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We are finishing the seventh day of the cruise and we are starting to get into the rhythm of the tasks that we must do. This time it is the second cruise of the project for many of the researchers and it shows in the incredible organization that is observed in the lab. Now each person knows their tasks and we all have time to prepare both physically and mentally for the first days of sampling that will arrive in less than 24 hours when we find the center of the eddy, which will determine where we will carry out the first biogeochemical transect.
During the first week of the cruise, it was the turn of the physical oceanographers, who have been following the trajectory of the SeaSoar to observe the data that this equipment was providing. The SeaSoar is a towed vehicle that is equipped with wings that have a propeller and can be rotated to allow the vehicle to undulate on the surface ocean, from approximately 5 to 400 meters deep. During its trajectory, the SeaSoar continuously measures physicochemical variables such as temperature, salinity, oxygen, turbidity and chlorophyll. This allows us to know the structure of the eddy in detail, therefore we can observe to what depth this anticyclonic eddy sinks water (using temperature and salinity data), or where most of the primary production accumulates (using chlorophyll and turbidity data).
Temperature section of a SeaSoar transect crossing the Bentayga eddie
Now that we have a detailed map of the eddy, we are dedicated to finding its center. We can do this by using the ADCP, which is a hydroacoustic current meter, which is used to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column. Therefore, with this equipment we can determine the point where the horizontal current will be zero, which will give us the center of the eddie.
Meanwhile, the biogeochemists have used these days to prepare the entire laboratory and carry out tests on the different equipment that are going to be used. For this reason, halfway through the SeaSoar sampling (in the transect that crossed near the center of the eddie) they began to take water samples from the continuous flow that the ship takes at a depth of 3 meters. For now, there is only good news, and everything works correctly, both the water filtration systems (to later obtain variables such as chlorophyll, DNA or dissolved and particulate organic matter) and the fluorometer (which allows us to measure primary production) or the cytometer (which allows us to study the structure of the planktonic community).
Lucia and Elena sampling water from the ship's continuous intake
We also had time to prepare the incubators where we can simulate the temperature and light conditions at different levels of the water column (hence the blue filters that simulate light attenuation) to study the biological processes carried out by the different phytoplanktonic communities, such as primary production or nitrogen fixation. If you want to know more about primary production, you can read this blog post from last cruise and in a few days we will write one about nitrogen fixation.
Aja and Álvaro cutting the filters to prepare the incubators