- Email: [email protected]
The biogeochemical cycling of carbon dioxide in the oceans — perturbations by man
The Science of the Total Environment 277 Ž2001. 1᎐6
The biogeochemical cycling of carbon dioxide in the oceans ᎏ perturbations by man 夽 David W. DyrssenU SE-412 96, Sweden Department of Analytical and Marine Chemistry, Gothenburg Uni¨ ersity, Goteborg ¨ Accepted 22 March 2001
Abstract The purpose of the paper is to follow up the contribution by Dyrssen and Turner to the Hemavan meeting in 1993 on CO 2 chemistry. Machta’s treatment from 1971 of the role of oceans and biosphere in the carbon dioxide cycle is reviewed. Using data on the emission of CO 2 and the atmospheric content in addition to the value recently presented by Takahashi et al. for the net sink for global oceans the following numbers have been calculated for the period 1990 to 2000, annual emission of CO 2 , 6.185 PgC ŽPetagram s 10 15 g.. Annual atmospheric accumulation, 2.930 PgC. Annual sinks, 3.255 PgC. Net uptake for 1990 by the oceans, 1.151 PgCryear. Solubility pump into the mixed layer, 0.828 PgCryear. Residual input Že.g. riverborne., 0.323 PgCryear. Annual uptake by land phytomass, 2.104 PgC. In addition, perturbations involving irrigation and fertilization, limestone dissolution, iron and clathrate addition are mentioned. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Biogeochemical; Carbon dioxide; Oceans
1. Purpose In the proceedings of the meeting at Hemavan in 1993 Dyrssen and Turner Ž1994. contributed with a paper on the uptake of carbon dioxide by the oceans. In that paper the authors presented an atmospheric budget, a brief description of the
CO 2 chemistry in seawater and the solubility and biological pumps. The estimated oceanic sink for 1980᎐1989 was 2.0" 0.6 PgC per year Žs Gton C per year.. The purpose of this paper is to update the 1993 paper with knowledge1 CO2 in the Oceans, that was presented at the 2nd International Sympo-
夽
ICCDU 5. 5th International Conference on Carbon Dioxide Utilisation, 1999 Karlsruhe, Germany, 5᎐10th September 1999. U Fax: q46-31-7722785. E-mail address: [email protected] ŽD.W. Dyrssen..
1 CO2 in the Oceans, Extended Abstracts, Tsukuba Center for Institutes, Tsukuba, Japan. The papers referred to in this volume are denoted with two numbers, e.g. 18᎐01 or P-01 for posters.
0048-9697r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 8 - 9 6 9 7 Ž 0 1 . 0 0 8 2 8 - 2
2
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
sium on ‘CO 2 in the Oceans’ at Tsukuba in January 18᎐21, 1999. Many of the papers that were presented at this meeting were based on the immense amount of data gathered by large programs such as GEOSECS, TTO, JGOFS and WOCE as well as by more regional expeditions, e.g. to polar waters ŽCherici et al., 1999.. The global investigations of the carbon species and isotopes, nutrients Žnitrate, phosphate, silica.,
oxygen and tracers Ž 14 C, 3 H᎐ 3 He, freons. have been finished. However, the interpretations vary and a lot of work remains until uncertainties are removed and a general consensus is obtained.
2. An early prediction At the Nobel Symposium ‘The Changing
Fig. 1. A 1971 prediction of the 20th century carbon dioxide concentration in the atmosphere according to Lester Machta Žthe article has been reprinted, cf. Ayres et al., 1999.. Machta suggested corrections that would lower the 1860 value to 290 ppmv and increase the 2000 value to 380 ppmv.
