The substances which are included in the structure of Oceanic water are conditionally divided into five groups: main elements, dissolved gases, biogenic substances, trace elements and organic substances.

Eleven main chemical elements comprise about 99.99% of the whole weight of dissolved substances, or about 47.8 x 10¹⁵tons, thus having the greatest influence on the physical properties of water. The stability of ratios between concentrations of main elements is the most important feature of its chemical structure.

Basically, dissolved gases in the World Ocean are nitrogen, oxygen, carbon dioxide, argon and hydrogen sulphide. The gases are derived from the atmosphere, biochemical processes in different layers of the water, at river mouths and estuaries, from degassing of the mantle into the Earthнs crust and from other geochemical processes. The weight of atmospheric gasses entering the waters of the World Ocean are on the order of 32.4 x 10¹² t. Most chemically and biologically-derived substances dissolved in the World Ocean are oxygen and carbon dioxide.

Biogenic substances, that is, inorganic concentrations of nitrogen, phosphorus and silicon, are consumed by water plants, mainly by phytoplankton. The concentration of biogenic substances is determined by the amount and degree of biological processes, ocean dynamics, and to a lesser degree, by coastal mixing and outpouring of rivers.

Trace elements, of which there are 60, are found in minute quantities in ocean water and comprise only 0.01% of the total sum of elements in the Ocean, or 0.33 x 10¹² t. They have practically no influence on the physical properties of sea water, but play an important role in biochemical processes occurring in the Ocean.

Organic substances are found in dissolved and suspended states in the water column. The greatest concentrations are seen in the surface layer of the Ocean.
 
 

1 - dissolved trace elements

1. Lines of equal temperature (isotherms) in degrees Celsius(ѓC) 2. Average limits of sea ice distribution 3. Cross-sections

1. Isolines of salinity in parts per million (0/00) 2. Average limits of sea ice distribution 3. Cross-section

1. Isolines of oxygen in milligrams/atom per litre of sea water (mg-at O2/l) 2. Mean limit of sea-ice distribution 3. Cross-section

Warmer surface and near-surface layers transmit heat to underlying waters, forming a productive layer. Hydrological, biological and other processes act within it. The thickness of an active layer ranges from 200-400 m. Down to depths of 1,000-1,800 m, the temperature gradually decreases, and below 1800 m, cold waters of almost constant temperature exist.

The salinity of water in the surface layer of the World Ocean depends mainly on evaporation and atmospheric precipitation. In coastal regions, fresh water outflows near the mouths of rivers, and in polar regions, the processes of freezing and thawing of ice greatly influence surface salinity. Below than surface layer, the salinity field is formed as a result of the interaction between the transport of salts by currents and diffusion by the intermixing of waters.

High salinity (>35⁰/₀₀) is encountered in surface waters at tropical latitudes, where evaporation is greater than at other latitudes. The lowest average salinity of oceanic waters (~29⁰/₀₀) is observed in the summer in the Arctic Ocean. In coastal regions with significant river run off, salinity does not exceed 15-20⁰/₀₀. The salinity of deep and near bottom waters in the oceans about 35⁰/₀₀. Salinity and temperature together affect the density of water. Many physical characteristics depend on density distribution, for example, water exchange processes, intermixing and sound transmission.

Oxygen enters the Ocean from the atmosphere and also as a result of photosynthesis in phytoplankton in the upper layers of water. The oxygen content essentially depends on temperature. When temperature decreases, oxygen solubility increases. In deep layers, the oxygen content is mainly determined by processes of intermixing and transport of water masses by currents.

The total amount of dissolved oxygen in the Ocean is ~7.5 x 10¹² t, which is 158 times less than in the atmosphere. Oxygen is expended during respiration by marine organisms and by processes of oxidation. Oxygen saturation of the Ocean surface layers occurs only when the atmospheric oxygen budget is exceeded.
 
 

There are direct and indirect methods to determine the speed of sound in sea water. Direct methods require the help of instrumentation. Indirect measurement are made by calculating the sound speed based upon available temperature, salinity and depth data.

In the 1940s, layers were detected in the Ocean in which sound waves are transmitted over super-long distances in a so-called мunderwater sound channel.о The axis of the channel is at the depth where the speed of sound is at a minimum. The sound is spread with the least transmission power loss and can travel thousands of kilometres in the channel axis. The axial depth of the underwater sound channel may be from 100 m and less in polar latitudes up to 1,500-2,000 m in the Tropics.

USC Axis of USC Upper boundary Lower boundary

Information provided by HDNO:  http://www.oceansatlas.com/unatlas/about/ContactInfoForHDNO.html