The Role of Physical Processes on Oil Pollutants Distribution in the Persian Gulf

Persian Gulf for having the world's major oil and gas fields exposed to contaminants such as oil pollution and the pollutants are associated with them. In this study the distribution of pollution in various conditions is simulated by a hydrodynamic model to determine the behavior of the oil pollutants spill into the sea and the effect of the physical processes such as wind, heat fluxes and wind stress on the distribution of these contaminants. The COHERENS model was used to simulate the oil pollutants distribution which coupled with biological and contaminant modules and has the ability to solve transport equation using sigma coordinate in the vertical direction and Cartesian coordinate in horizontal.
The Persian Gulf ecosystem is facing a variety of stresses due to its location within the richest oil province in the world that hosts more than 67% of the world oil reserve. In recent years, researchers have studied the pollution diffusion in the Persian Gulf using different approaches, but nobody have done a complete work in the Persian Gulf that contain both oil pollution modelling, and the effect of physical processes on it. There is no published research about the effect of wind forces and heat fluxes on oil pollution distribution in the Persian Gulf.
In fact the main idea of this study is to notify the role of wind, heat fluxes and wind stress in oil pollution diffusion which accomplished by set up an Eulerian model, i.e. COHERENS.
COHERENS is a three-dimensional, multi-purpose numerical model for coastal and shelf seas. The hydrodynamic model is coupled with biological, re-suspension and contaminant models, and resolves mesoscale to seasonal processes. The code has been developed over the period 1990 to 1998 by a multinational group as part of the MAST projects. The numerical model calculates in Cartesian coordinates, with the vertical axis representing sigma coordinates, the horizontal axis representing Arakawa C grid.
The model domain includes the Persian Gulf with one open boundary in the Gulf of Oman, covering the area of 47°–58° E; 24°–31°N, five sigma layers are used in the vertical direction. As the input data, the meteorological parameters (wind components at 10 meters above ground, air temperature relative humidity, cloud cover and precipitation) are needed. All these data were derived from the National Oceanic and Atmospheric Administration (NOAA) and applied in the model as monthly mean values.
The model equations are derived with the following assumptions: The Boussinesq approximation is applied which means that the density is constant except for the Earth’s gravity force.
The vertical component of the momentum equations reduces to the hydrostatic balance between the vertical pressure gradient and the gravity force.
The horizontal component of the Earth’s rotation vector is set to zero. The assumption becomes invalid for non-hydrostatic water masses or near the equator.
The equations for the three-dimensional mode consist of the momentum equations, the continuity equation and the equations of temperature and salinity.
The winter winds are predominantly from northwest, along the axis of the Gulf basin. During summer the northwesterly winds of the Gulf are affected by the cooler winds of the southwest monsoon.
Changes in energy stored in the upper ocean are the results of an imbalance between input and output of heat through the sea surface. The heat transfer across or through a surface is called a heat flux.
The wind stress is the shear stress exerted by the wind on the surface of large bodies of water such as oceans or seas—in other words, it is the vertical transfer of horizontal momentum from the atmosphere to the ocean.
Model results show that oil spill in the northern Persian Gulf moves toward the northern Persian Gulf and Bushehr coast along the Iranian coast. Afterwards, due to the counterclockwise currents of that region it moves toward southwest of Gulf along the Arabian coast. The results of simulation indicate that the wind speed and its effect on heat fluxes component is the main reason how the oil pollution is distributed. The results of numerical simulation are in good agreement with what has been observed regarding oil pollution distribution and its circulation patterns in the region.
The influence of forces of wind, heat flux, and wind stress on oil pollution distribution was studied separately. The effect of wind on the distribution of oil pollution is more significant than the heat fluxes and the wind stress. The results of numerical simulation show that the wind stress mainly affects surface diffusion of oil pollution. In summary, the wind speed and its effect on heat flux component are the main factors influencing the distribution of oil pollution.