Chapter 13 – Water (Oceans)
- What is the hydrosphere?
The hydrosphere includes all the water on Earth—oceans, seas, rivers, lakes, glaciers, underground water, and atmospheric moisture. Oceans cover about 71% of Earth’s surface and regulate climate. - How much of Earth’s water is in oceans?
About 97.3% of Earth’s water is in oceans and seas. Freshwater makes up only 2.7%, most of which is locked in glaciers and polar ice. - What are the major oceans of the world?
Pacific (largest), Atlantic, Indian, Southern, and Arctic Oceans. The Pacific is the deepest, with the Mariana Trench as its lowest point. - What is salinity?
Salinity is the amount of salt dissolved in seawater, usually expressed in parts per thousand (ppt). Average ocean salinity is about 35 ppt. - What factors affect salinity in oceans?
Evaporation, precipitation, river inflow, ice melting, and ocean currents. High salinity is found in hot, dry regions; low salinity near river mouths and polar areas. - Which sea has the highest salinity?
The Dead Sea and the Red Sea have the highest salinity due to high evaporation, low freshwater inflow, and enclosed geography. - What is the vertical distribution of temperature in oceans?
Surface water is warmest; temperature decreases with depth. There are three layers: surface (mixed layer), thermocline (rapid drop), and deep cold layer. - What is thermocline?
A layer in the ocean where temperature decreases rapidly with depth—typically lies between 300m and 1000m below the surface, separating warm surface from cold deep water. - What factors influence ocean temperature?
Latitude, ocean currents, season, depth, and salinity. Equatorial waters are warmer; polar waters are cold; surface temperatures change more than deeper layers. - What are ocean currents?
Large-scale movements of surface water driven by wind, Earth’s rotation, temperature, salinity differences, and the Coriolis effect. They transfer heat across the globe. - What are warm currents?
Ocean currents originating in equatorial regions and flowing toward the poles. Example: Gulf Stream. They warm coastal areas and influence weather patterns. - What are cold currents?
Currents that flow from polar or sub-polar regions toward the equator. Example: Labrador Current. They lower coastal temperatures and bring nutrient-rich water. - What is the Gulf Stream?
A warm ocean current originating in the Gulf of Mexico, flowing into the North Atlantic. It moderates Western Europe’s climate and supports navigation. - What is upwelling?
An oceanographic process where deep, cold, nutrient-rich water rises to the surface, supporting marine life. Common along the western coasts of continents. - What is downwelling?
It is the sinking of surface water due to cooling or high salinity, pushing oxygen-rich water to deep zones, important for deep-sea life. - How do ocean currents affect climate?
They distribute heat globally, influencing temperature, rainfall, and storm patterns. Warm currents increase coastal rainfall; cold currents reduce it and cause arid climates. - What are tides?
Tides are the periodic rise and fall of sea levels caused by gravitational pull of the Moon and Sun on Earth’s oceans. - What is high tide and low tide?
High tide is when water level rises due to Moon’s pull. Low tide is when water level falls. Typically, two high and two low tides occur daily. - What is spring tide?
It occurs during full and new moons when Sun, Moon, and Earth align. Gravitational forces combine to produce higher high tides and lower low tides. - What is neap tide?
Occurs during first and third quarter moons when Sun and Moon are at right angles. Tidal range is minimal due to opposing forces. - What are ocean waves?
Waves are surface disturbances caused by wind blowing across the water surface. Their size depends on wind speed, duration, and fetch (distance wind travels). - What is tsunami?
A series of large sea waves caused by underwater earthquakes, volcanic eruptions, or landslides. They travel fast and cause destruction upon reaching shores. - What is the importance of oceans?
Oceans regulate climate, absorb CO₂, provide oxygen, food, minerals, transportation, and support biodiversity. They are vital for the Earth’s survival and balance. - What are submarine ridges?
Underwater mountain ranges formed by tectonic activity. The Mid-Atlantic Ridge is the longest, formed at divergent plate boundaries. - What are ocean trenches?
Deep, narrow depressions in the ocean floor, formed at subduction zones where one tectonic plate slides beneath another. Example: Mariana Trench. - What is continental shelf?
The extended margin of a continent submerged under shallow seas. Rich in marine life and resources, it is important for fishing and oil exploration. - What is the continental slope?
A steep slope connecting the continental shelf to the deep ocean floor. It marks the true edge of continental landmass. - What is the abyssal plain?
A flat, deep-sea floor found beyond the continental slope. It’s one of the most extensive and least explored parts of the ocean. - What are oceanic resources?
They include fish, salt, sand, oil, gas, and minerals like manganese nodules. Oceans also support trade and tourism industries. - Why is ocean conservation important?
Oceans face threats from pollution, overfishing, warming, and acidification. Conserving them ensures climate balance, food security, and survival of marine ecosystems.