Cruise NBP01-02. Weekly Science Report #1.

April 7, 2001.

Chief Scientist: Joann Stock

Co-chief scientist: Robert Clayton

Report prepared by Joann Stock

The major educational and scientific objectives of this transit are:

1) Teach a hands-on marine geophysics class while on board (10 students are

participating).

2) Survey magnetic anomalies, gravity, and SeaBeam along a flow line parallel to the Falkland-Agulhas fracture zone and deviate in some places from this flow line in order to image the fracture zone trace seismically and/or with swath bathymetry.

We left port on April 1 in the late afternoon and have been making excellent progress and getting good scientific data since then. The support of ECO crew and Raytheon staff has been excellent on all counts. We have had reasonably good weather and have been able to travel at optimal speeds (10 or 11 kts except during the seismic recording when we traveled at 6-6.5 kts). Below we discuss the specifics of the different data collection systems.

Gravity:

On 3/31, the day before leaving port in Cape Town we did a gravity tie at the Taal Monument near Paarl, South Africa. This site is about 45 km from Cape Town and is a reference gravity station used by the Land Surveying division of the South African government. On 4/1 we investigated 2 other gravity base station locations near the docks at Duncan Docks at Cape Town (DOD stations 0033-9 and 0033-A, location information given to us by NIMA) but there were no benchmarks visible at these locations so we did not do any additional gravity ties. In the process of having the students reduce the gravity data we noticed a mistake in the calibration factor being used in the shipboard gravimeter software. Raytheon staff investigated this problem and have corrected it.

Magnetics:

We began recording magnetics at the 200 mile limit out of Cape Town. We recorded anomaly M0 shortly thereafter. (The older Mesozoic anomalies are closer than 200 miles to Cape Town and thus we were not able to record them.) We covered Cretaceous quiet zone crust and recorded chrons 33 -29 on our way down to the Falkland-Agulhas fracture zone. The magnetics were affected somewhat by a magnetic storm on Julian Day 096 (April 6) but are now behaving well again with less high-frequency noise.

We are investigating a possible problem with the IGRF field magnitudes generated by the software used to reduce the magnetics data.

Bathy2000:

We have been recording bottom-50 and have seen some folding and truncated near-surface layers in some locations with the subbottom penetration. The system appears to be working well. We are recording the data to magneto-optical disk.

SeaBeam:

Raytheon personnel gave us an excellent training class in ping editing prior to our departure from the port. We have been able to keep up with the ping editing of the data files. This has revealed some very interesting features, particularly along the Falkland Agulhas fracture zone, where there appear to be multiple parallel fault scarps along the north side. The system appears to be working reasonably well. XBTs were launched on April 2 and April 7 to determine soundspeeds to use for the corrected bathymetry.

Seismics:

We ran 24 hours of single-channel seismics on April 6-7. We used two 210 cubic inch GI guns, the Syntron gun controller, the OYO Data acquisition system (writing to 90 m DAT tapes), and the EPC chart recorder for a real-time image of the data. It worked well and we were able to see basement along most parts of our lines. RPS personnel found that channel 1 on the OYO DAS tends to drop out randomly (or get false triggers) but that the auxiliary channel did not do this, so we ended up recording the data on 2 channels (1 and Aux) and using the data from the Aux channel. We are able to read this data into the Caltech in-house seismic processing package we brought with us (Xena) and work with it.

The scientific objectives of these seismic lines were to traverse the Falkland Agulhas fracture zone in several places in order to see its structure. We traversed it obliquely (so as not to lose too much time) and we were able to see up to ~1 km of relief on the sediment-basement interface across the fracture zone, as well as various packages of deformed sedimentary rocks.

We are very grateful for all of the effort the RPS personnel have put in to help us get the seismic and other systems working.

