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1 Chemical Equilibrium in Seawater R. M. PYTKOWICZ, E. ATLAS, and C. H. CULBERSON
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School of Oceanography, Oregon State University, Corvallis, Ore. 97331
The concept of chemical equilibrium can be applied to the oceans in three ways; it enters the study of the geochemical control of the oceanic composition, for fast reactions equilibrium constants are used to calculate the concentrations of species present in seawater, and for slow reactions departures from equilibrium are useful for kinetic studies. Seawater differs from the solutions that are usually examined by chemists because of the large number of solutes and, at times, of suspended particles that are present in the oceans. Also, one must consider the concurrent effects of purely chemical, hydrographic, biological, and geological processes upon the composition of seawater. One must consider as well the gravitational field and pressure, temperature, and compositional gradients that result from the extent and depth of the oceans. The study of the equilibrium chemistry of the oceans is facilitated because the major ions are present in almost constant proportions. This makes seawater an ionic medium which can be characterized by one compositional parameter, the chlorinity or the salinity. The constancy of the relative composition is not always present in estuaries because river water, which mixes with seawater, has its major ions in proportions which differ from those in seawater. Still, it will be shown that equilibrium data obtained for seawater can often be applied to estuarine waters. In this work we will first examine briefly the composition of seawater. Then, we will outline some major aspects of equilibria as applied to the oceans. Next, we will consider to what extent these equilibrium considerations are relevant to estuaries and finally, we will examine some topics on the control of the oceanic composition. We will not attempt a compre1
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
2
MARINE CHEMISTRY
h e n s i v e c o v e r a g e of the s u b j e c t but w i l l e m p h a s i z e b a s i c c o n cepts a n d methods. T h e C o m p o s i t i o n of S e a w a t e r A l l the n a t u r a l l y o c c u r r i n g e l e m e n t s a n d m a n y of t h e i r c o m p o u n d s f i n d t h e i r w a y i n t o the o c e a n s t h r o u g h r i v e r s , g r o u n d w a t e r s , a e r i a l t r a n s p o r t , a n d s u b m a r i n e v o l c a n i s m . A few m a j o r c o n s t i t u e n t s , shown i n T a b l e I, a c c o u n t f o r o v e r 90% Y weight o f the s o l u t e s present i n seawater ( 1 ) .
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b
T a b l e I.
M a j o r C o n s t i t u e n t s of S e a w a t e r of 34. 3%o S a l i n i t y (19%o C h l o r i n i t y )
Constituent Cl" Na
so
+
4
2
"
Mg
ppm
Constituent
18,971
Ca
10,555
K
2+
+
2,657
HCO ~
1,268
Br"
Constituent
ppm
403.9
B(OH)
391
Sr
142
F"
2
ppm
25. 6 7.7
+
1. 3
65.9
T h e s e m a j o r constituents a r e p r e s e n t i n a l m o s t constant p r o p o r t i o n s i n the o c e a n s (1_,2) i n d i c a t i n g that the m i x i n g t i m e of the o c e a n s , w h i c h i s of the o r d e r of 1,000
y e a r s , i s fast r e l a t i v e
to the i n p u t r a t e s a n d to the r e a c t i v i t y of the c o n s t i t u e n t s (3.-5). T h e c o n s t a n t r e l a t i v e c o m p o s i t i o n a l s o l e d to the d e f i n i t i o n s of chlorinity and salinity which a r e presented i n standard oceanographic texts,
e. g. , R i l e y a n d C h e s t e r (6).
It i s i m p o r t a n t to
r e a l i z e that the c h l o r i n i t y c a n be u s e d to r e p r e s e n t the extent of m i x i n g of r i v e r w a t e r w i t h s e a w a t e r i n a n e s t u a r y .
The defined
s a l i n i t y l o s e s i t s m e a n i n g , h o w e v e r , w h e n the o c e a n i c p r o p o r tions of the m a j o r i o n s a r e a l t e r e d i n e s t u a r i n e w a t e r s o r i n the p o r e w a t e r s of s u b m a r i n e
sediments.
T h e m i n o r e l e m e n t s v a r y g r e a t l y i n t i m e a n d s p a c e (1_) a n d a r e i n g e n e r a l quite i m p o r t a n t b e c a u s e of t h e i r p a r t i c i p a t i o n i n c h e m i c a l , b i o l o g i c a l , and geological p r o c e s s e s .
These
elements
a r e e x a m i n e d e l s e w h e r e i n this v o l u m e . T h e g e n e r a l g e o c h e m i c a l c o n t r o l of the c h e m i c a l c o m p o s i t i o n of the o c e a n s i n t e r m s of e q u i l i b r i a ,
steady s t a t e s , and
fluxes between n a t u r a l r e s e r v o i r s i s a v i t a l t o p i c .
I t s study
y i e l d s i n s i g h t s i n t o the c h e m i c a l h i s t o r y of s e a w a t e r a n d h e l p s u s u n d e r s t a n d the p o t e n t i a l i m p a c t of m a n - m a d e p e r t u r b a t i o n s
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1.
PYTKOWICZ ET AL.
3
Chemical Equilibrium in Seawater
upon the e n v i r o n m e n t ( 5 , 7 - 1 1 ) .
T h i s s u b j e c t w i l l be e x a m i n e d
b r i e f l y at the e n d of t h i s w o r k , a f t e r a c r i t i c a l r e v i e w of the m a i n r e a c t i o n s w h i c h i n f l u e n c e the l o c a l d i s t r i b u t i o n s of c h e m i cal species i n seawater.
T h e f i r s t t o p i c r e l a t e d to l o c a l e q u i -
l i b r i a w i l l be the d i s s o c i a t i o n of w e a k a c i d s . D i s s o c i a t i o n of W e a k A c i d s T h e d i s s o c i a t i o n c o n s t a n t s of w e a k a c i d s a n d b a s e s c a n be u s e d for the c a l c u l a t i o n of the c o n c e n t r a t i o n s of m o l e c u l e s
and
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i o n s of o c e a n o g r a p h i c i n t e r e s t b e c a u s e the d i s s o c i a t i o n r e a c t i o n s a r e f a s t r e l a t i v e to c o m p e t i n g b i o l o g i c a l a n d g e o l o g i c a l p r o c e s s e s and r e a c h e q u i l i b r i u m .
C a r b o n i c a c i d is an especially
i m p o r t a n t weak e l e c t r o l y t e b e c a u s e of the r o l e s i t p l a y s i n l i f e a n d i n the f o r m a t i o n of l i m e s t o n e s a n d d o l o m i t e s . s e r v e s a s a m o d e l s y s t e m f o r the s t u d y of other w h i c h a r e p r e s e n t i n the
Also,
it
electrolytes
oceans.
T h e u s e of t h e r m o d y n a m i c d i s s o c i a t i o n constants i s not r e c o m m e n d e d for c a r e f u l w o r k in seawater because it r e q u i r e s the e s t i m a t e of the t o t a l a c t i v i t y c o e f f i c i e n t s of s i n g l e i o n s These coefficients are conventional quantities and, their a c c u r a c y i s unknown.
Still,
(12).
therefore,
t h e r m o d y n a m i c constants
may
be a n d a r e often u s e d for f a s t l o w a c c u r a c y e s t i m a t e s b y m a r i n e geochemists
w h e n c o n s t a n t s m e a s u r e d i n a c t u a l s e a w a t e r a r e not
available. B u c h et a l . (13) i n t r o d u c e d to o c e a n o g r a p h y the
so-called
apparent d i s s o c i a t i o n constants m e a s u r e d d i r e c t l y i n seawater. In t h e i r p r e s e n t f o r m , for a g e n e r i c a c i d H A , these a r e defined by
constants
(14) ka (A R
K
=
)
T
(1)
(HA)
P a r e n t h e s e s r e p r e s e n t c o n c e n t r a t i o n s a n d T r e f e r s to t o t a l ( f r e e plus i o n - p a i r e d ) quantities,
apj i s the c o n v e n t i o n a l h y d r o g e n i o n
a c t i v i t y d e f i n e d , for e x a m p l e ,
on the N B S s c a l e ,
k is a constant,
w i t h i n the r e p r o d u c i b i l i t y of p H d a t a , w h i c h i s c a n c e l l e d out between the d e t e r m i n a t i o n a n d the a p p l i c a t i o n of K ' (14).
Thus,
k does not affect the a c c u r a c y w i t h w h i c h ( A " ) ^ » a n d H A c a n be determined.
A p p a r e n t c o n s t a n t s have b e e n shown to be i n v a r i a n t
for m a n y p r o c e s s e s
of o c e a n o g r a p h i c i n t e r e s t
(14).
A n o t h e r d e f i n i t i o n of d i s s o c i a t i o n c o n s t a n t s , f r o m K ' o n l y i n that ( H ) +
T
which differs
i s u s e d i n s t e a d of k a ^ , w a s
proposed
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
4
MARINE CHEMISTRY
b y H a n s son (15).
(H ) +
T
c a n be d e t e r m i n e d e i t h e r w i t h t r i s
b u f f e r s p r e p a r e d i n s e a w a t e r (16) o r w i t h c o n v e n t i o n a l N B S b u f f e r s (17).
W e w i l l r e t u r n to a l t e r n a t e d e f i n i t i o n s of the p H
later. T h e a p p a r e n t d i s s o c i a t i o n c o n s t a n t s a n d the c o n s t a n t s d e f i n e d b y H a n s son f o r c a r b o n i c a c i d a n d f o r b o r i c a c i d w e r e d e t e r m i n e d i n s e a w a t e r at a t m o s p h e r i c p r e s s u r e b y s e v e r a l workers (13,15,18-20).
D i s t e c h e a n d D i s t e c h e (21),
Culberson
et a l . (22), a n d C u l b e r s o n a n d P y t k o w i c z (23) e x t e n d e d the m e a s u r e m e n t s to the h i g h p r e s s u r e s w h i c h a r e e n c o u n t e r e d i n the
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deep o c e a n s .
