Water, heat and salt budgets over South East Asia seas : a high resolution modeling approach

South East Asia seas, that include the South China Sea and the Indonesian Seas, transfer the warm and light waters of the surface branch of the global thermohaline circulation between the Pacific and Indian Oceans. To better understand the key contribution of South East Asia seas in the regional and global climate and ocean circulation, it is therefore essential to improve our knowledge of the functioning and variability at different scales of water, heat and salt budgets over this region. The complex topography of this region makes it difficult to study those budgets based on in-situ measurements only. Numerical studies are necessary and relevant to complement and interpret those measurements, however until now, most of numerical studies were performed at low resolution and/or on short periods.

 

To better quantify and understand the contributions of ocean, rivers and atmosphere to the variability at different scales of the water, heat and salt budgets over South East Asia seas, high resolution configurations (< 5 km) of the SYMPHONIE ocean model are developed over the area. State of the art datasets available from COPERNICUS and ECMWF are used to prescribe boundary conditions. Each term of the budgets is computed online in order to obtain rigorously closed budgets.

 

This methodology applied on the 2009-2018 period, that includes strong El Niño and La Niña years as well as neutral years, allows us to better characterize the seasonal to interannual variability of water, salt and heat budgets over the South East Asia seas, by quantifying and explaining the contribution of each factor (lateral fluxes, surface fluxes, rivers, internal variations, ENSO). We examine in particular the surface salinification of the South China Sea that was observed by previous authors between 2012 and 2016 (Zeng et al. 2018, doi:10.1002/2017GL076574) : our simulations suggest that it is mostly related to an increase of net lateral water influx at Luzon strait, itself induced by a deficit of precipitation over the region, rather than to an increase of the salinity of the inflowing water. We finally also explore the role of tides and mesoscale processes. This methodology, our key results and the future steps of this work, that include the on-going development of an ocean-atmosphere regional coupled model, will be synthetically summarized.