Tigris–Euphrates river system through the central plain and combine at Al-Qurnah to form the Shatt al-Arab and discharge into the Persian Gulf. The region has historical importance as part of the Fertile Crescent region, in which civilization is believed to have first emerged. The ecoregion is characterized by two large rivers, the Tigris and Euphrates. The rivers have several small tributaries which feed into the system from shallow freshwater lakes, swamps, and marshes, all surrounded by desert. The hydrology of these vast marshes is extremely important to the ecology of the entire upper Persian Gulf. Historically, the area is known as Mesopotamia. As
Bottom water in temperature and salinity, especially compared to wind-driven surface ocean currents. The bottom water of the Arctic Ocean is more isolated, due to the topography of the Arctic Ocean floor and the surrounding Arctic shelves. Bottom water by an estuary of a river discharging into a saline body exhibits peculiar transport of mud. Due to fresh/saline water intermixing by the estuary, a horizontal isohale gradient is created, with lower salinity levels upstream, which generates the upstream flow of the bottom water. Mud particles carried by river begin settling down as the current and turbulence decrease. When the particles nearly reach