C u l b e r s o n a n d P y t k o w i c z (23) p r o d u c e d c o r r e c t i o n
t a b l e s f o r the i n c r e a s e i n p H that o c c u r s w h e n deep
seawater
s a m p l e s a r e b r o u g h t to s h i p b o a r d . The carbon dioxide s y s t e m i n seawater
c a n be d e s c r i b e d b y
four e q u a t i o n s i n s i x unknowns once the a p p a r e n t d i s s o c i a t i o n c o n s t a n t s a r e k n o w n a n d the b o r a t e c o n t r i b u t i o n i s s u b t r a c t e d f r o m the a l k a l i n i t y (24).
One c a n , therefore,
completely
specify
the s y s t e m b y m e a n s of a n y two r e l e v a n t m e a s u r e m e n t s . h a s l e d to a p r o l i f e r a t i o n of m e t h o d s , tages a n d d r a w b a c k s .
This
e a c h w i t h i t s own a d v a n -
O n e c a n m e a s u r e the p H a n d the t i t r a t i o n
a l k a l i n i t y w h i c h c a n be o b t a i n e d a c c u r a t e l y b y a s i n g l e a c i d a d d i t i o n (17).
A l t e r n a t i v e l y one c a n d e t e r m i n e the t i t r a t i o n a l k a l i n i t y
a n d the t o t a l C 0 C0
2
2
b y a G r a n t i t r a t i o n (25), the p C 0
gasometrically,
a n d so on.
2
a n d the t o t a l
T h e c h o i c e of a m e t h o d depends
upon the q u a n t i t y of p r i m a r y i n t e r e s t . In s i t u p H p r o b e s ,
s u c h a s those d e v e l o p e d b y M a n h e i m
(26) a n d b y G r a s s h o f f (27), a r e of s p e c i a l i n t e r e s t f o r t i m e series measurements
i n estuaries.
p r o b i n g p o r e w a t e r s of s e d i m e n t s .
T h e y a r e adaptable f o r This eliminates
possible
shifts i n m i n e r a l - s e a w a t e r e q u i l i b r i a that m a y o c c u r w h e n s e d i m e n t s a r e b r o u g h t to d i f f e r e n t t e m p e r a t u r e s a n d p r e s s u r e s i n the laboratory. T h e a p p a r e n t d i s s o c i a t i o n c o n s t a n t s of p h o s p h o r i c a c i d i n seawater,
n e e d e d f o r the s t u d y of the f o r m a t i o n of a p a t i t e s a n d
p h o s p h o r i t e s , w e r e d e t e r m i n e d b y K e s t e r a n d P y t k o w i c z (28). K ' j f o r h y d r o g e n s u l f i d e w a s m e a s u r e d b y G o l d h a b e r (29).
Cul-
b e r s o n et a l . (17) d e t e r m i n e d the d i s s o c i a t i o n c o n s t a n t s of h y d r o f l u o r i c a c i d a n d of b i s u l f a t e i o n s .
C u l b e r s o n a n d P y t k o w i c z (30)
m e a s u r e d the i o n i z a t i o n of w a t e r i n s e a w a t e r . It s h o u l d be e m p h a s i z e d that t o t a l a c t i v i t y c o e f f i c i e n t s a n d , therefore,
apparent constants,
w h i c h a r e r e l a t e d to t h e r m o d y -
n a m i c ones b y these c o e f f i c i e n t s , c o m p o s i t i o n of the m e d i u m .
d e p e n d upon the m a j o r i o n
T h u s , one s h o u l d u s e these q u a n t i -
t i e s w i t h c a r e i n e s t u a r i e s a n d i n the p o r e w a t e r s of s e d i m e n t s
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1.
because
5
Chemical Equilibrium in Seawater
PYTKOWICZ ET AL.
the m a j o r i o n c o m p o s i t i o n of these m e d i a m a y d i f f e r
f r o m that of o c e a n i c
waters.
p H of S e a w a t e r It was m e n t i o n e d e a r l i e r that the N B S buffer s c a l e , a p p l i e d to s e a w a t e r ,
y i e l d s a q u a n t i t y ka^j a n d that k i s
out i n p r a c t i c e , w i t h i n the r e p r o d u c i b i l i t y of p H d a t a .
when
cancelled T h u s , it
i s the r e p r o d u c i b i l i t y r a t h e r than the a c c u r a c y of p H data w h i c h i s r e l e v a n t to o c e a n o g r a p h i c m e a s u r e m e n t s .
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l a b o r a t o r y that c a r e f u l p H m e a s u r e m e n t s
We found i n our
in seawater
are r e p r o -
d u c i b l e to w i t h i n ± 0. 01 p H u n i t s between d i f f e r e n t e l e c t r o d e s
and
that the r e p r o d u c i b i l i t y a p p e a r s to be l i m i t e d b y the l i q u i d j u n c tion p o t e n t i a l s . H a n s son (16) p r o p o s e d a p m H - p s c a l e b a s e d upon b u f f e r s B a t e s a n d M a c a s k i l l (31)
p r e p a r e d i n seawater.
b u f f e r s but d e t e r m i n e d p m H j r i n s t e a d of p m H - p .
also used such (H ),p and +
(H )p +
w h e r e the s u b s c r i p t s F a n d T r e f e r to the f r e e a n d to the t o t a l concentrations,
a r e r e l a t e d by (H ) +
T
T h e N B S , the p m H , T
= (H ) +
F
(17)
+ (HS0 ~) + (HF)
(2)
4
a n d the p m H - p s c a l e s
can be r e l a t e d b y
m e a n s of the data p r e s e n t e d by C u l b e r s o n et a l .
(17).
It i s p o s s i b l e that the u s e of b u f f e r s p r e p a r e d i n m a y r e d u c e the l i q u i d j u n c t i o n p o t e n t i a l a n d , t h e r e f o r e , the r e p r o d u c i b i l i t y of p H data.
seawater, increase
O n the other h a n d , the p r e p a r a -
t i o n of s e a w a t e r b u f f e r s a n d of r e f e r e n c e e l e c t r o d e s b y i n d i v i d u a l investigators may introduce systematic
errors.
W i t h r e g a r d to the g e n e r a l c o n t r o l of the o c e a n i c p H , S i l l e n (7) s u g g e s t e d that c l a y - s e a w a t e r
interactions exert a p r i m a r y
p H - s t a t t i n g r o l e . P y t k o w i c z (5J c o n c l u d e d , h o w e v e r ,
that the
c a r b o n d i o x i d e s y s t e m i s the m a j o r p H b u f f e r i n g agent i n the present
oceans.
S o l u b i l i t i e s of M i n e r a l s The m o s t i n t e n s e l y studied salt i n seawater has been
calci-
u m c a r b o n a t e b e c a u s e of i t s b i o l o g i c a l a n d g e o l o g i c a l i m p o r t a n c e . In a d d i t i o n , w o r k on c a r b o n a t e s h a s y i e l d e d c o n c e p t s a n d t e c h n i q u e s w h i c h a r e a p p l i c a b l e to the i n t e r a c t i o n s of other s a l t s a n d of s o l i d s i n g e n e r a l w i t h Wattenberg
{32)
seawater.
f i r s t d e t e r m i n e d the s o l u b i l i t y of c a l c i t e i n
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
6
MARINE CHEMISTRY
s e a w a t e r at a t m o s p h e r i c p r e s s u r e .
H e u s e d the s t o i c h i o m e t r i c
solubility product
K'
(3)
SP
w h e r e the s u b s c r i p t S r e f e r s to the c o n c e n t r a t i o n at s a t u r a t i o n . T h e u s e of s t o i c h i o m e t r i c s o l u b i l i t y p r o d u c t s o b v i a t e s the n e e d to e s t i m a t e the a c t i v i t y c o e f f i c i e n t s o f s i n g l e i o n s .
These products
r e m a i n e s s e n t i a l l y c o n s t a n t at a g i v e n s a l i n i t y f o r p r o c e s s e s ,
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s u c h a s the d i s s o l u t i o n a n d the p r e c i p i t a t i o n of c a r b o n a t e s i n the o c e a n s , w h i c h h a v e o n l y a s l i g h t effect u p o n the m a j o r i o n c o m p o s i t i o n of s e a w a t e r .
T h e r e h a v e b e e n m a n y m e a s u r e m e n t s of
the s o l u b i l i t y of c a r b o n a t e s i n s e a w a t e r at a t m o s p h e r i c p r e s s u r e s i n c e W a t t e n b e r g (32), the m o s t r e c e n t ones b e i n g those of Mclntire
(33) a n d of Ingle et a l . (34).
P y t k o w i c z a n d c o - w o r k e r s ( 3 5 - 3 9 ) e x t e n d e d the r e s u l t s on c a r b o n a t e s to h i g h p r e s s u r e s b y m e a n s of p o t e n t i o m e t r i c m e a s u r e m e n t s w h i l e B e r n e r (40), M i l l e r o a n d B e r n e r (41), a n d D u e d a l l (42) u s e d the p a r t i a l m o l a l v o l u m e a p p r o a c h . S e v e r a l i n t e r e s t i n g f e a t u r e s e m e r g e d f r o m the study of the s o l u b i l i t y of c a l c i u m c a r b o n a t e i n s e a w a t e r , v a n t to other s o l i d s .
w h i c h m a y be r e l e -
S o m e of these f e a t u r e s a r e ; the m e t a s t a b l e
s u p e r s a t u r a t i o n of n e a r - s u r f a c e w a t e r s ,
the h y s t e r e s i s a n d l a c k
of r e p r o d u c i b i l i t y of s o l u b i l i t y data f o r c a l c i t e , the f a c t o r s that c o n t r o l the c r y s t a l f o r m that p r e c i p i t a t e s f r o m s e a w a t e r a n d the d i a g e n e t i c a l t e r a t i o n of s e d i m e n t s ,
the k i n e t i c b e h a v i o r of c a r -
bonate m a t e r i a l s at d e p t h , the c y c l i n g of c a r b o n a t e s i n n a t u r e , the p H b u f f e r i n g of s e a w a t e r ,
a n d the d i s t r i b u t i o n a n d f l u x e s of
the c a r b o n d i o x i d e s y s t e m i n n a t u r e . T h e m e t a s t a b i l i t y of the c a l c i u m c a r b o n a t e s u p e r s a t u r a t i o n i n n e a r - s u r f a c e w a t e r s r e s u l t s f r o m the i n h i b i t i o n of n u c l e a t i o n a n d g r o w t h b y m a g n e s i u m i o n s , o r g a n i c m a t t e r , a n d phosphate ions (43-46).
