Marine Chemistry in the Coastal Environment - American Chemical

1 Chemical Equilibrium in Seawater R. M. PYTKOWICZ, E. ATLAS, and C. H. CULBERSON

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

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 ) .


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


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


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


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


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


1.

because

5


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 .


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


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 ,


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


1.

7


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 -


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


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 -


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


1.

PYTKOWICZ ET AL.

e m p l o y e d (72).

9


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 .


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


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


(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 ,


(5)

1.

11


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%


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


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


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 -



(#)

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 .


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 -


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


1. PYTKOWICZ ET AL. Table VI.


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


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


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


+

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


1.

PYTKOWICZ ET AL.

Table VIIL

17


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


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


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


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


(8)

1.

19


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


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


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


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.


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PYTKOWICZ ET AL.



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.



22

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.



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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, .



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