929
NOTES AND COMMENT
sion is not a definition
of salinity, since
Copenhagen Normal Water or a silver precipitation must be used to determine the
35%0salinity required for establishing R15.
Because of the growing number of definitions of chlorinity, it is important in reporting salinities to state explicitly
how
chlorinity was determined and how it was
converted to salinity.
JOHN LYMAN
Department of Environmental
Sciences and Engineering,
University of North Carolina,
Chapel Hill
27514,
and
Department of Geosciences,
North Carolina State University,
Raleigh.
DISTRIBUTION
OF SUSPENDED
REFERENCES
Cox,
R. A., F. CULKIN, AND J. P. RILEY.
1967.
The electrical conductivity/chlorinity
relationDeep-sea Res., 14:
ship in natural sea water.
203-220.
FORCH, C., M. KNUDSEN, AND S. P. S~~RENSEN.
1902. Berichte
iiber die Konstantenbestimmungen zur Aufstellung
der hydrographischen
Tabellen.
Kgl. Dan, Vidensk. Selsk. Skr., 6.
Raekke, Naturvidensk.
Mat. Afd. XII, 1. 151
P*
JACOBSEN, J. P., AND M. KNUDSEN. 1940. Urnorma1 1937 or primary standard sea-water 1937.
Assoc. Intern. Oceanog. Phys., Sci. Publ. 7.
38 p.
KNUDSEN, M.
1901. Hydrographical
tables.
G.
E. C. Gad, Copenhagen.
63 p.
LYMAN, J,, AND R.H. FLEMING.
1940. Composition of sea water. J. Marine Res., 3: 134-146.
WOOSTER, w. s., A. J. LEE, AND G. DIETFWH.
1969. Redefinition
of salinity.
Int. Mar. Sci.,
A&o in Limnol. Oceanog., 14:
7( 1) : 4-5.
437-438.
CARBONATE
It has generally been considered that the
pH of seawater is maintained by the buffering capacity of the carbonate system. If
one considers only the reactions of dissolved
CO2 and water, this buffering capacity is
not impressive, However, if one also considers the possibility of re-solution of suspended and deposited calcium carbonate,
the system becomes both more plausible
and more complicated.
The calcium carbonate on the sea floor, while present in
amounts sufficient to take part effectively
in such a buffer system, is in contact with
a relatively small proportion of the total
volume of seawater. The calcium carbonate
in suspension in seawater should be a much
more effective component of the buffer
system. Very little information is available
concerning the distribution
of this suspended material.
Theoretical considerations of the changes
to be expected in ion activities and solubility
constants with pressure, secondary changes
reflecting the primary variable, and the
changing structure of water suggest that
seawater should be undersaturated
with
respect to calcium carbonate at all depths
below the immediate surface layers. According to Berner ( 1965)) Lyakhin ( 1968))
WITH
DEPTH
IN
THE
OCEAN
and Pytkowicz ( 1965 ) , undersaturation may
begin a few hundred meters below the
surface. An increase in the solubility of
calcium carbonate in artificial seawater with
pressure was measured by Pytkowicz and
Connors ( 1964), and direct measurements
of the changes in apparent dissociation constants of carbonic acid in artificial seawater
at increased pressures were made by Culberson, Kester, and Pytkowicz ( 1967).
Until recently, experimental evidence for
undersaturation
at depth has been largely
inferential, based on the well-known “snow
line,” the depth of disappearance of calcium
carbonate in the sediments. This disappearance is considered to be the result of a
balance between supply of material from
surface waters and increased solubility with
depth. The reality of this concept has been
questioned by Turekian
(196s) and by
Smith, Dygas, and Chave ( 1968), who feel
that there is no single depth of disappearance common to all of the oceans.
The first in situ measurement of increased
rates of solution with depth was made by
Peterson (1966), who suspended preweighed
calcite spheres in Lucite cages at various
depths in the Pacific Ocean for four months.
From a few hundred meters down to about
930
TABLE 1.
