En route for a scientific station!

For the last few days Tara has been sailing between two routes. Various options are available to us regarding the next few scientific stations. Discussions are underway between Tara and the labs in Villefranche sur mer, Roscoff and Bremen, to determine the optimal program.

Storage space on board Tara can only stretch so far, so each sampling site must be well thought out. And we mustn’t forget that operations carried out during every leg of the journey have to be considered within the global framework of a two and a half year expedition! Studying satellite data is therefore crucial in identifying key sampling sites.

The option of a more northerly route appears to be gaining support.

All was calm this afternoon and the boat was making good progress at eight knots under sail, in a 250° direction. Celine and Vincent went out on deck to carry out a manoeuvre when all of a sudden Loïc’s cry of alarm rang out: "We’re luffing!!" The sails were tacking. The boat was sailing into the wind and veering south.

Later the crew are assembled and, with the help of two satellite maps, Nigel Grimsley, head scientist, explains the situation. The first map shows the distribution of chlorophyll and the second shows surface water temperature.

The colours of the maps speak for themselves: areas that are chlorophyll deficient and therefore nutrient deficient (oligotrophic) appear blue, and richer (mesotrophic) areas appear green. "We want to sample along an imaginary line going from a rich zone to a poor zone." The diversity of these zones and the transition from one to the other is what drives the scientists to study the characteristics of the plankton living there. "Instead of starting a new transect as we had originally planned, we’re now finally going to complete the transect carried out during the previous leg, which is why we’ve changed course," adds Nigel.

Tara had previously travelled through these two different types of environment between Easter Island (Chile) and Guayaquil (Ecuador). However we failed to complete one long station in the middle of that transect which is situated in a particularly interesting region due to the cold current coming from the south which crosses the transect. That point is not too far off-course, so we’re on our way!

We have two more days of sailing before we reach - definitely this time - the specified location for the station. The next few days of the journey afford us a welcome opportunity to sort out all the things we never have time to do when one station follows on so quickly from another.

There’s no room for respite on board a boat, especially one fitted out like Tara. Marc Picheral takes this opportunity to sort out the instruments and equip the bridge with an extra monitor. Thanks to him we will now be able to know the depth of all the instruments in real-time.

Yohann Mucherie checks all the life jackets (or VFIs), then tests the fireman’s uniform on Vincent Le Pennec, our makeshift mannequin. Paradoxically, at sea, fire is one of the most serious risks! Despite all the precautions, a fire can spread quickly, caused by a short circuit or a petrol leak etc...

The team of scientists - Sophie, Johan, Celine, Nigel and Hiro - prepare all their sampling tubes to be used at the next station (100 tubes). They label each receptacle with a bar code which corresponds to a file containing information regarding: depth; size fractions of micro-organisms; and products used to preserve the organisms (ethanol, formalin...). Everything is documented meticulously.

François Noël, chief engineer, is also in charge of a health and safety task: today the desalinator has broken down.

Meanwhile, the three fishing lines hanging off the boat are providing proof that we are not yet in a nutrient poor region... ‘Mahi mahi’ - the Polynesian word for dolphinfish - inhabit these waters in abundance and after our unsuccessful attempts over the last few days, our first catch, like revenge, is sweet. Cries of victory welcome aboard each fish which has succumbed to the small plastic octopus hooked on to the end of our line.

Everyone is keen to offer a recipe - variety is the spice of life - but it has to be Polynesian-themed. Loïc cooks us ‘mahi mahi’ marinated ‘à la’ Tahitian in lemon and coconut milk. The bonito is it served tartare, thanks to Vincent, equally at home at his workbench, as he is at the kitchen worktop. He marinates the sea bream in a jar of vinegar. Naturally Hiro is called upon for sushi...


Sibylle Orgeval

 
Terminology:

Long station: a series of observations and samplings spread over 48 hours in one location. All the instruments (nets, rosette, pump...) are deployed at three depths: the surface; the DCM layer (Deep Chlorophyll Maximum) where photosynthetic organisms are concentrated (the oceans’ equivalent of the canopy); and the mesopelagic layer (between 400m and 800m on this leg).


Transect: a series of observations carried out along a fixed line which cuts through different regions we wish to study.