Magnesium

Field studies

Administrative data

Endpoint:

field studies

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: handbook with reliable values

Data source

Reference

Reference Type:

review article or handbook

Title:

The chemical composition of seawater

Author:

J Floor Anthoni

Year:

2006

Bibliographic source:

www.seafriends.org.nz/oceano/seawater.htm

Materials and methods

Test guideline

Qualifier:

no guideline followed

GLP compliance:

not specified

Type of measurement:

concentration of Magnesium ion Mg in seawater

Media:

seawater

Test material

Test material information

Constituent 1

Reference substance name:

Magnesium

EC Number:

231-104-6

EC Name:

Magnesium

Cas Number:

7439-95-4

Molecular formula:

Mg

IUPAC Name:

magnesium

Test material form:

solid: compact

Results and discussion

Any other information on results incl. tables

 

Detailed composition of seawater 
at 3.5% salinity

Element  Hydrogen H2O  Oxygen H2O  Sodium NaCl  Chlorine NaCl  Magnesium Mg  Sulfur S  Potassium K  Calcium Ca  Bromine Br	At.weight    1.00797  15.9994  22.9898  35.453  24.312  32.064  39.102  40.08  79.909	ppm  110,000  883,000    10,800    19,400     1,290         904         392         411           67.3		Element  Molybdenum Mo  Ruthenium Ru  Rhodium Rh  Palladium Pd  Argentum (silver) Ag  Cadmium Cd  Indium In  Stannum (tin) Sn  Antimony Sb	At.weight  0.09594  101.07  102.905  106.4  107.870  112.4  114.82  118.69  121.75	ppm  0.01  0.0000007  .  .  0.00028  0.00011  .  0.00081  0.00033
Helium He  Lithium Li  Beryllium Be  Boron B  Carbon C  Nitrogen ion  Fluorine F  Neon Ne  Aluminium Al  Silicon Si  Phosphorus P  Argon Ar  Scandium Sc  Titanium Ti  Vanadium V  Chromium Cr  Manganese Mn  Ferrum (Iron) Fe  Cobalt Co  Nickel Ni	4.0026  6.939  9.0133  10.811  12.011  14.007  18.998  20.183  26.982  28.086  30.974  39.948  44.956  47.90  50.942  51.996  54.938  55.847  58.933  58.71	0.0000072  0.170  0.0000006  4.450  28.0  15.5  13  0.00012  0.001  2.9  0.088  0.450  <0.000004  0.001  0.0019  0.0002  0.0004  0.0034  0.00039  0.0066		Tellurium Te  Iodine I  Xenon Xe  Cesium Cs  Barium Ba  Lanthanum La  Cerium Ce  Praesodymium Pr  Neodymium Nd  Samarium Sm  Europium Eu  Gadolinium Gd  Terbium Tb  Dysprosium Dy  Holmium Ho  Erbium Er  Thulium Tm  Ytterbium Yb  Lutetium Lu  Hafnium Hf	127.6  166.904  131.30  132.905  137.34  138.91  140.12  140.907  144.24  150.35  151.96  157.25  158.924  162.50  164.930  167.26  168.934  173.04  174.97  178.49	.  0.064  0.000047  0.0003  0.021  0.0000029  0.0000012  0.00000064  0.0000028  0.00000045  0.0000013  0.0000007  0.00000014  0.00000091  0.00000022  0.00000087  0.00000017  0.00000082  0.00000015  <0.000008
Copper Cu  Zinc Zn  Gallium Ga  Germanium Ge  Arsenic As  Selenium Se  Krypton Kr  Rubidium Rb  Strontium Sr  Yttrium Y  Zirconium Zr  Niobium Nb	63.54  65.37  69.72  72.59  74.922  78.96  83.80  85.47  87.62  88.905  91.22  92.906	0.0009  0.005  0.00003  0.00006  0.0026  0.0009  0.00021  0.120  8.1  0.000013  0.000026  0.000015		Tantalum Ta  Tungsten W  Rhenium Re  Osmium Os  Iridium Ir  Platinum Pt  Aurum (gold) Au  Mercury Hg  Thallium Tl  Lead Pb  Bismuth Bi  Thorium Th  Uranium U  Plutonimu Pu	180.948  183.85  186.2  190.2  192.2  195.09  196.967  200.59  204.37  207.19  208.980  232.04  238.03  (244)	<0.0000025  <0.000001  0.0000084  .  .  .  0.000011  0.00015  .  0.00003  0.00002  0.0000004  0.0033  .

