The Regional Earth System Model RegCM‐ES: Evaluation of the Mediterranean Climate and Marine Biogeochemistry

Abstract

We introduce a new version of the Earth System Regional Climate model RegCM‐ES and evaluate its performances for the first time over the Mediterranean region. The novel aspect of this coupled system is the possibility to simulate the dynamics of the marine ecosystem through a biogeochemical model, BFM (Biogeochemical Flux Model), coupled online with the ocean circulation model MITgcm (MIT general circulation model). The validation of atmosphere and ocean components has shown that the model is able to capture interannual and intermonthly variabilities of the atmospheric heat fluxes and spatial patterns of land surface temperature, precipitation, evaporation, and sea surface temperature with a general improvement compared to previous versions. At the same time, we diagnosed some prominent deficiencies as a warm and dry bias associated in summer with the resolution of the atmospheric module and the tuning of the boundary layer and convective precipitation scheme. On the biogeochemical side, RegCM‐ES shows good skills in reproducing mean values and spatial patterns of net primary production, phosphate, and horizontal/vertical patterns of chlorophyll‐a. Limitations in this case include deficiencies mainly in the simulation of mean values of nitrate and dissolved oxygen in the basin which have been associated with too large vertical mixing throughout the water column, deficiencies in the boundary conditions, and solubility computations. Overall, RegCM‐ES has the potential to become a suitable tool for the analysis of the impacts of climate change on the ocean and marine biogeochemistry in the Mediterranean region and many other domains.

Influence of large-scale atmospheric circulation patterns on nutrient dynamics in the Mediterranean Sea in the extended winter season (October-March) 1961-1999

“…In the case of NO 3 , intense signals are located in the Gulf of Lions, Adriatic Sea, Aegean Sea and Rhodes Gyre. The NO 3 input from rivers in the Northern Adriatic (associated with the Po River inflow) and Aegean Sea (associated with the inflow at the Dardanelles Strait) is particularly remarkable, and is in good agreement with ded- icated regional studies (Solidoro et al 2009, Souvermezoglou et al 2014, Richon et al 2018b, Di Biagio et al 2019, Reale et al 2020).…”

“…Crise et al 1999, Manca et al 2004, Richon et al 2018a,b, 2019, Di Biagio et al 2019, Reale et al 2020. Relative high values of PO 4 are found in the Alboran Sea and Gulf of Lions (Crise et al 1999, Manca et al 2004, Richon et al 2018a,b, Di Biagio et al 2019, Reale et al 2020, while relatively low PO 4 val-ues are found in the Southern Adriatic, Northern Ionian, Aegean Sea and the Rhodes Gyre. In the case of NO 3 , intense signals are located in the Gulf of Lions, Adriatic Sea, Aegean Sea and Rhodes Gyre.…”

“…The latter is a biogeochemical dataset covering the period 1999−2015, built using the offline coupling between OGSTM-BFM and the physical reanalysis MyOcean, both produced and routinely updated within the Copernicus Marine Environmental Marine Service (Simoncelli et al 2019, Teruzzi et al 2019a). It has a horizontal resolution of 1/16° and 72 vertical levels, and has already been used for validating different biogeochemical simulations in the Mediterranean Sea, such as those based on the MEDMIT12-BFM system (Di Biagio et al 2019) and the RegCM-ES system (Reale et al 2020). The use of the CMEMS physical reanalysis and the assimilation of chl a satellite data through the 3DVarBio scheme (see details in Teruzzi et al 2014Teruzzi et al , 2018Teruzzi et al , 2019a impose a constraint in the dataset on the seasonal dynamics of the nutrients, which are driven in the basin by both physical and biogeochemical processes.…”

“…From a biogeochemical point of view, the Mediterranean Sea is considered an oligotrophic basin with low annual primary production (Sournia 1973, Azov 1991, Robarts et al 1996, Moutin & Raimbault 2002, Siokou-Frangou et al 2010, Lazzari et al 2012, Di Biagio et al 2019, Reale et al 2020 and a negative west− east trophic gradient in productivity and nutrient availability, namely nitrate (NO 3 ) and phosphate (PO 4 ) (Crise et al 1999, D'Ortenzio & Ribera d'Alcalà 2009, Lazzari et al 2012, Richon et al 2018a,b, 2019, Di Biagio et al 2019, Reale et al 2020. The cause of this oligotrophy is ascribed to the relative nutrient-depleted Atlantic water entering the Strait of Gibraltar and undergoing a further depletion of nutrients while moving eastwards across the basin.…”

Climatological distribution of dissolved inorganic nutrients in the Western Mediterranean Sea (1981–2017)

“…Nutrient patterns in the Alboran Sea have been associated with the distinct vertical mixing that supplies the surface layer with nutrients (Lazzari et al, 2012;Reale et al, 2020).…”