15 May 2019
How many ROV dives can you fit into single day? This appears to have become the secondary research objective of this cruise as we continue to push the ROV team more and more as we work ISIS harder and harder. Today we managed not 2, not 3, but an unprecedented 4 dives in a 24-hour period.
The first dive late last night continued our regular microprofiler surveys, moving the lander progressively closer to seep site. Or should I say seep sites – plural! As the experiment has progressed the area has become a real hive of activity. We’ve seen dozens of small CO2 gas seeps appear and disappear in the area, with a few long-lasting ones forming small pockmarks (craters in the sediment surface, formed by the bubbles). This dive also included the traditional gas and water sampling alongside sediment core collection for analyses back on board.
The second dive was comparatively simply as ISIS collected one of the hydrophone walls from the site and brought it back on deck. The hydrophone wall has been recording noise around the seep. This gives us an important insight into manmade sounds in the North Sea – notably the ROV and James Cook itself, but also things like the laying of undersea cables far away. All these data help inform our analysis of bubble acoustics.
The third dive was a classic switcheroo as one benthic chamber was swapped out for another to ensure a continuous time series of data throughout the experiment. And of course the dive was rounded off with more gas and water samples.
The fourth and final dive of the day saw the return of a fan favourite, as the newly resurrected bubble frame was sent back down (see the blog entry from 13 May). The team managed to salvage one of the camera housings and dipped it over the side of the boat to ensure it really is waterproof this time before risking our final camera in it. And as a great example of inter-team cooperation the AUV guys have lent us one of their cameras to use on the lander as well. We should know tomorrow whether the newly dubbed “Zombie Lander” has worked or not. Which means Thursday’s blog will either include amazing close ups of bubbles or a new author as I go into mourning…