T h e r e s u l t s of P y t k o w i c z (43_,45) s h o w e d that the
i n o r g a n i c p r e c i p i t a t i o n of c a r b o n a t e s i n the o c e a n s c a n o n l y o c c u r i n a few s p e c i a l e n v i r o n m e n t s a n d that the r e m o v a l of c a r b o n a t e s f r o m seawater i s p r i m a r i l y biogenic. W e y l (47) o b s e r v e d that the s o l u b i l i t y of c a l c i t e i n s e a w a t e r u n d e r g o e s h y s t e r e s i s - t y p e effects w h i c h w e r e not o b s e r v e d to a n y s i g n i f i c a n t extent f o r a r a g o n i t e .
H e a t t r i b u t e d h i s r e s u l t s to
the a d s o r p t i o n of m a g n e s i u m i n s u r f a c e c o a t i n g s .
H y s t e r e s i s due
to s u r f a c e c o a t i n g s m a y be the c a u s e of the p o o r r e p r o d u c i b i l i t y o b s e r v e d i n c a l c i t e s o l u b i l i t y data.
T h e p r e s e n c e of h y d r a ted
p h a s e s , w h i c h m a y affect the s o l u b i l i t y b e h a v i o r of c a l c i t e , h a s
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1.
7
Chemical Equilibrium in Seawater
PYTKOWICZ ET AL.
r e c e n t l y b e e n p r o p o s e d (48). T h e o r g a n i c a n d i n o r g a n i c f a c t o r s that c o n t r o l the c r y s t a l f o r m of c a l c i u m c a r b o n a t e that i s p r e c i p i t a t e d i n o r g a n i c a l l y f r o m s e a w a t e r w e r e s t u d i e d b y K i t a n o (49) a n d K i t a n o et a l . (50). A l t h o u g h m o s t of the c a r b o n a t e s e d i m e n t a t i o n i n s e a w a t e r i s b i o g e n i c ( 4 3 , 4 5 ) , these r e s e a r c h e s m a y l e a d to i n s i g h t s i n t o p r o c e s s e s w i t h i n the b o d y f l u i d s of o r g a n i s m s .
T h e f o r m of c a l c i u m
c a r b o n a t e that p r e c i p i t a t e s f r o m n o r m a l s e a w a t e r , to w h i c h a s o l ulbe carbonate s a l t has been, added to supersaturate i t , i s aragon i t e C a l c a r e o u s o r g a n i s m s p r o d u c e p r i m a r i l y a s e r i e s of m a g n e s -
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ian calcites although some aragonite i s a l s o f o r m e d .
The m e c h -
a n i s m s w h i c h c o n t r o l the c r y s t a l f o r m s of c a l c i u m c a r b o n a t e i n the s h e l l s of c a l c a r e o u s o r g a n i s m s have not y e t b e e n e l u c i d a t e d . A r a g o n i t e i n s e d i m e n t s i s c o n v e r t e d g r a d u a l l y to the m o r e stable c a l c i t e (51) a n d m a g n e s i a n c a l c i t e s tend to be d i a g e n e t i c a l l y a l t e r e d to p u r e r c a l c i t e s a n d to d o l o m i t e (52, 53).
C h a v e et a l .
(54) found that the s t a b i l i t y of c a r b o n a t e s i n s e a w a t e r i n the o r d e r ; h i g h m a g n e s i a n c a l c i t e , a r a g o n i t e ,
increases
low magnesian
c a l c i t e , p u r e c a l c i t e , d o l o m i t e , but B e r n e r (46) r e c e n t l y c o n c l u d e d that c a l c i t e s w i t h 2 - 7 % m o l e - f r a c t i o n of M g C O ^ a r e t h e r m o d y n a m i c a l l y stable i n s e a w a t e r . Intermediate
o c e a n i c w a t e r s a r e u n d e r s a t u r a t e d i n the
North Pacific Ocean.
T h i s i s the r e s u l t of the h i g h c o n c e n t r a t i o n
of c a r b o n d i o x i d e p r e s e n t t h e r e b e c a u s e the w a t e r s a r e o l d a n d e x t e n s i v e o x i d a t i o n of o r g a n i c m a t t e r h a s taken p l a c e i n t h e m . A l l deep o c e a n i c w a t e r s a r e u n d e r s a t u r a t e d a s the r e s u l t of the effects of h i g h p r e s s u r e s a n d l o w t e m p e r a t u r e s upon the s o l u b i l i t y of c a l c i u m c a r b o n a t e ( 3 6 - 3 9 ,
55).
D e g r e e of s a t u r a t i o n data i n d i c a t e that c a r b o n a t e
sediments
can p e r s i s t u n t i l b u r i a l w h i l e e x p o s e d to u n d e r s a t u r a t e d w a t e r s (55,56).
T h i s c o n c l u s i o n i s c o n f i r m e d b y the fact that the l y s o -
c l i n e , the depth at w h i c h c a l c a r e o u s t e s t s f i r s t show s i g n s of d i s s o l u t i o n , i s w e l l above the c a r b o n a t e c o m p e n s a t i o n d e p t h , w h i c h m a r k s a sudden d e c r e a s e i n the c a r b o n a t e content of s e d i m e n t s (57, 58).
M o r s e a n d B e r n e r (59) c o n c l u d e d f r o m t h e i r k i n e t i c
r e s u l t s that the l a r g e i n c r e a s e i n d i s s o l u t i o n r a t e at the c o m p e n s a t i o n depth c o r r e s p o n d s to a change i n the m e c h a n i s m of solution. D i s s o l u t i o n of c a r b o n a t e s at depth l e d to s t u d i e s of the c a r bon d i o x i d e - c a r b o n a t e c y c l e s w i t h i n a n d t h r o u g h the o c e a n s a s w e l l a s to s t u d i e s of the f a c t o r s w h i c h c o n t r o l the c a r b o n d i o x i d e c o m p o n e n t s a n d the p H ( 5 , 8 , 9 , 6 0 ) . O t h e r m i n e r a l s w i t h s o l u b i l i t i e s that have b e e n d e t e r m i n e d i n s e a w a t e r a r e c a l c i u m p h o s p h a t e s (61), s i l i c a (62, 63), the l e a s t
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
8
MARINE CHEMISTRY
s o l u b l e c o m p o u n d s of a s e r i e s of t r a c e m e t a l s (64),
and clays
(65). In s o l u b i l i t y w o r k a s w e l l as i n the c a s e of d i s s o c i a t i o n c o n s t a n t s i t i s i m p o r t a n t , before a p p l y i n g e q u i l i b r i u m data o b t a i n e d i n seawater to e s t u a r i e s and to pore waters to a s c e r t a i n t h a t there have been no l a r g e changes i n the major i o n p r o p o r t i o n s . Ion A s s o c i a t i o n T h i s i s an i m p o r t a n t t o p i c b e c a u s e the f o r m a t i o n of i o n -
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p a i r s , b y a f f e c t i n g the d i s t r i b u t i o n s of solute s i z e s a n d c h a r g e s , m o d i f i e s m o s t p h y s i c o - c h e m i c a l p r o p e r t i e s of s e a w a t e r ,
includ-
ing solubility equilibria. G a r r e l s a n d T h o m p s o n (66) p i o n e e r e d w o r k on the f o r m a tion of i o n - p a i r s i n s e a w a t e r .
T h e y w e r e f o r c e d to m a k e a l a r g e
n u m b e r of a s s u m p t i o n s b e c a u s e n e e d e d data w a s not a v a i l a b l e to them.
Even so,
s o m e f e a t u r e s of t h e i r r e s u l t s w e r e
by subsequent i n v e s t i g a t i o n s .
confirmed
K e s t e r a n d P y t k o w i c z (67)
and
P y t k o w i c z a n d H a w l e y (68) u s e d p o t e n t i o m e t r i c m e t h o d s to d e t e r m i n e the c o n c e n t r a t i o n s of f r e e i o n s a n d of i o n - p a i r s i n
seawater
a n d w e r e a b l e to a v o i d m o s t of the a s s u m p t i o n s m a d e b y G a r r e l s and T h o m p s o n
(66).
T h e r e s t i l l a r e s o m e c o n t r a d i c t i o n s i n the r e s u l t s of d i f f e r ent i n v e s t i g a t o r s r e g a r d i n g the i n t e r a c t i o n s a m o n g the m a j o r of s e a w a t e r .
ions
In a d d i t i o n , f u r t h e r w o r k i s n e e d e d to c h a r a c t e r i z e
p o s s i b l e t r i p l e i o n s a n d the effects of t e m p e r a t u r e ,
salinity, and
p r e s s u r e upon i o n - p a i r i n g (68). Activity Coefficients W e w i l l d w e l l at s o m e l e n g t h u p o n this t o p i c b e c a u s e
much
of the m a t e r i a l p r e s e n t e d h e r e h a s not b e e n p u b l i s h e d b e f o r e . A c t i v i t y c o e f f i c i e n t s a r e v a l u a b l e b e c a u s e they p r o v i d e i n s i g h t s into solvent-ion and i o n - i o n interactions.
Also,
they a r e u s e f u l
for s t o i c h i o m e t r i c computations made when apparent d i s s o c i a t i o n c o n s t a n t s a n d s t o i c h i o m e t r i c s o l u b i l i t y p r o d u c t s a r e not a v a i l a b l e . One m a y u s e f r e e o r t o t a l m e a n a c t i v i t y c o e f f i c i e n t s free or total single ion activity coefficients, p r o b l e m under consideration. m i n e d i n solutions actions.
and
d e p e n d i n g upon the
F r e e c o e f f i c i e n t s a r e those d e t e r -
w h i c h t h e r e a r e no s p e c i f i c i o n i c i n t e r -
In s e a w a t e r they a r e c o n s t r u c t s w h i c h c o r r e s p o n d to the
f r e e i o n s i f the i o n - p a i r i n g m o d e l i s u s e d (68)
o r to l o n g - r a n g e
i o n i c i n t e r a c t i o n s , of the D e b y e - H u c k e l type (69),
i f the s p e c i f i c
i n t e r a c t i o n m o d e l of B r ^ n s t e d (70) a n d G u g g e n h e i m (71)
is
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1.