Station
NOTES
Analytical
Position
38
08” OO’N
19”58’W
52
lO”05’N
24”28’W
65
12” 13’N
38”53’W
68
14”58’N
44”Ol’W
70
17”08’N
46”45’W
74
23” 14’N
52”38’W
results, AFRAM
Depth
(ml
100
900
2,170
3,160
3,910
0
1,165
2,340
2,635
3,130
3,675
4,170
4,720
10
740
1,690
2,660
3,155
3,695
4,200
4,750
10
1,080
2,130
3,110
3,610
10
1,135
2,040
2,985
10
1,055
2,050
3,075
3,565
4,050
4,600
AND
deep stations
CaC03
( fig/liter 1
47
30
41
59
42
37
38
41
37
45
51
35
14
41
36
32
43
42
40
34
52
48
35
40
37
38
43
45
34
38
148
38
286
20
44
33
45
1,700 m, a small, fairly constant weight loss
was found. Below 1,700 m a slight increase
in solution rate was evident. The most
important change in rate of solution occurred below 3,700 m. Between 3,500 and
5,000 m, the rate of solution increased by
at least a factor of 10. Similar results were
found by Berger ( 1967), studying rates of
solution of calcitic foraminifera1 tests suspended from the same moored buoy.
These experiments suggest that the traditional concept of control of carbonate sedimentation by a balance between surface
productivity and solution at depth is at least
possible. The interaction
between suspended carbonate and seawater necessary
COMMENT
for local control of pH seems reasonable,
and the undersaturation of subsurface seawater is undeniable.
On the other hand, Chave and Suess
(1967) have demonstrated that calcite grains
coated with naturally
occurring organic
materials were stable in greatly undersaturated seawater. Such coated grains were
not dissolved at pH 6.15 and were totally
dissolved only at ;pH 3.0. In the Caribbean
Sea, the Gulf of Mexico, and the North
Atlantic Ocean off Bermuda they found
suspended calcium carbonate in water undersaturated in calcite. They postulated
that this suspended material was isolated
from contact with the surrounding water
by a coating of organic materials. Thus, the
naturally occurring calcite particles in seawater might be effectively removed from
the carbonate buffer system until such time
as this organic coating is destroyed by
biological activity, possibly by bacteria or
bottom organisms.
The importance of this protective mechanism might be measured by determining
the distribution of suspended calcium carbonate with depth. If re-solution were important, a definite decrease in suspended
calcium carbonate with depth should be
apparent. In the course of investigations
into the particulate organic carbon content
of seawater, the particulate carbonate content was determined as well. Some of these
results have been published ( Wangersky
and Gordon 1965); these, along with the
results of later cruises, are discussed here.
This work could not have been done without the help of the scientists and crew of
the RV Trident, Narragansett Marine Laboratory, University of Rhode Island. The
investigation was supported by U.S. Atomic
Energy Commission Contract AT(30-1)2882.
METHODS
All water samples were taken with Niskin
30-liter PVC samplers. The samples were
filtered through Gelman A glass-fiber filters
with a nominal 10-p retention size. The
filter pads were washed with distilled water
and refrigerated until analysis ( Wangersky
and Gordon 1965).
NOTES
AND
931
COMMENT
0
IO
I
p9
30
20
I
CaCO,
40
--.
--
50
I.8
-.
..-
.
l
60
70
.
I
l .
.
6000
*
55
.
.. .
-:v*
l
.
E
w2000-
8..*...
2
z
.
.
l
.
5
.
.
l
3286
.
F
$3000-
l
:
a
88*
.
.
.
.
4000-
.
.
.
l
l:
.
g..
.
.
.
.
l
.
.
.
.
5000
80-w
FIG.
76*
1.
72'
Position
66.
64'
24.N
6(rw
-
.
.
FIG. 2. Distribution
bonate with depth.
.
of particulate
calcium
car-
of stations, RV Trident cruises,
1964.
