I found the compostion of seawater to be remarkably constant,
independent of the ocean.
You will find a total of more than 70 elements in seawater, however a
rather small group of only 6 Ions makes up 99 % of all dissolved
"As well as major elements, there are many trace elements in seawater
- e.g., manganese (Mn), lead (Pb), gold (Au), iron (Fe), iodine (I).
Most occur in parts per million (ppm) or parts per billion (ppb)
concentrations. They are important to some biochemical reactions -
both from positive and negative (toxicity) viewpoints."
( http://www.usask.ca/geology/classes/geol206/geol206rr2.html )
a) Inorganic substances
"Seawater is a complex mixture of 96.5 percent water, 2.5 percent
salts, and smaller amounts of other substances, including dissolved
inorganic and organic materials, particulates, and a few atmospheric
The six most abundant ions of seawater are chloride (Cl-), sodium
(Na+), sulfate (SO24-), magnesium (Mg2+), calcium (Ca2+), and
potassium (K+). By weight these ions make up about 99 percent of all
sea salts. The amountof these salts in a volume of seawater varies
because of the addition or removal of water locally (e.g., through
precipitation and evaporation). The salt content in seawater is
indicated by salinity (S), which is defined as the amount of salt in
grams dissolved in one kilogram of seawater and expressed in parts per
thousand. Salinities inthe open ocean have been observed to range from
about 34 to 37 parts per thousand.
Inorganic carbon, bromide, boron, strontium, and fluoride constitute
the other major dissolved substances of seawater. Of the many minor
dissolved chemical constituents, inorganic phosphorus and inorganic
nitrogen are among the most notable, since they are important for the
growth of organisms that inhabit the oceans and seas. Seawater also
contains various dissolved atmospheric gases, chiefly nitrogen,
oxygen, argon, and carbon dioxide."
"Principal Constituents of Seawater*
ionic constituent g/kg of seawater moles/kg** relative
Chloride 19.162 0.5405 1.0000
Sodium 10.679 0.4645 0.8593
Magnesium 1.278 0.0526 0.0974
Sulfate 2.680 0.0279 0.0517
Calcium 0.4096 0.01022 0.0189
Potassium 0.3953 0.01011 0.0187
Carbon (inorganic) 0.0276 0.0023 0.0043
Bromide 0.0663 0.00083 0.00154
Boron 0.0044 0.00041 0.00075
Strontium 0.0079 0.00009 0.000165
Fluoride 0.0013 0.00007 0.000125
*Concentrations at salinity equal to 34.7. **Ionic concentrations are
conventionally expressed in molecular units. One mole per kilogram is equivalent
to 6.023(10^23) ions or molecules per kilogram of seawater. The relative
concentrations in column 4 provide the number of ions of each constituent in one
kilogram of seawater as compared to the number of chloride ions in one kilogram
of seawater. ^ indicates exponentiation. "
( The Encyclopedia Britannica CD ROM Deluce Version 2003 )
b) Organcic substances
Dissolved organic carbon
"Dissolved organic substances
Some other components of seawater are dissolved organic substances,
such as carbohydrates and amino acids, and organic-rich particulates.
These materials originate primarily in the upper 100 m (300 feet) of
the ocean, where dissolved inorganic carbon is photosynthetically
transformed into organic matter."
"Processes involving dissolved and particulate organic carbon are of
central importance in shaping the chemical character of seawater.
Marine organic carbon principally originates in the uppermost 100
metres of the oceans where dissolved inorganic carbon is
photosynthetically converted to organic materials. The "rain" of
organic-rich particulate materials, resulting directly and indirectly
from photosynthetic production, is a principal factor behind the
distributions of many organic and inorganic substances in the oceans.
A large fraction of the vertical flux of materials in the uppermost
waters is converted to dissolved substances within the upper 400
metres ofthe oceans. Dissolved organic carbon (DOC) accounts for at
least 90 percent of the total organic carbon in the oceans. Estimates
of DOC appropriate to the surface of the open ocean range between
roughly 100 and 500 micromoles of carbon per kilogram ofseawater. DOC
concentrations in the deep ocean are 5 to 10 times lower than surface
values. DOC occurs in an extraordinary variety of forms, and, in
general, its compositionis controversial and poorly understood.
Conventional techniques have indicated that, in surface waters, about
15 percent of DOC can be identified as carbohydrates and combined
amino acids. At least 1?2 percent of DOC in surface waters occurs as
lipids and 20?25 percent as relatively unreactive humic substances.
The relative abundances of reactive organic substances, such as amino
acids and carbohydrates, are considerably reduced in deep ocean
waters. Dissolved and particulate organic carbon in the surface ocean
participates in diel cycles (i.e., those of a 24-hour period) related
to photosynthetic production and photochemical transformations. The
influence of dissolved organic matter on ocean chemistry is often out
of proportion to its oceanic abundance. Photochemical reactions
involving DOC can influence the chemistry of vitaltrace nutrients such
as iron, and, even at dissolved concentrations on the order of one
nanomole/kg (1 × 10-9 mole/kg), dissolved organic substances in the
upper ocean waters are capable of greatly altering the bioavailability
of essential trace nutrients, as, for example, copper and zinc."
from the same source as above
A more detailed list inl. thge trace elemnenst mentioned above:
( http://www.seafriends.org.nz/oceano/seawater.htm )
Interesting facts about the composition of seawater
( http://www.njscuba.net/biology/eco_water.html )
Standard seawater composition
( http://www.njscuba.net/biology/eco_water.html )
I hope this solves you problem. If you need further assistance please
post a request for clarification.
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