WP4 : Quantification of the sources of uncertainty due to scale interactions.

Starting date : T0 + 18 duration : 24 months

Main contributors : Postdoc-LOCEAN, M. Levy, X. Capet

• The purpose of this task is to quantify how the scale that are not resolved in eORCA025 affect nutrient supply and productivity in the Southern Ocean.

• The study will focus on the region of Kerguelen plateau because of the relatively high density of observations in this regions. The region downstream the plateau will here be considered as representative of Southern Ocean bloom regimes downstream ACC obstacles. We will use ZKERG36 model configuration and the simplified iron model of Wadley et al. (2014). We will produce a series of short simulation (5 years) with the reference forcing and the perturbation due to winds. The simulations will be reproduced at several other model grid resolutions (1/2°, 1/4°, 1/12°). The simulations will be used to quantify how small scale dynamics contribute to transporting iron both laterally from the plateau and vertically to the surface layers. A key question is in particular to contrast the role of small scale dynamics versus large scale advection by the ACC or versus seasonal entrainment to the mixed layer. The response of submesoscale dynamics to changes in winds will also be carefully quantified.
  

• The expected outcome is the first quantitative assessment of the role of sub-mesoscale dynamics on Southern Ocean productivity. This study will provide indications of the limitations of ocean components of CMIP6 ESMs in the Southern Ocean. The results will be presented in a dedicated science paper.
  

Starting date : T0 + 18 duration : 18 months

Main contributors : Postdoc-LSCE, J. Orr, XX, M. Gehlen , T. Penduff,

• The purpose of this task is to quantify how «eddy-driven » intrinsic low frequency variability of physical variables affect Southern Ocean biogeochemistry.  

• This study will be carried out on the basis of the material produced in WP2.3. We will mostly focus on the ensemble of references simulations (2 to 5 members). We will first quantify systematically the fraction of the interannual variability of biogeochemical variables that is not driven by the forcing. This will be done using the metrics developed by OCCIPUT project. We will focus in particular on primary production and air sea CO2 fluxes with a specific focus on the impacts at large scale. Then we will study what are the routes for the intrinsic variability of physical variables to imprint Southern Ocean biogeochemistry. We will in particular study how the changes in surface stratification and surface temperature actually drive changes in primary production.

• The expected outcome is the first quantification of the magnitude of « eddy-driven» intrinsic low frequency variability of Southern Ocean biogeochemistry. This will provide error bars for WP3.3 and material for WP5.3. The results will be presented in a dedicated science paper.