S0ME NOTES ON ITS COMPOSITION AND NATURALLY OCCURING
VARIATIONS IN COMPONENTS
Variations in recorded salinities are small. With
the exception of areas such as the Baltic, which is extremely low in dissolved
salt the regions immediately adjacent to melting polar ice, and certain
localities in the Red Sea it rarely exceeds 38
Ã‚Â°/oo and is normally not less
than 33Ã‚Â°/oo. Nine major ions constitute in excess of 99% of these readings.
The salinity value was originally obtained by titration but more modern
estimations are usually made by methods using a range of techniques electrical
conductivity its refractive index, density, or the velocity of transmitted sound
CARBON DIOXIDE CONTENT / pH
If in addition to its salinity and temperature (from which its S. G. or specific gravity , can be calculated) the
pH is known ,then its content of bicarbonate, carbonate, molecular carbon dioxide & total carbon dioxide can be calculated. The total carbon dioxide present
solution varies almost in direct proportion to salinity , when the, salinity is within the range shown above . If 35Ã‚Â°/oo water at 15 deg. C. is brought into equilibrium with the atmosphere it will show a pH of about 8.16,which is increased by the growth of any plants and decreased by the respiration of animals.
THE MAJOR COMPONENTS
As shown in Table 1 the major components vary little. It is
accepted practice to represent these as ratios to chlorinity.
The ratios for the nine major ions are listed below together with any natural variations.
Sodium. Na+ .556+/- .0003 Magnesium Mg++ .0671+/-.0005
Calcium. Ca++ .0210+/-.0005 Potassium.
Strontium. Sr++ .00060+/-.00015 Chlorine as chloride, Cl- Sulphur as sulphate,SO4.1395+/-0005
Bromine as bromide,O033+/-0001
Boron as H3B03 ,00134+/-00005
(Bicarbonate carbonate and CO2 contents are variable.)
The above ratios are all taken from modern analyses. Older figures may differ.
There are very few natural exceptions to the above ratios, and most of these when they occur are extremely localised. Those
that may be of significance to this report are briefly discussed below.
Magnesium: Slightly higher ratios are recorded for the Gulf of Aden and the
eastern Mediterranean, being 0.0681 and 0.O678 respectively.
Calcium: Most records prior to about 1938 have to be recalculated as they include Strontium readings.
Strontium: (See remark on calcium above). Strontium is used by many radiolarians an3 is heavily adsorbed by diatoms and red and green algae.
Boron: Ratios increase in the deep Pacific and may exceed .00162 . It is used by many marine plants and contributes to the basicity.
THE MINOR CONSTITUENTS
The minor ions present in seawater exert an influence far greater
than their concentrations suggest. They represent less than
half of one percent of" the total, most of which is silicate or fluoride and
vary considerably from season to season and area to area. Of the 67 so far identified approximately 24 are either known or
thought to be of some biological importance. Of the remaining 38 little information is available save for the occasional research paper, though it is known that some occur in remarkably stable concentrations in all open ocean
waters. Six of these are included in Table 3 in addition to the eighteen of biological interest listed. Much more research into other microconstituents is needed.
As has already been mentioned the concentrations of some of these traces do vary for a number of reasons and this has to be taken in -to consideration in the
formulae. Most earlier types of synthetic waters were based on minor constituent readings taken from
waters around the coasts of temperate continents and are not accurate for the central areas of larger Water masses these being
in general much lower in nutrients such as phosphate nitrate and
iron than their continental counterparts:
Some microconstituents, notably nitrate, nitrite and ammonia which occur naturally in ocean waters, are probably unnecessary additions to any synthetic formulation unless it is to be used solely for plants and algae. These are formed quite quickly in waters by the metabolic activity of higher animals, and indeed this process can cause dangers in small closed circuit systems. It is notable that open ocean waters and tropical reef waters seem to contain much lower concentrations of many microconstituents than
waters from equivalent temperate zones However, despite the fact records show overall lower concentrations, the ratios of those that have been recorded seem to agree with readings for open ocean water.
It is probable that the ratios of-many minor constituents one to another beers far more overall significance than the individual concentrations and some certainly have a controlling effect when present even in minute quantities. Results have been published - some very recently-on the following relationships.
Phosphate-Iron, Phosphate-Molybdenum, Copper-Zinc, Nitrate-Nitrite, Lithium-Rubidium, Strontium-Calcium, Phosphate-Arsenate, and many
more, a full list of which is not practicable here.
Some of the ratios are of greater importance than others and are
useful in the comparison of waters. It is for this reason that we
have examined the formulae in the report proper with regard to
both concentrations and ratios of importance.
The basicity, pH and carbon dioxide systems of a seawater are rather complex issues, but extremely important ones with regard to synthetic seawaters and
are further discussed later in the text
definition see glossary.