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
Chemistry of the Oceans’ held in August 16᎐20, 1971 at Lerum, outside Gothenburg, Lester Machta presented a model to predict future atmospheric concentrations of CO 2 and seasonal variations for the two hemispheres. In his model Machta used a CO 2 storage time of 40 years for trees Žlong term land biosphere. and a lag of two years cycle for crops Žshort-term biosphere.. For the marine biosphere he used a lag of 1 year. With adjustments, the calculations ŽFig. 1. predicted a partial pressure of 380 ppmv Žppm by volume. in year 2000, but it looks like it will be close to 368. Machta overestimated the annual release of CO 2 to the atmosphere for 1986᎐1999. Permission has been granted to reproduce Machta’s article ŽAyres et al., 1999.. At the time Machta made his prediction one could see the diminishing content of radioactive 14 CO 2 in the atmosphere due to the exchange of 14 CO 2 with 12 CO 2 in surface waters, for 1970᎐2000 the reduction is 50% in 11 years Ž t 12 s 11 years.. The stratospheric content of 14 CO 2 had been considerably increased Žcf. Machta, Fig. 2. during the testing of heavy nuclear devices in 1958᎐1963. This supplied Machta with a global exchange rate Žfractional transfer into the oceans of 0.54 per year and fractional transfer out of the mixed layer of 0.10 per year.. Furthermore, Keel-
3
ing at Scripps Institution of Oceanography had run the measurements of the atmospheric concentration of CO 2 at Mauna Loa on Hawaii since 1958. The results up to 1970 showed an increase of approximately 0.3% per year as well as an annual variation of approximately 1.3% due to the production and decay of mainly the land vegetation in the Northern Hemisphere. Now the data are available on the Internet. The concentration unit ppm by volume Žppmv. can be recalculated to ppm by weight Ž44.01r28.94. and then the weight of carbon as CO 2 in the atmosphere can be compared with the weight of carbon released as CO 2 from fossil-fuel burning and cement production. This is done in Fig. 2 for accumulated weights during the 20th century. The similarity between Figs. 1 and 2 is obvious.
3. Emissions and accumulation Using the table attached to Fig. 2 one may calculate the following numbers: 䢇
1980᎐1985: emission 5.175 PgCryear; atm. increase 3.052 PgCryear; and difference 2.123 PgCryear,
Fig. 2. The figure shows the changes during the 20th century. Diamonds: accumulated emission of fossil fuel carbon ŽPgC. since 1860. Squares: accumulated carbon ŽPgC. as carbon dioxide since 1860 calculated from Žp ᎐ 288.6.2.117 where 288.6 ppmv is the partial pressure of carbon dioxide in year 1860.
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
4
1985᎐1990: emission 5.886 PgCryear; atm. increase 3.498 PgCryear; and difference 2.388 PgCryear, 1990᎐1995: emission 6.185 PgCryear; atm. increase 2.930 PgCryear; and difference 3.255 PgCryear.
䢇
䢇
Thus, the annual emission is rising rather steadily, while the atmospheric increase varies approximately 3.160 PgCryear. In the budget of anthropogenic CO 2 in the atmosphere for 1980᎐1989 presented by Dyrssen and Turner Ž1994. the numbers were 5.4" 0.5 for the emission and 3.2" 0.2 PgCryear for the accumulation in the atmosphere. 4. Global sinks In the treatments of global ocean data the effect of wind speed on the CO 2 gas transfer according to Wanninkhof Ž1992. was used in several contributions at the Tsukuba meeting of the 2nd International Symposium on ‘CO2 in the Oceans’. Based on two million measurements for the P CO 2 in surface waters and available temperature and wind speed data ŽTakahashi et al., 1999. arrived at the 1990 numbers in Table 1. Negative values indicate that the ocean is a sink for atmospheric CO 2 . Around the equator CO 2 is released Ž0.719 PgCryear.. The global ocean sink is 1.151 PgCryear according to Table 1. This is only 19.1% of the emitted 6.0355 PgCryear for the 1985᎐1995 decade. The value of 1.151 is within the value of 1.6" 0.7 PgCryear presented
