Summary

The beginning of the expedition was rough with several issues occurring with both JR6A units (see details below and on the JR6 Spinner Magnetometer Laboratory Notebook page). After that issue was resolved, the expedition went smoothly for the Pmag lab. A relatively small number of sediment and hard rock sections were processed in the Pmag Lab (see details in the Table below) due to the low recovery and high disturbance of the sediment cores. Several sediment sections contain coarse grain clasts and pumice and after initial tests it was decided to exclude these sections, reducing the amount of work in the lab. NRM was measured for the sections of Halite. Hard rock sections mostly consisted of peridotites and caused frequent flux jumps. Several rock magnetic experiments (ARM and IRM demagnetization) were performed using the SRM, coupled with the DTech D-2000 AF demagnetizer and IM-10 Impulse magnetizers to impart the laboratory fields.

Expedition 402 Material Measured

Instruments

Superconducting Rock Magnetometer (SRM)

The SRM was used to measure sediments and hard-rock sections, and discrete samples. The instrument was extensively used to perform rock magnetic measurements (demagnetization of ARM and IRM) on discrete samples.

A new field (with an intensity of ± 4nT) was trapped in port during the crossover with the X401 Tech.

At the beginning of the expedition (Sites U1612, U1613, U1614) sediments sections were measured using the Slow Speed (1 Hz) mode. Then, the scientists decided to move to Fast Speed (10 Hz) mode for the remaining sites (Sites U1615, U1616 and U1617). Header and trail was set up by the scientists at 14 cm.

Initially, the scientists decided to measure the coarse-grained sand with pumice. Then, it was decided to do not measure these sections as they were strongly disturbed by drilling and redeposited during handling/sand curation. To avoid any sediment remaining under the tray and within the SRM, these sections were wrapped before being measured. The same procedure was requested in case of soupy/water rich sections to prevent any mud to remain within the SRM.

Demagnetization of Halite cores was tested on one section to evaluate the intensity of the remanence. The NRM step was measured for all the halite sections as the Intensity was higher then the background and varying in agreements with the impurities in the salt.

As suggested during the crossover with the X401 Tech, the Pause & Confirm mode was used during Outreach & Education tours, allowing the scientists to inspect the data before saving and proceed with a following demagnetization step.

Minor Issues

• One of the scientists was worried about the in-used section tray which has a peak in both XYZ-Moment and intensity at around 80 cm (See Figure 1), possibly related to the accumulation of dusts around a long crack in the tray. The tray was substituted and a new background was measured. If needed, the previous tray is still available in the tray above the SRM.  There are other trays available in the shelf, but they have a noisier background and are longer than our typical trays.  We opted not to use these.

• The motor cable fell off two times because the sections got stuck within the instrument. The issue was related to the sections not being set in the tray well, without verifying if the cling wrap remained pinched below the tray. During one of these accidents, the tray pins broke. The pins were glued onto the tray using epoxy. Luckily, these issues happened at the 20 mT demagnetization step, with no loss of data. A new 20 mT step was remeasured for these sections (U1616A-30X-1A and U1615A-25X-2A) and the data were deleted from LIMS/LORE.

• As expected, in peridotites, flux jumps were frequent. Slow Speed (1 Hz) mode was used in case of peridotites. The flux jumps were still occurring up to the 5-10 mT demagnetization step. Cleaning at 80 mT, background monitoring and new background tray measurements were performed any time before measuring new sediment sections to reduce/disperse any flux count remaining.

SRM Data (duplicate and errors)

Due to the significant amount of rock magnetic experiments and changing in the SRM setting by the scientists, a lot of effort was necessary to clean the inconsistency and duplicates within the dataset. Several comments were added post-measurements on LIMS/LORE to identify the nature of the demagnetization steps performed. In addition, a few sections were demagnetized immediately at 20 mT, losing significant information.

Haskris Water Chiller

The sediment sump system was typically cleaned every 2 weeks with little deposition of sediments. A slight rise in temperature can be observed during the cleaning procedure, but always within the temperature range of the Cryowatch parameters (see Figure 2).

An extraordinary accumulation of sediments occurred in a couple of hours, related to operations on the water system by the SIEM Crew. After these operations, limited accumulation of sediments was observed.

In general, no rise in Temperature were observed and the SRM vital signs has been stable all expedition.

JR6A Spinner Magnetometers

The JR-6A was used extensively during the expedition for both demagnetization of the remanent magnetization and rock magnetic experiments, coupled with the IM10 impulse magnetizer. For IRM experiments, the manual holder was mounted to perform measurements using the 1 position mode and speed up the measurement sequence.

In case of hard-rock, parafilm was used to wrap the samples and prevent the possible dispersion of dust or small fragment inside the JR6A.

