Our second cruise out of Woods Hole is a short one. We are set to sail for eight days, just out to the continental shelf and back. Behind us, we tow a half-a-kilometer-long streamer, dotted with an array of aluminum bottles. Using a series of electrodes and conductivity sensors, the science party is scouring the coastal area for a fresh water aquifer, which allegedly stretches all the way out to the shelf.
Sub-ocean groundwater is a relatively new discovery, and the knowledge of where these untapped, freshwater caches are located is of great interest to countries with large populations and dwindling aquifers. Turns out, a future where off-shore rigs are built to pump drinking water to land is not as far-out as it sounds. In order to find these sources, a team of electromagnetic physicists and engineers from WHOI have teamed up to create an entirely new instrument-essentially a gigantic conductivity cell-that is able to determine the salinity of a huge swath of ocean as it is towed behind the ship.
It takes an entire day to deploy the array. Hand over hand, we cast 850 meters of fiber optic cable off the back deck. Every so often, an aluminum bottle, about three feet in length, is wired into the array and sent overboard. They are slightly buoyant, so I watch each one faintly disappear as they trail behind us into the silver-blue waves. When the end of the line is reached, a weight is attached and the array is drawn down, down, down, below the surface. Next, we deploy a set of copper pipes on a conductive cable. These remain at the surface, and when live, transmit an electromagnetic field through the water column that the receivers within the aluminum bottles are able to interpret.
Between the deployment on the first day and the recovery on the last, the rest of our time is spent towing at a speedy two knots per hr. I fill my time with small projects; I practice my coding skills, work my way through a Raspberry Pi tutorial, and take time to sit on the bow and watch the dolphins and whales that surf our wake. It is a relaxing cruise, and after a busy few months, I am grateful for it.