at the Tsukuba meeting by ŽGruber and Keeling, 1999.. The sink of 1.151 Pg for 1990 calculated by ŽTakahashi et al., 1999. is only a fraction of the CO 2 exchange with the ocean surface mixed layer Žestimated depth of 270 m. which is approximately 270 PgCryear according to Machta. The CO 2 exchange with the living land phytomass was approximately 56 PgCryear according to Machta. At the Tsukuba meeting Gruber and Keeling presented a table with the flux values 87 PgCryear Žatm. into oc. and 23 PgCryear for the flux with terrestrial biosphere. One should notice that the land area of the Northern Hemisphere Žapprox. 99 = 10 6 km2 . is larger than the land area of the Southern Hemisphere Žapprox. 48 = 10 6 km2 .. The industrial belt where most of the CO 2 is emitted extends over 30⬚ to 60⬚N in the Northern Hemisphere. The emission during 1990᎐1995 was 6.185 PgCryear. This amount should be compared with the increase in atmospheric CO 2 of 2.930 PgCryear Ž47.4%.. This number is calculated from the mean increase in the atmospheric concentration of CO 2 during 1990 to 2000 of 1.4 ppmvryear Ž354᎐368 ppmv.. Dyrssen and Wedborg Ž1982. have calculated the increase in total dissolved inorganic carbon ŽTDIC. for the range 250᎐400 ppmv at 0⬚ and 25⬚ and a salinity of 35 and total alkalinity ŽTA. of 2325 molrkg. A mean value of TDIC of 52 molrkg Žor 0.052= 1.03 molrm3 . for an increase of CO 2 of 280 to 375 ppmv may be used in order to calculate an input of 0.828 PgCryear for an increase of 1.4
Table 1 Net sea-air CO 2 fluxes for the global oceans ŽTakahashi et al., 1999. a Latitudes o
N. of 50 N 50o N᎐14o N 14o N᎐14o S 14o S᎐50o S S. of 50o S Total Uptake Ž%. Area Ž106 km2 . a
Pacific
Atlantic
Indian
y5 y309 q538 y252
y356 y257 q83 y162
q18 q98 y298
y692 60 72.7 Ž22.4%.
y182 16 52.7 Ž16.3%.
y28 2 153.5 Ž47.4%.
The numbers are given in TgCryear for 1990 ŽTg, teragram s 10 12 g..
Southern
Global
y249 y249 22 44.9 Ž13.9%.
y361 y548 q719 y712 y249 y1151 100 323.9 Ž100%.
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
ppmvryear and a mixed depth of 270 m w1.4Ž0.052 = 1.03r95.270 = 323.9= 10 12 = 12x. If a somewhat lower value is chosen for the depth of the mixed layer Ž d . the input will be lowered by dr270. Thus, it is possible to calculate the net transfer of CO 2 into the oceans and the land vegetation for the period of 1990 to 2000 as follows: 䢇
䢇
䢇
Annual emission of CO 2 , 6.185 PgC. Annual accumulation in the atmosphere, 2.930 PgC. Annual sinks, 3.255 PgC Ž51%.. Net uptake by the oceans for 1990, 1.151 PgC. Solubility pump into the mixed layer, 0.828 PgCryear. Residual input Že.g. by rivers., 0.323 PgCryear. Annual uptake by land phytomass, 3.255y 1.151s 2.104 PgCryear.
The further diffusion of the CO 2 input into the deeper waters Žcf. Feely et al., 1999. is not considered in this rough calculation, nor is the formation of dense water masses, e.g. in the Northeast Atlantic Ocean Žcf. Tait et al., 1999.. The vertical exchange of seawater between the mixed layer and the deep ocean involves less CO 2 than the exchange between the troposphere and the mixed layer. The exchange is, however, large enough to restore nitrogen and phosphorus lost by the fallout from the biological production. The transfer of organic nitrogen to nitrate in the deep ocean NH 3 Ž org. q 2O 2 « Hqq NO 3y qH 2 O affects both the oxygen concentration and the alkalinity. One way to correct for the further transport of carbon into the deep ocean is to use the residence time of the deep water. Machta, ŽAyres et al., 1999. used 1600 years, but the average value is probably closer to 1000 years. 5. The biocycling-perturbations by man 5.1. Land Even if the CO 2 exchange with the land vegetation is in the order of 100 PgCryear an annual
5
