Cruise Blog by Frances Cooke: Day 10
July 16th, 2021
Text: Frances Cooke (PhD Candidate in the Gas Hydrates and Free Gas Reservoirs research group at CAGE, working within the SEAMSTRESS project).
We continued shooting seismic for the active survey experiment. Some inlines were dropped, to make up time so that we would be ready by 16:00 to start the circular lines. The weather conditions remain perfect for seismic, the sea is calm and there is a moderate breeze.
One thing is certain while working at sea; you can never be too confident that things will go to plan! We had planned to recover the OBS tomorrow morning after completion of the seismic lines, however a large number of whales showed up within 500m of the ship. As there were so many whales showing up so close to the vessel, we shut down all our acoustic systems, including the seismic guns. On the bridge they saw plenty of finwhales and Knølhval (horn whale) breaching the surface. The ‘Havforskningsinstitutet’ (Institue for marine research) specify that the Greenland whale and Narwals are species that require the most protection.
The mini GI air guns we use for the seismic are 15 and 30 cu.in. The guns are significantly smaller than conventional seismic guns used in industry. Higher powered guns are used to send signals much deeper into the subsurface. We are only interested in high detail in the near surface sediments (top ~300m).
While on the bridge deck looking out in awe, we spoke about how long we should wait before starting the seismic back up. This depends on the water depth. Whales spend up to 45 minutes beneath the surface in deep (+1000m) water, so we could be waiting an hour before knowing whether the whales are still close by. I worked on a seismic vessel where we had a marine mammal observer onboard. However, she would not observe the whales. Instead, with her own hydrophone, would spend the whole shift with headphones on, listening for whale calls. Relaxing shift?
As time is precious, we decided to move away from the active seismic survey site and move south to Svyatogor ridge to complete some seismic lines for our colleagues not on the cruise – in whale free areas.
Whales as far as the eye can see. (photo: Vera Schlindwein)
Read more about the SEAMSTRESS project here.