Expedition 401 Underway Geophysics

Zenon Mateo

Summary

Expedition 401 started on 10 December 2023 at Berth 1 of the Damen Shipyard in Amsterdam, the Netherlands, and ended in Napoli, Italy  on 9 February 2024. To investigate the oceanographic and climatic effect of changing gateways between the Mediterranean Sea and the Atlantic Ocean during the Miocene, three new sites were occupied around the Strait of Gibraltar:  U1609 (ALM-03B) and U1610 (GUB-02A) on the Atlantic side and U1611 (WAB-03A) in the Mediterranean side of the gateway. After U1610A, Site U1385 was re-occupied to core hole K and L.

Outbound transit to ALM-03B (U1609) was about 4.46 days from December 13 at 0718H (UTC+1) to December 17at 1720H (UTC), covering 1238 nm (2293 km), for an average speed of 11.5 knots. Cruise mode for inbound transit started at 09:36 on 5 February 2024 from U1611B, arriving in Napoli, Italy on February 9.

And, that is it for scientific drilling expeditions for this crew.

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Figure 1: General transit line for Expedition 401 from Amsterdam, The Netherlands to Napoli, Italy.

Activities

Navigation data was compiled and collected using NaviPac 4.6.0.15803 (rev81339). Ship-wide navigation display used Google Earth and JRGE

During the Expedition 400T dry dock at Damen Shipyard in Amsterdam, The Netherlands, the sonardome was removed and the flooded and burnt junction box of the 3.5 kHz transducer array was fixed by Eric Moortgat and Etienne Claassen. Expedition 401T tested and benefited from this long and tedious troubleshooting effort. Both 12 and 3.5 kHz transducers were powered up to Level 1 towards the deeper southwestern end of the English Channel, near the Chapelle Bank on Dec 15 at 10:02H UTC. Measured depth started from about 250 mbtf and both tracked similar depth readings.

Figure 2: (Left) Knudsen 360 display of 3.5 and 12 kHz bottom profile and depth readings after fixing the sonar dome wiring during the Exp. 400T dry dock. (Right) Sub-bottom profile collected in the middle of The Bay of Biscay, with the JR running close to 12 knots and transducer power level still at 1.

On January 18, 2024, a few hours after departing from site U1385, the Knudsen power level was tested. Previously, the system would trip out at power level 4. With the work done during Expedition 401T, this problem did not happen during the incremental increase in power level from 1 to 4. In shallower regions such as around the strait, the ping frequency was also lowered without any issues.

Notes:

1. The 3.5 kHz array was changed from 3 in series and 4 in parallel to 2 transducers connected in series and these 6 pairs are connected in parallel, as per Knudsen's recommendation for using their system. Also, the resistance was reduced from 150 ohms to 50 ohms (verify values; Claassen, pers. comm.). Other references: 390R Sonar System Evaluation

2. IP address for laptop controller in the gym network locker is 192.168.140.49

Table 1: List of CHIRP profiles acquired during Expedition 410.

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Figure 3: Tracklines of CHIRP profiles acquired and sites cored during Expedition 401. Not included is the inbound trackline (Line 8) from U1611B to Napoli.

The gyroscope data feed continues to receive empty cycles as before, but it has not forced NaviPac into a red state as before. Nonetheless, it is still recommended that the Input Monitor be open and the counter reset regularly, about once every 12 hours.

No issues were encountered. Recorded data was used to verify actual heave values during the downhole wireline logging operation in U1609A.

No major issues encountered, except for the short (~6 hours) disconnection with the aft GPS. In such an event, turn off the problematic GPS in NaviPac and re-start (i.e., place online) the system to re-acquire navigation data.