.There is no change in the salinity, temperature and density of ocean, after around the depth of how many metres?
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Answer:
The physical properties of seawater include both 'thermodynamic properties' like density and freezing point, as well as 'transport properties' like the electrical conductivity and viscosity. Density in particular is an important property in ocean science because small spatial changes in density result in spatial variations in pressure at a given depth, which in turn drive the ocean circulation.
Physical properties can be measured directly. However, direct measurements can be complicated to carry out, especially in the field, and in many cases it is more convenient to measure a few important 'state variables' on which the properties depend, and then look up the desired property as a function of the measured state in a table, or calculate it using a mathematical formula. The table or formula that is used is usually derived from careful laboratory measurements. Such a table or formula, when formally defined in a published document and endorsed by a scientific authority, is known as a standard.
Physical properties vary with the amount of heat and the amount of dissolved matter contained in the water, as well as the ambient pressure. Important state variables measured for parcels of water in the ocean are therefore temperature, which is related to the heat content, salinity, which is related to the amount of dissolved matter, and the pressure (Table 1). In addition to controlling physical properties, the variation in space and time of temperature and salinity are also important water mass tracers that can be used to map the ocean circulation. Density is usually calculated using a mathematical function of temperature, salinity, and pressure, sometimes called an equation of state. For many years the internationally accepted standard for seawater densities has been the 1980 International Equation of State, known by the acronym EOS-80. However, a new international standard for seawater density, as well as all other thermodynamic properties, has recently been developed. This new standard is called the Thermodynamic Equation of Seawater (2010), or TEOS-10. In turn, standards like EOS-80 or TEOS-10 rely on other international standards that precisely define the state variables of temperature and salinity. Standards thus play an important role in ocean science.
Variable Ocean Range Ocean Mean Required Accuracy
Temperature -2°C to 40°C 3.5°C ±0.002°C
Absolute Salinity 0 g/kg to 42 g/kg 34.9 g/kg ±0.002 g/kg
Pressure 0 dbar to 11000 dbar 1850 dbar < ±3 dbar
In-situ Density 1000 to 1060 kg/m3 1036 kg/m3 ±0.004 kg/m