ENIGME: Interannual Evolution of the Dynamics in the Bay of Biscay and the English Channel

In a context of global change, ocean regions as the Bay of the Biscay and the English Channel represent key domains to estimate the local impact on the coasts of these evolutions. Indeed, the coastal (considering in this project regions above the continental shelf) and regional (including the continental slope and the abyssal plain) environments are sensitive to these long- term evolutions driven by the open ocean, the atmosphere and the watersheds. These evolutions can have impacts on the whole ecosystem. To understand and, by extension, forecast evolutions of these ecosystems, we need to go further in the description and the analysis of the past interannual variability over decadal to pluri-decadal periods. The ENIGME project is organised following three main axes: (a) the interannual evolutions (haline and thermal budgets, currents), (b) the occurrence of intermittent events and the mesoscale dynamics, (c) the sea level in regional models. To illustrate the first results from the ENIGME project, we introduce the study of the interannual variability based on 53-years long simulations. These numerical experiments have been performed using the MARS3D model with a 4 km spatial resolution. In terms of hydrological content, daily results show a broad agreement between temperature/salinity decadal trends and climatology (regional climatology BOBYCLIM). Obtained evolutions have also been compared with the global DRAKKAR simulation (GRD100 configuration, 0.25° spatial resolution). Following this comparison, we can note that the dynamics at regional scale improves our estimation of decadal trends. Further interannual metrics (in temperature and salinity) have been computed to evaluate the improvements related to a high resolution solving of the shelf and regional dynamics. The bathymetry of the Bay of Biscay, including a wide continental shelf, induces different current regimes (i.e. wind driven, tidal, density driven and slope currents). In this framework, we analyse the interannual occurrence of the autumn current over the Armorican shelf as one of the main features of the shelf circulation. This poleward current has been observed using drifters in 2002 and its strong interannual variability has been highlighted. Based on our simulation and after validating this current, it has been described and analysed during the whole period. Beyond these two major hydrodynamical concerns, this numerical experiment is a first step in the analysis of the interannual variability in the Bay of Biscay. Following exploration will target, for example increasing the spatial resolution, to understand this variability and the associated processes.

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Charria Guillaume, Vandermeirsch Frederic, Cailleau Sylvain, Enigme’s Group (2014). ENIGME: Interannual Evolution of the Dynamics in the Bay of Biscay and the English Channel. MyOcean Science Days - Open Science Conference on Operational Oceanography in Europe. 3rd Edition, 22-24 September 2014, Toulouse. https://archimer.ifremer.fr/doc/00242/35285/

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