393-U1558D 30 2022-07-04 05-13-55 Down.csv | 2022 July 4 05:13:55 | Deployed during planned dropping of bit on seafloor; VIT reached only ~4100 mbsl due to raised funnel and casing. Immersed in freshwater to equilibrate to ambient conditions before deployment. | No sample | |
| u1558d_8_20220704.log | 393-U1558D 1 2022-07-04 11-21-21 Up.csv 393-U1558D 1 2022-07-04 11-21-21 Down.csv | 2022 July 4 11:21:21 | 2nd deployment to investigate drill string, casing and funnel. No pre-immersion of sensors due to time constraint BUT produced lowest hysteresis of all 3 runs! | Yes | |
U1583F | u1583f_1_20220717.log | 393-U1583F 1 2022-07-17 10-32-02 Down.csv 393-U1583F 1 2022-07-17 10-32-02 Up.csv | 2022 July 17 10:32:02 | Deployed with VIT to inspect FFF. No pre-deployment immersion of sensors, but produced very low hysteresis of 0.064 deg C. | Yes |
U1560B | u1560b_1_20220719.log | 393-U1560B 1 2022-07-19 07-13-52 Down .csv 393-U1560B 1 2022-07-19 07-13-52 Up .csv | 2022 July 19 07:13:52 | Deployed with VIT to re-enter U1560B. (No pre-deployment immersion of sensors) | Yes |
| u1560b_2_20220723.log | 393-U1560B 51 2022-07-23 01-16-08 Down .csv 393-U1560B 51 2022-07-23 01-16-08 Up .csv | 2022 July 23 1:16:08 | Deployed with VIT to ensure uneventful POOH from U1560B | Yes | |
| u1560b_3_20220723.log | 393-U1560B 3 1 2022-07-23 16-54-37 Down .csv 393-U1560B 3 1 2022-07-23 16-54-37 Up .csv | 2022 July 23 16:54:37 | Deployed for 2nd re-entry to U1560B | Yes | |
| u1560b_4_20220727.log | 393-U1560B 66 2022-07-27 16-05-26 Down .csv 393-U1560B 66 2022-07-27 16-05-26 Up .csv | 2022 July 27 16:05:26 | Deployed for 3rd re-entry to log U1560B | Yes |
1 Exported_Depth in DHML PC C:\MinosX_31067\Exports\393\393_depth; Exported_Pressure in DHML PC C:\MinosX_31067\Exports\393\393_dBar
Given the derived sonic velocity (SV) from the CTD runs, different averaging techniques were also calculated and used as input in the Knudsen EchoSounder. Result from this single site show that the integral harmonic or arithmetic mean as defined by Maul and Bishop (year) provide the most accurate water depth estimate.
Niskin Water Sampling
The expedition microbiologists, Jessica Labonte (TAMU Galveston) and Shu Ying Wee (TAMU CS), requested that the Niskin bottle be deployed with the VIT in order to collect deep water samples that are closer in composition to what is circulated within the rocks, as compared to the surface water that was often used in the past. The closing mechanism designed during Expedition 391 was used and tested on deck, and was given approval by SIEM Electrical Supervisor that the 3D-printed PLA shear pin is of the proper strength to prevent stripping off the gear mechanism of the beacon release system. The previous mounting was modified by using a U-bolt to hold the bottle. The visual indicator for the release was made more discrete to the search camera view by using a clear nylon line with a rubber weight. The sequence of video still captures from the search camera shows the nylon lanyard across the lower right corner of the field of view, and how it swung out during the release.
Below are annotated photos of (L) the lanyard and chord routing and attachments; and (R) the pre-deployment closed set-up for the petcock assembly and air vent: turn the upper air vent screw clockwise and the lower petcock pull disc out. Also, make sure that there's minimum slack on the trigger chord because the beacon release mechanism rotates only once for every command sent from topside (too much slack will require sending the trigger signal several times).
