STABLE CARBON ISOTOPE VARIATIONS IN THE
OCEAN
K. K. Turekian, Yale University, New Haven, CT, USA
Copyright & 2001 Elsevier Ltd.
The two stable isotopes of carbon,
12
C and
13 C, vary
in proportions in different reservoirs on earth. The
ratio of
13 C to
12
C is commonly given relative to a
standard (a belemnite from the Peedee formation in
South Carolina and therefore called PDB). On the
basis of this standard d
13 C is defined as:
13 C=
12 C sample
13 C=
12 C standard
À 1
"
#
 1000
The values for some major carbon reservoirs are:
marine limestones, d
13
C ¼ 0; C-3 plants, d
13
C ¼ À 25;
air CO 2 , d
13
C ¼ À 7. The inorganic carbon in the
surface ocean is in isotopic equilibrium with atmospheric CO 2 and has a value of about 2. Organic matter
in the shallow ocean ranges from À 19 at high latitudes to À 28 at low latitudes. The midlatitude value
is around À 21. The transport of organic matter to
depth and subsequent metabolism adds inorganic
carbon to the water. The isotopic composition of dissolved inorganic carbon then reflects the amount of
addition of this metabolic carbon. Figure 1 is a profile
of d
13
C for the North Pacific. It is typical of other
profiles in the oceans.
Carbon isotope measurements in all the oceans
were made on the GEOSECS expedition. These values are given in the GEOSECS Atlas (1987).
See also
Carbon Cycle. Carbon Dioxide (CO 2 ) Cycle.
Further Reading
Chesselet R, Fontagne M, Buat-Menard P, Ezat U, and
Lambert CE (1981) The origin of particulate organic
matter in the marine atmosphere as indicated by its stable
carbon isotopic composition. Geophysical Research
Letters 8: 345--348.
GEOSECS Atlantic, Pacific, and Indian Ocean Expeditions,
vol 7: Shorebased Data and Graphics. National Science
Foundation. 200 pp. (1987).
Kroopnick P, Deuser WG, and Craig H (1970) Carbon-13
measurements on dissolved inorganic carbon at the North
Pacific (1969) GEOSECS station. Journal of Geophysical
Research 75: 7668--7671.
Sackett WM (1964) The depositional history and isotopic
organic composition of marine sediments. Marine Geology 2: 173--185.
δ
13
)
C(‰
0
1
2
3
4
5
0
1
2
Bottom
13 C
Depth (km)
Figure 1 Variation of d
13 C in dissolved inorganic carbon with
depth in the Pacific Ocean at GEOSECS Station 346 (281N,
1211W) (Kroopnick, Deuser and Craig, 1970).
566
OCEAN
K. K. Turekian, Yale University, New Haven, CT, USA
Copyright & 2001 Elsevier Ltd.
The two stable isotopes of carbon,
12
C and
13 C, vary
in proportions in different reservoirs on earth. The
ratio of
13 C to
12
C is commonly given relative to a
standard (a belemnite from the Peedee formation in
South Carolina and therefore called PDB). On the
basis of this standard d
13 C is defined as:
13 C=
12 C sample
13 C=
12 C standard
À 1
"
#
 1000
The values for some major carbon reservoirs are:
marine limestones, d
13
C ¼ 0; C-3 plants, d
13
C ¼ À 25;
air CO 2 , d
13
C ¼ À 7. The inorganic carbon in the
surface ocean is in isotopic equilibrium with atmospheric CO 2 and has a value of about 2. Organic matter
in the shallow ocean ranges from À 19 at high latitudes to À 28 at low latitudes. The midlatitude value
is around À 21. The transport of organic matter to
depth and subsequent metabolism adds inorganic
carbon to the water. The isotopic composition of dissolved inorganic carbon then reflects the amount of
addition of this metabolic carbon. Figure 1 is a profile
of d
13
C for the North Pacific. It is typical of other
profiles in the oceans.
Carbon isotope measurements in all the oceans
were made on the GEOSECS expedition. These values are given in the GEOSECS Atlas (1987).
See also
Carbon Cycle. Carbon Dioxide (CO 2 ) Cycle.
Further Reading
Chesselet R, Fontagne M, Buat-Menard P, Ezat U, and
Lambert CE (1981) The origin of particulate organic
matter in the marine atmosphere as indicated by its stable
carbon isotopic composition. Geophysical Research
Letters 8: 345--348.
GEOSECS Atlantic, Pacific, and Indian Ocean Expeditions,
vol 7: Shorebased Data and Graphics. National Science
Foundation. 200 pp. (1987).
Kroopnick P, Deuser WG, and Craig H (1970) Carbon-13
measurements on dissolved inorganic carbon at the North
Pacific (1969) GEOSECS station. Journal of Geophysical
Research 75: 7668--7671.
Sackett WM (1964) The depositional history and isotopic
organic composition of marine sediments. Marine Geology 2: 173--185.
δ
13
)
C(‰
0
1
2
3
4
5
0
1
2
Bottom
13 C
Depth (km)
Figure 1 Variation of d
13 C in dissolved inorganic carbon with
depth in the Pacific Ocean at GEOSECS Station 346 (281N,
1211W) (Kroopnick, Deuser and Craig, 1970).
566