University of Leicester
2023AlhassanYPhD.pdf (11.05 MB)
Download file

Study of Oxygen Minimum Zones via Oxygen-Plankton Dynamics: A Mathematical Modelling Approach

Download (11.05 MB)
posted on 2023-06-26, 09:18 authored by Yazeed N. Alhassan

Understanding the dynamics of the dissolved oxygen in the ocean is important for several reasons. Dissolved oxygen is known to be an important characteristic of the marine ecosystem’s health. Also, it is estimated that more than half of the oxygen present in the atmosphere is produced in the oceans due to the photosynthetic activity of phytoplankton. Any decrease in phytoplankton oxygen production is thus likely to have catastrophic consequences not only in marine systems but more globally.

This thesis aims to provide an investigation into possible routes of oxygen depletion where the rate of oxygen production depends on water temperature due to climate change. In Chapter 2, we will show by considering a reaction–diffusion model of oxygen– phytoplankton dynamics that the travelling front can be linked to oxygen minimum zone (OMZ) growth, which generally agrees with observations.

The distribution of oxygen in the ocean is highly heterogeneous, resulting in the formation of oxygen minimum zones in the vertical direction. Factors and processes controlling the dynamics of OMZs have recently been attracting considerable attention. In Chapter 3 , we attempt to address this issue theoretically by developing a novel mathematical model. This model considers the oxygen production by phytoplankton in photosynthesis and its diffusion through the water column.

Depending on the values of model parameters, the oxygen-plankton model can exhibit a variety of dynamical behaviors. In particular, the large population gradient can facilitate the persistence of the oxygen-plankton system, which exhibits irregular spatiotemporal oscillation patterns in their habitat. Such large gradients can be interpreted as ocean front-like shape that are typical in the ocean. As an assisted investigation by means of computer simulations, in Chapter 4, we observe that irregular oscillations emerge when the water temperature parameter is within the instabilities of the Hopf-bifurcation region.



Sergei Petrovskii

Date of award


Author affiliation

School of Computing and Mathematical Sciences

Awarding institution

University of Leicester

Qualification level

  • Doctoral

Qualification name

  • PhD