PYTKOWICZ ET AL.
e m p l o y e d (72).
9
Chemical Equilibrium in Seawater
T o t a l a c t i v i t y c o e f f i c i e n t s a r e those o b t a i n e d i n
solutions i n which i o n - p a i r s or s h o r t - r a n g e specific interactions o c c u r a n d a r e r e l a t e d to the f r e e ones b y a = f (F) p
(12)
= f (T)
(4)
T
a i s the a c t i v i t y , f the a c t i v i t y c o e f f i c i e n t , w h i l e ( F ) a n d ( T ) r e p r e s e n t the c o n c e n t r a t i o n of f r e e i o n s a n d the s t o i c h i o m e t r i c (total) c o n c e n t r a t i o n .
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T h e m e a n f r e e a c t i v i t y c o e f f i c i e n t c a n be o b t a i n e d f r o m data i n c h l o r i d e s o l u t i o n s i f s u c h s o l u t i o n s a r e i n d e e d u n a s s o c i a t e d (67).
T h i s m u s t be done at the s a m e e f f e c t i v e i o n i c s t r e n g t h
a s that of the s e a w a t e r of i n t e r e s t .
The effective i o n i c strength
i n c l u d e s the e f f e c t s of i o n - p a i r i n g a n d y i e l d s a n e x t e n d e d i o n i c strength p r i n c i p l e for n o n - s p e c i f i c i n t e r a c t i o n s i n m o d e r a t e l y concentrated m u l t i - e l e c t r o l y t e s o l u t i o n s , as was b y P y t k o w i c z a n d K e s t e r (73).
demonstrated
O t h e r s p r e f e r to o b t a i n m e a n
f r e e c o e f f i c i e n t s b y a s s u m i n g that the D e b y e - H i i c k e l e q u a t i o n i s v a l i d at the i o n i c s t r e n g t h of s e a w a t e r , t i o n (74)
with a h y d r a t i o n c o r r e c -
o r without it (72).
T o t a l m e a n a c t i v i t y c o e f f i c i e n t s can be m e a s u r e d d i r e c t l y i n the a s s o c i a t e d s o l u t i o n s of i n t e r e s t o r c a n be c a l c u l a t e d f r o m f r e e c o e f f i c i e n t s c o u p l e d to
i o n - p a i r or specific i n t e r a c t i o n
terms. C o r r e s p o n d i n g f r e e a n d t o t a l a c t i v i t y c o e f f i c i e n t s of s i n g l e i o n s a r e c o n v e n t i o n a l q u a n t i t i e s w h i c h d e p e n d upon n o n - t h e r m o dynamic assumptions and a r e , therefore,
of u n k n o w n a c c u r a c y .
S t i l l , they a r e u s e f u l for m a n y of the o c e a n o g r a p h i c a n d g e o c h e m i c a l c o m p u t a t i o n s w h i c h a r e b a s e d upon t h e r m o d y n a m i c e q u i l i b r i u m constants. N e x t , we w i l l c a l c u l a t e a c t i v i t y c o e f f i c i e n t s b y the m e a n s a l t m e t h o d c o u p l e d to i o n - p a i r m o d e l s a n d w i l l c o m p a r e t h e m to those o b t a i n e d b y other i n v e s t i g a t o r s . T h e f r e e a c t i v i t y c o e f f i c i e n t s of s i n g l e i o n s , T a b l e II, w e r e o b t a i n e d b y u s i n two s t e p s .
First,
shown i n an i n t e r p o l a -
tion e q u a t i o n w a s u s e d to o b t a i n v a l u e s of the m e a n a c t i v i t y c o e f f i c i e n t s i n t e r m e d i a t e to those c o m p i l e d b y H a r n e d a n d O w e n a n d b y R o b i n s o n a n d Stokes (76).
of the s i n g l e i o n s w e r e o b t a i n e d b y the m e a n - s a l t m e t h o d T h i s m e t h o d depends upon the v a l i d i t y of the M a c l n n e s (77) vention, (%)p
(75)
T h e n , the a c t i v i t y c o e f f i c i e n t s (66). con-
= ^Q\» w h i c h i s b a s e d u p o n t r a n s f e r e n c e n u m b e r s .
T h i s c o n v e n t i o n cannot be v e r i f i e d u n a m b i g u o u s l y b e c a u s e a c t i v i t i e s of s i n g l e i o n s cannot be m e a s u r e d .
the
The m e a n salt
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
10
MARINE CHEMISTRY
T a b l e II.
F r e e A c t i v i t y C o e f f i c i e n t s of P o t a s s i u m , S o d i u m ,
C a l c i u m , M a g n e s i u m a n d C h l o r i d e V e r s u s the I o n i c S t r e n g t h at 25 ° C , Ionic Strength
Downloaded by 117.253.227.139 on November 30, 2015 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0018.ch001
(molal)
K
+
O b t a i n e d b y the M e a n - S a l t M e t h o d
Na
+
0. 00 0. 05
1. 000 0. 816
1. 000 0. 826
0. 10 0. 15
0. 769
Ca
2+
Mg
2+
Cl"
1. 000 0. 486
1. 000
0. 473
0. 787 0.765
0. 392
0. 408
0. 351
0. 368
0.750
0. 325
0. 343
0.769 0.739 0.718
0. 307
0. 326
0. 701
0. 294
0. 313
0. 687
0. 305
0. 676
1. 000
0. 816
0. 20
0.739 0.718
0. 25
0.701
0. 30
0. 687
0.739 0.732
0. 35
0. 676
0. 726
0. 284
0. 40
0. 666
0.721
0. 277
0. 298
0. 666
0. 45
0. 657
0. 657
0. 650
0. 271 0. 266
0. 293
0. 50
0.718 0.716
0. 290
0. 650
0. 55
0. 643
0.714
0. 263
0. 288
0. 643 0. 637
0. 60
0. 637
0. 712
0. 260
0. 286
0. 65
0. 631
0.712
0. 258
0. 285
0. 631
0.70 0. 75
0. 626
0.711 0.711
0. 256 0. 255
0. 285
0. 626
0. 286
0. 622
0. 80
0.711
0. 254
0. 286
0. 85
0. 618 0. 614
0. 253
0. 288
0. 618 0. 614
0.90 0.95
0. 610 0. 607
0.711 0.712 0. 712
0. 253 0. 253
1. 00
0. 603
0.713
0. 253
0. 289 0. 291 0. 293
0. 622
0. 610 0. 607 0. 603
m e t h o d s h o u l d not be u s e d f o r a n i o n s u n l e s s they do not a s s o c i ate w i t h p o t a s s i u m i o n s . M e a s u r e d m e a n a c t i v i t y c o e f f i c i e n t s r e f l e c t two types of hydration effects;
the d i r e c t effect of i o n - s o l v e n t i n t e r a c t i o n s
u p o n c h e m i c a l p o t e n t i a l s a n d the c h a n g e s i n c o n c e n t r a t i o n a n d i o n i c s t r e n g t h due to the r e m o v a l of w a t e r of h y d r a t i o n f r o m the bulk solution.
T h e f i r s t effect i s t a k e n i n t o a c c o u n t a u t o m a t i c a l -
l y i n the m e a n - s a l t m e t h o d a s the m e t h o d i s b a s e d upon m e a s u r e d mean coefficients.
W e m a d e a c o r r e c t i o n f o r the s e c o n d
effect b y m e a n s of the e q u a t i o n I
A
= 1(1 + 0. 018h I / n ) A
1^ i s the c o r r e c t e d i o n i c s t r e n g t h , h i s the h y d r a t i o n n u m b e r ,
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
(5)
1.
11
Chemical Equilibrium in Seawater
PYTKOWICZ ET AL.
a n d n i s 1 for 1 -1
s a l t s a n d 3 for 1 -2 s a l t s .
T h e effect of the
change i n the i o n i c s t r e n g t h upon a c t i v i t y c o e f f i c i e n t s w a s
found
to be n e g l i g i b l e . T h e data i n T a b l e II c a n be u s e d for e s t u a r i n e a n d f o r p o r e w a t e r s as f r e e a c t i v i t y c o e f f i c i e n t s
at a g i v e n i o n i c s t r e n g t h a r e
i n s e n s i t i v e to the c o m p o s i t i o n of the s o l u t i o n (67, 6 8 , 7 3 , 7 8 ) . F u r t h e r m o r e , we c a l c u l a t e d f r o m the H a r n e d r u l e of R o b i n s o n a n d B o w e r (79)
coefficients
that the m e a n a c t i v i t y c o e f f i c i e n t s
of
N a C l a n d C a C l 2 , i n g o i n g f r o m a p u r e N a C l to a p u r e C a C ^ s o l u t i o n at 0. 75 i o n i c s t r e n g t h ,
o n l y change b y 1. 8 a n d b y 0.
1%
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respectively. B a t e s et a l . (74) u s e d a h y d r a t i o n e q u a t i o n to e s t i m a t e free activity coefficients
of
single
ions.
They
the
assumed
that the D e b y e - H u c k e l e q u a t i o n can be u s e d to d e s c r i b e
the
e f f e c t s of n o n - s p e c i f i c e l e c t r o s t a t i c i n t e r a c t i o n s f o r i o n i c s t r e n g t h s up to I = 6 a n d that c h l o r i d e i o n s a r e not h y d r a t e d . Our results,
shown i n T a b l e II, a n d those of B a t e s et a l .
(74)
d i f f e r b y about 3% for p o t a s s i u m a n d s o d i u m a n d b y up to
16%
f o r c a l c i u m a n d m a g n e s i u m at I = 1. 0.
to
It i s not p o s s i b l e
d e c i d e w h i c h set of r e s u l t s i s m o r e a c c u r a t e b e c a u s e , m e n t i o n e d e a r l i e r , the a c t i v i t y c o e f f i c i e n t s
as
was
of s i n g l e i o n s a r e
conventional. Marine chemists
often n e e d a c t i v i t y c o e f f i c i e n t s
as a f u n c t i o n of the s a l i n i t y .
expressed
T h e c o e f f i c i e n t s i n T a b l e II w e r e
e x p r e s s e d i n t e r m s of the s a l i n i t y , as i s shown i n T a b l e III,
by
m e a n s of the i o n i c s t r e n g t h - s a l i n i t y r e l a t i o n s h i p of L y m a n a n d F l e m i n g (80).