input of 6 PgC is not a negligible quantity. Machta’s, ŽAyres et al., 1999. plain approach with a long term storage time of 40 years and a short term storage time of 2 years may be revised and extended, but its simplicity is beneficial. It is reasonable that an increase of the atmospheric concentration stimulates the growth on land, especially as man has introduced irrigation and improved the fertilizers by balancing nitrate, urea and ammonium, using soluble forms of phosphate and adding limestone, magnesium, cobalt, copper, zinc and molybdenum. Within the industrial belt acid rain has damaging effects, but it brings back ammonia that has evaporated from farmlands and nitrate originating from NO x in exhaust gases. Part of the organic matter produced on land is brought to the sea as dissolved and particulate organic matter in rivers, runoff and sewage and waste water pipes Žcf. Aumont et al., 1999.. A river inflow of 1 Sv Ž10 6 m3rs. into the mixed layer with 10.2 gCrm3 would explain an input of inorganic and organic carbon of 0.323 PgCryear. 5.2. Ocean The solubility pump, i.e. the increase of CO 2 ŽTDIC. in the mixed layer, is increasing with the atmospheric concentration as calculated above. Since the main carbonate equilibrium is the autoprotolysis of the major species HCOy 3 2HCO 3ym CO 2 q H 2 O q CO 32 y the increase of the atmospheric CO 2 concentration from 280 to 368 ppmv has only slightly shifted the equilibrium. TDIC Žsum of conc. of CO 2 , 2y . H 2 CO 3 , HCOy has been increased 3 and CO 3 by 48 molrkg from the pre-industrial time around 1750 to year 2000. This has lowered the pH by approximately 0.1 unit, which is negligible in relation to the effects of the carbohydrate production in the euphotic zone and decomposition below this zone together with the production of biogenic calcite. This might shift the pH between 8.5 and 7.5. Since the carbohydrate production is approximately 4᎐5 times larger than the calcite production the surface Žeuphotic.
6
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
waters are always supersaturated with respect to the chemogenic formation of calcite. However, the magnesium and sulfate ions hamper this formation. The phytoplankton production is the basis for the marine life in the upper ocean. This life secretes organic material Ždetritus. into deeper waters together with plankton shells of calcite Žforaminipheres and pteropodes.. Since fish feed on plankton overfishing is diminishing the secretion. The surface waters are refertilized by the consumption of the primary photosynthetic production and in the sub-polar waters by vertical mixing in the mixed layer which brings back the nitrate and phosphate for new production. Man is also perturbing the calcium cycle. Kremling and Wilhelm Ž1997. have measured an increase of calcium in Baltic waters. The action of acid rain and an increase of the atmospheric CO 2 concentration and organic matter on Central European limestone may explain this CaCO 3 Ž s . q Hq« Ca2qq HCO 3y CaCO 3 Ž s . q CO 2 Ž g. q H 2 O « Ca2qq 2HCO 3y CaCO 3 Ž s . q CH 2 O Ž org. q O 2 « Ca2qq 2HCO 3y . The carbonate dissolution approach suggested by Caldeira and Rau , at the Tsukuba meeting, in order to sequester CO 2 will also increase the flux of CaŽHCO 3 . 2 into the oceans. Iron is brought into the sea by rivers in the form of ironŽII. Žmainly Fe 2q . which is then retained in the coastal zones as FeOOH wironŽIII. hydroxidex. The plankton production in the open sea may, therefore, suffer from iron deficiency. Also polar waters close to the Antarctic continent may at times suffer from a shortage of iron ŽHannon et al., 1999.. It has, therefore, been suggested to increase the production by fertilizing the ocean with iron Žcf. Watson et al., 1999.. This could be done with leaking gyre floats filled with a solution of ironŽII. sulfate or, as was suggested at the Tsukuba meeting, with a water-soluble glass containing ironŽII. ŽHirose et al., 1999..
