Hydrosphere — Important Questions

35‰

The average salinity of ocean water is 35‰ (parts per thousand), meaning 35 grams of salt dissolved in 1,000 grams of seawater. This salinity comes mainly from sodium chloride (table salt) washed from land over millions of years. The ‰ symbol indicates parts per thousand, different from percentage (%).

200 meters

The continental shelf extends from the shoreline to a depth of 200 meters. It occupies about 7.6% of the ocean area and is important for fishing, oil drilling, and port construction. Beyond 200m begins the continental slope (200-3000m), then the deep sea plains (3000-6000m), and finally ocean trenches (beyond 6000m).

Mariana Trench

The Mariana Trench (also called Challenger Deep) in the Pacific Ocean is the deepest at 11,022 meters. The Puerto Rico Trench in the Atlantic is 10,475m deep, and Java Trench in the Indian Ocean is 7,450m deep. These trenches are important for understanding plate tectonics and are often located near continents rather than in the middle of oceans.

Ocean depth

Ocean depth itself does not cause ocean currents. Currents are caused by wind effects (friction from wind movement), solar energy (heating causes expansion and water movement), centrifugal force (Earth's rotation), precipitation, and salinity differences. Ocean depth affects where currents flow but doesn't generate them. Understanding these factors helps explain global circulation patterns.