A 3d high resolution coupled hydrodynamic-biogeochemical model for the Western Mediterranean Sea. Interannual variability of primary and export production

Resumo

A hydrodynamic model based on the parallelized version (sbPOM) of the Princeton Ocean Model has been configured for the Western Mediterranean Sea with horizontal resolution of 1/20 degree and 52 sigmalayers in the vertical dimension. The model has been nested in oneway offline into an Ocean General Circulation Model for the whole Mediterranean Sea in order to specify the open lateral boundary conditions. The atmospheric forcing is based on the ERAinterim reanalysis data, provided by the European Centre for MediumRange Weather Forecast (ECMWF). A biogeochemical model has been coupled to the hydrodynamic component in order to resolve nonconservative dynamics. The biogeochemical model uses nitrogen as currency and it has a partially described cycle of carbon associated to it. The coupled model has been run in hindcast mode for the 20012008 period and the outputs have been quantitatively and qualitatively validated with remote sensing data for sea surface temperature (SST), chlorophyll, Sea Level Anomaly (SLA) and Primary Production (PP). The validation of results demonstrates that the model is able to reproduce with accuracy the interannual variability of spatial and seasonal patterns of SST, chlorophyll and PP. The simulated Mean Dynamic Topography (MDT) and the geostrophic circulation associated is in agreement with the principal patterns described in the area. The model estimates higher levels of Eddy Kinetic Energy (EKE) with respect to those obtained from remote sensing SLA maps. This is probably due to the high spatial resolution of the model that would be able to resolve mesoscale structures not captured by altimeter data. Simulated PP presents a low mean interannual variability (1.5%; mean=143.8 g C m-2 year -1) while the Export Production (EP) is characterized by higher fluctuations (18.29%; mean=34.13 g C m-2 year -1). Model results suggest that in the northern areas, the variability of the Mixed Layer Depth is the main responsible for the interannual variability of PP and EP. On the other hand, in the southern portion of the area, mesoscale activity and frontal dynamics are responsible for maintaining high levels of PP and EP, reducing the interannual fluctuations linked to seasonal atmospheric dynamics.