Studying the impact of ocean dynamics on heat distribution and how this will change with climate change
Anthony Bosse is in charge of WP2 Physical Processes as part of the BioSWOT-Med campaign. He describes the various physical processes that will be studied during the campaign and the different sampling platforms that will be used, with the aim of understanding how ocean dynamics, from the mesoscale (eddies and fronts of 10-50km) to the dissipation scale (turbulence on the scale of millimetres), influence the distribution of heat, its evolution with climate change, and how these processes influence the development of phytoplankton.
Anthony Bosse
RESEARCH THEMES - Anthony Bosse is an oceanographer with a background in physics, which has led him to combine the two disciplines to analyse observations made from research vessels or collected by autonomous platforms. The main aim of his research is to understand how ocean dynamics, from the mesoscale (eddies and fronts of 10-50 km) to the dissipation scale (millimetre-scale turbulence), influence the distribution of heat and its evolution with climate change, as well as the impact that these processes can have on the development of phytoplankton. His research focuses on two regions: the Mediterranean Sea and the Nordic Seas. He is a researcher at the Institut Méditerranéen d'Océanographie in Marseille and is affiliated to the University of Aix-Marseille. During the BioSWOT-Med campaign, he is the leader of WP2 Physical Processes.
As part of the BioSWOT-Med campaign, you are the leader of WP2 on physical processes and you coordinate the work of 8 other people. What are your team's main contributions to the campaign?
The BioSWOT-Med campaign is an ambitious research campaign with a strong multidisciplinary approach to study the physical/biological coupling in the context of the CalVal SWOT. In this context, WP2 dedicated to physical processes will have the important task of describing the different aspects of the physical context that determine the distribution and fluxes of biogeochemical tracers (such as nutrients) and plankton. To do this, a strong team of WP2 researchers will use Lagrangian surface drifters, on-board current meters and on-board temperature and salinity sensors, as well as underwater gliders, to characterise fluxes at a sub-mesh scale (typically 1-10 km) and at high resolution, assess vertical velocities using a vertical velocity profiler and a free-falling current profiler, and finally characterise the level of turbulence using dedicated sensors.
What are you referring to when you say "flow"?
The term "flow" is a generic term in oceanography that refers to water currents with significant velocities (typically 0.1 to 1 m/s). They are similar to oceanic rivers, which transport water with specific physical (temperature and salinity) and biogeochemical (nutrients, oxygen, carbon, etc.) properties. The only difference is that the scale of these rivers is much larger, and the volume transported by a single river is around 10 times greater than that of the Amazon.
What are "vertical speeds"?
Vertical velocities refer to vertical movements in the oceans. They are ubiquitous, but generally much less significant than horizontal movements: of the order of mm/s or even smaller, yet they are essential for maintaining biological activity and sequestering carbon, because vertical velocities move nutrients upwards towards the sunlit layer, where they can be consumed to support primary production, and transport fresh organic matter to the great depths, where it will die and eventually fill the sediment layers with carbon.
What is 'turbulence'?
Energy is injected into the ocean on a large scale by winds, for example, and atmospheric forcing. Once a parcel of water is set in motion, a large amount of energy is transported over great distances while being slowly dissipated. This dissipation involves turbulent movements on a scale of a few millimetres. Turbulence describes the chaotic three-dimensional movements of water on this scale, where kinetic energy is converted into heat by the friction of the water. We (oceanographers) like to calculate the rate of energy dissipation, because it affects the vertical flows of heat or tracers, and ocean circulation as a whole. In other words, turbulence is comparable to the movements created in a cup by a spoon when stirring milk with tea, and the rate of energy dissipation controls the speed at which the homogeneous process occurs.
To study these processes, you will use the instruments on board the R/V L'Atalante, as well as instruments deployed in the water. What instruments will you use to measure these processes?
As already mentioned, we will be using a wide range of instruments. In collaboration with Italian partners (CNR-ISMAR and OGS), we will be deploying Lagrangian drifters, which record their position in real time and drift with the surface currents, as well as subsurface Argo profiling floats, which drift at depth, descending to 2000 m every day and profiling the water column by measuring temperature and salinity. Some of these floats will even be able to measure vertical profiles of nutrients, oxygen and chlorophyll-a fluorescence. From the ship, we will have three instruments on board that will record currents under the hull down to 1000m. We will be towing the MVP (Moving Vessel Profiler) behind the ship during the crossing to obtain high-resolution properties of the water column from the surface down to 400 metres. On the station, we will deploy conventional CTD instruments to measure temperature, salinity and horizontal currents and collect water samples. What is more interesting is the deployment of two new instruments developed at the Mediterranean Institute of Oceanography (MIO) capable of tracking vertical velocities (VVP and FF-ADCP) using two different techniques, as well as a turbulence profiler to quantify its impact on vertical flows (of nutrients, for example).
BioSWOT-Med is an international campaign involving several partners. With your colleagues from Norway and the United States, you will be deploying four gliders. What are gliders and how do they work?
In fact, we will be using several autonomous platforms called 'gliders' during the campaign. These are long-range autonomous underwater vehicles that can stay in the water for several months while profiling from the surface to a certain depth and carrying low-power sensors. They dive and ascend by changing their volume using an oil bladder and are equipped with wings that convert their vertical movement into horizontal translation. During the BioSWOT-Med cruise, we will deploy two gliders piloted by the French MIO team, one glider equipped with a turbulence sensor will be piloted by a Norwegian partner (University of Bergen) and another piloted by an American partner (SCRIPPS) carrying acoustic and optical sensors to observe zooplankton. In addition, Spanish colleagues from SOCIB will also be deploying two gliders in the region as part of another cruise (FastSWOT). It will therefore be difficult to coordinate all these platforms, but it's a very exciting time and the data collected will make it possible to make ground-breaking discoveries.
Contact us: Tosca Ballerini
More information
Anthony Bosse aboard the R/V L'Atalante during the BioSWOT-Med campaign
Deployment of the glider during the BioSWOT-Med campaign