Study of the multi-decadal evolution of the Black Sea hydrodynamics and biogeochemistry using mathematical modelling

• Main Author: Capet, Arthur
• Other Authors: Grégoire, Marilaure, Beckers, Jean-Marie, GHER, Laboratoire d'Océanologie
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: ULiège - Université de Liège 2014
• Subjects: Black Sea; Modelling; Biogeochemistry; Hydrodynamics; Multidecadal variability; Hypoxia; Benthic/Pelagic Coupling; Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; North Atlantic
• Online Access: https://orbi.uliege.be/handle/2268/163502; https://orbi.uliege.be/bitstream/2268/163502/1/CapetPhD.pdf.zip

This thesis addresses the biogeochemical cycles in the Black Sea (BS) during the shifting environmental context that affected the BS during the last decades of the 20th century. The study is based on sophisticated data analysis tools and on the development and implementation of a coupled 3D biogeochemical model on the BS domain. The long term variability of the BS hydrodynamical structure was first examined on the basis of in-situ profiles (1950-2012), satellite imagery (1985-2000) and 3D modelling (1960-2000). Profiles of temperature and salinity were used to derive vertical characteristics of the BS structure: the mixed layer depth and the cold content of the Cold Intermediate Layer. To untangle the spatial and temporal trends from this heterogeneous dataset, a general methodology was proposed and embedded in the data analysis software DIVA. The detrended climatologies and long-term time series provided by this approach were used to assess statistical relationships with local atmospheric conditions. Satellite data (sea surface temperature and altimetry) and model results were then analyzed to relate observable surface dynamics to internal hydrodynamic properties. The main multivariate modes of variability of the BS hydrodynamic structure were highlighted on the basis of Empirical Orthogonal Function analysis. Their temporal evolution was explained by the occurrences of specific atmospheric patterns, identified on the basis of neural algorithm analysis and related to the phases of well known teleconnection systems (i.e. the North Atlantic and East Asia/West Russia oscillations). To study the dynamics of eutrophication in the shallow Black Sea NorthWestern Shelf (BS-NWS), a benthic model component was developed that considers the environmental control on diagenetic processes and the bottom shear stress restriction on organic matter deposition. The model accurately reproduced the seasonal and spatial variability depicted by in-situ estimates of benthic nutrients and oxygen fluxes in the BS-NWS. Outputs were used ...