Just on time

It’s been 10 Days since we announced the experiment was stopped few days before what we scheduled. Since this date, all the material have been bring back in land (the last buoys just arrived this afternoon). And it was just on time because the passengers ferry season has started. And when one of this big floating building enter the Bay, this one seems to be very tiny. We experienced at the beginning of the experiment how it is to work on mesocosms with a ferry next to us and didn’t really liked it…

The remaining buoys near one of the first passenger ferry of the season!

The remaining buoys near one of the first passenger ferry of the season!

So, in 10 Days the local team did a huge work of destruction and carrying the material to their place. Like for the instalation it has been a bit challenging as our marine station is in very old buildings with stairs, doors and no lift… Here are some of the pictures of the destruction activity:

The first thing we receive in land are the roofs on which only the plastic cover is removed

The first thing we receive in land are the roofs on which only the plastic cover is removed

Then we have to remove all the rings from the plastic cover...all the material which can be re-used has to be taken!

Then we have to remove all the rings from the plastic cover…all the material which can be re-used has to be taken!

And in between 2 activities Justine and Laure create the new fashion collection of the OOV...

And in between 2 activities Justine and Laure create the new fashion collection of the OOV…

After that the very dirty, smelly, sticky activity can start: remove the plastic of the bags of the pipe structure....In total 3 very unlpeasant days...

After that the very dirty, smelly, sticky activity can start: remove the plastic of the bags of the pipe structure….In total 3 very unlpeasant days…

And don't beleive we had perfect weather condition for this last step: the wind and rain are still here!!

And don’t beleive we had perfect weather condition for this last step: the wind and rain are still here!!

The pontoon full of the drum (upper part): we have to deconstruct one by one after a big cleaning!

The pontoon full of the drum (upper part): we have to deconstruct one by one after a big cleaning!

The start of the stack of  smelly non-reusable plastic bags...

The start of the stack of smelly non-reusable plastic bags…

Dear readers,

Forced by the meteorological conditions that we have faced in the last days, we have to stop the experiment. On March 6th, the wind blew at more than 110 km/h, creating lots of waves in the bay. We have continued the experiment for few more days, but we realized something went wrong when looking at the CTD profiles. Although our mesocosms are well covered with a Teflon roof in order to prevent rain to enter inside the bags, we saw that salinity dropped significantly at surface in all mesocosms after March 7th. Divers from LOV inspected the bags and our fear was justified. All of the bags with no exceptions presented many scratches in the first meters. We have considered (and actually tried) lifting up the bags in order to put these scratches above the sea level, but we had to give up as for some of them the bag was deteriorated way too deep below the sea surface. That is very unfortunate, Villefranche bay is a safe sheltered place for more than 350 days a year, our experiment coincided with very windy conditions from the East, allowing waves and swells to enter inside the bay. All is not dark of course, this could have happened at the start of the experiment and all in all I think we have been lucky collecting more than 2 weeks of data.

Now it’s time for us to start removing the mesocosms from the bay, our partners will move back to their home countries in the coming days and will start analysing the precious samples. We’ll come back for more news at a later stage!

Keep posted
F

Example of salinity profiles acquired since the start of the experiment and showing the continuous intrusion of external waters in the bags after the storm of March 6th.

Example of salinity profiles acquired since the start of the experiment and showing the continuous intrusion of external waters in the bags after the storm of March 6th.

The Winkler method

Background

Oxygen represents about 21% of the air and it naturally dissolves into the ocean through gas exchanges between the water and the atmosphere. The concentration of dissolved oxygen in seawater is an important parameter used by physicist, chemist and biologist in oceanography. It enables to study the water masses, the redox potential of a water column or the biological processes that consume/release oxygen for example.

The Winkler method is a rapid and accurate way to measure dissolved oxygen in water samples. It owes its name to its inventor Lajos Winkler, a Hungarian chemist, who made it up in 1888 while he was still a doctorate student. The method was then improved in 1965 by Carpenter.

Filling 225 BOD right after the 5am sampling ...

Filling 225 BOD right after the 5am sampling …

Winkler equipment

Winkler equipment

Special materials

  • BOD Bottles: glass bottles specially designed to carry out the Winkler test. Our enemies are air bubbles and the special shape of these bottles makes easier the exclusion of these bubbles that will affect the accuracy of the oxygen measurements. All the bottles used have been numbered and calibrated so the exact volume of each BOD is known;
  • Reagent 1: MnCl2 (manganese (II) chloride solution);
  • Reagent 2: NaI, NaOH (sodium iodine basique solution);
  • Reagent 3: H2SO4 (sulphuric acid);
  • Sodium Thiosulfate: NaS2O3;
  • Metrohm titrator;
  • Computer & Tiamo software;
  • Teflon plunger

In theory

The objective is to estimate the production and the respiration of the planktonic community inside the mesocosms. As we study two oxygen-related biological processes, we are going to estimate them measuring oxygen differences after light or dark incubations.