We found that the u s e of the e f f e c t i v e
ionic
s t r e n g t h (73) i n s t e a d of the c o n v e n t i o n a l one h a s a n e g l i g i b l e effect u p o n the a c t i v i t y
coefficients.
The total a c t i v i t y coefficients this w o r k f o r K ,
Na ,
+
+
Ca
2
+
of the s i n g l e i o n s o b t a i n e d i n
and M g
w e r e c a l c u l a t e d f r o m the f r e e o n e s , *T
=
^F^M^),
l e y (68).
a n c
* ^
e
2
+
,
a n d shown i n T a b l e I V ,
E q u a t i o n 4 i n the f o r m
s p e c i a t i o n m o d e l of P y t k o w i c z a n d H a w -
T h e c o e f f i c i e n t of sulfate w a s o b t a i n e d b y the m e t h o d
of K e s t e r a n d P y t k o w i c z (67) w h i l e those of b i c a r b o n a t e a n d c a r bonate i o n s w e r e c a l c u l a t e d f r o m the r a t i o s of the a p p a r e n t d i s s o c i a t i o n constants
of c a r b o n i c a c i d to the t h e r m o d y n a m i c
ones,
the a c t i v i t y c o e f f i c i e n t of c a r b o n i c a c i d , a n d the a c t i v i t y of water i n seawater.
The total mean a c t i v i t y coefficients
were
then c a l c u l a t e d f r o m those for the s i n g l e i o n s a n d a r e shown i n Table V .
T h e r e s u l t s of B e r n e r (81_) a n d of v a n B r e e m e n
(82)
w e r e e s t i m a t e d b y p r o c e d u r e s a k i n to those of G a r r e l s a n d Thompson
(66).
W h i t f i e l d (72)
a s s u m e d that n o n - s p e c i f i c i o n i c i n t e r a c t i o n s
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
12
MARINE CHEMISTRY
T a b l e III.
F r e e A c t i v i t y Coefficients
of S i n g l e Ions at 25 ° C
V e r s u s the S a l i n i t y
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S a l i n i t y (%)
K
+
Na*
^ 2+ Ca
Mg
2
+
Cl"
25
0. 648
0.715
0. 265
0.646
0. 714
0. 264
0. 289 0. 288
0. 648
26 27
0. 643
0.714
0. 263
0. 288
0. 643
28
0. 641
0. 260
0. 287 0. 286
0. 641
0.637
0. 713 0. 712
0. 261
29 30
0. 635
0. 712
0. 635
31
0. 633
0. 285
0. 633
32
0. 630
0.712 0.711
0. 259 0. 258 0. 257
0. 286 0. 285
0. 630
33
0. 628
0.711
0. 257
0. 285
34
0. 626
0.711
0. 256
0. 285
0. 628 0. 626
0. 646
0. 637
35
0. 625
0.711
0. 255
0. 285
0. 625
36
0. 623
0.711
0. 255
0. 285
0. 623
37
0. 620
0.711
0. 254
0. 286
0. 620
38
0. 618
0.711
0. 254
0. 286
0. 618
39 40
0. 617 0. 615
0. 711
0. 254
0. 287
0. 617
0. 711
0. 254
0. 287
0. 615
Table IV.
T o t a l A c t i v i t y C o e f f i c i e n t s of S i n g l e Ions a t about 35%o S a l i n i t y a n d 25 ° C
Reference
K
Na
+
^ 2+ Ca
+
Mg
CI
*>.*-
This work
0. 618
0. 695
0. 225
0. 254
0. 625
0. 084
(8j_)
0. 624
0.703
0. 237
0. 252
0. 630
0. 068
(82) (72)
0. 620 0. 617
0. 228 0. 203
0. 254 0. 217
0. 630 0. 686
0. 090 0. 122
(83)
0. 630
0. 695 0. 650 0. 680
0. 214
0. 234
0. 658
0. 108
HCG ~
C0
0. 501
0.030
3
This work
3
2
"
can be d e s c r i b e d b y the m o d i f i e d D e b y e - H u c k e l e q u a t i o n w i t h B a = 1. H e d i d not i n t r o d u c e a h y d r a t i o n c o r r e c t i o n e v e n though both h y d r a t i o n e f f e c t s m e n t i o n e d e a r l i e r s h o u l d be taken i n t o consideration. The specific short range interactions were a c c o u n t e d f o r b y a d d i t i v e i n t e r a c t i o n t e r m s between c a t i o n s a n d anions. T h e good a g r e e m e n t b e t w e e n h i s c a l c u l a t e d m e a n c o e f -
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
(#)
2
2
2
2
2
3
3
4
4
4
3
3
4
3
3
s
2
2
0. 0. 0. 0.
299 323 127 131
0. 627 0. 666 0. 455 0.464
0. 0. 0. 0. 0. 0. 0. 0. 449 465 326 352 143 151
625 662
(82)
0. 0. 0. 0. 0. 0. 0. 0.
650 668 457 467 360 372 157 163
(72)
644 666 453 466 355 368
0. 151
0. 0. 0. 0. 0. 0.
(83)
0.090
0. 378
0. 672
(*)
(87)
(86)
Experimental
s o l u b i l i t y p r o d u c t of c a l c i u m
0. 158
0. 467 0. 345 0. 366
0. 639 0. 669
(84)
at about 35%o S a l i n i t y a n d 25 ° C
O b t a i n e d f r o m the r a t i o of the s t o i c h i o m e t r i c to the t h e r m o d y n a m i c carbonate.
2
0.621
0. 659 0.445 0.463 0.318 0. 343 0.137 0. 146 0. 56 0. 59 0.39 0.40 0.23 0. 24 0.083 0. 087
NaCl CaCl MgCl K S0 Na S0 CaS0 MgS0 KHCO3 NaHC0 Ca(HC0 ) Mg(HCO ) K C0 Na C0 CaC0 MgCQ
(81)
Total Mean A c t i v i t y Coefficients
This work
KC1
Reference Salt
Table V .
Downloaded by 117.253.227.139 on November 30, 2015 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0018.ch001
MARINE CHEMISTRY
14
f i c i e n t s a n d e x p e r i m e n t a l data i n d i c a t e s that h y d r a t i o n e n t e r s i n a d v e r t e n t l y i n t o the i n t e r a c t i o n t e r m s .
Leyendekkers
i n c l u d e d i n t e r a c t i o n s b e t w e e n i o n s of the s a m e c h a r g e The total a c t i v i t y coefficients methods are i n rough agreement.
(83)
types.
c a l c u l a t e d b y the v a r i o u s A c o m p a r i s o n of T a b l e s I V
a n d V shows that the l o w v a l u e of ( f i N a z S O ^ T o b t a i n e d i n t h i s w o r k r e l a t i v e to that of W h i t f i e l d (72) i s p r i m a r i l y due to the c o n t r i b u t i o n of sulfate i o n s .
O u r v a l u e of ( f s o ^ x
w
a
°°tained
s
without r e s o r t to the m e a n - s a l t m e t h o d a n d i s e s s e n t i a l l y upon p o t e n t i o m e t r i c m e a s u r e m e n t s .
based
T h i s indicates an i n c o m -
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p a t i b i l i t y between the e x p e r i m e n t a l r e s u l t of K e s t e r a n d P y t k o w i c z (67)
obtained with glass and ion-exchange electrodes and
that of P l a t f o r d (87) w h i c h w a s m e a s u r e d w i t h a m a l g a m trodes.
R o b i n s o n a n d W o o d (84)
elec-
c a l c u l a t e d the t o t a l m e a n a c t i v -
i t y c o e f f i c i e n t s b y a n e x t e n s i o n of the m e t h o d of F r i e d m a n (85). Other E q u i l i b r i a T h e e q u i l i b r i a i n v o l v i n g the c o m p l e x a t i o n of t r a c e
metals
h a v e r e c e n t l y b e e n r e v i e w e d b y S t u m m (88) a n d a r e f u r t h e r e x a m i n e d elsewhere i n this v o l u m e .
K e s t e r (89) p r e s e n t e d a
r e v i e w of g a s - s e a w a t e r i n t e r a c t i o n s .
M a n y other a s p e c t s
of
m a r i n e c h e m i s t r y and g e o c h e m i s t r y have been d e s c r i b e d i n H o m e (90),
R i l e y a n d C h e s t e r (6J,
M a c k e n z i e (91), (5).
We w i l l ,
B r o e c k e r (92),
therefore,
B e r n e r (81),
G a r r e l s and
G o l d b e r g (93), a n d P y t k o w i c z
l i m i t t h i s w o r k to the t o p i c s a l r e a d y
d e s c r i b e d a n d to a l o o k at the e q u i l i b r i u m c h e m i s t r y of e s t u a r i n e w a t e r s f o l l o w e d b y a b r i e f e x a m i n a t i o n of the c o n t r o l of the oceanic composition. Equilibrium in Estuaries L i t t l e a p p e a r s to h a v e b e e n done c o n c e r n i n g e q u i l i b r i a i n estuaries.
We w i l l e x a m i n e ,
t h e r e f o r e , h o w one m a y a s c e r t a i n
whether e q u i l i b r i u m constants m e a s u r e d in seawater a p p l i e d to e s t u a r i e s .
c a n be
T h i s w i l l be i l l u s t r a t e d b y c o n s i d e r i n g the
d i s s o c i a t i o n r e a c t i o n s of c a r b o n i c a c i d . T h e c o m p o s i t i o n of r i v e r s depends upon the g e o l o g i c a l n a t u r e of t h e i r d r a i n a g e b a s i n s (91). we w i l l ,
therefore,
F o r illustrative purposes
d i s c u s s the e f f e c t s of m i x i n g s e a w a t e r w i t h
a h y p o t h e t i c a l r i v e r of a w o r l d - a v e r a g e shown i n T a b l e V I .
composition which is
T h e r e l a t i v e c o m p o s i t i o n of r i v e r w a t e r
d i f f e r s f r o m that of s e a w a t e r a n d t h e i r m i x i n g y i e l d s i n p r i n c i p l e e s t u a r i n e w a t e r s i n w h i c h the p r o p o r t i o n s of the m a j o r
ions
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1. PYTKOWICZ ET AL. Table VI.