It has also been suggested to increase the removal of CO 2 by forming CO 2 ŽH 2 O.5.75 clathrates at depth. An experiment at 3650 m was presented at the Tsukuba meeting ŽBrewer et al., 1999.. In the long run such clathrates would react with biogenic calcite at the sediment surface CaCO 3 Ž s . q CO 2 Ž H 2 O . 5.75 Ž s . « Ca2qq 2HCO 3y q4.75H 2 O. Eddy diffusion will then slowly bring back calcium and hydrogen carbonate to surface waters. Considering the scale of the natural processes and the huge changes of land vegetation the perturbations by adding iron and forming clathrates might be rather small. It seems better to go easy on the burning of fossil fuels until reliable climate models have been worked out. Saving coal and oil and using gas is one way to produce energy with less CO 2 and air pollution. An industrial process to remove CO 2 might, in some cases, prove to be less costly than to check certain uses of fossil fuels. References Aumont O, Orr JC, Monfray PC, Ludwig W, Probst J-L, 1999:18-13. Ayres RU, Button K, Nijkump P. Global Aspects of the Environment. Cheltenham, UK: Edward Elgar, 1999. Brewer PG, Friederich G, Pelzer ET, Orr F Jr, 1999:22-12. Caldeira K, Rau GH, 1999:22-13. Chierici M, Drange H, Anderson LG, Johannessen T, 1999:21-03. Dyrssen D, Wedborg M. Mar Chem, 1982:183. Dyrssen D, Turner DR. In: Paul J, Pradier C-M, editors. Carbon Dioxide Chemistry: Environmental issues. London: The Royal Society of Chemistry, 1994:405. Feely RA, Sabine CL, Key RM, Peng T-S, Wanninkhof R, 1999:20-01. Gruber W, Keeling CD, 1999:20-11. Hannon E, Lancelot C, Stoll M, De Baar H, 1999:19-13. Hirose N, Watanuki A, Kitao S, Sennon Y, 1999:P-05. Kremling K, Wilhelm G. Mar Pollut Bull 1997;34:763. Tait KK, Gershey RM, Jones EP, 1999:20-03. Takahashi T, Wanninkhof RH, Feely RA, Weiss RF, Weiss, Chipman DW, Bates N, Olafsson J, Sabine C, Sutherland SC, 1999:18-01. Wanninkhof R. J Geophys Res 1992;97:7373 19-01. Watson AJ, Jickells TD, Maher BA, 1999:21-01.
The biogeochemical cycling of carbon dioxide in the oceans ᎏ perturbations by man 夽 David W. DyrssenU SE-412 96, Sweden Department of Analytical and Marine Chemistry, Gothenburg Uni¨ ersity, Goteborg ¨ Accepted 22 March 2001
Abstract The purpose of the paper is to follow up the contribution by Dyrssen and Turner to the Hemavan meeting in 1993 on CO 2 chemistry. Machta’s treatment from 1971 of the role of oceans and biosphere in the carbon dioxide cycle is reviewed. Using data on the emission of CO 2 and the atmospheric content in addition to the value recently presented by Takahashi et al. for the net sink for global oceans the following numbers have been calculated for the period 1990 to 2000, annual emission of CO 2 , 6.185 PgC ŽPetagram s 10 15 g.. Annual atmospheric accumulation, 2.930 PgC. Annual sinks, 3.255 PgC. Net uptake for 1990 by the oceans, 1.151 PgCryear. Solubility pump into the mixed layer, 0.828 PgCryear. Residual input Že.g. riverborne., 0.323 PgCryear. Annual uptake by land phytomass, 2.104 PgC. In addition, perturbations involving irrigation and fertilization, limestone dissolution, iron and clathrate addition are mentioned. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Biogeochemical; Carbon dioxide; Oceans
1. Purpose In the proceedings of the meeting at Hemavan in 1993 Dyrssen and Turner Ž1994. contributed with a paper on the uptake of carbon dioxide by the oceans. In that paper the authors presented an atmospheric budget, a brief description of the
CO 2 chemistry in seawater and the solubility and biological pumps. The estimated oceanic sink for 1980᎐1989 was 2.0" 0.6 PgC per year Žs Gton C per year.. The purpose of this paper is to update the 1993 paper with knowledge1 CO2 in the Oceans, that was presented at the 2nd International Sympo-
夽
ICCDU 5. 5th International Conference on Carbon Dioxide Utilisation, 1999 Karlsruhe, Germany, 5᎐10th September 1999. U Fax: q46-31-7722785. E-mail address: [email protected] ŽD.W. Dyrssen..