For this expedition, we collected 7 bottom water samples from 3 sites. The noted collection time is when the visual cue for the closing of the Niskin bottle is observed via the live-stream search camera feed over the VIT Console in the Sub-Sea Shop. The VIT cable depth and sonar altitude are also noted then. When possible, collection time is later verified through a replay of the search camera video saved in the network folders :\data1\1.3 Ops Video or :\data1\1.0 Operations.
| Hole | Seafloor depth (mbsl) | VIT cable depth (mbsl) | VIT sonar (m above sf) | CTD depth (mbsl) | Volume collected (mL) | Date/Time collected | Notes | In situ CTD Salinity | In situ CTD Temp (oC) | Lab pH | Lab Salinity | Lab Temp (oC) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| U1578A | 3793.8 (Tagged) | Test run conducted during Exp. 391 (Walvis Ridge) | ||||||||||
| U1558D | 4345 (Tagged) | 4339 | 9.17 | 4327.2 | ~1600 | 6/28/2022 14:16 | Sample collected before re-entry, before lowest VIT elevation at about 5 m above SF (altimeter). Minimal SF sediment cloud. Sample divided into 1L, 0.5L and 0.2L wide-mouth plastic bottles. Filtered and incubated for microbiological analysis, | 34.743 | 1.246 | 7.54 | 35 | 13 |
| 4168 | 4156.4 (ave.) | 0 | 7/4/2022 07:16 | Triggering mechanism failed: no sample | --- | --- | --- | |||||
4324 | 25.192 | 4314.7 | 1600 | 7/4/2022 13:17:23 | Four attempts to trigger release, using 2 Falmouth Scientific Inc. Table Acoustic Command Unit (#90705 and 90704) Sample quality: filtered a few rust particles from subsequent VIT deployment along non-vertical drill-string. | 34.745 | 1.237 | 7.6 | 35 | 15 | ||
| U1583F | 4210.05 (Mud line core) | 4216 | 8.293 | 4204.96 | 1580 | 7/17/2022 12:10:12 | Visual release cue on camera remained; sonic command triggered only once from box #90705. Closest to seafloor sample during this expedition. | 34.783 | 1.562 | 7.64 | 35 | 20 |
| U1560B | 3723.66 (APC Calc) | 3725 | 16.251 | 3706.37 | 1550 | 7/19/2022 9:32:43 | Sample collected after re-entry. No solid residues detected on filter. | 34.836 | 1.986 | 7.71 | 35 | 16.5 |
| 3717 | 15.140 | 3707.26 | 1600 | 7/23/2022 2:45:48 | Sample collected when VIT was deployed to ensure uneventful pull-out for bit change. | 34.834 | 1.984 | 7.71 -7.76 | 35 | 9.3 - 12.3 | ||
| 3723 | 13.314 | 3709.61 | 1520 | 7/23/2022 19:10:50 | 2nd re-entry. Shear ring did not break, but the release mechanism was triggered. A few rust particles and fibrous material in Milipore filter | 34.84 | 1.985 | 7.76 | 35 | 13 - 14 | ||
| 3725 | 13.776 | 3710.28 | 1620 | 7/27/2022 17:53:11 | 3rd re-entry for wireline logging. | 34.838 | 2.001 | 7.76 -7.79 | 35 | 16- 16.6 |
Notes:
- VIT cable depth: two values based on the two counters at the VIT winch operator's console. The upper counter for RigWatch has a small timing delay that causes the discrepancy.
- Date/time collected is when the trigger was sent and visual cue for closing was seen through the survey camera, possibly refined through a video playback after the operation.
- Lab salinity was measured using a refractometer.
- Lab temperature was measured on the 500 or 1000 ml bottles.
Water collection procedure
Each water sample is divided into 3 bottles: 250ml, 1000 ml and 500 ml (wide-mouth Nalgen bottles). A small red-white cooler (like the one previously used for the TCON station) can be used to transport these sample bottles.
