Jeanne and I have had an intense week of 12 hours and 12 hours off shift
work (and it's continuing). We don't see each other much except for a quick 5 minute handover
and to tell her that most importantly that I've saved her some pancakes
and strawberries! So our job on this cruise is to calibrate instruments. These instruments include the CTD, instruments like microcats which are placed on the mooring buoys. These mooring buoys will be measuring pressure (depth), salinity, temperature, oxygen and many other oceanographic parameters. The most important one on that list for us is the oxygen sensors that are both on the CTD and the moorings. So Jeanne and I conduct oxygen titrations using a Titrino Winkler Titrator (photos of titrator http://sazreed.blogspot.com/2018/06/what-we-got-up-to-on-jr17005-nerc.html ) to measure the dissolved oxygen concentration at different depths (using the grey niskins fired at different depths) and this is then compared against the sensors measurement to see if there is any drift in the sensors over time.
This is the CTD we used to take vertical oceanographic measurements. Here Femke washes down the CTD with fresh water to prevent salt corrosion!
We then use these volume calibrated bottles (as its affected by temperature) and fix the oxygen with this following process, written by Tim and Rich at SAMs:
Manganous
sulphate and alkaline sodium iodide solutions are added to the seawater sample
and the bottle is stoppered and shaken.
A precipitate of manganous hydroxide results (as seen in the photo below). The oxygen dissolved in seawater oxidises
some of the hydroxide to a tetravalent manganese compound. The quantity of this tetravalent manganese is
determined by making the solution acid, at which point the compound oxidises
iodide ions (present in the added alkali) to iodine. The iodine is then determined by titration
with sodium thiosulphate.
So this process after lots of steps which include taking the sample where you can easily add atmospheric oxygen to the sample, or you can add the wrong amount of chemicals, if you forget to shake it all of the dissolved oxygen may not bind to the manganese, if you make up the reagents wrong...anyway you get the gist you have to concentrate when preforming this titration as these measurements are being used to back a lot of peoples science up from each of these moorings and CTDs...to put even more pressure on the oxygen calibrations that were done 2 years ago prior to the deployment of the moorings that we have just recovered failed as the titrator and the chemicals broke down leaving un-calibrated instruments with Jeanne and I as the last hope...terrifying.
However, seen here is a graph showing the CTD data in colour and our oxygen measurements in grey..they're lining up and match woo. That means everything is working well, everyone back at HQ SAMs has been busy plotting the data everyday we send them about 8 CTDs worth...woo! So happy days I can now relax a bit.
Stalking us like the ravens from the lion king.
Working the midnight to midday shifts has meant that I've seen some epic sunrises...good morning world!
Continuing West back toward Iceland!
