Diapycnal oxygen dynamics in the ventilated surface layer of the North East Black Sea continental slope waters.

Supervisor: Arthur Capet (University of Liège).
Earth-science modelling research techniques are advancing our understanding of the evolving state of seawater, particularly regarding the influence that perturbations transmit between interconnected processes and systems. Internal Waves (IW’s) contribute to the complex composite of physical processes influencing biogeochemical cycles, through transfer of energy states, internal mixing and transport of biogeochemical elements necessitating global cycles. Decomposing the influence IW’s impose on biogeochemical processes, contributing to the oxygen dynamics in seawater bodies, is essential in understanding and combating the declining trend of oxygen content in global oceans and coastal waters (Breitburg et al, 2018). Data analysis was performed on oxygen observations obtained from the northeastern Black Sea continental slope waters, across the oxygen gradient from the ventilated surface layer to the deeper permanently anoxic water masses, between January and March of the 2016 winter period. Water column oxygen conditions were decomposed relative to localised oxygen regimes to ultimately identify anomalous observations pertinent to enveloped processes such as IW’s. The Observational data was then qualified within the state-of-the-art NEMO-BAMHBI 3D biogeochemical open-ocean physics Model, for a finer understanding of mechanistic biogeochemical implications. The northeastern Black Sea Rim Current zone was observed to transmit IW perturbations throughout the oxygenated water column, conveying low to high frequency bands as coastaltrapped Kelvin Waves (~15 day period), Near-Inertial Waves (from ~8 to- ~3 day periods), and the latitudinal locked Inertial period Wave (~17 hr), respectively. Investigation of Black Sea biogeochemical processes through the NEMO-BAMHBI 3D Model validated both the presence and seasonal migration of the primary Kelvin Wave signal (2.149 ms-1), and the maintenance of a biological ‘pump’ exerted along the ventilated layer isopycnals (14 – 15 kg m-3), influencing multiple biogeochemical cycles. The Kelvin Wave importance on the Black Sea basin oxygen budget is defined through modelled increases of ~500 % in Net Primary Production concentrations through a basin-wide cyclonic, vertical displacement of isopycnals, directly respective of coastal regions but with further implications suggested for the greater basin processes.