- Email: [email protected]
The influence of the partial pressure of carbon dioxide on the total carbonate of seawater
Marine Chemistry, 11 (1982) 183--185
183
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Short Note THE I N F L U E N C E O F THE P A R T I A L P R E S S U R E O F C A R B O N DIOXIDE ON THE T O T A L C A R B O N A T E OF SEAWATER DAVID DYRSSEN and MARGARETA WEDBORG
Department of Analytical and Marine Chemistry, Chalmers University of Technology and University of GSteborg, S-412 96 G•teborg (Sweden) (Received August 31, 1981;revision accepted November 23, 1981)
ABSTRACT Dyrssen, D. and Wedborg, M., 1982. The influence of the partial pressure of carbon dioxide on the total carbonate of seawater. Mar. Chem., 11 : 183--185. The dependence of the total carbonate concentration of ocean water on temperature and atmospheric partial pressure of carbon dioxide is calculated. The results show that the increase in total carbonate caused by the increase of carbon dioxide in the atmosphere is ca. 25--50 times larger than the precision in the experimental determination of Ct.
The GEOSECS expedition provides a worldwide survey of total carbonate (Ct) and alkalinity (At) of the Atlantic, Pacific and Indian Oceans, (Ostlund and Dyrssen, 1980). Conclusions a b o u t the carbonate system of the sea should, in our opinion, be primarily based on the analytical values of A t and Ct, since these data are pressure and temperature independent (Dyrssen and Sill6n, 1967). In this short note the dependence of Ct on the partial pressure of carbon dioxide in the atmosphere is calculated. A direct iterative procedure where [H +] is adjusted until ( A t - - A t . c a l c ) < 0.05 pMw is preferred to the procedure suggested b y Keir (1979). His m e t h o d involves redundant approximations and elimination of the free concentration of hydrogen carbonate in a set of equations. Most of the deep water seems to be f o r m e d in the Norwegian and Weddell Seas (Broecker, 1974). This water is slowly spread to other parts of the main oceans. Broecker (1974) calculated a mean residence time of water in the deep ocean of ca. 1600 y. The sinking of surface water in the Greenland Sea m a y be faster than in the Norwegian Sea. This might, however, mainly influence the deep water in the Eastern Arctic Ocean. The partial pressure of carbon dioxide in the atmosphere has probably increased from a pre-industrial value of a b o u t 260--290 ppm to the present value of approximately 335 ppm. As a result, the total carbonate of the ocean has increased. Considering the residence time of water in the deep ocean, it is expected that a major portion of the present deep water was equilibrated with the pre-industrial atmospheric carbon dioxide concentration. As a consequence, depth profiles of Ct involve n o t only shifts caused
0304-4203/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company
184
by biological activity, and formation and dissolution of carbonates (cf. Dyrssen, 1977) b u t also a time scale. The precision o f the GEOSECS data on A t and Ct, as well as the data of others (cf. Almgren et al., 1977) is ~ 1--2 gMw (micromoles per kg seawater). In order to find o u t whether the increase of atmospheric carbon dioxide has caused a measurable change in Ct the following calculations were made: Since the total alkalinity, At, and total borate, Bt, are n o t affected b y the dissolution of carbon dioxide, the present values (ratios to chlorinity) of At / C1 = 120 #Mw/%0 and Bt/C1 = 21.3 gM w/%0 were used. A salinity of 35 °/00 was used to calculate C1 = 3 5 / 1 . 8 0 6 5 5 %0. These values, together with the solubility constants for carbon dioxide of Weiss (1974) and the acidity constants of Hansson (cf. Almgren et al., 1975), were used to calculate Ct for different values of temperature and Pco~ (partial pressure of carbon dioxide). The results are shown in Table I. Table I shows that Ct will increase a b o u t 0.6 pMw for an increase of the partial pressure of CO 2 of 1 ppm. Table I also demonstrates that Ct will decrease a b o u t 8 #Mw for an increase in temperature of one degree. Table I has been used b y Anderson and Dyrssen (1981) in their treatment of alkalinity and total carbonate data from the eastern Arctic Ocean. It is concluded that Ct of the Norwegian Sea surface water has increased by 25--50 pMw since 1850. The corresponding shift in the pH of surface seawater is --0.05 to --0.1 using the pH scale of Hansson (cf. Almgren et al., 1975). In considering the time influence on Ct b y the increase in atmospheric carbon dioxide (cf. Brewer, 1978; Chen and Millero, 1979; Jones and Levy, TABLE
I
Calculation of the total c a r b o n a t e c o n c e n t r a t i o n in seawater for d i f f e r e n t temperatures pressures (in ppm) of carbon d i o x i d e in t h e a t m o s p h e r e ( t h e chlorAt/C1 (= 120 /~lVlw per %o) and Bt/C1 (= 21.3 p-Mw per %o) are
and d i f f e r e n t partial inity (---- 19.374°/00), maintained constant)
p
0°
5°
10 °
15 °
20 °
25 °
30 °
250 260 270 280 290 300 310 320 330 340 350
2133 2139 2145 2151 2157 2162 2168 2172 2177 2182 2186
2089 2096 2103 2110 2116 2122 2128 2133 2138 2143 2148
2045 2052 2060 2067 2074 2080 2086 2092 2098 2103 2109
2000 2008 2016 2024 2031 2038 2045 2051 2057 2063 2068
1956 1965 1973 1981 1989 1996 2003 2010 2016 2023 2029
1914 1923 1932 1940 1948 1955 1963 1970 1977 1983 1989
1874 1883 1892 1900 1908 1916 1924 1931 1938 1945 1951
185
1981) one has to assume t h a t the biological processes influencing A t and Ct are the same t o d a y as before the impact of industrialization.