In practice

The sampling of the mesocosms has to be done before the sunrise (5 am ready to leave the harbour)! Back on land, the BOD are filled with the seawater collected and a part of the bottles is directly fixed (means that the dissolved oxygen is trapped) adding reagents 1 & 2. The amount of oxygen measured is the initial concentration (T0), the initial state of the system. The rest of the BOD are incubated in the dark or in the light for 24H. After that time period, these bottles are also fixed and the concentration of oxygen is measured.

The oxygen difference between T0 and T24 light incubations represents the production while the difference between T0 and T24 dark incubations represents the respiration of the community.

Just a bit of chemistry…

From left to right: BOD filled with only seawater; the precipitate resulting from the addition of reagent 1 & 2; before the analysis, when reagent 3 has been added.

From left to right: BOD filled with only seawater; the precipitate resulting from the addition of reagent 1 & 2; before the analysis, when reagent 3 has been added.

The addition of reagents 1 & 2 in the sample (the fixation) traps the oxygen: in the basic environment created by the addition of NaOH, manganic hydroxides are formed resulting in a brown precipitate. The dissolved oxygen oxidize the manganese and convert the Mn(II) hydroxides into Mn(III) hydroxides, so the amount of Mn(III) actually corresponds to the amount of oxygen. This first reaction needs at least 5h to take place. After that, the sample is acidified just before the analysis. In an acid environment, the manganic hydroxides dissolve. The Mn(III) released oxidise the iodide ions (I-) previously added (reagent 2) to iodine (I2). Finally, the iodine is titrated by the thiosulfate (iodine is reduced and thiosulfate oxidised), the orange colour of the sample disappear slowly during the titration. At the end, the equivalent volume of thiosulfate is determined by the titrator and as we know that four moles of thiosulfate react with one mole of oxygen, the amount of oxygen in the sample can be determined. Considering the exact volume of the bottle (the BOD have all been previously calibrated) the oxygen concentration can be computed in µmol/L.

The advantage of getting up at 4:30 am to go sampling…

The advantage of getting up at 4:30 am to go sampling…

Welcome to the cave…. (by Alex)

Welcome to the cave (or wet lab), home to a special group of people known as team SFES (sample, filter, eat & sleep), complete with sterile gloves, wellington boots (rubber boots/sailing boots for the internationals), many bottles of seawater and filtering rigs.

Home to Lisa, Alex, Bruno, Amélie and Federica

Home to Lisa, Alex, Bruno, Amélie and Federica

The day starts off with a refreshing early morning at 5am to…. you’ve guessed it, sample the mesocosms. Next on the agenda is filtering for ~ 8 hours, this sometimes has a bit of a cave disco vibe to it with flashing head torches, questionable music taste and wonderfully poor singing.
As the sun starts to dip we emerge from the cave in search of food and a nice pillow to rest our heads. After a few weeks of eating out in Villefranche, we could probably write a paper on how to confuse the waiter by ordering in 4 languages.
Time for bed and alarm set for 04:15am.

Cave Paintings by Alex, Anastasia and Laure

Cave Paintings by Alex, Anastasia and Laure

All you need is…(2)

The song says ‘All you need is love‘ in mesocosms experiment we’ll say ‘All you need is GLOVES’!! When we are sampling some of the parameters need to be protected from us. That maybe sound strange but we are a source of contamination because of our skin and hairs. To measure some of the nutrients (ammonium, nitrate, nitrite, phosphate, …) as well as metals. So, the best way we could sample would be cover from head to toe and change every day… but not very doable as we have to wear sailing clothes!

To minimize the contamination, we have few things to do. First of all is to wear gloves but also avoid to touch our hair or skin (not very easy when we want to itch or to blow its nose!). The boxes have to be rinsed every day and even on the cubis, the back of the box with the sampler has to be rinsed into seawater before placing the sampler on it…. All a clean process taught by Cécile and Justine the two “clean room’s” scientists.

When Cécile and Justine aren’t dressed with nice sailing clothes they are with white labcoat, ‘charlotte’ to avoid contamination with hairs and overshoes…all this to avoid contamination. Justine, is measuring nano-nutrients which are the elements used by phytoplankton to growth but very easy to contaminate. She already explained her part during the previous experiment.

NB: pictures for this post are coming soon…

Mesocosms by night….

In our experiment, there is a type of people who work by night: it’s the 5am sampling team. We explained you why we have to do it in a previous post.

Here are some of the pictures we took while it wasn’t raining during a dark beautiful night! and there is more pictures in the Gallery.

A mesocosms being sampled by night...even more mysterious what's inside..

A mesocosms being sampled by night…even more mysterious what’s inside..

A night team in action...

A night team (Lisa and Mauro in case you didn’t recognise them😉 ) in action…

But the best it’s always the sunrise. A little sunlight’s moment before we hole up in our laboratories…

The best moment of the day: after 1hour of sampling in the dark (and under the rain most of the time), sunrise! We can admire the sun light effect at the forefront.

The best moment of the day: after 1hour of sampling in the dark (and under the rain most of the time), sunrise! We can admire the sun light effect at the forefront.