By Jessica Bolin, University of the Sunshine Coast
Time is flying by – it’s day six of CAPSTAN Voyage #2, and we’ve now had the chance to explore different fields of oceanographic research during our group rotations: hydrochemistry, birds and mammals, plankton, geophysics, and sedimentology. Because we all have diverse backgrounds and areas of research, we’ve started to decide what our favourite stations are. My favourite, so far, is hydrochemistry, because we get to work with the CTD!
CTD stands for conductivity, temperature, and depth, and is one of the main pieces of scientific equipment that oceanographers use, because it measures changes in water properties throughout the water column. The CTD we’re using on board the RV Investigator holds 36 ‘Niskin’ bottles in a circular rosette frame, which is lowered from a huge boom on the starboard side of the ship, into the depths below. Upon deployment, each bottle’s plug is held open under tension by a spring-loaded metal hook. It’s an impressive piece of gear – the frame is taller than me (1.8 m), and each bottle can hold up to 12 L of seawater.
Our target site is a submarine canyon near Portland, Victoria, and we’re dropping the CTD at various sections along the canyon to further understand the circulation and other physical processes occurring within. As the CTD descends through the water column, sensors attached to the bottom of the frame sample the water’s properties, including temperature, oxygen, and conductivity; the latter which is used to calculate salinity. The data are pinged back to the ship’s operations room, where we all watch the vertical profiles of these parameters developing in real-time.
Once the CTD has nearly reached the bottom and starts ascending to the surface, each bottle is remotely ‘fired’ by an observer in the operations room at regular depth intervals. ‘Firing’ a bottle relays a signal to the CTD to release the hook on the target bottle’s plug, closing the bottle and trapping the water at that depth inside. After we have fired every bottle, the CTD is carefully retrieved by the crew and prepped for subsampling on deck… and the real fun begins!
From each bottle, we’ll take three subsamples of water for further testing: one to test for nutrients, one for salinity, and one for dissolved oxygen, whilst also recording water temperature. From these subsamples, we can calculate the density of the seawater, which is a primary driving force for major ocean currents. It blows my mind to think that the water we’re working with has come from up to 2200 m within a submarine canyon, which in turn, has travelled along ocean currents all over the world!
It is safe to say that I’ve developed a new-found love for physical oceanography and all things ocean currents. The ocean is inherently dynamic, and constantly changes in real-time. Teasing apart the mechanisms underpinning the circulation within our site is both challenging and fascinating. Once we start processing and analysing our data, we’ll hopefully be able to pick up the signature of the Flinders Current that flows west along the Great Australian Bight, and perhaps internal waves from within the canyon. Also, with a bit of luck, *fingers crossed* we can pick up the signature of a deep-water ocean current, that Veronica Tamsitt – our token physical oceanographer on board – recently discovered in the Bight, and collect some much needed data to ground-truth the current’s existence. In short, we are discovering SUPER exciting stuff this voyage, so stay tuned!
Check out my group’s blog on The Field!
Jessica is a PhD student at the University of the Sunshine Coast. Follow her on Twitter @JessieABolin