EPFL Doctorate Award - 2024 - Seyed Mahmood Hamze-Ziabari

For uncovering, identifying and explaining processes controlling multiscale flow patterns in large, temperate lakes, as well as their implications for mixing and water quality.

Assessments of biological, chemical, and physical processes in large lakes, as well as investigations into the effects of climate change on these processes, primarily rely on single-station monitoring. However, large lake hydrodynamics, which constitute a first-order control on all limnological processes, are inherently three-dimensional (3D). My thesis explores the dynamics of rotating coherent water masses and their associated submesoscale processes in Lake Geneva by integrating field observations, 3D numerical simulations, Lagrangian particle tracking, remote sensing, and statistical analyses. The main objective was to study unobserved 3D physical processes that were previously overlooked by limnologists. Further, based on these processes, the thesis explored the implications of these dynamics for water quality heterogeneity. A novel framework was developed that permits identification of targeted spatiotemporal characteristics of multiscale processes during different seasons, allowing for the efficient design of field sampling strategies with unprecedented precision in time and space. This framework facilitated the identification of submesoscale processes such as filaments and chimney-like upwellings generated by large-scale gyres, a limnological discovery first made in Lake Geneva. Overall, this thesis offers new insights into how (sub)mesoscale processes affect the horizontal and vertical heterogeneity of heat, contaminants, nutrients, and oxygen in large lakes and oceanic contexts.