Wednesday, 9 December 2015

Going South Part 3: Doing some science!...by PhD student Rowan Dejardin

Rowan collecting samples from the seafloor sediment
As described in my previous blogs, I’m travelling south with the British Antarctic Survey (BAS) to collect samples from the South Georgia shelf, as part of my PhD (jointly funded by the BGS and the University of Nottingham, and within the Centre for Environmental Geochemistry). Having dropped off a team of scientists and technical staff on the remote island of Signy we started heading north in the general direction of South Georgia. After a day of slow sailing through the brash ice we head in to open waters. Whilst we’re going to miss the ice behind, with its attendant penguins and seals, the entry into open water means it will now be possible to undertake some science! Also, a gigantic tabular iceberg, that fills the horizon at times, is soon sighted and keeps us company for much of the day, with other smaller bergs.

The first proper science deployment is the CTD, and impressive contraption made up of many instruments to measure a range of oceanographic properties, including conductivity, temperature and depth, and 24 bottles to take water samples at various depths. The first couple of CTD deployments are at locations where data has been collected in previous year and therefore add data to ongoing studies of the Southern Ocean. The instrument first descends to its maximum deployment depth (approximately 1km at these initial locations) continuously recording data as it goes. As the CTD ascends the bottles are activated by an observing scientist on the ship collecting water at different depths for later analysis.

The CTD equipment
Having deployed the CTD at two stations we then sailed to the location of a scientific mooring, known as P2. The mooring consists of a buoy, with a range of instruments measuring parameters such as pH, salinity, CO2, connected to the seafloor more than 3km below by a very long and strong Kevlar rope. Attached to the rope at various depths are sediment traps, measuring variation in sediment flux through the year, and water samplers. Once we arrive at the approximate location of the buoy an acoustic signal from the ship fires the releases and everyone rushes to the monkey island, at the top on the ship to watch out for the buoy breaking the surface. Despite being left in some of the roughest waters in the world the P2 mooring was just where it had been left, unfortunately after it was recovered to the ship it became clear that the buoy had been hit by a huge iceberg that had dragged it to a huge depth, damaging many of the instruments.

Humpback whales circling the ship
Whilst we deployed the CTD at the P2 location we could see whales blowing all around the ship, presumably feeding on the large krill swarm that was visible in the ship's acoustic data. Initially, the whales were quite distant from the ship but they slowly got closer and closer until a pair of humpbacks were circling the ship, repeatedly surfacing just a few metres away!! Apparently humpbacks are often quite curious and attracted to the noises of the ship and the scientific instruments, and this pair spent the next couple of hours hanging out with us.

Leaving P2, and the whales behind, we continued towards South Georgia where we would be resupplying bases at Bird Island and King Edward Point. On the way we were able to deploy the box corer to sample the sediment on the South Georgia shelf, the reason I joined the cruise! The box corer is essentially a big box with a shovel that closes when it hits the seafloor, collecting around 30cm of surface sediment. We were able to deploy the box corer at two locations, in around 250m water depth, and recovered sediment from both locations, in spite of the box corer failing to fire a couple of times! Once the box corer was on deck, I subsamples the sediment with my supervisor, Vicky Perk, collecting four cores and as much of the top 1cm of sediment as possible. I am now processing the sediment so that can study the foraminifera (a single-celled organism that grows carbonate shells in a range of beautiful forms) in the sediment. Observations of which species live in the surface sediment, under current oceanographic conditions, will inform how I interpret fossil data from the Holocene cores that make up my PhD project.

Rowan is supervised at the BGS by Melanie Leng, at the University of Nottingham by Sev Kender, and at BAS by Vicky Peck and Claire Allen. 







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