Response of shelf waters in the northern Gulf of Oman to the passage of tropical Cyclone Shaheen (2021)

On September 29, 2021, Cyclone Shaheen attained significant development in the Arabian Sea. It proceeded to cross the Gulf of Oman on October 3, causing substantial economic damage and casualties due to the heavy rain and high waves it generated. Using meteorological and satellite data, measuring the physical and chemical properties of the water column by CTD a few days before and after the cyclone, and coastal observations, we analyzed the impact of Cyclone Shaheen on the northern shelf of the Gulf of Oman, Iran. High sea surface temperature in the Arabian Sea favored to strengthen the cyclone toward the Gulf of Oman. Strong winds over 20 m s^-1 caused a dust storm on the Iranian Makran coast followed by heavy rains of 72 mm during a day with extensive flooding. Before the passage of cyclone Shaheen, the surface water temperature in the northern shelf of the Gulf of Oman was about 32°C and the dissolved oxygen concentration was 6 mg l^-1, which reached the hypoxia threshold at a depth of about 60 m. The cyclone intensified the vertical mixing in the upper layer, leading to a decrease in surface water temperature by approximately 2–5 °C. Additionally, it pushed the hypoxia boundary down to a depth of 110 m, thereby causing the oxygenated upper layer to become thicker. The current research demonstrates that the Gulf of Oman stratified waters above the oxygen minimum zone could benefit from the passage of the tropical cyclone during the warm season in terms of temperature, dissolved oxygen, and probably dissolved nutrients.