By Guest Author 16/02/2021

Alysha Johnson

They say a good day is a busy day, and aboard the R/V Falkor (Seafloor to Seabirds in the Coral Sea – Schmidt Ocean Institute), almost every day is busy!

On this particular day, we deployed a CTD, which stands for Conductivity, Temperature and Density. It is a device lowered to the ocean floor to provide live readings of salinity, density, oxygen concentrations, fluorescence and turbidity throughout different the ocean layers.

Left: CTD assembled before opening Niskin bottles Photo: Sienna Blanckensee. Right: Alysha Johnson opening Niskin bottles prior to launch

Deploying a CTD is a perfect example of how different parts of the ship need to work together for science to happen. The R/V Falkor’s crew are expert and run the CTD like a well oiled machine.

“Science Control to Bridge.  CTD preparation beginning in aft bay.”

“Copy that.”

Marine Technicians prepare the CTD by mounting sensors and twenty-four Niskin bottles on a large frame attached to a winch. Here I help out as a student, opening and preparing the Niskin bottles so that water can flow through them during deployment.

“Science Control to Bridge. CTD is ready to deploy.”

“Copy that. “

Next up the Bridge Officers stop the ship. It is crucial that the ship stays in the same location while the CTD is in the water. To do this, the Bridge Officers turn the ship into the dominant current and lightly engage the engine to keep us stationary.

“Bridge to Science Control. Ship is in position.”

“Copy that. Deck Team, standby for deployment.”

Deploying the CTD in the Tasman Sea. Photo: Alysha Johnson

Next, the Deck Team can begin to operate the winch to lift the CTD cast off the ship. Watching from the science control room, there is nervous energy between all scientists. If the CTD does not send us data, there may be something faulty.

“Deck Team to Science Control. CTD is in the water.”

But as soon as the first lines of data wiggle onto the screens, I sigh my relief, and the CTD can start it’s journey through the seawater column to the seafloor.

“Copy that. release winch at 50m per minute.”

Today the CTD was deployed to 4680m below sea-level. On the way down the CTD logs, oxygen, salinity, fluorescence and turbidity through the different ocean layers. The ocean is a bit like a cake, it is made up of different layers with distinct changes in salinity and temperature.

As the CTD gets closer and closer to the seafloor, a hush falls through the control room again. We aim to suspend it 10m above the seafloor, but as there is 3km of wire between the ship and the CTD, 10m leaves little room for error. Due to the tumultuous nature of the ocean, when something is deployed off a ship, there is always a chance it will not come back.

Marine Technician, Science Team and students in the Science Control Room watching the deployment of the CTD. Photo Sienna Blanckensee

Finally, as the altimeter says “10m”, the first six Niskin bottles are fired (closed), capturing water from the ocean’s base. A whoop of celebration goes up as we radio the Bridge.

“Science Control to Bridge. CTD on its way up.”

“Copy that! CTD coming home.”

The CTD makes three more stops at 800m, 50m and 5m deep to fill the Niskin bottles. The whole process takes four hours and requires co-ordination from over half of the ship to keep things running smoothly.

“Science Control to Deck Team. CTD at 50m, prepare for hand-over.”

“Copy that. Deck Team now have winch control.”

“CTD at 5m”

“Copy that”

So when the CTD finally returns, full to the brim with new data, it is not just the success of the science team, but of the whole crew.

“Deck Team to Bridge. Permission to retrieve CTD.”

” Permission granted.”

As a student, this is the most technical and high-risk science I have participated in. It highlights that good science requires knowledge and teamwork of a whole array of people expert in their skill. Regardless of background, excitement in what we have achieved is shared all over the ship.

“Deck Team to All Stations. CTD back on board! CTD successful”

“Copy copy. Well done team!”

“Whoop, Copy that.”

“Copy that!”

Alysha Johnson (@AlyshaJohnsonNZ) is a PhD student at the University of Wollongong studying the geomorphic evolution of volcanic islands, seamounts and guyots.

Featured image: Clem Onojeghuo on Unsplash