Student class:

Of the 10 students participating, several were seasick the first day, so we did not have a formal class on April 2 (our first full day at sea). After that, everybody recovered. Here is the list of class activities that have taken place thus far:

March 31 - gravity tie, gravity tie calculation (J. Holik & RPS staff)

April 1 - check of additional gravity base stations, ping editing class, IT orientation (RPS

staff)

April 2 - observe deployment of magnetometer, XBT launch (RPS staff)

April 3 - class on theory of gravity & gravity anomalies (J. Stock)

April 4 - class on magnetic field & magnetometer (J. Stock)

April 5 - class on daily data processing of gravity & magnetics (J. Holik)

April 6 - class on Single Channel Seismic Reflection profiling (R. Clayton); observe

deployment of airguns and streamer (RPS staff)

April 7 - first weekly science wrap-up (J. Stock and R. Clayton); observe retrieval of air

guns & streamer, and XBT launch (RPS staff)

We are very grateful to the RPS personnel for standing science watch for the 1 hour per day that we have our class meeting. We also thank the RPS emergency medical technicians for treating the seasickness experienced by several of the students.

Cruise NBP01-02. Weekly Science Report #2.

April 14, 2001.

Chief Scientist: Joann Stock

Co-chief scientist: Robert Clayton

Report prepared by Joann Stock

The major educational and scientific objectives of this transit are:

1) Teach a hands-on marine geophysics class while on board (10 students are

participating).

Since April 7, the date of the last report, we have had rougher seas, but have still been able to collect the data to fulfill our objectives. The support of ECO crew and Raytheon staff has continued to be excellent. Here is an update on what has been happening with the different data collection systems.

Gravity: Data collection and processing continue to go well.

Magnetics:

We continued to record magnetic anomalies on our flow line just to the north of the Falkland-Agulhas fracture zone. We recorded the magnetic anomalies on either side of the active South America-Africa ridge crest and westward on the South America plate out to about chron 21. The magnetometer has been behaving fairly well except for a few intervals of data loss on April 12. The Raytheon staff worked to fix various problems with the deck box, to restore data collection capabilities.

We confirmed that there had been an error in the IGRF field magnitudes generated by the software used to reduce the magnetics data. This was caused by a mistake in one line of the file containing the IGRF2000 magnetic field coefficients. Raytheon personnel have now fixed their files and corrected this problem. They reprocessed all of the gravity/magnetics data for the current cruise to fix the errors in the gravity and magnetic anomaly calculations. They will also reprocess some of the previous cruises for which these errors affected the magnetic and gravity anomalies. (The error in the gravity was discussed in last week's science report.)

Bathy2000: Continues to be fine and to give us useful data with some sub-bottom penetration in sedimented areas.

SeaBeam: We continue to keep up with the ping editing of the data files. The data have revealed some very interesting features, including good abyssal hill fabric lineations along much of our track, and a system of en-echelon topographic ridges in the deep ocean just north of the Maurice Ewing bank These ridges are oblique to the overall trend of the Falkland-Agulhas FZ. The system appears to be working reasonably well. An XBT was launched on April 14 to determine soundspeeds to use for the corrected bathymetry.

Seismics: We did not run any seismics this week, as we had planned to do only 24 hours of seismics during the cruise, and those were done the first week. There is one aspect of seismics that was inadvertently omitted from last week's comments but that needs to be mentioned. Namely, we had hoped to also deploy a few sonobuoys during our 24 hours of shooting seismics. The sonobuoys had been brought to Port Hueneme on about March 13, in the expectation that they would be air freighted to Cape Town in time for the cruise. However they never made it to Cape Town.

Student class: Here is the list of class activities that have taken place this week:

April 8: Reflection seismology - single channel (R. Clayton)

April 9: Marine magnetic anomalies (J. Stock)

April 10: Acoustic Doppler Current Profiler (E. Firing)

April 11: Discussion of research projects to be done based on the cruise data (R. Clayton

and J. Stock)

April 12: Tectonics of the South Atlantic (J. Stock)

April 13: Multichannel Seismic Reflection Profiling (R. Clayton)

April 14: Observation of XBT deployment and data collection; no class (fire drill)

We are very grateful for all of the effort the RPS personnel have put in to keep everything working and to respond to our requests for various science support activities. In addition, they have been kind enough to stand science watch for the 1 hour per day that we have our class meeting. Again we thank the RPS emergency medical technicians for their continued help in treating the seasickness that has been a problem for a few of the students.