RESULTS
The analytical results are expressed in
Table 1, condensed from the earlier paper,
and Table 2, the data from a series of cruises
between Narragansett and Bermuda in June
and July 1964. The stations in Table 1 were
taken on a transect between Freetown,
Sierra Leone, and Bermuda in May and
June 1963. The positions of the stations in
Table 2 are shown in Fig. 1.
DISCUSSION
In 18 deep stations, taken over a large
area of the North Atlantic Ocean, no decrease in suspended calcium carbonate with
depth was found. The scatter of the data
points is shown in Fig. 2. At least that
fraction of the suspended calcium carbonate
large enough to be collected by our filters
apparently is protected from reaction with
the surrounding seawater. Even prolonged
washing with distilled water will not put it
into solution.
The calcite collected by the 30-liter samplers probably contains little, if any, foraminiferal carbonate. No foram tests could
be found by casual visual inspection of the
filter pads. It is possible that the distribution of tests is less than 1 per 30 liters of
seawater. Berger’s ( 1967) work suggested
that at least some of the foraminifera1
calcite is susceptible to solution at depth,
although there is some evidence (Wangersky and Joensuu 1967) that even these tests
are relatively resistant to solution as long
as their outer organic coating is intact. The
rate of solution of unprotected calcite in
deep water, as measured by Peterson (1966),
suggests that the greater part of the suspended calcite either must be protected
from solution or must have an incredibly
rapid settling rate.
In discussions of the carbonate system in
seawater, it should be considered that the
reactions involving calcium carbonate precipitation may not be truly reversible except
at the sea floor. Once particles have formed,
by either chemical or biological precipitation, the carbonate enclosed may be isolated
from seawater by a protective organic coating. The formation of particles may act
effectively as a calcium carbonate sink. The
measurement of rate constants and solubilities for the COZ-CaC03 system may
932
NOTES
2.
TABLE
Station
Analytical
m
9”“;”
35”OO’N
69”25’W
10
1,000
2,000
3,000
48
37
32
34
10
1,000
2,000
3,000
4,000
4,500
28
24
26
20
17
43
10
1,000
2,000
2,500
3,000
3,500
4,000
4,500
30
20
25
23
30
29
24
18
10
1,000
2,000
2,500
32”07’N
68”OO’W
32”43’N
67”OO’W
COMMENT
results, Trident
CaC03
Position
34” 54’N
69”25’W
3
AND
( ,&liter 1
Station
9
cruises, 1964
y;h
m
Position
34”28’N
69”44’W
4,000
5,000
49
44
10
100
35
37
32
1,000
10
39”52’N
67”28’W
11
39”51’N
67 “27’W
CaC03
( bcLg/liter1
10
100
1,oQo
90
47
38
1,500
2,000
50
35
35
33
39
10
25
50
775
59
53
85
57
100
2,000
3,000
60
41
41
55
10
100
1,000
12
39" 50'N
67”27’W
16
31
25
16
23
38”21’N
68”2O’W
10
100
27
36
24
37”Ol’N
67” 02’W
32” 06’N
68” 13’W
100
500
1,000
31
61
26
325
1,000
2,000
3,000
4,000
46
37
53
26
34
25
32”02’N
68” 14’W
2,000
3,000
4,000
80
30
33
34” 36’N
64”32’W
100
1,000
34”24’N
69”48’W
10
100
2,000
3,000
37
45
29
46
33
39
44
34
36
32”17’N
67”36’W
therefore be irrelevant to the situation in
seawater. The governing rate in re-solution
could well be the rate of degradation of
protective organic coatings by bacterial
activity. For the most part, the incorporation of calcite into organic aggregates and
the adsorption of surface-active
organic
compounds on chemically or biologically
precipitated calcite may represent a delay
mechanism with a long time constant built
into the carbonate cycle in seawater.
PETER
Institute of Oceanography,
Dalhousie University, Halifax,
J.
WANGERSKY
Nova Scotia.
1,000
2,000
3,000
4,000
26
30” OO’N
6O”OO’W
100
2,500
5,000
37
32
26
REFERENCES
W. H. 1967. Foraminifera1
ooze: soluScience, 156 : 383-385.
tion at depths.
