The coastal ocean is defined as the region extending from the coast (including the nearshore zone) to the offshore regions (including the continental shelf, the continental slope and the deep regions directly interacting with the shallow zones). The coastal zone is an area where major issues are at stake, due to the anthropic pressure it is subject to, the socio-economic activities that develop there, the natural risks to which it is highly exposed (e.g. storms, harmful algal blooms), as well as the impacts linked to climate change. However, this is a particularly complex area in terms of physics and biogeochemistry. The phenomena are transient and therefore difficult to observe. Furthermore, they are characterised by important spatio-temporal variability. The interfaces with the open sea, the continent, the atmosphere and the seabed play a key role. They are places of complex exchanges.
From the point of view of physical oceanography, due to the constraints of this environment (e.g. complex bathymetry), the scales of processes to be explored and understood are spatially smaller (a few metres to a few kilometres) and temporally shorter (processes at frequencies of the order of a second to a few days) compared with the open ocean.
The challenges of the coastal ocean research team therefore lie in understanding the dynamics of these fine scales (through observation or simulation) as well as understanding the role of these processes on related compartments (biogeochemical, biological including halieutic aspects, sedimentary, geophysical).
This thematic positioning opens the team up to work aimed at improving our understanding of coastal processes and to interdisciplinary work in collaboration with other research groups.
The research activities for the Coastal Ocean team are based on 4 scientific themes:
(1) fine-scale dynamics and the coastal environment,
(2) extreme (or rare) events and climate change,
(3) boundary layer dynamics,
(4) involvement in research support infrastructures.
(1) Fine-scale dynamics and the coastal environment
The coastal ocean, at the interfaces with the continent, the seabed, the atmosphere and the open ocean, is an extremely constrained environment (e.g. uneven bathymetry, very short and transient time scales) in which numerous physical processes interact in a complex way at different scales, leading to a specific approach to the coastal domain. In recent years, advances in in situ and satellite observations and in numerical modelling have highlighted the importance of fine-scale processes in the structuring and dynamics of the coastal environment.
Dealing with fine scales in the coastal environment means making progress in understanding various processes linked to frontal dynamics (upwelling and upwelling fronts, river plumes, density fronts), shelf (sub)mesoscale dynamics (eddies, filaments) and the dynamics of internal waves on the continental shelf and slope, whose characteristic scales are smaller than one kilometre and one day.
The Coastal Ocean team will contribute to understanding the dynamics of these fine scales (processes that are poorly identified, characterised and explained, or even theorised) and the role they play in structuring coastal environments: sediment dynamics, the element cycle and the functioning of marine ecosystems. This is one of the major challenges for the team's future research work.
To complete and improve its studies on (sub)mesoscale coastal dynamics, the Coastal Ocean team will continue to develop the tools needed to study these processes. The interpretation and theoretical understanding of fine-scale processes must be accompanied by numerical modelling tools such as CROCO and PISCES. The limits of current models will be explored: at the LOPS scale in collaboration with other teams such as the OSI team and through the transverse physics-biology-ecology axis / at the site scale in collaboration with other laboratories such as LEMAR and DYNECO for biogeochemical issues.
For the observation component, several solutions have been developed or are being developed within the team to observe fine oceanic scales in coastal environments. In situ observation is moving towards high-frequency observation (e.g. low-cost Mastodon-3D), autonomous systems (e.g. AUVs) and integrated systems for monitoring physical, biogeochemical and biological parameters (e.g. plankton communities). In remote sensing, the use of airborne measurements to complement satellites (i.e. development of a microlight dedicated to coastal oceanographic observation) and HF radar will be among the resources deployed to address these issues. In addition to these observation resources, the Coastal Ocean team will remain closely involved in future technological developments that could improve observation of these fine scales.
(2) Extreme (or rare) events and climate change
This is one of the Coastal Ocean team's emerging areas of research, which should be developed and consolidated in the coming years. Its aim is to study long-term changes in extreme events (surges and large waves, strong desalination, marine heat waves / cold spells, hypoxia/anoxia, massive blooms), which are probably the main significant manifestations of climate change likely to affect coastal ocean dynamics. The project is divided into three parts.
The first involves identifying extreme events (how can they be defined? how can they be detected?), characterising their evolution (what are the parameters? what are the changes in terms of occurrence and intensity?) and explaining the mechanisms behind these changes (what is the link with climate indices?). The second part consists of investigating the impact of extreme events on coastal ecosystems: what role do physical processes play in dissolved oxygen levels and harmful algal blooms that impact organisms, and in species mortality? A third component involves assessing how the coastal environment reacts to these extreme events, particularly in terms of resilience. The team is clearly committed to the first two points (projects under the ISBlue, ANR, LEFE-EC2CO and Ifremer labels). The third point is still exploratory, and will be carried out in collaboration with other teams, such as DYNECO and LEMAR.
To answer these questions on the evolution of extremes, the Coastal Ocean team will draw on all available observations, some of which are long-term: in situ observation networks (e.g. COAST-HF, networks in Senegal), satellite data (e.g. altimeters) and seismic data (e.g. detection of storm events). For data analysis, the team will combine traditional statistical methods (theory of extremes, classification) with more advanced data mining methods such as deep learning. These generic transdisciplinary methods can be applied to physical, biological or seismic data. The exploratory part on the methods will be carried out in collaboration with the joint Ifremer/IMT/INRIA Artificial Intelligence research team currently being set up at LOPS. The changes observed in extreme events will be investigated in relation to large-scale atmospheric and oceanic circulation (e.g. North Atlantic Oscillation, North Atlantic Gyres). One of the difficulties will be to separate natural interannual variability from long-term trends in extremes. In the years to come, detailed analysis of historical data could help to predict the evolution of extremes.
