Sediment traps, the best part !!! (by Amélie)

Mesocosms are like iceberg, the big part is underwater, the bottom is around 14m of depth and at the bottom of the bag there are the famous sediment traps.

Underwater view of the meso

I am in charged of sediment traps, they need to be changed everyday! It’s the best part of the mission, every afternoon I go with Sylvain to replace the sediment traps (which consiste in a plastic bottle screwed on the sediment particules manifold). We are totally independent, we go under water from the station to the mesocosms using underwater scooter, it’s so cool!!! It’s very fast around 20 minutes to go, change the nine traps and come back.

Sylvain and Amélie leaving the harbor to change the sediment traps

Under water it’s so calm (even when very windy at the surface), everyday we are welcomed by a multitude of curious fish.

We found a lot of swimmers in sediment traps and sometimes jellyfish!

The plastic bottles which are changed every day.

A jellyfish in the sediment trap!!

The sediment traps collection is done to measure the export of organic and inorganic carbon and see if there are differences between treatments.

I would like to sincerely thank Sylvain who come with me everyday and Alex (the Sunday afternoons) as well as Stephen who took a really nice pictures of mesocosms.


Nutrients sampling

The Mediterranean Sea in general, and the Calvi Bay in particular, are very oligotrophic areas. As a result, organisms living in their waters are adapted to low nutrient concentrations, and even small changes in these concentrations can cause big perturbations of natural communities.

Thanks to the mesocosm experiment, we (Sylvie Gobert from University of Liège, and Loïc Michel, from the Stareso research station) will try to understand if ocean acidification could modify nutrient concentrations in Calvi Bay. To do so, we take daily samples to monitor nitrates and nitrites, ammonium, phosphates and silicates concentrations in each of the mesocosms, as well as an “extra” sample out of the mesocosms. We look forward to seeing which trends emerge from the data, and we hope that they can be useful for other scientists taking part of the experiment too…

Once the water is sampled, we have to condition the samples. This is the most critical part of our jobs, because by this time, it is usually around 11 AM. Since labs are quite crowded, we work directly on the Stareso dock, under the burning Corsican sun. During this dangerous task, the only things that prevent us from baking are 1) our beloved straw hats (see fig. 1) and 2) a very good hydration plan based on refreshing Corsican beer. After conditioning, we place the samples in the freezer (for NO2- + NO3-, NH4+ and PO43-) or in the fridge (for SiO44-).

Nutrient conditioners hard at work under the Corsican sun.

Now the experiment is nearly finished, and nearly all samples are stored, patiently awaiting analysis. On Sunday (July 15th), our colleague Renzo Biondo (also from Lab of Oceanology, University of Liège) will join us, and we will start the analysis step. All nutrient concentrations will be determined at Stareso, using our Skalar automated continuous flow automated analyser. Methods differ for each compound, but all are based on colorimetric detection. When everything runs smoothly, this type of analysis is rather quick, and we hope to be done in about a week… However, the analyser is a whimsical machine, and a lot of things can go wrong. To ensure that the Nutrient God is with us, we consider sacrificing one of the station’s cats to him. Let’s hope it will be enough to please him!

Do you think it is too hot? (By Eija)

We “atmospheric people” are working on that! Let me explain.

Ocean is a source of gases and tiny particles which help to make clouds and cool the atmosphere. Isn’t this great news during these super hot days at Stareso?

Bubble bursting aquarium

To be more exact: The goal of the atmospheric experiments here is to understand which type of particles and in which quantities are released into the atmosphere from Mediterranian Sea. We take samples from three mesocosms of different levels of acidification. Then we “bubble” the samples in an aquarium simulating the particle release process by winds and waves over the sea. For this, a bit noisy pump is needed.. When we have the particles in the air inside the aquarium, we study their ability to form clouds (to make the climate less hot). This depends, at most, on the particle chemical composition and size. In addition to this, several types of samples are taken of the aquarium air, in order to analyse the gas and particle phase compositions afterwards in the lab. Quantities and properties of organics are on top of our interest list. Thanks to Alina, we can also sometimes “enrich” our samples with the surface layer – this is important since surface is in direct contact with the atmosphere.