- Drain about 100 ml into the 250 ml bottle. Rinse.
- Successively transfer and use the 100 ml to rinse the 1000 ml and 500 ml bottles. Return the wash water water to the 250ml bottle.
- Fill the 1000 ml bottle.
- Fill the 500 ml bottle.
- If there's any remaining water, empty it into the 250 ml bottle.
- Take the temperature, ideally from the bigger bottles, but can also be from the 250ml bottle. Take note of the time.
- Hand over the water sample bottles to the scientist. Record other measurements made on the sample (e.g., pH, salinity, etc.)
- The bottles might be returned after. If so, thoroughly rinse the bottles with DI water, ready for the next use.
Photographs: Niskin bottle on VIT, sample collection, filtration and use for microbiological culture experiments during Expedition 393. (In pictures are Jurie Kotze, Jessica Labonte and Ying Wee. Photo credits: Eric Bravo, Ying Wee and Julia Reece)
Issues
- APCT-3 Calibration files: Calibration files saved into the electronic board are missing. The latest files were sent back from CS and every time data is downloaded from the APCT3, Wintemp has to be pointed to the corresponding calibration file. This will be the routine until Wintemp can be run as an administrator and save the files into the APCT3 electronics board.
- Power loss on logging tools: During the Triple-Combo run into U1583F, the tool was pulled back up from 500 mbrf due to a power loss or electrical short. A similar incident happened during Exp. 392 (Agulhas Plateau) which was traced to the HNGS, but was fixed during Exp. 390. However, this time, the problem is traced to the HRLA. Given that this is now the third straight expedition that such power issue has happened from two different sonde, the main HRLA will also be sent back to SLB for further diagnosis and fix.
- Damaged FMS: During the logging operation in U1583F,at least one of the pads was damaged, likely at the beginning of the 1st uplog. At the second descent to start the 2nd pass, the toolstring got stuck, forcing the decision to retrieve the tool. However, the FMS also was unable to enter back into the pipe. After a few maneuvers in an effort to retrieve the tool, the entire toolstring was recovered, but the FMS was badly damaged. A spare FMs is available onboard.
Documentation
- The CTD casts in U1559B provides a complete sonic velocity profile of the water column and a chance to apply this data to those domains that the instrument was initially intended for (see Underway Geophysics Technical Report). The CTD data would better refine the VSI results by providing an accurate water column sonic velocity correction for the total transit time. However, in the SLB software and in some IODP proceedings, it appears that the required sonic velocity of the water column is only for the interval between the source (7 mbsl) and the nearfield hydrophone (9 mbsl). However, this surface water sonic velocity is higher than the average of the water column, which are respectively 1521 m/s and 1496 m/s in U1559B. The later yields a more accurate estimate of the seafloor TWT vis-a-vis with the 2D reflection seismic profile. Therefore, using an integrated harmonic or arithmetic average of the water column sonic velocity would also result in a synthetic seismogram that requires minimal bulk shift.
- The multiple CTD profiles over Hole U1560B, between expeditions 390C and 393, provide text-book examples of the seasonal and diurnal variation of the upper mixed layer of the oceans, as illustrated by the graphs below. For more information, see Guemas et al. (2011) Impact of the Ocean Mixed Layer Diurnal Variations on the Intraseasonal Variability of Sea Surface Temperatures in the Atlantic Ocean, Journal of Climate 24 (12), 2889-2914, doi.org/10.1175/2010JCLI3660.1
Shipping
- Sclumberger logging tools
- main FMS: damaged during U1583F logging (for repair)
- 3rd FMS for spare parts
- main HRLA: caused electrical short during U1583F logging (for repair)
- UBI (2 tools on loan)
- CTD sensors sent for calibration
- Conductivity/Temperature Sensor with part number RF53791 and serial number 450735
- Pressure Sensor with part number RF53794 and serial number serial 306526