BERNER, R. A.
1965. Activity
coefficients
of bicarbonate, carbonate and calcium ions in sea
water.
Geochim. Cosmochim. Acta, 29: 947965.
CHAVE,
K. E., AND E. SUESS. 1967. Suspended
minerals in sea water.
Trans. N.Y. Acad. Sci.,
29 : 991-1000.
CULBERSON, C., D. R. KESTER, AND R. M. PYTKOWICZ.
1967.
High-pressure
dissociation
of
carbonic and boric acids in seawater.
Science,
157: 59-61.
LYAKHIN,
Yu. I.
1968. Calcium carbonate saturation of Pacific water.
Oceanology, 8: 5868.
BERGER,
NOTES
AND
PETERSON, M. N. A. 1966. Calcite:
rates of dissolution in a vertical profile in the Central
Pacific.
Science, 154: 1542-1544.
PYTKOWICZ; R. M.
1965. Calcium carbonate saturation in the ocean.
Limnol. Oceanog., 10:
220-225.
-,
AND D. N. CONNORS. 1964. High pressure solubility
of calcium carbonate in seawater.
Science, 144: 840-841.
SMITH, S. V., J. A. DYGAS, AND K. E. CHAVE. 1968.
Distribution
of calcium carbonate in pelagic
sediments.
Marine Geol., 6: 391-400.
A
933
COMMENT
TUREKIAN, K. K. 1965. Some aspects of the geochemistry of marine sediments, p. 81-126.
In
J. P. Riley and G. Skirrow [eds.], Chemical
oceanography,
v. 2. Academic.
WANGERSKY, P. J., AND D. C. GORDON, JR. 1965.
Particulate
carbonate,
organic
carbon,
and
Limnol. Oceanog.,
Mn++ in the open ocean.
10: 544-550.
AND 0. I. JOENSUU. 1967.
tion of carbonate
75 : 148-177.
deep-sea
MODIFICATION
OF MAUCHA'S IONIC DIAGRAM
INCLUDE IONIC CONCENTRATIONS~
Inland saline astatic waters differ markedly from one another in total concentration
of salts and ionic composition, and, in addition, undergo large seasonal changes in
concentration as a result of dilution and
evaporation. In our work with these waters
we need to symbolize visually both differences in concentrations of ions and differences in relative proportions
of ions.
Though Maucha’s (1932) ionic field diagrams illustrate relative proportions of ions,
they give no indication of actual concentrations.
Hedgpeth (1959) modified Maucha’s diagrams to indicate total concentration as well
as ionic proportions. His solution indicates
total salinity by including a log scale for
salinity with the ionic field diagram. Furthermore, for salinities less than or equal to
seawater, the circle of the diagram is represented by a dashed line and the polygons
are shaded by diagonal lines. For salinities
greater than seawater, the circle is represented by a continuous line and the
polygons are crosshatched. However, Hedgpeth’s modification
does not show differences in actual concentration of ions between waters.
The method presented in this paper is a
modification of Maucha’s method, so first
it is necessary to look at his work.
The construction of Maucha’s ionic dia1 Supported by Washington
State Initiative
171
Fund and by National Science Foundation
Grant
GB-5052.
The fractionacores. J. Geol.,
TO
gram begins with a regular, 16-sided polygon with an area of 200 mm2. To calculate
the radius (R) of the circle inside which
this regular polygon is constructed, use the
formula :
R2 *sin 22.5 O/ 2 = A/ 16,
(1)
in which A represents the area of the 16sided polygon and sin 22.5” = 0.38268. Thus
R = 25 mm/0.38268, or 8.082 mm.
The polygon is then subdivided into 16
identical isosceles triangles ( Fig. 1 ), each
with an area of 12.5 mm2. This polygon is
divided vertically along AB, leaving an area
of 100 mm2 on each side. The total equivalent per cents for the major anions as well
FIG. 1.
diagram.
First step in constructing
Maucha’s
ionic