INTERVIEW. Andrea Doglioli, BioSWOT-Med’s Chief Scientist, explains the objectives of the campaign and how he and his collaborators will try to disentangle the plankton paradox in the Mediterranean Sea by studying fine scales in the ocean. Results from the campaign will provide insights on the physical-biological coupling relevant for most of the global ocean.
THE RESEARCH THEMES – Andrea Doglioli is the Chief Scientist of the BioSWOT-Med campaign and Associate Professor in physical oceanography at Aix-Marseille University. His research at the Mediterranean Institute of Oceanography (MIO) focuses on oceanic circulation and in particular on oceanic eddies, filaments and turbulence, and their impact on the dispersion of nutrients, marine organisms, sediments and pollutants. For his research, Andrea Doglioli deals with both numerical modeling and field measurements at sea, with a preference for Lagrangian methods. SWOT AdAC interviews him about the goals of the BioSWOT-Med cruise.
What are the main research questions of the BioSWOT-Med campaign?
I could summarize by saying that the goal of the BioSWOT-Med campaign is to try to solve the plankton paradox. In ecology there is a principle that says that when there are few resources living organisms fight among themselves to access them and only a few individuals, the most adapted ones, can survive. In reality when we study the microscopic organisms that belong in the marine plankton, we realize that, despite the very low availability of nutrients, there is an enormous biodiversity. This leads to the plankton paradox! We hypothesize that this biodiversity is possible thanks to the continuous mixing of very small movements generated by the currents on the surface of the ocean.For this reason, during the BioSWOT-Med campaign we will measure the vertical nutrient fluxes, the zooplankton grazing on phytoplankton and the horizontal movements separating different plankton communities. We will acquire data that will allow us to study what happens at fine scales.
The ocean region around the Balearic Islands is one of the places where there will be a SWOT crossover. In the past you have already made other oceanographic campaigns in this region. How is this region characterized? Why is it interesting to study physical-biological coupling in this region?
The oceanic region around the Balearic Island is particularly interesting because it is characterized by the presence of different types of surface water, the one recently coming from the Atlantic by the Gibraltar strait and the water resident by several years in the Mediterranean. In the past we have already observed that these different types of water are populated by different plankton communities, separated by ephemeral currents. Seeking to understand the mechanisms underlying these previous observations is the aim of this new campaign. Since oligotrophic (i.e. poor in nutrients) and moderately energetic regions are representative of a very large part of the world ocean, our results may have global significance when extrapolated to the global ocean.
During the campaign you will investigate the ocean processes at the submesoscale. Can you explain what it a submesoscale is?
The term “scale” is used to represent the size in space and the duration in time of a dynamical phenomenon. For example the Gulf Stream is a “large” scale current: it crosses the entire Atlantic Basin and it is permanent; the big vortices generated by the Gulf Stream are called “mesoscale” eddies since they have a radius of about 100 km and can live several months or few years; zooming a little bit more, it is possible to observes also small and ephemeral vortices or current filaments between the rings, these features characterize the oceanic “submesoscale”. Finally, with the term “fine scale” we put together meso and submesoscale.
The BioSWOT-Med campaign will follow an adaptive sampling strategy. What does it mean?
Since the submesoscale features are small and ephemeral, to sample waters inside them you need to use the satellite images of the ocean surface to identify them in your study area. Then, we design the research vessel route to meet them: this is what we call an adaptive sampling strategy.
During the campaign there will be times in which you will let the boat drift at sea with currents. Can you explain how you do so and why?
Yes, this technique is called Lagrangian sampling, from the XVIII century mathematician Joseph-Louis Lagrange, who suggested sampling the ocean currents following their movement and using drifting objects. Then, we will deploy drifting buoys that we can follow thanks to satellite positioning. The interesting thing is that in this way we can obtain a time series of, for example, plankton concentration in a target water mass not affected by the transport of the current itself and then we can focus on the processes affecting their concentration, such as the nutrients fluxes or the zooplankton grazing.
The BioSWOT-Med’s sampling strategy includes taking the same types of measurements three times. Why do you do so?
We will repeat the samplings three times because we need to observe temporal variation, increase the precision of our estimates, and test the reproducibility of our measurement.
Life onboard a research vessel needs to be organized. What will be your daily rhythms and the organization of research activities?
Indeed, to work efficiently during an oceanographic cruise we will need to be well organized! The people in charge of the adaptive and Lagrangian strategy will have daily meetings between them to study the satellite images, the position of the buoys and also with the crew to define the route. During the sampling stations, precise protocols are respected to exploit at best the water sample coming from the ocean depths. Moreover, being BioSWOT a multidisciplinary cruise, we will also organize onboard seminars to share the preliminary results obtained by the specialists of each discipline, as physics, chemistry and biology.
This BioSWOT-Med campaign is a collaboration among different institutions, both in France and internationally. What are they?
Yes, indeed. BioSWOT-Med is an interdisciplinary and international campaign! The researchers that will take part in the BioSWOT-Med cruise are affiliated to Université d’Aix-Marseille, CNRS, Sorbonne Université, Musée National d’Histoire Naturelle (France), CNR and OGS (Italy), Thünen Institute (Germany), University of Arizona (USA) and University of Auckland (New Zealand).
Moreover we collaborate with colleagues from SHOM, CEA, IFREMER, ULCO, Université Gustave Eiffel (France), CSIC (Spain), SZN (Italy), University of Bergen (Norway), UCSD, MBARI, NWRA and University of Washington (USA).
These are more than 50 people involved in BioSWOT-Med. They work for important oceanography laboratories such as MIO, LOCEAN (France), ISMAR (Italy), IMEDEA, SOCIB (Spain), SCRIPPS (USA).
Left: Andrea Doglioli during a class with Masters’ students in oceanography. Right: Gérald Gregori and Andrea Doglioli with a CTD rosette.
Tosca Ballerini (email@example.com)