Several issues were encountered with both the Main and Spare JR6A.

Main Issue

The holders of the JR6A got randomly magnetized (with values > 10^-3, see Figure 3) while doing measurements. The issue occurred with both Main JR6A (Tag Number: 91063) and Spare JR6A (Tag Number: 90769). We attempted several tests to identify the source of the induced field. But even after cleaning and demagnetizing, the holder would be remagnetized and the data would be suspicious.   The issue was related to the Main JR6 Power Supply (Serial Number 09105) and associated cables. The electronic board of the power supply (AGICO JR6-U model) was substituted with a spare and the issue was resolved. Actually, on board there are 2 electronic board AGICO JR6-U (Item number MN1002) that are mounted in the Main and Spare power supply with no extra spare available in the inventory.

Due to this issue, data from site U1612A are not reliable, additional samples were taken from similar intervals and test comments were added on LORE.

Minor Issues

Main JR6A

• The manipulator was not rotating the holder correctly between measurements.  This was noticed because the holder was not in the correct position after measurements (Figure 4a-b). This was due to physical damage of the manipulator set screw inside the JR6 (Figure 4c-d). The set screw was replaced and the issue was resolved.  

a)	b)	c)	d)
Figure 4 - (a) Misalignment of the holder from the Initial Position after measurement. (b) Proper configuration of the Holder Initial Position. (c) Location of the set screw. (d) Comparison between the damaged and a new set screws.

• Sometimes the manipulator was squealing, the worm screw of the manipulator was cleaned and greased with a silicon spray.

Spare JR6A

• The spare JR6 (Tag Number: 90769) was tested and adjusted to remove the physical noise identified during Exp. 401.
• The manipulator was not responding promptly to commands (i.e., delay in turning the manipulator using the Rema6 auxiliary commands, and later not finding the initial position) due to a loose connector of the optocoupler that was fixed (see Figure 5). 

See the JR6 Spinner Magnetometer Laboratory Notebook page for details.

JR6 Data (duplicate and errors)

Several mistakes were found in the datafiles with a lot of duplicates and measurements errors. In addition, sometimes measurements were missing in the .csv files. For some reason, the data were preserved only in the .txt and .jr6 file. The issue is not related to any bug in the software but more likely connected with the way of managing the data and moving them from the folder “IN” to personal folders on the PC by the scientists. Several duplicates of the same measurement steps were performed by the scientists and they personally requested to preserve that in the system.

Magnetic Orientation Tools (MOTs)

The Icefield MI-5 Multishot Orientation Tools 2052 and 2007 were returned from vendor after new calibrations and were deployed during APC coring. Orientation Data were analyzed and uploaded on LIMS for Hole U1614A, U1615A, U1616A, U1616B, and U1617A.

The software CreateInclinFile.exe is not updated with the new calibration values and should not be used. To create the XXXX_edited.raw file, the .raw and .txt file must manually be combined.

Apart of this very minor inconvenience, no issues were encountered with the tools and data looks goods.

DTech D-2000 AF demagnetizer

The AF demagnetizer was used extensively to demagnetize discrete samples measured with the JR6A and to impart ARM to discrete samples, then measured and demagnetized with the SRM. The Dell laptop connected to the D-2000 worked fine for most of the expedition. It crashed two times, losing the connection with the instrument. After turning Off and restarting, both instrument and laptop, no further issues were encountered and it seems stable.

MFK2 Kappabridge

The MFK2 was used to measure the AMS of all discrete samples, using the 1-AXIS Rotator.  The Insert Box was used for cubic (hard rock) samples. Parafilm was used to wrap all the cubic discrete sample, preventing the accumulation of small fragment or powder within the instrument. In case of slightly bigger samples, a broken cube insert was preferred since it allows a better allocation of the sample within the 1D rotator. Two longer spare screws were damaged/broken and substituted. A total of 9 spare screw (5 normal and 4 long) are still available.

Thermal demagnetizer TD-48SC

The oven was not used.

IM10-30 and IM-10 Impulse magnetizers

The IM-10 impulse magnetizer was used to perform IRM acquisition up to 1 T and few discrete samples up to 1.2 T since it takes a lot of time to stabilize at the voltage necessary to impart high fields. The instrument works fine and no issues were encountered. The IM10-30 was not used and the configuration is still the same as after X401, with coil number 3 insert in the instrument.

Shipments

Items received

• Icefield MI-5 Multishot Orientation Tools 2052 and 2007 were returned after new calibrations.
• 4 cubic specimen holders for the JR6A model #JRACCUB (Item: MN5037).

Items ordered

None

Items shipped

Damaged electronic board of the Main JR6A power supply (Serial Number 09105)