Following the successful completion of the bathymetric survey we moved on to our next station I04D. Everything proceeded as planned, so we thought! We first released the ocean bottom magnetometer and then conducted a survey to precisely locate the ocean bottom seismometer (OBS) on the ocean floor. At the end of the survey, we sent a burn command that triggers the OBS to release its anchors and rise to the surface. After waiting for the burn sequence to complete, which takes about 15 minutes, we communicated with the OBS to check if it is rising. But unlike all the previous stations, this OBS turned out to be a bit stubborn. We sent a few more burn commands, hoping that it would rise eventually. An instrument stuck on the ocean floor was a likely scenario that we were all prepared for. There are many possible reasons for an instrument to get stuck on the ocean floor – it landed in a wrong position or perhaps it sank into the soft sediments, or the release mechanism malfunctioned. It would be heart breaking to abandon this instrument behind especially because it was still active and communicating.
Captain Antonio Gatti came up with a bold plan. We were to pay out a cable a few hundred meters around the instrument and then slowly start to pull the cable till it nudges the instrument. We had to winch out 4991 meters of cable to reach the bottom of the ocean that took us about 2 hours. We then slowly moved, paying out a total of 5600 meters of cable around the instrument which took us another 2 hours. We then started sailing away from the instrument pulling the cable slowly whilst constantly communicating with the instrument. The ordeal that started at 18:00 finally ended at 23:20 when the instrument confirmed that it was rising! The entire science party was on deck looking for a flashing beacon in the dark when the instrument finally made it to the surface at 00:50 hours. It was a big moment of satisfaction for all of us – mission accomplished!!