Weather or not to CTD ...

Unfortunately, 35 knot winds and high seas meant a period of 16 hours of science downtime today. The captain reassessed the conditions at 8 pm tonight and operations have since resumed. We aim to have completed our north-south section across the Scotia Sea by Monday evening. In the meantime, Uriel and Xinfeng took some great photos of the sunset last night, which they have kindly shared with us… 

Scientist Profile: Katy Sheen

I work at the National Oceanography Centre in Southampton, UK as a postdoctoral researcher for the DIMES project. I primarily look at the data that we collect using the vertical microstructure probes (VMP). These data are important as they provides 'on-the spot' estimates of the vertical mixing present in the ocean, in contrast to the time and space averaged values determined from the yearly spread of the tracer (dye). On the James Cook, my main role has been helping to deploy and recover the VMP, and to process the data. It can be a little nerve-racking, making sure that you have programmed the VMP correctly so that it doesn't crash into the sea bed!

Back in the office, I have been looking in detail at what kind of processes cause the variations in mixing that we observe in the VMP data. One source of mixing is the breaking of waves produced from the interaction of bottom currents with bumps in the sea-bed. These waves (internal waves) radiate through the ocean interior along density layers. When the internal waves lose enough energy, they  break, mixing up the water - just like waves breaking on the beach. High levels of ocean mixing are therefore associated with rough topography and strong currents, as in the DIMES region of study. The energy from internal waves contributes to pumping deep ocean waters back to the surface through vertical mixing, powering the global overturning circulation.

Internal waves typically have wavelengths of about 100 m, and information about the internal wave field can be obtained from the temperature, salinity and current velocity data collected by the CTD which is deployed at the same time as the VMP.  (The data obtained by the VMP is on the millimetre scales). These CTD data, along with theoretical ideas about how and when internal waves break, can be used to estimate mixing too. One of my main areas of research is to look at how well mixing estimates from CTD data compare to those measured directly by the VMP.

What do you enjoy about being at sea?

I enjoy working in a completely different environment , especially somewhere as beautiful and remote as the Southern Ocean - it's not a place where many people get the opportunity to visit! It's also a lot of fun meeting the other scientists and crew working on the project and exciting to be involved in such a dynamic and cutting-edge science programme. I normally manage to sneak in some travelling too - this year I spent a week camping in Uruguay before joining the ship in Montevideo.

What do you hope to gain?

Hopefully lots of data, new friends and I'd love to see an ice-berg!

Mooring operations complete!

Just a quick update to let you all know that we successfully recovered the rest of our mooring equipment and have started downloading the data from all the instruments. We steamed northwards overnight to start a north to south transect of the Scotia Sea, including both CTD and VMP work. We had a showery day today, though the upside of that was a great double rainbow, captured below by Uriel.

Scientist Profile: Dhruv Balwada

Today we spoke to Dhruv, who has spent much of the cruise busily helping the tracer team with their work in the container.

Where are you are studying?

I am a second year PhD student at Florida State University working with Kevin Speer. My current research is related to understanding how the numerous eddies and jets in the Antarctic Circumpolar Current (ACC) control the mixing.

What is your involvement is with the DIMES project?

My involvement with the DIMES project has been related to processing the RAFOS float trajectories. These density layer following floats were deployed along with a tracer at key sites in the ACC to get a picture of the effect of eddies and jets. Each float has a story to tell about where it went, how fast it went, what kind of events it witnessed during its time in the water, did it get stuck in situations out of which it was hard to get out and a lot more. Each story is very interesting in itself, but we need to combine all the stories together and then an image starts to emerge. This image gives us an idea about the mixing rates, the scales of flow, where the dominant patches of energy are located, what eddies do to fluid particles and a lot more. In a few words, I do processing, analysis and statistics on Lagrangian (flow-following) particles to get estimates of mixing regimes at play in the region.

What do you personally want to get out of this cruise?

For me this cruise is a learning experience about going to sea and how research cruises operate. It also gives me to opportunity to see first hand how the data are collected for both the tracer and microstructure components of DIMES. I have been working with the tracer team and have gained experience in sampling and analyzing sea water for the tracer and a few other CFCs.

What do you enjoy about going to sea?

I enjoy the rocking motion of the ship, it’s like being on a never ending amusement park ride! It also gives us oceanographers the opportunity to get closer to our element.

Making 'moor' progress...

Under clear skies and with light winds, we recovered four of our six moorings today. These moorings, which contain instruments at a variety of different depth levels measuring current speed, pressure, temperature and salinity, were deployed on the UK2 DIMES Cruise in December 2010 and have collected 14 months of data. The aim of the experiment is to investigate mixing and internal wave breaking processes over a sea-floor rise close to the Subantarctic Front.

Mooring operations on the aft deck

Disassembling and storing buoyancy spheres

Mick and Steve at work with the crane

A typical mooring recovery involves ranging the mooring to find out its exact location, then acoustically releasing the instruments and mooring wire from its anchor on the seabed. The mooring then drifts to the surface and the ship is positioned to allow recovery on the aft deck. The mooring line is then slowly hauled onboard ship and the buoyancy and instruments removed from it.

To complement this work, we aim to complete a VMP and tow-yo CTD overnight tonight, before recovering the final two moorings tomorrow. Many thanks to Uriel for the recovery photos.

How does the ship work? It’s Engine-ious…

Control room

Ship's main engines

After we had finished our CTD operations this morning, a group of scientists were shown around the engine room by Third Engineer Bill. We spent an hour clambering around amongst the engines and generators and were even shown what happens to all the ship’s sewage! RRS James Cook has four engines, generating the same amount of power as used by the Falkland Islands! Fuel consumption onboard generally averages around 10 tonnes per day, though this increases to 24 tonnes at maximum speed (16 knots). The ship can make 11 m³ of fresh water per day and the vessel has four thrusters for maneuverability and stability. The ship can also move up to 6 knots sideways!

Many thanks to Bill for the excellent tour. Uriel and Katy have kindly shared some photos.

The sewage system and test toilet!

Crawling around ...

Alex cooling off by the air vent

Ben and Katy trying out the tools for size...