Chemical Equilibrium in Seawater
C o n c e n t r a t i o n P a r a m e t e r s f o r M i x t u r e s of R i v e r
Water and Seawater.
The Concentrations a r e E x p r e s s e d
in Molality x 1 0 .
i s the T o t a l I o n i c S t r e n g t h .
3
. 0078
7. 60^ 4
3.80
60
40
20
0
378. 1
281.7
186. 6
92.78
. 274
10. 37
8. 247
6. 157
4. 096
2. 063
. 0588
54. 06
42.98
32. 05
21. 27
10. 65
. 1687
Ca
10. 44
8. 372
6. 330
4.318
2. 332
.374
Cl"
544.4
440.4
328. 1
217. 3
108. 0
. 2200
28. 68
22. 80
17. 01
11. 30
5. 671
. 1166
2. 122
1.883
1. 646
1.414
1. 184
.9575
.7078
. 5626
.4196
. 2785
. 1393
. 002074
Cl%o
19.0
15. 20
SW%
100
80
476.0
Na K
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15
+
+
Mg
+
2
HCQ 3
][
11.40
d i f f e r f r o m those i n the o c e a n s .
2
T h u s , estuarine waters
to be i o n i c m e d i a of constant c o m p o s i t i o n ,
cease
the s i m p l i f y i n g f e a -
ture which r e n d e r s apparent constants useful. however,
6
Fortunately,
r i v e r w a t e r i s so d i l u t e that e s t u a r i n e w a t e r s t e n d to
r e t a i n the m a j o r i o n p r o p o r t i o n s of s e a w a t e r down to f a i r l y l o w chlorinities. T h e extent of m i x i n g i n a n e s t u a r y depends upon a l a r g e n u m b e r of f a c t o r s s u c h a s the s e a s o n a l l y v a r i a b l e r i v e r f l o w , the t i d a l c y c l e , the w i n d s t a t e ,
the t o p o g r a p h y , a n d the r e l a t i v e
t e m p e r a t u r e s of the r i v e r w a t e r a n d the s e a w a t e r .
One m u s t
a l s o c o n s i d e r i n a c t u a l e s t u a r i e s the i n f l o w of g r o u n d a n d m e l t waters.
T h e c o n v e n t i o n a l s a l i n i t y depends upon the r e l a t i v e
c o m p o s i t i o n of s e a w a t e r a n d , t h e r e f o r e ,
the c h l o r i n i t y a n d the
t o t a l s a l t content a r e b e t t e r c o m p o s i t i o n a l v a r i a b l e s than the s a l i n i t y to a s c e r t a i n the extent of m i x i n g at a n y g i v e n l o c a t i o n . In T a b l e VII we p r e s e n t the r a t i o s of the c o n c e n t r a t i o n s of the m a j o r i o n s i n s e a w a t e r a n d i n e s t u a r i n e w a t e r at the s a m e chlorinities.
It c a n be s e e n that the c o n c e n t r a t i o n s r e m a i n
s i m i l a r i n the two m e d i a down to l o w v a l u e s of the c h l o r i n i t y . N e x t , l e t us c o n s i d e r by how m u c h e q u i l i b r i u m constants d e t e r m i n e d i n s e a w a t e r m a y d i f f e r f r o m those i n e s t u a r i n e w a t e r s at the s a m e c h l o r i n i t i e s .
T h e e x a m p l e w i l l be h y p o t h e t i -
c a l b e c a u s e we a r e c o n s i d e r i n g a w o r l d - a v e r a g e r i v e r a n d
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
16
MARINE CHEMISTRY
Table VII.
R a t i o s of C o n c e n t r a t i o n s a n d of the I o n i c S t r e n g t h i n
S e a w a t e r to T h o s e i n the E s t u a r i n e W a t e r at the Same C h l o r i n i t y % SW Na K
+
Mg
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+
Ca
+
+
2
2
Cl" S O / 4 I
100
80
60
1. 00
1.0000
.9999
.9997
.9993
1.00
.9981
.9964
.9919
.9786
1.00
.9993
.9781
. 9958
. 9889
1. 00
.9909
.9742
.9478
. 8721
.9990
.9975
.9943
.9852
• 999
.9982
.9961
.9897
20
40
1. 00 1.00
2
LOO
T
b e c a u s e a p p a r e n t d i s s o c i a t i o n c o n s t a n t s have not yet b e e n d e t e r m i n e d at the l o w c h l o r i n i t i e s w h i c h m a y be found n e a r the h e a d s of e s t u a r i e s . A p p a r e n t d i s s o c i a t i o n constants a r e r e l a t e d to the c o r r e s ponding t h e r m o d y n a m i c constants by total a c t i v i t y coefficients. T h e s e c o e f f i c i e n t s i n t u r n a r e r e l a t e d to the f r e e ones b y f*p = f ( F ) / ( T ) w h e r e f p r e f l e c t s the i o n i c s t r e n g t h effect a n d ( F ) / ( T ) F
r e p r e s e n t s the i o n - p a i r
effect.
T h e i o n i c s t r e n g t h effect c a n be c a l c u l a t e d f r o m the data i n T a b l e II a n d f r o m the f r e e a c t i v i t y c o e f f i c i e n t s of b i c a r b o n a t e a n d c a r b o n a t e i o n s (94).
T h e effect of i o n - p a i r i n g c a n be c a l c u -
l a t e d f r o m the e q u a t i o n s of P y t k o w i c z a n d H a w l e y (68) w h i c h r e l a t e a p p a r e n t d i s s o c i a t i o n c o n s t a n t s to s t o i c h i o m e t r i c a s s o c i a tion constants a n d free cation concentrations. example,
F o r K \ , for
the e q u a t i o n s y i e l d
(
K
1>EW
1
+
S
K
= ( K
'l>SW
1
+
S
K
# MHCO, 2 (
M H C 0
3
c+ >F(EW)
M
_ (
M
( 6
)
W)
w h e r e K i s the s t o i c h i o m e t r i c a s s o c i a t i o n c o n s t a n t , M represents c a t i o n s , E W r e f e r s to e s t u a r i n e w a t e r s a n d SW r e f e r s to seawater. T h e r e s u l t s of the c o m b i n e d effects a r e shown i n T a b l e VIII. T h e a s s o c i a t i o n c o n s t a n t s a n d the f r e e i o n c o n c e n t r a t i o n s
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1.
PYTKOWICZ ET AL.
Table VIIL
17
Chemical Equilibrium in Seawater
R a t i o s of K ' j a n d K ^ , the A p p a r e n t D i s s o c i a t i o n
C o n s t a n t s of C a r b o n i c A c i d ,
i n S e a w a t e r to T h o s e
i n E s t u a r i n e W a t e r s at the S a m e C h l o r i n i t i e s % Seawater
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100
< K ' > S W VE W
^
(K^ ^ / ( K ^
/(K
2
1.000
1.000
80
0.9994
0.9981
60
0.9986
0.9943
40
0.9977
0.9877
20
0.9953
0.9670
10
0.9914
0.9290
a r e w e l l known o n l y at 19%o c h l o r i n i t y .
Still,
one m a y e s t i m a t e
the m a x i m u m a n d the m i n i m u m e f f e c t s of c o m p o s i t i o n a l
differ-
e n c e s u p o n the a p p a r e n t d i s s o c i a t i o n c o n s t a n t s b y u s i n g v a l u e s of i n E q u a t i o n 6 at 19%o c h l o r i n i t y a n d at i n f i n i t e d i l u t i o n r e s p e c tively.
T h e a s s o c i a t i o n c o n s t a n t s at i n f i n i t e d i l u t i o n a r e c o n s i d -
e r a b l y l a r g e r than those at 19%o a n d enhance the effect of c o m positional variations.
O n l y the m a x i m u m e f f e c t s a r e shown i n
Table VIIL It c a n be s e e n f r o m the r e s u l t s i n T a b l e VIII that K ^ a n d K ^ determined for oceanic waters
c a n be u s e d i n e s t u a r i e s
by a hypothetical w o r l d - a v e r a g e w h i c h contain only 20% seawater.
r i v e r down to e s t u a r i n e
supplied waters
T h i s c a n be done w i t h a n
e r r o r of l e s s than 4%, w h i c h i s w i t h i n the l i m i t s of u n c e r t a i n t y of m e a s u r e d a p p a r e n t c o n s t a n t s (20). C o n t r o l of the O c e a n i c C o m p o s i t i o n A n u n d e r s t a n d i n g of the c o n t r o l m e c h a n i s m s
f o r the c h e m i -
c a l c o m p o s i t i o n of the o c e a n s i s i m p o r t a n t b e c a u s e i t h e l p s u s u n d e r s t a n d the g e o c h e m i c a l h i s t o r y of the o c e a n s a n d the i m p a c t of p e r t u r b a t i o n s upon the c h e m i c a l n a t u r e of s e a w a t e r .
This
subject w a s e x a m i n e d c r i t i c a l l y b y P y t k o w i c z (5J a n d w i l l o n l y be mentioned briefly here. T h e c o n t r o l of the c o m p o s i t i o n of s e a w a t e r
c a n be approached
f r o m two p o i n t s of v i e w ; that of v a r i a t i o n s i n t i m e a n d s p a c e w i t h i n the o c e a n s a n d the b r o a d g e o c h e m i c a l v i e w i n w h i c h the o c e a n s a r e but one of s e v e r a l l i n k e d r e s e r v o i r s .
