The Development of the Oceanic Mixed Layers and the Processes Governing the Evolution of their Properties in the Red Sea

The importance of understanding the Red Sea (RS) circulation and its response to external forcing variability has become increasingly recognized in recent years. The RS circulation presents a complex behavior and is driven by both strong air-sea buoyancy fluxes and winds. The air-sea exchanges are mediated by the oceanic Mixed Layers (MLs), which constitute the active part of the ocean that interacts with the atmosphere and plays a critical role in the general circulation. The goal of this thesis is to build a deeper understanding of the processes that drive the evolution of the upper layer properties of the Red Sea, focusing on the development of the ML and its spatiotemporal variability. On account of the sparsity of observations, this is primarily achieved using state-of-the-art high resolution regional oceanic simulations, which are extensively validated against the available observations. We first analyze the model results to examine the relative contribution of the different components of the atmospheric forcing (buoyancy fluxes and momentum forcing) to the variability of the upper layer properties and the ML depth (MLD) distribution. Using closed and complete tracer (potential temperature and salinity) budgets, integrated over the MLD, we further investigate the role of internal oceanic processes in the evolution of the RS MLs. Our analysis separately considers the advective fluxes, diapycnal mixing, and entrainment of heat and salt that ultimately define the tracer concentration inside the ML. We further identify anomalous years in terms of their annual MLD and investigate the dependence of the ML development on the interannual accumulation of heat and salt in the water column. In light of recent reports of warming trends in the RS that raise concerns about the response of the RS under an increasingly warming climate, we extend our analysis on longer timescales than the model simulation period, using sea surface temperature (SST) as a proxy of the long-term RS upper layers’ variability. Increased understanding of the processes governing the evolution of the RS will not only serve to improve our knowledge on the basin’s dynamical functioning but also lead to greater understanding of the physical-biological interactions in the RS.