Regional Ocean Biogeochemical Model to Assess the Influence of Climate Change on the Arabian Gulf and Sea of Oman Waters

Abstract

The effects of climate change on the Arabian Gulf region are already evident and are expected to be amplified due to its specific geographical location, meteorological peculiarities and human induced stresses. Arabian gulf is home to a diverse ecosystem, which is fragile and vulnerable to climate change, especially ocean warming. The Arabian Gulf marine nutrients and primary production have not yet been thoroughly evaluated using a coupled region ocean and biogeochemical model. The objective of this study is to establish a high resolution ocean model MITgcm coupled to DARWIN biogeochemical model to study the Arabian gulf marine biogeochemical properties in a warming climate. In the first study The study examines two scenarios of projected warming in the Gulf, focusing on 2°C and 6°C atmospheric warming. The Gulf is vertically well-mixed in winter, allowing surface temperature increases to be felt through the entire water column. As the region warms, density differences across the Strait of Hormuz decrease, leading to a 30% decrease in volume exchange. The study also explains circulation changes through water mass transformation due to air-sea fluxes. Marine heatwaves are already occurring in the Gulf and are likely to become widespread with continued warming. Our study identifies a 1.8°C anomaly at 40m depth in a southern hot spot, with 2°C warming resembling prolonged MHW conditions. A 6°C rise could have major ecological impacts, warranting further investigation.
The second objective analyzed how MHWs have evolved across the Gulf over the past few decades. The study uses satellite sea surface temperature (SST) and atmospheric reanalysis datasets to analyze variations in MHWs in the region from 2003 to 2024. The spatial patterns of MHW days, duration, count, and intensity are analyzed, finding significant increases in summer season MHW days, duration, and frequency, particularly in the southeastern Gulf and the Sea of Oman. The first empirical orthogonal function mode accounts for 62% of the total variance, with a high negative correlation with wind stress curl in upwelling regions. The onset of MHWs is influenced by decreased cooling fluxes, anomalous high pressure systems, and large-scale atmospheric circulation patterns, as well as the intensification of Kaus winds. The study highlights the growing threat of MHW in marginal seas like the Arabian Gulf, highlighting their link to climate patterns, aiding in predicting future extremes and mitigating their impacts, contributing to global marine ecosystem protection.
In the third objective the local effect of warming due to an anthropogenic activity such as thermal effluent from power plants and industrial activities. These poses risks to the Gulf ecosystem, including coral reef bleaching and species extinction. This study examines the dispersion characteristics and heat flux estimation for thermal effluent from Barakah Nuclear Power Plant (BNPP) along the UAE coast using a three-dimensional unstructured-grid hydrodynamic model. The study identified three major and four minor effluent dispersion plume modes, influenced by tidal currents, wind speed, and ambient air temperature. The vertical dispersion is influenced by seasonal characteristics like convective mixing and stratification. Heat flux analysis reveals that advection and turbulent mixing govern the distribution of excess heat, while momentum balance calculations show the initial discharge momentum is rapidly dissipated by pressure gradients and friction in the near-field zone. Farther from the outlet, plume movement is primarily driven by ambient circulation. The study found that the thermal effluent is of high concern due to its fragile ecosystem and provides valuable insights into the likely impacted regions and time scales of dispersion.
Lastly, this thesis also examined the influence of warming using the coupled bio geochemical MITgcm-DARWIN model on the nutrient dynamics and chlorophyll as well as plankton population the Arabian Gulf. The model accurately predicts future biogeochemical changes in the Arabian Gulf and Sea of Oman, despite minor coastal underestimations. Warming-induced changes in nutrient distribution are more pronounced under the 6°C scenario, with deeper layers showing more complex patterns. Phytoplankton responses to warming vary across seasons, with picocyanobacteria and picoeukaryotes declining under 6°C warming, while diatoms and dinoflagellates exhibit mixed responses. Despite these changes, net primary productivity increases in all seasons except spring, reflecting the ecological impacts of warming on phytoplankton dynamics. Annually, the Gulf basin experiences a 3.6% increase in net primary productivity under 2°C warming and 7.7% under 6°C warming, while the Sea of Oman experiences a slight decrease under 2°C and a 4.2% increase under 6°C. Zooplankton abundance consistently decreases across both basins and warming scenarios. The study emphasizes the significance of high-resolution, region-specific modeling and the urgent need for adaptive strategies to protect marine biodiversity and ecosystem services.

Date of Award	2025
Original language	American English
Supervisor	Maryam Alshehhi (Supervisor)