The first
a p p r o a c h c o n s i s t s b a s i c a l l y i n d e t e r m i n i n g the p a r a m e t e r s f o r a n d s o l v i n g the e q u a t i o n
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
18
MARINE CHEMISTRY
dN TT ot
^
d
A.
oN
=) ^ < — £j d i p i
oi
"
-
v
N
>
+
R
7
1 A
i
N i s the c o n c e n t r a t i o n of a non - c o n s e r v a t i v e c o n s t i t u e n t , — the e d d y d i f f u s i o n c o e f f i c i e n t ,
is
a n d V - i s the a d v e c t i v e v e l o c i t y .
R r e p r e s e n t s the e f f e c t s o f s o u r c e s a n d s i n k s s u c h a s uptake b y the b i o t a a n d the s e d i m e n t s a n d g a s e x c h a n g e (95).
Considerable
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w o r k h a s b e e n done w i t h v a r i o u s f o r m s of E q u a t i o n 7 i n the open o c e a n a n d i n e s t u a r i e s (5). The g e o c h e m i c a l d e s c r i p t i o n of the o c e a n s i s not a s straightf o r w a r d b e c a u s e of the c o m p l e x i t y of r e a c t i o n s d u r i n g w e a t h e r ing and sedimentation, d i s c u s s i o n (5J.
a n d h a s b e e n the subject of c o n s i d e r a b l e
S o m e of the m a i n s i n k s f o r n a t u r a l l y o c c u r r i n g
a n d m a n - p r o d u c e d c h e m i c a l s b r o u g h t i n t o the o c e a n s b y r i v e r s , w i n d s , a n d s u b m a r i n e v o l c a n i s m a r e a d s o r p t i o n a n d exchange r e a c t i o n s on the s u r f a c e of s e t t l i n g d e t r i t a l p a r t i c l e s , p r e c i p i t a t i o n of o x i d e s a n d s u l f i d e s ,
authigenie
d i f f u s i o n i n t o the s e d i m e n t s ,
b i o g e n i c s e t t l i n g , a n d the d i a g e n e t i c a l t e r a t i o n of s e d i m e n t s . One a s p e c t of r e m o v a l m e c h a n i s m s ,
namely,
seawater-clay
i n t e r a c t i o n s , h a s r e c e i v e d c o n s i d e r a b l e a t t e n t i o n be c a u s e S i l l e n (7) p r o p o s e d that the e q u i l i b r i a f o r s u c h i n t e r a c t i o n s m a y c o n t r o l the c o n c e n t r a t i o n s of the m a j o r i o n s a n d the p H of s e a w a t e r . C l a y s p r o b a b l y do e x e r t a m e a s u r e of c o n t r o l b y a d d i n g a n d removing
some seawater ions.
It i s d o u b t f u l , h o w e v e r ,
that
e q u i l i b r i a a r e a c h i e v e d i n the open o c e a n s a n d i t i s l i k e l y that the m a j o r i o n c o m p o s i t i o n of s e a w a t e r ,
w h i c h m a y have
r e m a i n e d s o m e w h a t c o n s t a n t f o r a l o n g t i m e , h a s done so a s the r e s u l t of s t e a d y states r a t h e r than of e q u i l i b r i a ( 5 , 8 - 1 0 ) .
Also,
it h a s b e e n shown that the p r i m a r y c o n t r o l s of the p H a n d of the b u f f e r i n g c a p a c i t y of s e a w a t e r i n the r e c e n t o c e a n s r e s u l t f r o m the a c t i o n of the c a r b o n d i o x i d e s y s t e m .
Still, aluminium s i l i -
c a t e s do p l a y a r o l e b e c a u s e t h e i r w e a t h e r i n g c o n t r i b u t e s about 15% of the p r i m a r y b u f f e r i n g a g e n t ,
b i c a r b o n a t e i o n s , to the
o c e a n s ( 5 , 8 , 9 , 60). T h e r e i s s o m e p o s s i b i l i t y that c l a y - s e a w a t e r
equilibria may
be r e a c h e d w i t h i n the p o r e w a t e r s of s e d i m e n t s (11).
This
s h o u l d l e a d , i f f i r s t order models are used as g u i d e l i n e s f o r thought
( 5 ) , t o s o l u t i o n s o f the type B = (k
A B
/k )A e
+
B
e
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
(8)
1.
19
Chemical Equilibrium in Seawater
PYTKOWICZ ET AL.
A a n d B a r e the contents of a g i v e n c o n s t i t u e n t i n the w e a t h e r i n g a n d i n the o c e a n i c r e s e r v o i r s , B u m , and k ^ B and k
e
e
i s the v a l u e of B at e q u i l i b r i -
r e p r e s e n t the r a t e c o n s t a n t s for the r i v e r
a n d the e x c h a n g e f l u x e s .
It c a n be s e e n f r o m E q u a t i o n 8 that
e q u i l i b r i u m i n p o r e w a t e r s w o u l d l e a d to an e v e n t u a l s t e a d y state B i n the o c e a n s d i f f e r e n t f r o m the e q u i l i b r i u m v a l u e B
e
unless
the r i v e r input w a s m u c h s m a l l e r than the f l u x i n t o the s e d i ments.
It c a n a l s o be seen that the t e r m B
e
w o u l d be a b s e n t i f
the p o r e w a t e r s w e r e not at e q u i l i b r i u m w i t h the s e d i m e n t s . equations governing the removal of p o l l u t a n t s
Thus
could be q u i t e
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d i f f e r e n t i n the p r e s e n c e o r i n the a b s e n c e of e q u i l i b r i a . It i s i m p o r t a n t for the m o d e l l i n g of f l u x e s i n the p r e s e n c e of m a n - m a d e p e r t u r b a t i o n s to d e t e r m i n e a n d u s e a c t u a l r a t e l a w s for the t r a n s f e r of c h e m i c a l s between n a t u r a l r e s e r v o i r s . example,
A s an
Donaghay, S m a l l and Pytkowicz (unpublished results)
m a d e p r e l i m i n a r y l a b o r a t o r y s t u d i e s of the t r a n s f e r of i n c r e a s i n g a m o u n t s of c a r b o n d i o x i d e i n s e a w a t e r ton.
to m a r i n e p h y t o p l a n k -
T h i s i s a v i t a l t o p i c b e c a u s e the o c e a n i c b i o t a c a n take up a
c o n s i d e r a b l e f r a c t i o n of the c a r b o n d i o x i d e r e l e a s e d to the a t m o s p h e r e a n d the o c e a n s b y the c o m b u s t i o n of f o s s i l f u e l s a n d , t h u s , attenuate the g r e e n h o u s e
effect.
The experiments were p e r f o r m e d i n chemostats, I s o c h r y s i s galbana c u l t u r e , while bubbling
with an
a i r containing v a r i o u s
a m o u n t s of c a r b o n d i o x i d e t h r o u g h the s y s t e m .
The
biomass
went f r o m 7 m g / 1 f o r a s e a w a t e r w i t h a n o r m a l c a r b o n d i o x i d e content to 16 m g / 1 at f i v e t i m e s n o r m a l to 13 m g / 1 at ten t i m e s n o r m a l carbon dioxide.
T h u s , a tenfold i n c r e a s e i n c a r b o n d i o x -
i d e c a n double the b i o m a s s .
T h e d e c r e a s e f r o m 16 to 13
mg/1
m a y p e r h a p s r e f l e c t the effect of the d e c r e a s i n g p H upon b i o l o g i c a l a c t i v i t y , a h y p o t h e s i s that i s u n d e r study.
B y generalizing
the e q u a t i o n s a n d the e x t r a p o l a t i o n s of P y t k o w i c z (96)
to i n c l u d e
the m a r i n e p h y t o p l a n k t o n , one f i n d s that the a t m o s p h e r i c c a r b o n d i o x i d e m a y i n c r e a s e i n a c e n t u r y b y a f a c t o r of ten i n s t e a d of fourteen, Of c o u r s e ,
the v a l u e o b t a i n e d i n the a b s e n c e of the m a r i n e b i o t a . this i s o n l y a p r e l i m i n a r y r e s u l t
plankton species was u s e d
since a single phyto-
A l s o n u t r i e n t l i m i t a t i o n , the l a n d b i o t a ,
a n d b i o t i c a d a p t a t i o n w e r e not c o n s i d e r e d , a n d the p r e d i c t i o n of the f u t u r e c o n s u m p t i o n of f o s s i l f u e l s (96) w a s p e s s i m i s t i c . illustrates, however,
the i m p o r t a n c e of d e t e r m i n i n g r a t e
It
laws
for the c h e m i c a l f l u x e s i n n a t u r e . A c k n ow l e dg e m e n t T h i s w o r k w a s s u p p o r t e d b y the O c e a n o g r a p h y S e c t i o n of the
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
20
MARINE CHEMISTRY
National Science Foundation through G r a n t D E S T2-01631 and by the O f f i c e of N a v a l R e s e a r c h C o n t r a c t N 0 0 0 1 4 - 6 7 - A - 0 3 6 9 - 0 0 0 7 under NR083-102.
Abstract
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Concurrent chemical, biological and geological processes, in addition to the presence of the gravitational potential and of temperature and pressure gradients must be taken into consideration in the study of chemical equilibria in the oceans. A simplifying feature occurs because the approximate constant ratios of the concentrations of the major ions mean that seawater is an ionic medium of constant relative composition. Estuarine waters differ from normal seawater be cause of time and spacial variations in composition due to the input of river water. The equilibrium chemistry of estuarine waters has not been studied to any significant extent but it will be shown that equilibrium data for open ocean waters are often applicable to estuaries. Literature Cited 1. Pytkowicz, R. M., Kester, D. R., "Oceanogr. Mar. Biol. Ann. Rev., "H. Barnes, ed., Vol. 9, pp. 11-60, Allen and Unwin, London, 1971. 2. Culkin, F., "Chemical Oceanography," J. P. Riley and G. Skirrow, eds., Vol. 1, pp. 121-161, Academic, New York, 1965. 3. Barth, T. F. W . , "Theoretical Petrology," Wiley, New York, 1952. 4. Goldberg, E. D . , "Chemical Oceanography," J. P. Riley and G. Skirrow, eds., Vol. 1, pp. 163-196, Academic, New York, 1965. 5. Pytkowicz, R. M., Earth Sci. Rev., Vol. 11, p. 1, 1975. 6. Riley, J. P., Chester, R . , "Introduction to Marine Chemistry," Academic, New York, 1971. 7. Sillen, L. G., "Oceanography," M . Sears, ed., Am. Assoc. Adv. S c i . , Washington, D. C., 1961. 8. Pytkowicz, R. M., "The Changing Chemistry of the Oceans," D. Dyrssen and D. Jagner, eds., pp. 147 -152, Almqvist and Wiksell, Stockholm, 1972. 9. Pytkowicz, R. M., Schweizer. Zeitsch. Hydrol. (1973) 35, 8. 10. Broecker, W. S., Quatern. Res. (1971) 1, 188. 11. Siever, R., Earth Planet. Sci. Letters (1968) 5, 106.
