By Kelsey Archer Barnhill
Leg 0 continues on board the R/V Sarmiento de Gamboa. Unfortunately, due to ROV connectivity technical issues we could not have our planned second dive. The hope was to return to the location of our first dive and continue our ascent up the seamount. Despite having to forgo this, the geology team on board are hopeful that they were able to collect enough samples during the first dive to meet their scientific objectives, which is a big positive.
The ROV repairs mean we have shifted our focus to bathymetric mapping. The EMEPC team have identified target areas to map and the science team on board are divided into three shifts to acquire this data. The shifts are from 8:00-12:00 AM/PM, 12:00-4:00 AM/PM, and 4:00-8:00 AM/PM. As the bathymetric multibeam data is largely self-sufficient, we jokingly refer to these shifts as ‘babysitting’ the multibeam.
During these shifts the science teams keep their eye on the different monitors to make sure everything is functioning properly. The ATLAS Hydrographic multibeam acquisition software should be green or yellow at all times as this indicates higher quality data. Every 20 minutes a log is recorded where we note down the survey line number, date, time, velocity, saved file name, width of the bathymetric swatch, the depth, number of beams, and coordinates. Those on shift must also keep track of the range manually set in the multibeam programme as the depth must be between the beam range. For example, this morning the depth was 5300 meters so the scientists had manually entered a 4000-5700 meter beam range. When we are transiting we sail at around 10-12 knots and can acquire decent data, however we slow down to 6-8 knots when we are mapping a target area to ensure higher quality data. I was surprised at just how much area we cover whilst mapping – we are currently mapping a swath width of 7.4 km.
The most exciting part of a seafloor mapping shift is when an Expendable Bathythermograph (XBT) is launched. An XBT probe measures the temperature profile down the water column. These are deployed whilst mapping to calibrate the multibeam data. As the multibeam uses sound to acquire seafloor bathymetry data, understanding water column parameters such as water density and velocity of sound in water are important information for calibration.
One team on board whose work has not been impacted by the cancellation of the second ROV dive is the seabird survey team. This small team of three ornithologists conduct seabird surveys whilst we are in transit. They are not able to collect data during ROV dives as the ship must be moving between 7-10 knots. This hardworking team works from morning to night as they survey during most daylight hours. After an 8:00 breakfast they contact the ship’s bridge for permission to stand in front of the bridge overlooking the bow. Once the captain or on-duty officer gives them the go-ahead they climb upstairs to their survey location. Two people survey at a time, with each scientist responsible for surveying the 90 degree section on their side of the ship. With two people on watch they can cover the entire 180 degrees of sea ahead. The third team member stands by ready to help identify any bird spotted and take photographs. They switch positions every 2 hours so no one has to be on alert for more than 4 hours at a time. So far they have identified 10 species and counted between 200-300 individuals across over 190 surveys. This is low density for a bird survey, but not unexpected as we are far out in the Atlantic. Species seen include pomarine skua (Stercorarius pomarinus), Bulwer’s petrel (Bulweria bulweri), and Cory’s shearwater (Calonectris borealis). I spent a few hours observing the seabird team at work and was extremely impressed with their bird-spotting abilities. I don’t think I have a future in conducting sea bird surveys as I didn’t spot a single bird, including ones they tried to point out to me!
I am looking forward to the rest of the day on board as we are scheduled to cut open the geological samples today. I may even get a chance at sawing one of the samples which would be an at-sea first for me!