It is amazing how little we still know on the fluxes of particles (and gases which can condense on the particles) from the oceans. And even less on the possible effects of ocean acidification on these fluxes. So this can be really mind blowing science we’re doing (mind blowing not only because of the noise…)! Bear with us for couple of more days…

Ocean Acidification impact on trace elements (by Justine)

The target of the experiment is to study the impact of the acidification on the physical and chemical speciation of the nutrient elements as phosphorus, nitrogen and iron. Since ten days, the typical day at Stareso begins by the sampling inside the nine mesocosmes and outside mesocosms thanks to the cubi platforms. Oooohh the cubi … it’s very funny … and again more with the wind like yesterday and today!! Fortunately, a yoga class have been installed in Stareso (appointment time: 6:00 pm !!) and I’m going to try it !
After sampling, we go to the lab to filter the samples at two different fractions (0.2 µm and 0.015 µm).

Filtration device used in Stareso

After analysis of Dissolved Inorganic Nitrogen (DIN), Dissolved Inorganic Phosphorus (DIP) and Dissolved Iron (DFe) by spectrophotometry at the lab (LOV), in cleaned and controlled conditions, these filtrations will allow us to quantify the nutrient elements on two forms: dissolved (0.015 µm) and colloidal (0.2 µm).

UV irradiation system

With Cecile, we use also the samples filtered at 0.2 µm to determine the organic nitrogen and organic phosphorus. For that, the samples are irradiated by UV during 1h30. We are very impatient to discover the relation between inorganic and organic phosphorus after to have seen the data of alkaline phosphatase of Mauro in the most perturbated mesocosmes (P4-P5-P6).

Other experience: thanks to Alina’s help the microlayer (=thin layer between the ocean and the atmosphere) is taken, and so we have decided to analyze its composition at nutrients on forms inorganic and organic.

Les radeaux de Stareso…

After 5 days of delay, we finally really start the sampling!! To place the events, last week-end the mesocosms tangled in the ropes and water went out of the bags. We had to re-open the bags wait one night close them again and start the acidification step by step during 3 days. The last acidification was on Saturday and to be on time we had to work late the days before (till 11pm sometime!).

The zodiac with the broken board and motor nearly on the seawater!!

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.

The boats we use to go to the working area (=the mesocosms): the kayak; the zodiac and the Mini-Jeanne (and the biggest one is the Marie-Jeanne but we don’t use it).

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.

Winkler Method (by Walter)

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

Phases of the method

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.

Winkler Team

Sampling the Sea Surface Microlayer (by Alina)

While we wait for the mesocosms to be acidified, a Saharan dust plume came across the Mediterranean Sea. Since the sea surface microlayer is heavily affected by atmospheric influences, I took this downtime as an opportunity to get some samples outside the mesocosms in hopes of seeing large differences between the microlayer and the water column below with regard to trace metals.

I have devised a new sampling method to get microlayer samples for trace metals.  The sampler is a quartz tube that is dipped vertically into the water; then slowly raised out of the water vertically. The water that drips off the tube is, in theory, the microlayer and is collected into a funnel that is connected to a receiving bottle.

Cécile and I were joined by Karine and Clémence, who study aerosol formation from surface water bubble bursting, in a small Zodiac out into the Bay (well, Karine swam and Clémence took a kayak).  Once we got to the site right off the coast, Clémence and I switch places and soon I was sitting in the kayak with my bottles and microlayer sampling apparatus.  I have never thought of using a kayak before, but it is actually the easiest thing I’ve used so far (besides standing in a lab sampling from a tank, that was pretty easy)! At first Cécile was going to help hold things on the kayak, but we thought better of it after she hopped onto the kayak and nearly flooded us out of it. So, despite having soaking wet pants and my arm being very tired, sampling was great and I could not have asked for a better team!

Alina sampling for the microlayer trace elements