June 13th, 2021
The morning began by returning to the tubeworm gardens. This short dive is to deploy and recover Lauren’s trees and trampolines. Due to the size of the equipment we can’t put all our instruments in one basket and need to dive twice. Carefully, Jason has to hover around the deployment sites, avoiding crushing tube worms and stirring up the sediment too much. Time was of the essence however, so we couldn’t spend too long on the seafloor. With the science deployed we quickly resurfaced, and immediately left GC-234 to head to our next site: Brine pool.
What’s a brine pool? It’s a pool of very dense, salty, water at the seafloor. These form throughout the Gulf of Mexico. Our brine pool was formed through salt intrusions called salt diapirs. The diapirs are buoyant and a lower density than the overlying sediment, which forces them through the bottom. Essentially these diapirs dissolve in the water and create these hypersaline pools. The brine pool we are studying is unique to others in that there is a ring of mussels surrounding the pool like a beach. Mussel beach. This break in the seafloor from the diapir is also allowing methane gasses (and oil) to seep into the surrounding water that provide the basis of this methanotrophic community. The brine pool is 120 PSU, with the density high enough that our deep-sea submersibles float on top, and most organisms can’t survive inside. This video is a great introduction to what our site looks like, created by Avery Calhoun on the spring cruise last year.
Tonight, we had a night recovery of Jason. Both Sentry and Jason and their teams work hard around the clock, with the scientists always ready to support. While unloading the ROV and gathering our samples, we all became familiar with the fact of nighttime in the Gulf in June is still very warm. In heat and less light than we’re used to, the scientists were still cracking jokes while we extracted and sieved the water from our bioboxes. We’ve been together for over three weeks and had our limited interactions during quarantine. We’ve become a close group of friends that are supportive, keep the moral up, and are excited to conduct science at sea.
Once we arrived at brine pool, Jason was quickly put back into the water for our first brine pool dive. On top of our usual habits of collecting mussels and carbonate rocks, recovering and deploying tube traps, sipuncollectors, and tilt meters, we were interested in snails! At this site we find snails called Thalassonerita naticoidea (previously Bathynerita naticoidea) living amongst the mussels and even laying egg cases on the mussel shells. While diving we also visited another site called snail mound, where these snails are abundant, and conducted a partial video transect of both sites. Within the Jason van, we have a sonar system called BlueView and here’s a photo that shows the entire brine pool on that radar screen!
Here’s another awesome video that Avery Calhoun put together on the last cruise, showing the famous brine pool site! There was even a Blue Planet episode on this very brine pool!