Seawater
The majority of the earth's surface is covered by sea water. Sea water is chemically an aqueous solution, mainly of various salts (salt water). However, natural sea water still contains in addition a variety of other ingredients ( see below).
Salinity
Seawater has an average salt content (salinity ) of 3.5 % by weight. The total salt content varies depending on the sea. The Baltic Sea has a salinity of 0.2 to 2 %. Some inland lakes without outflow have far higher salt in the water,; the Dead Sea is known for its salt content of 28 %.
The average chief objective is for the main volume of the oceans and also for most dependent seas such as the North Sea. 1819 Alexander Marcet discovered that the ratio of the major ions of sea water in all the oceans is exactly the same. This principle of constant proportions applies regardless of the total salt content of the respective sea.
The salt is dissociated in seawater, so split into ions. The latter are only deposited in the evaporation of water to form salts, which are formed according to their solubility and in layers. The major part of the anions is chloride, followed by sulfation. The cations outweighs the sodium ion, and therefore the bulk of the crystallized sea salts consisting of sodium chloride (salt ). Magnesium, calcium and potassium ions are represented with smaller proportions. Traces are still more ions, of which the trace element iodine is worth mentioning because, consequently, in earlier times near the coast and fewer people suffering from iodine deficiency than in Germany.
Salt balance
The freezing point of sea water is at -1.9 ° C with an average salinity of 3.5%. The salts are washed out by rain and melt water from the soil and rock layers of the mainland and registered by rivers into the oceans. Evaporation originally dilute salt solution is further concentrated, and there is salty sea water. This effect would be slow but steady increase the salinity of the oceans, if not at the same time would be withdrawn from the sea salt again. This is done firstly by the drying of oceans, causing the salt is deposited back on the mainland. This salt is found later, eg in salt mines again. Second, the sea water is trapped in the pores of the sediments on the seabed and thus the salt is extracted from the water. The second process is the more important.
Saline lakes
In addition to the accumulation of salt in the oceans, there is an accumulation of salt in all waters with high evaporation and low to the absence of drainage.
Apart from the lakes with extremely high salt content, which are called salt lakes (eg, Dead Sea, Great Salt Lake in Utah, with a salinity above 25 % ), there is this effect in a more moderate form, eg, in the Neusiedler See with a salinity of 0.2%. Salt lakes are usually lakes with a low average water depth. This leads to the following effects: First, the salt content varies depending on the location ( flat spots too salty ) to other temporally ( in the dry season increases the salinity).
The composition of the salt in salt lakes differs in some cases significantly from those in the world's oceans. Especially in low-sulfate waters ( Dead Sea, Don Juan Lake) can accumulate calcium ions, which are found in the oceans only with low concentration. Carbonate-rich lakes have a high pH - value and are referred to as soda lakes.
In addition to the formation of salt lakes by evaporation enrichment, there are also rare cases of direct origination of salt lakes on salt- rich ground, eg Ocna Sibiului ( former salt mining in the open pit ).
More content materials
In addition to the salts in the sea water (as well as in other surface waters ) Carbon dioxide ( CO2), oxygen (O2) and other dissolved atmospheric gases. The ability to store the greenhouse gas CO2 is partly due to the water temperature and is an important factor for the global climate. Dissolved oxygen is the basis for the respiration of aquatic organisms, such as fish, deal with the gas exchange via their gills.
Finally, found in seawater organic compounds from "natural" sources and pollution.
Unfiltered sea water contains suspended fine particles, microorganisms and plankton.
The density of seawater is (again depending on the salt content ) 1020-1030 kg · m- third The pH is slightly alkaline and is 7.5 to 8.4. The increasing concentration of carbon dioxide in the atmosphere, the pH decreases slowly ( " ocean acidification ").
Desalination
With different methods of desalination, the proportion of solutes reduce as far as to obtain potable water. Appropriate facilities are operated in many hot regions of the world. However, all procedures are so expensive that they are used only in tourism regions or prosperous settlements in the operation or construction.