Hydrosphere
A hydrosphere in physical geography describes the combined mass of water found on, under, and over
the surface of a planet. Water is a chemical substance with the chemical formula H2O, a liquid at
ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state (water
vapor). Water on Earth moves continually through the hydrological cycle of evaporation and
transpiration , condensation, precipitation, and runoff, usually reaching the sea.
The total mass of the Earth's hydrosphere is about 1.4 billion km3. The World Ocean or global ocean is
the interconnected system of the Earth's oceanic (or marine) waters, covering almost 70.8% of the
Earth's surface (an area of some 361 million square kilometers). Oceanography, also called oceanology
or marine science, is the branch of Earth science that studies the ocean.
The World Ocean is divided into a number of principal oceanic areas that are delimited by the
continents and various oceanographic features: these divisions are the Atlantic Ocean, Arctic Ocean,
Indian Ocean, Pacific Ocean, and Southern Ocean (typically reckoned instead as just the southern
portions of the Atlantic, Indian, and Pacific Oceans). In turn, oceanic waters are interspersed by many
smaller seas, gulfs, and bays. The Pacific Ocean is the largest and the deepest of the oceans.
A sea generally refers to a large body of salt water, but it also means a large expanse of saline water
connected with an ocean. In oceanography, a mediterranean sea is a mostly enclosed sea that has
limited exchange of water with outer oceans and it can be either intercontinental or intracontinental.
The term marginal sea indicates a partially enclosed sea, adjacent to or widely open to the open ocean,
but bounded by submarine ridges.
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the
surrounding sea, due to the surrounding land blocking some waves and often reducing winds. A large
bay may be called a gulf. These include the Gulf of Guinea, Persian Gulf, Gulf of Alaska, Gulf of Mexico
and the Bay of Bengal which is the largest bay in the world. Lagoons are expanses of shallow coastal salt
water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks. A
ria is a coastal inlet, a drowned river valley that remains open to the sea.
A strait is a narrow, typically navigable canal of water that connects two larger, navigable bodies of
water. Well-known straits in the world include: Bab el Mandeb, connecting the Red Sea and the Gulf of
Aden, Bering Strait (85 km), between Alaska and Siberia, Strait of Gibraltar (14 km), the only natural
passage between the Atlantic Ocean and the Mediterranean Sea etc.
Sea Water
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It has been traditional to express
salinity not as percent, but as permille (‰), which is approximately grams of salt per kilogram of
solution. Contour lines of constant salinity are called isohales. On average, seawater in the world's
oceans has a salinity of about 35%o. Salinity is an ecological factor of considerable importance,
influencing the types of organisms that live in a body of water.
The Atlantic Ocean (ocean with the highest salinity)
The Red Sea
Temperature
The average temperature of the ocean surface waters is about 17.5 degrees Celsius.
The Pacific Ocean 19.4oC
The Persian Gulf, the Red Sea 36oC
The hydro isotherms – contour lines for equal temperature of water on the map
The ice on the sea surface- (origin: rivers- sea- glaciers (icebergs))
Transparency
Sunlight can penetrate into the ocean, because the ocean is relatively transparent. Transparency of
water is greatly affected by the substances that are in the seawater. For example, a lot of plankton can
reduce the transparency of seawater. To measure the transparency of sea water, the Secchi disk is
lowered into the water from the shaded side of the ship until the disk disappears. The depth reading in
meters when the disk disappears is taken.
The Sargasso Sea – 66.5m