REFERENCES Almgren, T., Dyrssen, D. and Strandberg, M., 1975. Determination of pH on the moles per kg seawater scale (M w ). Deep-Sea Res., 22: 635---646. Almgren, T., Dyrssen, D. and Strandberg, M., 1977. Computerized high-precision titrations of some major constituents of seawater on board the R.V. Dmitry Mendeleev. DeepSea Res., 24 : 345--364. Anderson, L. and Dyrssen, D., 1981. Chemical constituents of the Arctic Ocean in the Svalbard area. Oceanol. Acta, 4: 305--311. Brewer, P.G., 1978. Direct observation of the oceanic CO2 increase. Geophys. Res. Lett., 5 : 997--1000. Broecker, W.S., 1974. Chemical Oceanography. Harcourt Brace Jovanovich, pp. 22--26 and 59--67. Chen, C.-T. and Millero, F.J., 1979. Gradual increase of oceanic CO 2 . Nature, 277: 205-206. Dyrssen, D., 1977. The chemistry of plankton production and decomposition in seawater. In: N.R. Andersen and B.J. Zahuranec (Editors), Ocean Sound Scattering Prediction. Plenum Press, New York, 1977, pp. 65--84. Dyrssen, D. and Sill~n, L.-G., 1967. Alkalinity and total carbonate in seawater. A plea for p-T-independent data. Tellus, XIX: 113--121. Jones, E.P. and Levy, E.M., 1981. Oceanic CO 2 increase in Baffin Bay. J. Mar. Res., 39 : 405--416. Keir, R.S., 1979. The calculation of carbonate ion concentration from total CO2 and titration alkalinity. Mar. Chem., 8: 95--97. {~stlund, H.G. and Dyrssen, D. (Editors), 1980. Workshop on oceanic CO2 standardization at La Jolla, CA, Nov 30--Dec 1, 1979. Weiss, R.F., 1974. Carbon dioxide in water and seawater: the solubility of a non-ideal gas. Mar. Chem., 2: 203--215.
183
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
Short Note THE I N F L U E N C E O F THE P A R T I A L P R E S S U R E O F C A R B O N DIOXIDE ON THE T O T A L C A R B O N A T E OF SEAWATER DAVID DYRSSEN and MARGARETA WEDBORG
Department of Analytical and Marine Chemistry, Chalmers University of Technology and University of GSteborg, S-412 96 G•teborg (Sweden) (Received August 31, 1981;revision accepted November 23, 1981)
ABSTRACT Dyrssen, D. and Wedborg, M., 1982. The influence of the partial pressure of carbon dioxide on the total carbonate of seawater. Mar. Chem., 11 : 183--185. The dependence of the total carbonate concentration of ocean water on temperature and atmospheric partial pressure of carbon dioxide is calculated. The results show that the increase in total carbonate caused by the increase of carbon dioxide in the atmosphere is ca. 25--50 times larger than the precision in the experimental determination of Ct.
The GEOSECS expedition provides a worldwide survey of total carbonate (Ct) and alkalinity (At) of the Atlantic, Pacific and Indian Oceans, (Ostlund and Dyrssen, 1980). Conclusions a b o u t the carbonate system of the sea should, in our opinion, be primarily based on the analytical values of A t and Ct, since these data are pressure and temperature independent (Dyrssen and Sill6n, 1967). In this short note the dependence of Ct on the partial pressure of carbon dioxide in the atmosphere is calculated. A direct iterative procedure where [H +] is adjusted until ( A t - - A t . c a l c ) < 0.05 pMw is preferred to the procedure suggested b y Keir (1979). His m e t h o d involves redundant approximations and elimination of the free concentration of hydrogen carbonate in a set of equations. Most of the deep water seems to be f o r m e d in the Norwegian and Weddell Seas (Broecker, 1974). This water is slowly spread to other parts of the main oceans. Broecker (1974) calculated a mean residence time of water in the deep ocean of ca. 1600 y. The sinking of surface water in the Greenland Sea m a y be faster than in the Norwegian Sea. This might, however, mainly influence the deep water in the Eastern Arctic Ocean. The partial pressure of carbon dioxide in the atmosphere has probably increased from a pre-industrial value of a b o u t 260--290 ppm to the present value of approximately 335 ppm. As a result, the total carbonate of the ocean has increased. Considering the residence time of water in the deep ocean, it is expected that a major portion of the present deep water was equilibrated with the pre-industrial atmospheric carbon dioxide concentration. As a consequence, depth profiles of Ct involve n o t only shifts caused
0304-4203/82/0000--0000/$02.75 © 1982 Elsevier Scientific Publishing Company
