What is thermocline in the sea

Sea water: a salty mixture

How much salt is there in the sea?

The average salinity of sea water is 3.47% - that's 34.7 g of salt in every kilogram of water. About 78% is accounted for by the compound sodium chloride (NaCl), i.e. pure table salt.

In various marine areas, the salinity differs significantly from the average. Only the South Atlantic and the South Pacific show the statistical mean over a large area. In the Red Sea the value rises to 4.1% due to the high evaporation, in the Gulf of Bothnia in the Baltic Sea it is 1%, in the mouth of large rivers it can decrease to almost 0%.

Which gases are stored in the sea?

The natural constituents of substances include enormous amounts of dissolved gases, in addition to nitrogen (N2) especially carbon dioxide (CO2) and oxygen (O2). They handle the gas exchange between the atmosphere and the hydrosphere, which is important for life on earth.

Oxygen enters the water through the atmosphere and through photosynthesis in marine plants and is consumed again through respiration and decomposition processes. Surface water is oversaturated with oxygen, while there is an oxygen deficit at depth.

Much attention is currently being paid to the role of carbon dioxide, which has a greenhouse effect, because the oceans play an important role in global climate change as carbon dioxide stores. Sea water contains 45 times as much CO2 as occurs in the whole atmosphere. The huge number of marine organisms need the gas to build up body substance.

Where is it warmest?

The warmest water is measured at the surface of the sea. In the tropics, temperatures of up to 30 ° C are reached, in some marginal seas such as the Red Sea or in coastal areas even up to 40 ° C.

In the temperate seas, the surface temperatures are between 10–20 ° C. The warm surface waters of the tropical and temperate seas swim as a thin layer on the oceans. At a depth of 200–1000 m, the temperature drops rapidly everywhere - this is the so-called thermocline. From a depth of around 1000 m, temperatures of around 0–5 ° C are almost constant. Due to the thermocline, the water is very stable and there is hardly any exchange between the light, warm surface water and the heavy, cold deep water.

Where is it coldest?

In the polar regions, because here the water temperature of the upper water layers is always below 10 ° C, even in summer, and mostly between –2 ° C and 5 ° C in winter.

The surface temperatures hardly differ from those of deep water, and a thermocline does not form. Without a stable temperature stratification, the water can also be circulated to great depths, so that the surface regions are always supplied with mineral nutrients from the depths.

At what temperature does sea water freeze?

While fresh water reaches the freezing point at 0 ° C, seawater with an average salinity of 3.47% does not freeze until -1.91 ° ​​C before it has reached its maximum density. With a salt content of 2.47%, the freezing point is -1.35 ° C. So: the higher the salt content, the lower the freezing point.

Are icebergs made from fresh or salt water?

"Real" icebergs swim in the sea, but consist of fresh water and not salt water, as they have broken off either from the Antarctic ice shelf or from Arctic glaciers.

But ice can also form in the sea. When the sea surface cools, the surface water sinks before it can freeze and is replaced by rising, warmer deep water until the freezing point is reached. Seawater can only freeze when the water temperature drops below freezing point, even at greater depths. When freezing, only pure water is solidified into ice. Therefore, the salinity increases in the area. Ice in the oceans forms almost exclusively in the polar regions or in shallow coastal seas of temperate latitudes.

Did you know that …

can almost all chemical elements in seawater be detected, even if only in tiny amounts?

1000 m³ of sea water contain around 6 g of pure gold? The gold reserves in the North Sea alone are around 220,000 t.

the salty taste of sea water comes from table salt and the bitter from the magnesium salts?

a 60 cm thick layer of salt would remain on the entire surface of the earth if all the water evaporated?