All the best to the mesocosm team for a successful sampling and great results!
My last day today and feeling kind of sad that I am going, knowing that I leave work behind for my colleague Anastasia and good friends that I met during my stay. It was a pleasure. Somewhere between the hard work we had our moments…our moments of silliness. We managed even to laugh with our mistakes especially during the tests on how to sample, how to save the boxes when they fall in the water, how not to let go the rope because you start your journey to Genova…Oh we helped…we helped Villefrance team to realize almost anything that could go wrong on the cubi (platform). But as I said we laughed and I use the word kukurukoo for each silly action.
Trying to explain this to our colleagues here was some kind of difficult. Thank fully Raquel helped me a lot. She did the best kukurukoo action of the experiment so far. This is how the story goes:
We were all having dinner as usual, all together with our trays and plates in order. That day was the days that Patricia Ziverri (MedSeA coordinator) had arrived and by coincidence she was sitting near us and she was making polite conversation with all. Out of a sudden, Raquel with her poor English but with a beautiful heart says to Patricia: ‘Hello, I am Raquelle, and you??’ Patricia replies politely: ‘I am Patricia, how are you doing’. Raquel replies: ‘I am well, thank you. Are you working with us???’……at that point we all froze and stared at each other…It was then that Francesca said to Raquel: ‘She is the coordinator’…..And after that awkward moment passed, we started laughing so hard because Raquelle had explained in a really good way what kukurukoo is…….
Will miss you all
Since yesterday the wind weakened in Stareso area but that mean the sun is harder to support! For the early morning sampling it isn’t a problem but for the 8.30am, 10.30am and instruments samplings it’s hard to stay 2hours in the cubis without sun protection. As it became to hard for Vincent and Raquel they’ve decided to bring a sun umbrella on the cubis and here is the new cub is style (click on the picture to see the video made by Louisa during a sampling):
Today we also had to remove all our empty boxes stored outside: an helicopter had to land at the station 15min later! It was spectacular to see the landing and takeoff in a so small area!!
All these experiences made us stronger and ready for the real samplings and subsequent processing of the samples. In my case it meant filtering about 80 liters of water. These because I want to see coccolithophores, marine calcifying phytoplanktonic organisms that are at the base of the food web and particularly sensitive to the changing ocean carbonate chemistry. Coccolithophores produce plates (coccoliths) of calcium carbonate which they use to cover their bodies (single cells).
For these organisms, a decreasing pH of the ocean is expected to affect the production of calcium carbonate by coccolithophores (see Image from Beaufort et al. 2011 article where evidence from sediment samples seem to agree this hypothesis). From each of the nine mesocosms I will be filtering 9 liters of water to later observe the filters under the scanner electron microscope (SEM). I will check whether those coccolithophores living in the more acidic ambient have more malformed, incomplete or thinner coccoliths than those living under normal conditions (in the Mediterranean “normal” means high alkalinity and saturation state for calcite, impeding the dissolution of calcium carbonate). Half of the water will be used to measure Ca in the smaller than 40um fraction (if I manage to get sufficient material). First samples are in the oven!
So, yesterday (Time 0) we had the first departure at 4am to sample the processes. Well, in theory was 4am but…Louisa, Anggeliki and Mauro didn’t wake up!! Hopefully they don’t sleep in the lighthouse so, we could wake them up and we left only 15min late. But the teams on the sampling platforms were efficient and we arrived at the quay at 6.30am which was more or less the time expected for this team. Not even the time for a coffee and we prepared the vials for the incubations and other.
Fred and myself (Laure) we had to fill 8 vials of 60mL per mesocosm, inject “heavy water” (it’s water with 18 oxygen) in 5 of them and fixe the 3 others for the initial values. Then we incubate the 5 vials during the light period, phytoplankton will split this marked water to O2 by photosynthesis. Later in the laboratory we’ll be able to quantify the production of marked O2 and the decrease of marked water and so, have the Gross Primary Production data. The incubations are done near the mesocosms at 6 meter depth (half of a mesocosm).
The day wasn’t finish and we had a last important step to do: the addition of few grams of heavy stable Carbon (Carbon 13) which will allow us to follow the Carbon in the community.
Stop for the “science” and back to the event of the day: le radeau de la méduse. Yesterday, as a big day we had our first problem with the zodiac. While Vincent and Raquel were coming to the mesocosms to run the CTD (instrument to measure many parameters at the same time directly) the board on which the motor is kept broke!! they managed to join the Mini-Jeanne (the boat of the station) but we can’t use the zodiac anymore! We’ll to do a more extensive use of the kayaks to compensate this lost.
The oxygen is a fundamental element for the live in earth. The his amount in air, and in oceanic superficial layer, is 21% in constant balance in gas exchange air-sea.
The Winkler method is a test to determinate the concentration of dissolved oxygen in water samples: the quantity of dissolved oxygen is one of the measures of biological activities in seawater or freshwater. It’s necessary also, for example, to study water masses in the ocean or to measure the redox potential in water column. This test was originally developed by Lajos Winkler, an Hungarian analytical chemist, in 1888, modifying a preceding test. Winkler discovered a safer and more precise method of dissolved oxygen analysis thanks to an iodometric titration.
Carpenter in 1965 modified the Winkler method for analysis of dissolved oxygen, because he found some particularities about accuracy and errors, like air oxidation of iodide and volatilization of iodine, oxygen contributed by the reagent solution, iodate contamination of the iodide solutions, consumption or production of iodine by reagent contaminants, difference between titration end point and the equivalence point.
Principles of analysis
The production and respiration rates of microbial community will be calculate by variation in amount of dissolved oxygen in a defined time and comprehensive of all organisms activities in samples (autotrophs and heterotrophs).
The samples taken from mesocosms, will be fixed with a sequence of MnCl2 and NaI, resulting in a brown precipitate, and will be preserve a part in shadow and a part in light at same sea temperature on 24 h. The difference on amount of dissolved oxygen between T24 and T0 in shadow gives an estimate of planktonic respiration, a biological process of all organisms (in our case planktonic) where it obtains energy from oxidation of reduced organic compounds, realising CO2. Instead, the difference on amount of dissolved oxygen between T24 and T0 in light gives an estimate of planktonic production, a biological process of organisms that produce, by photosynthesis, organic molecules from carbon inorganic, by a reduction reaction, realising O2 (the photosynthetic organisms, primary producers, are at lower trophic level, supporting the total ocean and terrestrial life forming biomass).
After the incubation, it will be necessary proceed with a iodometric titration, because one mole of O2 reacts with four moles of thiosulfate and, by calculation of amount of thiosulphate, it’s possible calculate how many dissolved oxygen is in samples. Here I will try to explain shortly how.
Prior to start the analysis, it’s necessary standardize the titrator with a standard solution of KIO3 (potassium iodate), to minimize the error of the machine and to know the right concentration of the titrant solution. Moreover the sample is acidified with H2SO4 (sulfuric acid) to dissolve the hydroxides precipitated (MnCl2 + NaI) , liberating elementary iodine (I2) that reacts with surplus iodide ions, forming a complex (I3-) that is titrated with sodium thiosulphate. The total reaction is this following:
2S2O32- ↔ I2 ↔ ½ O2
Calculation and expression of results
With the iodometric titration, the titrator by the Tiamo software calculates the amount (equivalent volume) of thiosulphate that is necessary in titration at equivalent point of our samples. The calculation will be done by Excel, in which considering the real volume of bottles (approximately 50-60 ml) and putting the equivalent volume, by a formula it’s possible know the right oxygen amount (μmol/L). Furthermore, calculating the mean and standard deviation, crossing the fingers, we can do some considerations about our results.