184
by biological activity, and formation and dissolution of carbonates (cf. Dyrssen, 1977) b u t also a time scale. The precision o f the GEOSECS data on A t and Ct, as well as the data of others (cf. Almgren et al., 1977) is ~ 1--2 gMw (micromoles per kg seawater). In order to find o u t whether the increase of atmospheric carbon dioxide has caused a measurable change in Ct the following calculations were made: Since the total alkalinity, At, and total borate, Bt, are n o t affected b y the dissolution of carbon dioxide, the present values (ratios to chlorinity) of At / C1 = 120 #Mw/%0 and Bt/C1 = 21.3 gM w/%0 were used. A salinity of 35 °/00 was used to calculate C1 = 3 5 / 1 . 8 0 6 5 5 %0. These values, together with the solubility constants for carbon dioxide of Weiss (1974) and the acidity constants of Hansson (cf. Almgren et al., 1975), were used to calculate Ct for different values of temperature and Pco~ (partial pressure of carbon dioxide). The results are shown in Table I. Table I shows that Ct will increase a b o u t 0.6 pMw for an increase of the partial pressure of CO 2 of 1 ppm. Table I also demonstrates that Ct will decrease a b o u t 8 #Mw for an increase in temperature of one degree. Table I has been used b y Anderson and Dyrssen (1981) in their treatment of alkalinity and total carbonate data from the eastern Arctic Ocean. It is concluded that Ct of the Norwegian Sea surface water has increased by 25--50 pMw since 1850. The corresponding shift in the pH of surface seawater is --0.05 to --0.1 using the pH scale of Hansson (cf. Almgren et al., 1975). In considering the time influence on Ct b y the increase in atmospheric carbon dioxide (cf. Brewer, 1978; Chen and Millero, 1979; Jones and Levy, TABLE
I
Calculation of the total c a r b o n a t e c o n c e n t r a t i o n in seawater for d i f f e r e n t temperatures pressures (in ppm) of carbon d i o x i d e in t h e a t m o s p h e r e ( t h e chlorAt/C1 (= 120 /~lVlw per %o) and Bt/C1 (= 21.3 p-Mw per %o) are
and d i f f e r e n t partial inity (---- 19.374°/00), maintained constant)
p
0°
5°
10 °
15 °
20 °
25 °
30 °
250 260 270 280 290 300 310 320 330 340 350
2133 2139 2145 2151 2157 2162 2168 2172 2177 2182 2186
2089 2096 2103 2110 2116 2122 2128 2133 2138 2143 2148
2045 2052 2060 2067 2074 2080 2086 2092 2098 2103 2109
2000 2008 2016 2024 2031 2038 2045 2051 2057 2063 2068
1956 1965 1973 1981 1989 1996 2003 2010 2016 2023 2029
1914 1923 1932 1940 1948 1955 1963 1970 1977 1983 1989
1874 1883 1892 1900 1908 1916 1924 1931 1938 1945 1951
185
1981) one has to assume t h a t the biological processes influencing A t and Ct are the same t o d a y as before the impact of industrialization.
REFERENCES Almgren, T., Dyrssen, D. and Strandberg, M., 1975. Determination of pH on the moles per kg seawater scale (M w ). Deep-Sea Res., 22: 635---646. Almgren, T., Dyrssen, D. and Strandberg, M., 1977. Computerized high-precision titrations of some major constituents of seawater on board the R.V. Dmitry Mendeleev. DeepSea Res., 24 : 345--364. Anderson, L. and Dyrssen, D., 1981. Chemical constituents of the Arctic Ocean in the Svalbard area. Oceanol. Acta, 4: 305--311. Brewer, P.G., 1978. Direct observation of the oceanic CO2 increase. Geophys. Res. Lett., 5 : 997--1000. Broecker, W.S., 1974. Chemical Oceanography. Harcourt Brace Jovanovich, pp. 22--26 and 59--67. Chen, C.-T. and Millero, F.J., 1979. Gradual increase of oceanic CO 2 . Nature, 277: 205-206. Dyrssen, D., 1977. The chemistry of plankton production and decomposition in seawater. In: N.R. Andersen and B.J. Zahuranec (Editors), Ocean Sound Scattering Prediction. Plenum Press, New York, 1977, pp. 65--84. Dyrssen, D. and Sill~n, L.-G., 1967. Alkalinity and total carbonate in seawater. A plea for p-T-independent data. Tellus, XIX: 113--121. Jones, E.P. and Levy, E.M., 1981. Oceanic CO 2 increase in Baffin Bay. J. Mar. Res., 39 : 405--416. Keir, R.S., 1979. The calculation of carbonate ion concentration from total CO2 and titration alkalinity. Mar. Chem., 8: 95--97. {~stlund, H.G. and Dyrssen, D. (Editors), 1980. Workshop on oceanic CO2 standardization at La Jolla, CA, Nov 30--Dec 1, 1979. Weiss, R.F., 1974. Carbon dioxide in water and seawater: the solubility of a non-ideal gas. Mar. Chem., 2: 203--215.