Interview with Dr Rob Hall, physical oceanographer at University of East Anglia, UK.
Interview by Luis Greiffenhagen
Ocean health research certainly involves many disciplines – but it is impossible without oceanography. Therefore, our interdisciplinary team is lucky to have Rob (pictured right) on board the JC237 cruise as a physical oceanographer. Through his studies and expertise, we can understand the physical processes that occur within Whittard Canyon and link them to other disciplines. As this is incredibly interesting, we decided to ask him some questions for our iAtlantic blog. Enjoy!
How and why did you become a physical oceanographer?
I was going to study physics at university, but at the last minute changed I my mind and started a general oceanography degree at University of Southampton – I had always been interested in the ocean and marine environment. By my third year I had drifted back towards physics and during my master’s year and PhD at University of Liverpool I focused on physical oceanographic topics.
What makes the Whittard Canyon special from an oceanographer’s perspective?
From a physical oceanographic perspective, Whittard Canyon is unusual and interesting because it is highly dendritic (branching like a tree – see image below). Different physical processes are at play in different branches of the canyon, which we hypothesise impacts the local chemistry and benthic ecosystems.
What are you investigating on this cruise / What do you want to find out?
The physical process I am investigating in Whittard canyon is internal tide generation and breaking. These are the subsurface cousins of the surface tides most of us are familiar with and can exist because the interior of the ocean is stratified (the water at the surface is less dense than the water at depth). Internal tides are generated by surface tidal currents flowing over the steep geomorphic features of the canyon and can be up to 200 m high! When these giant waves break in other parts of the canyon, they mix the stratified water and help bring deep nutrients to surface, where they can be used by phytoplankton to bloom.
What equipment do you use to obtain oceanographic data?
The ‘core’ instrument for a physical oceanographer is the CTD rosette. This instrumented metal frame is lowered over the side of the research vessel on a conducting cable and measures the temperature and salinity (salt content) of the ocean beneath. From this we calculate the density of the seawater, which is what drives most deep-ocean currents.
We also use Acoustic Doppler Current Profilers (ADCPs), which send out pulses of high-frequency sound and measure the Doppler shift of sound reflected from particles in the water (such as sediment and phytoplankton). From this we can infer the movement of the seawater. We have ADCPs mounted both on the research vessel’s hull and the CTD rosette.
Finally, we have my favourite tool, an autonomous ocean glider. This glides through the water, driven by a buoyancy engine, and measures the temperature, salinity and oxygen concentration of the ocean as it goes along. Every few hours it surfaces and sends the data it has collected back to shore via satellite and it is emailed to me. This means that I can analyse the data from it in near-real-time.
How do you find life on a research ship?
Collecting new data is always exciting. With the hi-tech tools now available we can perform many analyses while still at sea and adapt the experiment as we go along. You can get fully immersed in the process as you don’t have the distractions of your usual daily life.
Thanks so much for the interview, Rob. If you want to know more, please read one of Rob’s previous publications on the physical dynamics and internal waves within the Whittard Canyon.