CONSERVATIVE ELEMENTS
D. W. Dyrssen, Gothenburg University, Go ¨ teborg,
Sweden
Copyright & 2001 Elsevier Ltd.
Introduction
If 1 kg of sea water is evaporated and ignited according to a special procedure 35 g of solids are
obtained. This is the normal (standard) salinity. Since
the salinity is mainly changed by evaporation or by
dilution with practically ion-free rain water the
composition of the major ions in sea water is not
changed by such processes. These constituents are
considered to be conservative, and as a consequence
their ratios are constant. Thus the concentration of
a conservative constituent (element) at a salinity
S is obtained by multiplying the values in Table 1 by
S/35.
Determinations
The salinity can be determined with five significant
figures from conductivity measurements as well as by
potentiometric titration of chloride þ bromide in m
g of sea water with v ml of t molar silver nitrate.
Thereby the chlorinity is given by:
Cl ¼ vt Á 107:87 Á 328:5233=1000m
where 107.87vt/1000 represents the mass in grams of
pure silver that is necessary to precipitate the halogens in 328.5233 g of sea water. The relationship
between salinity and chlorinity is:
S ¼ 1:80655Cl
Sodium cannot be determined with four significant
figures and the value in Table 1 has been calculated
from the ion balance
X
n X
nþ
Â
Ã
¼
X
n X
nÀ
½
Potassium can be determined gravimetrically with a
precision of 0.26% by precipitation with sodium
tetraphenylborate.
Calcium ( þ strontium) and magnesium can be
determined with four significant figures by titration
procedures.
Strontium may be determined with three significant figures by various procedures.
Fluoride can be determined with three significant
figures using a fluoride electrode. Otherwise, the
recommended procedure is a spectrophotometric
determination with lanthanum alizarin complexone.
Sulfate may be determined gravimetrically with a
precision of 0.14% using precipitation of barium
sulfate.
Boric acid, B(OH) 3 , together with borate,
B(OH) 4
À
, may be determined with three significant
figures by the spectrophotometric curcumin method.
Alkalinity is determined by titration with hydrochloric acid of the main basic constituent, HCO 3
À ,
together with minor basic components such as CO 3
2À
,
B(OH) 4
À , SiO(OH) 3
À
, H 2 PO 4
À
, and HPO 4
2À . It can be
determined with four significant figures.
When accurate methods are used for the determinations of the main constituents slight deviations from a conservative behavior may be detected.
The deviations, which are due to some fundamental
processes, will be discussed below.
Plankton Production
Plankton production involves the formation of hard
parts (biogenic calcium carbonate and biogenic opal)
in addition to soft material. The stoichiometry varies
around:
CH 2 O
ð
Þ 106 NH 3
ð
Þ 16 H 3 PO 4 CaCO 3
ð
Þ 20 SiO 2
ð
Þ 20
With this stoichiometry the increase in alkalinity due
to the uptake of nitrate
NO
À
3 þ H
þ þ H 2 O ) NH 3 org
ð Þþ2O 2
is almost balanced by the biogenic formation of
calcium carbonate
Ca
2þ þ HCO
À
3 ) CaCO 3 s
ð Þ þ H
þ
However, when the production sinks below the
euphotic zone the soft parts deteriorate
NH 3 org
ð Þþ2O 2 ) H
þ þ NO
À
3 þ H 2 O
lowering the increase in alkalinity due to the dissolution of calcium carbonate
CaCO 3 s
ð Þ þ CO 2 þ H 2 O ) Ca
2þ þ 2HCO
À
3
13
D. W. Dyrssen, Gothenburg University, Go ¨ teborg,
Sweden
Copyright & 2001 Elsevier Ltd.
Introduction
If 1 kg of sea water is evaporated and ignited according to a special procedure 35 g of solids are
obtained. This is the normal (standard) salinity. Since
the salinity is mainly changed by evaporation or by
dilution with practically ion-free rain water the
composition of the major ions in sea water is not
changed by such processes. These constituents are
considered to be conservative, and as a consequence
their ratios are constant. Thus the concentration of
a conservative constituent (element) at a salinity
S is obtained by multiplying the values in Table 1 by
S/35.
Determinations
The salinity can be determined with five significant
figures from conductivity measurements as well as by
potentiometric titration of chloride þ bromide in m
g of sea water with v ml of t molar silver nitrate.
Thereby the chlorinity is given by:
Cl ¼ vt Á 107:87 Á 328:5233=1000m
where 107.87vt/1000 represents the mass in grams of
pure silver that is necessary to precipitate the halogens in 328.5233 g of sea water. The relationship
between salinity and chlorinity is:
S ¼ 1:80655Cl
Sodium cannot be determined with four significant
figures and the value in Table 1 has been calculated
from the ion balance
X
n X
nþ
Â
Ã
¼
X
n X
nÀ
½
Potassium can be determined gravimetrically with a
precision of 0.26% by precipitation with sodium
tetraphenylborate.
Calcium ( þ strontium) and magnesium can be
determined with four significant figures by titration
procedures.
Strontium may be determined with three significant figures by various procedures.
Fluoride can be determined with three significant
figures using a fluoride electrode. Otherwise, the
recommended procedure is a spectrophotometric
determination with lanthanum alizarin complexone.
Sulfate may be determined gravimetrically with a
precision of 0.14% using precipitation of barium
sulfate.
Boric acid, B(OH) 3 , together with borate,
B(OH) 4
À
, may be determined with three significant
figures by the spectrophotometric curcumin method.
Alkalinity is determined by titration with hydrochloric acid of the main basic constituent, HCO 3
À ,
together with minor basic components such as CO 3
2À
,
B(OH) 4
À , SiO(OH) 3
À
, H 2 PO 4
À
, and HPO 4
2À . It can be
determined with four significant figures.
When accurate methods are used for the determinations of the main constituents slight deviations from a conservative behavior may be detected.
The deviations, which are due to some fundamental
processes, will be discussed below.
Plankton Production
Plankton production involves the formation of hard
parts (biogenic calcium carbonate and biogenic opal)
in addition to soft material. The stoichiometry varies
around:
CH 2 O
ð
Þ 106 NH 3
ð
Þ 16 H 3 PO 4 CaCO 3
ð
Þ 20 SiO 2
ð
Þ 20
With this stoichiometry the increase in alkalinity due
to the uptake of nitrate
NO
À
3 þ H
þ þ H 2 O ) NH 3 org
ð Þþ2O 2
is almost balanced by the biogenic formation of
calcium carbonate
Ca
2þ þ HCO
À
3 ) CaCO 3 s
ð Þ þ H
þ
However, when the production sinks below the
euphotic zone the soft parts deteriorate
NH 3 org
ð Þþ2O 2 ) H
þ þ NO
À
3 þ H 2 O
lowering the increase in alkalinity due to the dissolution of calcium carbonate
CaCO 3 s
ð Þ þ CO 2 þ H 2 O ) Ca
2þ þ 2HCO
À
3
13