(3) Dynamics of boundary layers
Knowledge of the dynamics of surface and bottom boundary layers is essential in coastal areas. Because of the shallow waters, their dynamics generally impact the entire water column. In shallow waters (< 30 m), surface and bottom boundary layers tend to merge. They mix (nutrients, temperature, salinity, oxygen) under the effect of wind, waves, currents, heat flows and internal waves.
The surface boundary layer is the key point of interaction between the atmosphere and the ocean. Waves play an essential role at this interface, and despite years of research, their impact is still the subject of debate within the scientific community. The Coastal Ocean team will continue its work on the impact of waves on air-sea flows, surface layer dynamics and surface fronts. We will also be interested in determining the first-order processes in the surface boundary layer. Finally, the team will continue its studies of the impact of fine atmospheric scales on coastal ocean circulation (coastal wind drop-off, land-sea interface, relaxation of intermittent upwellings).
The bottom boundary layer is where the impact of the bottom on circulation is measured. In this dynamic layer, the exchanges between water and sediment and the impacts on the benthic habitat (e.g. cold corals, benthic fauna) remain little known (lack of observations, complex processes to model). Various problems could be tackled using multi-disciplinary approaches: impact of bathymetry on circulation, water-sediment exchanges in relation to bottom currents. Processes above continental slopes and their canyons will also be studied (e.g. Capbreton/Cassidaigne, Cape Canyon).
(4) Involvement in tools and infrastructures to support research
The Coastal Ocean team has a key position in the strategy for long-term, multi-disciplinary in situ observation of coastal environments at national and European level, as well as locally in the "West Africa" project. It is responsible for the scientific leadership and coordination of several components of national and European observation infrastructures: the COAST-HF National Observation Service within the ILICO Research Infrastructure, and the JERICO-RI European Research Infrastructure.
Over the next few years, the Coastal Ocean team, by mobilising its human resources, will ensure that the team's scientific questions and future observation strategies converge, while contributing to national and European structuring efforts in order to ensure the sustainability of observations and the 'scientific' optimisation of observation networks.
As is the case at regional level with the proposed ObsOcean State-Region Project Contract, which includes an offshore component (ARGO) and a coastal component (ROEC-ILICO), observation structuring and funding strategies will be carried out in collaboration with the laboratory's various teams. On a European scale, the JERICO-RI community will aim to formalise the preparatory phase for the implementation of this infrastructure within the European roadmap (ESFRI) from 2022 onwards, with a view to being operational from 2030, backed up by the 9 national Research Infrastructures that have already been formalised and the political support of the 14 countries involved in the JERICO-DS project (2020-2023). In the team's projects in the South (Senegal, for example), observation infrastructures for coastal areas are being developed and structured (as part of the ECLAIRS International Joint Laboratory and the ANR SOLAB project).
In numerical modelling, the scientific community has also structured itself around various numerical codes, known as community codes, enabling users to explore coastal dynamics on different spatial and temporal scales. The Coastal Ocean team is contributing to the development of these numerical tools, in particular the CROCO codes with PISCES, WAVEWATCHIII and Meso-NH.
In addition to this contribution, the Coastal Ocean team's research work in numerical modelling will make it possible to revisit the modelling of turbulent exchanges in order to take into account fine-scale physics and the dynamics of boundary layers. Approaches such as LES (Large Eddy Simulation), non-hydrostatic modelling or the use of stochastic models (statistical approach to represent unresolved processes - ERC STUOD supported by LOPS/SIAM) will be explored in order to simulate turbulence in coastal environments and the dynamics of oceanic boundary layers. All of this will be carried out with due regard for the limitations imposed by the growing volumes of data generated. The question of coupling (air-sea, coupling with the ecosystem) will also have to be taken into account, as the importance of feedback from other compartments can be very different when processes are approached on finer scales. All of these issues will be addressed in order to propose modelling strategies that are appropriate to the problems that will be studied.
In conjunction with these developments in coastal modelling, the Coastal Ocean team is maintaining the MARC (Modelling and Analysis for Coastal Research) project to display and disseminate the results of LOPS research models (marc.ifremer.fr). The challenge for the project in the coming years will be to upgrade existing configurations (MARS3D) to state-of-the-art configurations (CROCO) in order to benefit from the contributions of the scientific community in terms of modelling.
Geographic regions of interest to the team
The team has a site-based strategy, focusing on the long-term investment of researchers in a limited number of geographical areas. This will enable us to build up the regional expertise that is essential for multi-disciplinary cooperation, carry out targeted scientific monitoring and respond to societal demand. These areas will be the coasts of mainland France (Atlantic, Mediterranean, English Channel), some overseas areas (Caribbean, Saint-Pierre and Miquelon) and the LOPS African areas (Benguela, Senegal). They will be approached according to the four scientific axes. Scientific leadership on measurement strategies, issues and dynamic processes common to the different zones will be encouraged. For example, the regions of Senegal, Benguela, the Bay of Biscay and the Mediterranean will be used to study frontal dynamics and vertical mixing processes.