By Jay Lunden, Research Assistant Professor, Temple University; Visiting Faculty Member, Haverford College
If you ask any marine scientist to describe her scientific bucket list, there is one item that would likely appear: a dive in the human-occupied submersible Alvin. For those of us that are fortunate enough to check this box off our lists, a dive in Alvin creates an opportunity to visit an environment most humans rarely think of, allowing us to physically visit the space that we study, collect samples, and enhance our understanding and the way that we think about the deep ocean. It’s an event that is so widely celebrated within our scientific community that each dive is followed by a friendly “initiation” for first-time passengers, and the trip itself is memorialized with a certificate documenting each person’s visit to the seafloor.
Each Alvin dive is staffed by three individuals: one pilot to control the sub and two scientists. Each of the two scientists has a specific role during the dive: the “port observer”—aptly named due to their seat on the port side of the sub—is typically the more senior scientist and is primarily responsible for leading the dive and completing the list of tasks set in the dive plan. The “starboard observer”—frequently a new passenger on Alvin—takes copious notes and assists the port observer. All three occupants, however, provide a critical shared role to the success of each dive: providing a set of human eyes to document observations from the seafloor. This perspective is one of the greatest benefits of working with deep-sea submersibles such as Alvin.
Having eyes on the seafloor is advantageous for the suite of sampling operations planned for the DEEP SEARCH project. On this cruise, Alvin will be visiting three different types of specialized deep-sea habitats: cold-water coral communities, cold seeps, and canyons; and we will use customized equipment onboard Alvin to collect samples from each of these habitats. While we will use this equipment interchangeably, each habitat possesses distinct biological and environmental features that we wish to study. Thus, we need to modify the “basket” or sampling platform for each dive in order to align with the sampling objectives for each habitat.
For our canyon study sites—which serve as conduits for sediment transport to the deep sea—we will devote significant effort to sampling sediments using push cores, which are tubes of plexiglass that can extract several inches of sediment from the seafloor. These sediment samples are then analyzed for microbial activity—which plays a major role in nutrient cycling—and other small animals that are important to the food web. We are also interested in the genetic connectivity, or relatedness, of corals within a canyon (and among our study region); thus, we have a number of PVC tubes that are partitioned to hold multiple corals from distinct locations on the seafloor. Finally, we include Niskin bottles to sample water directly next to the corals in order to characterize their immediate chemical environment, along with large insulated “bioboxes” that allow us to collect live animals for laboratory experiments and rocks for geological studies.
At coral sites, we will use a specialized piece of equipment called the “Bushmaster,” a hydraulically controlled net that enables us to sample a defined area of the coral community. From this collection, we can identify which species are associated with corals—and thus are likely reliant on them; additionally, we can study the exchange of carbon between these species using isotopic analyses in our home labs. Coral sites will also include Niskin bottles for water sampling and bioboxes for live animal collections.
Finally, at our cold seep sites, the primary sampling targets are chemosynthetic mussels that obtain nutrition from symbiotic microorganisms that live within their gills. We will employ a different community sampling tool—the “mussel pot” or circular chamber—to sample groups of mussels from the seafloor. We will also utilize push cores to sample sediments, Niskin bottles to sample water, and the bioboxes to collect live mussels and carbonate rocks for geological analyses.
In the midst of all the sampling, it’s easy to forget that basic life processes still apply and need to occur. The galley staff packs a lunch for each passenger—typically a sandwich and a chocolate bar. There is no bathroom on the sub, and with a typical dive length of 6-8 hours, most passengers make practical use of 1 liter bottles that are provided to each diver. Despite dives lasting for this long, the time generally goes extremely fast, and we are often pressed for time to complete the relevant tasks on the individual dive plan before it’s time for the submersible to the surface. Once the sub receives permission to resurface, it takes about 30 minutes to an hour before the divers return to the surface and emerge from the sub. Then, the busiest part of the day begins: processing the day’s catch in the ship’s labs.