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
1.
PYTKOWICZ ET AL.
Chemical Equilibrium in Seawater
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12.
21
Pytkowicz, R. M., Duedall, I. W . , Connors, D. N., Science (1966) 152, 640. 13. Buch, K . , Harvey, H. W . , Wattenberg, H., Gripenberg, S., Rapp. Cons. Int. Explor. Mer (1932) 79, 1. 14. Pytkowicz, R. M., Ingle, S. E., Mehrbach, C . , Limnol. Oceanogr. (1974) 19, 665. 15. Hansson, I., Deep-Sea Res. (1973) 20, 46. 16. Hansson, I., Deep-Sea Res. (1973) 20, 479. 17. Culberson, C . , Pytkowicz, R. M., Hawley, J. E., J. Mar. Res. (1970) 28, 15. 18. Buch, K . , Acta Acad. Aeboensis Mat. Phys. (1938) 11, 1. 19. Lyman, J . , Ph. D. Dissertation, University of California, Los Angeles, 1956. 20. Mehrbach, C., Culberson, C. H., Hawley, J. E., Pytkowicz, R. M., Limnol. (1973) 18, 897. 21. Disteche, A., Disteche, S., J. Electrochem. Soc. (1967) 114, 330. 22. Culberson, C . , Kester, D. R . , Pytkowicz, R. M., Science (1967) 157, 59. 23. Culberson, C . , Pytkowicz, R. M., Limnol. Oceanogr. (1968) 13, 403. 24. Park, P. K . , Limnol. Oceanogr. (1969) 14, 179. 25. Dyrssen, D . , Sillen, L. G., Tellus (1967) 19, 113. 26. Manheim, F., Stockholm Contrib. Geol. (1961) 8, 27. 27. Grasshoff, K . , Bull. Cons. Int. Explor. Mer (1964) 123, 1. 28. Kester, D. R . , Pytkowicz, R. M., Limnol. Oceanogr. (1967) 12, 246. 29. Goldhaber, M. B . , Ph.D. Dissertation, University of California, Los Angeles, 1974. 30. Culberson, C. H., Pytkowicz, R. M., Mar. Chem. (1973) 1, 309. 31. Bates, R. G., Macaskill, J. B . , "Analytical Methods of Oceanography, " R. F. Gould, ed., American Chemical Society, Washington, D. C., in press. 32. Wattenberg, H., Wiss. Ergebn. Dt. Atlant. Exped. 'Meteor' (1933) 8, 1. 33. Mclntire, W. G., Bull. Res. Bd. Canada No. 200, Ottawa, 1965. 34. Ingle, S. E., Culberson, C. H., Hawley, J. E., Pytkowicz, R. M., Mar. Chem. (1973) 1, 295. 35. Pytkowicz, R. M., Connors, D . N . , Science (1964) 144, 840. 36. Pytkowicz, R. M., Limnol. Oceanogr. (1965) 10, 220. 37. Pytkowicz, R. M., Disteche, A., Disteche, S., Earth Planet. Sci. (1967) 2, 430.
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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MARINE CHEMISTRY
38. Pytkowicz, R. M., Fowler, G. A., Geochem. J. (1967) 1, 169. 39. Hawley, J. E . , Pytkowicz, R. M., Geochim. Cosmochim. Acta (1969) 33, 1557. 40. Berner, R. A., Geochim. Cosmochim. Acta (1965) 29, 947. 41. Millero, F. J., Berner, R. A., Geochim. Cosmochim. Acta (1972) 36, 92. 42. Duedall, I. W., Geochim. Cosmochim. Acta (1972) 36, 729. 43. Pytkowicz, R. M., J. Geol. (1965) 73, 196. 44. Chave, K. E . , Suess, E . , Limnol. Oceanogr. (1970) 15, 633. 45. Pytkowicz, R. M., Am. J. Sci. (1973) 273, 515. 46. Berner, R. A., Geochim. Cosmochim. Acta, in press. 47. Weyl, P. K., Stud. Trop. Oceanogr. Miami (1967) 5, 178. 48. North, N. A., Geochim. Cosmochim. Acta (1974) 38, 1075. 49. Kitano, Y., Bull. Chem. Soc. Japan (1962) 35, 1973. 50. Kitano, Y., Kanamori, N., Tokuyama, A . , Am. Zool. (1969) 9, 681. 51. Bischoff, J. L., Fyfe, W. S., Am. J. Sci. (1968) 266, 65. 52. Peterson, M. N. A., Von Der Borch, C. C., Bien, G. S., Am. J. Sci. (1966) 264, 257. 53. Clayton, R. M., Jones, B. F., Berner, R. A., Geochim. Cosmochim. Acta (1968) 32, 415. 54. Chave, K. E . , Deffeyes, K. S., Weyl, P.K., Garrels, R. M., Thompson, M. E . , Science (1962) 137, 33. 55. Edmond, J. M., Deep-Sea Res. (1974) 21, 455. 56. Pytkowicz, R. M., Geochim. Cosmochim. Acta (1970) 34, 836. 57. Berger, W. H., Mar. Geol. (1970) 8, 111. 58. Heath, G. R., Culberson, C. H., Geol. Soc. Amer. Bull. (1970) 81, 3157. 59. Morse, J. W., Berner, R. A., Am. J. Sci. (1972) 272, 840. 60. Pytkowicz, R. M., Geochim. Cosmochim. Acta (1967) 31, 63. 61. Roberson, C. E . , M.S. Thesis, University of California, San Diego, 1965. 62. Krauskopf, K. B., Geochim. Cosmochim. Acta (1956) 10, 1. 63. Jones, M. M., Pytkowicz, R. M., Bull. Soc. Royale Sci. Liege (1973) 42, 125. 64. Krauskopf, K. B., Geochim. Cosmochim. Acta (1956) 9, 1. 65. Siever, R., Woodford, N., Geochim. Cosmochim. Acta (1973) 37, 1851.
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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1.
PYTKOWICZ ET AL.
Chemical Equilibrium in Seawater
23
66. Garrels, R. M., Thompson, M. E . , Am. J. Sci. (1962) 260, 57. 67. Kester, D. R., Pytkowicz, R. M., Limnol. Oceanogr. (1969) 14, 686. 68. Pytkowicz, R. M., Hawley, J. E., Limnol. Oceanogr. (1974) 19, 223. 69. Debye, P., Hückel, E . , Physik. Z. (1923) 24, 185. 70. Brønsted, J. N., J. Am. Chem. Soc. (1922) 44, 877. 71. Guggenheim, E. A., Philos. Mag. (1935) 19, 588. 72. Whitfield, M . , Mar. Chem. (1973) 1, 251. 73. Pytkowicz, R. M., Kester, D. R., Am. J. Sci. (1969) 267, 217. 74. Bates, R., Staples, B. R., Robinson, R. A., Analyt. Chem. (1970) 42, 867. 75. Harned, H. S., Owen, B. B., "The Physical Chemistry of Electrolytic Solutions," Am. Chem. Soc. Monogr. 137, Reinhold, New York, 1958. 76. Robinson, R. A., Stokes, R. H., "Electrolyte Solutions," Butterworths, 2nd ed., London, 1965. 77. MacInnes, D. A., J. Am. Chem. Soc. (1919) 41, 1086. 78. Gieskes, J. M., Z. Physik. Chem. (Frankfurt) (1966) 50, 78. 79. Robinson, R. A., Bower, V. E . , J. Res. NBS (1966) 70A(4), 313. 80. Lyman, J., Fleming, R. H., J. Mar. Res. (1940) 3, 135. 81. Berner, R. A., "Principles of Chemical Sedimentology, " McGraw-Hill, New York, 1971. 82. van Breemen, N., Geochim. Cosmochim. Acta (1973) 37, 101. 83. Leyendekkers, J. V., Mar. Chem. (1973) 1, 75. 84. Robinson, R. A., Wood, R. H., J. Solut. Chem. (1972) 1, 481. 85. Friedman, H. L., "Ionic Solution Theory," Inter science, New York, 1962. 86. Platford, R. F., J. Mar. Res. (1965) 23; 55. 87. Platford, R. F., Dafoe, T., J. Mar. Res. (1965) 23, 63. 88. Stumm, W., "Chemical Oceanography," J. P. Riley and G. Skirrow, eds., 2nd ed., Vol. pp. , Academic New York, 89. Kester, D. R., "Chemical Oceanography," J. P. Riley and G. Skirrow, eds., 2nd ed., Vol. , pp. , Academic, New York, .
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
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90. Horne, R. A., "Marine Chemistry: The Structure of Water and the Chemistry of the Hydrosphere," Inter science, New York, 1969. 91. Garrels, R. M., Mackenzie, F. T., "Evolution of Sedimentary Rocks," Norton, New York, 1971. 92. Broecker, W. S., "Chemical Oceanography," Harcourt Brace Jovanovich, New York, 1974. 93. Goldberg, E. D., ed., "The Sea: Ideas and Observations on Progress in the Study of the Sea," Vol. 5, Interscience, New York, 1974. 94. Walker, A. C., Bray, V. B., Johnston, J., J. Am. Chem. Soc. (1927) 49, 1235. 95. Redfield, A. C., Ketchum, B. H., Richards, F. A., "The Sea: Ideas and Observations on Progress in the Study of the Sea," M.N. Hill, ed., Vol. 2, pp. 26-77, Interscience, New York, 1963. 96. Pytkowicz, R. M., Comments on Earth Sci. : Geophys. (1972) 3, 15.
In Marine Chemistry in the Coastal Environment; Church, T.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.
