JC31: 'Ingredients' of the Southern Ocean


Cruise diary

Thursday 5 February 2009
Location: Drake Passage (57.13°S/68.25ºW)

Rounding Cape Horn and the first few stations of section A21

On Thursday we performed the test cast of the CTD at approximately 11am local time.  This was an opportunity for all the different science teams on board to acquire a set of seawater samples that could be analysed as a practice run. This cast was deep (approximately 4400m) so that it could be established whether the CTD and the other instruments, such as the LADCP, attached to the frame were operating as they should.  If mistakes are going to be made then it is best that they happen on the test station so that they can be ironed out by the time we reach the first real station.  The ship will return to these coordinates and take another real cast.  This can then be compared to the test station to see if the results are similar (which they should be, and hopefully will be).  

Throughout the night several CTD casts have been carried out.  On the first proper cast, the rosette was bought up with a salp (an organism with a gelatinous body that filter feeds on phytoplankton) attached to the top (but we threw him back).  Several articles have indicated that salps may be important for carbon dioxide uptake into the oceans.  This is because phytoplankton take up CO2 and are eaten by the salps which sink as they grow, and then die, drawing CO2 down into the deeper ocean.

The samples that are being collected from the Niskin bottles on the rosette are being analysed for CFC’s, dissolved Oxygen, Oxygen/Argon, Carbon, nutrients, salinity, and biological content. They are sampled from the bottles in this order, because it is most important to keep the samples for CFC analysis isolated from the atmosphere as much as possible, whereas for biological analysis it is not as essential.  The winch for the CTD is now out of operation for a few hours due to an oil leak.  The weather is absolutely gorgeous so the shorts and t-shirts have come out (in the Southern Ocean?!?) – well it is summer time here!

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