Note! ppm= parts per million = mg/litre = 0.001g/kg.

 

Salinity and the main salt ions 

The salinity of sea water (usually 3.5%) is made up by all the dissolved salts shown in the above table. Interestingly, their proportions are always the same, which can be understood if salinity differences are caused by either evaporating fresh water or adding fresh water from rivers. Freezing and thawing also matter.

 

Salinity affects marine organisms because the process of osmosis transports water towards a higher concentration through cell walls. A fish with a cellular salinity of 1.8% will swell in fresh water and dehydrate in salt water. So, saltwater fish drink water copiously while excreting excess salts through their gills. Freshwater fish do the opposite by not drinking but excreting copious amounts of urine while losing little of their body salts.

Marine plants (seaweeds) and many lower organisms have no mechanism to control osmosis, which makes them very sensitive to the salinity of the water in which they live.

The main nutrients for plant growth are nitrogen (N as in nitrate NO3-, nitrite NO2-, ammonia NH4+), phosporus (P as phosphate PO43-) and potassium (K) followed by Sulfur (S), Magnesium (Mg) and Calcium (Ca). Iron (Fe) is an essential component of enzymes and is copiously available in soil, but not in sea water (0.0034ppm). This makes iron an essential nutrient for plankton growth. Plankton organisms (like diatoms) that make shells of silicon compounds furthermore need dissolved silicon salts (SiO2) which at 3ppm can be rather limiting.

 

The main salt ions that make up 99.9% are the following: 
 

chemical ion	valence	concentration  ppm, mg/kg	part of  salinity %	molecular  weight	mmol/  kg
Chloride Cl	-1	19345	55.03	35.453	546
Sodium Na	+1	10752	30.59	22.990	468
Sulfate SO4	-2	2701	7.68	96.062	28.1
Magnesium Mg	+2	1295	3.68	24.305	53.3
Calcium Ca	+2	416	1.18	40.078	10.4
Potassium K	+1	390	1.11	39.098	9.97
Bicarbonate HCO3	-1	145	0.41	61.016	2.34
Bromide Br	-1	66	0.19	79.904	0.83
Borate BO3	-3	27	0.08	58.808	0.46
Strontium Sr	+2	13	0.04	87.620	0.091
Fluoride F	-1	1	0.003	18.998	0.068

 

 

By adding the µmol in last column up, multiplied by respective valences, like: -546 +468 -56.2 +106.6 + .... one ends up with almost 0, suggesting that the above values are about right. During the Challenger Expedition of the 1870s, it was discovered that the ratios between elements is nearly constant although salinity (the amount of H2O) may vary. Note that the figures above differ slightly in differing publications. Also landlocked seas like the Black Sea and the Baltic Sea, have differing concentrations. 
 

 

 

This world map shows how the salinity of the oceans changes slightly from around 32ppt (3.2%) to 40ppt (4.0%). Low salinity is found in cold seas, particularly during the summer season when ice melts. High salinity is found in the ocean 'deserts' in a band coinciding with the continental deserts. Due to cool dry air descending and warming up, these desert zones have very little rainfall, and high evaporation. The Red Sea located in the desert region but almost completely closed, shows the highest salinity of all (40ppt) but the Mediterranean Sea follows as a close second (38ppt). Lowest salinity is found in the upper reaches of the Baltic Sea (0.5%). The Dead Sea is 24% saline, containing mainly magnesium chloride MgCl2. Shallow coastal areas are 2.6-3.0% saline and estuaries 0-3%.

Applicant's summary and conclusion

Conclusions:

Due to magnesium ion's high solubility in water, it is the third most abundant element dissolved in seawater.
The average concentration of Magnesium ion Mg in seawater is 1295 mg/l.