1 CO2 in the Oceans, Extended Abstracts, Tsukuba Center for Institutes, Tsukuba, Japan. The papers referred to in this volume are denoted with two numbers, e.g. 18᎐01 or P-01 for posters.
0048-9697r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 8 - 9 6 9 7 Ž 0 1 . 0 0 8 2 8 - 2
2
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
sium on ‘CO 2 in the Oceans’ at Tsukuba in January 18᎐21, 1999. Many of the papers that were presented at this meeting were based on the immense amount of data gathered by large programs such as GEOSECS, TTO, JGOFS and WOCE as well as by more regional expeditions, e.g. to polar waters ŽCherici et al., 1999.. The global investigations of the carbon species and isotopes, nutrients Žnitrate, phosphate, silica.,
oxygen and tracers Ž 14 C, 3 H᎐ 3 He, freons. have been finished. However, the interpretations vary and a lot of work remains until uncertainties are removed and a general consensus is obtained.
2. An early prediction At the Nobel Symposium ‘The Changing
Fig. 1. A 1971 prediction of the 20th century carbon dioxide concentration in the atmosphere according to Lester Machta Žthe article has been reprinted, cf. Ayres et al., 1999.. Machta suggested corrections that would lower the 1860 value to 290 ppmv and increase the 2000 value to 380 ppmv.
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
Chemistry of the Oceans’ held in August 16᎐20, 1971 at Lerum, outside Gothenburg, Lester Machta presented a model to predict future atmospheric concentrations of CO 2 and seasonal variations for the two hemispheres. In his model Machta used a CO 2 storage time of 40 years for trees Žlong term land biosphere. and a lag of two years cycle for crops Žshort-term biosphere.. For the marine biosphere he used a lag of 1 year. With adjustments, the calculations ŽFig. 1. predicted a partial pressure of 380 ppmv Žppm by volume. in year 2000, but it looks like it will be close to 368. Machta overestimated the annual release of CO 2 to the atmosphere for 1986᎐1999. Permission has been granted to reproduce Machta’s article ŽAyres et al., 1999.. At the time Machta made his prediction one could see the diminishing content of radioactive 14 CO 2 in the atmosphere due to the exchange of 14 CO 2 with 12 CO 2 in surface waters, for 1970᎐2000 the reduction is 50% in 11 years Ž t 12 s 11 years.. The stratospheric content of 14 CO 2 had been considerably increased Žcf. Machta, Fig. 2. during the testing of heavy nuclear devices in 1958᎐1963. This supplied Machta with a global exchange rate Žfractional transfer into the oceans of 0.54 per year and fractional transfer out of the mixed layer of 0.10 per year.. Furthermore, Keel-
3
ing at Scripps Institution of Oceanography had run the measurements of the atmospheric concentration of CO 2 at Mauna Loa on Hawaii since 1958. The results up to 1970 showed an increase of approximately 0.3% per year as well as an annual variation of approximately 1.3% due to the production and decay of mainly the land vegetation in the Northern Hemisphere. Now the data are available on the Internet. The concentration unit ppm by volume Žppmv. can be recalculated to ppm by weight Ž44.01r28.94. and then the weight of carbon as CO 2 in the atmosphere can be compared with the weight of carbon released as CO 2 from fossil-fuel burning and cement production. This is done in Fig. 2 for accumulated weights during the 20th century. The similarity between Figs. 1 and 2 is obvious.
3. Emissions and accumulation Using the table attached to Fig. 2 one may calculate the following numbers: 䢇
1980᎐1985: emission 5.175 PgCryear; atm. increase 3.052 PgCryear; and difference 2.123 PgCryear,
Fig. 2. The figure shows the changes during the 20th century. Diamonds: accumulated emission of fossil fuel carbon ŽPgC. since 1860. Squares: accumulated carbon ŽPgC. as carbon dioxide since 1860 calculated from Žp ᎐ 288.6.2.117 where 288.6 ppmv is the partial pressure of carbon dioxide in year 1860.
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
4
1985᎐1990: emission 5.886 PgCryear; atm. increase 3.498 PgCryear; and difference 2.388 PgCryear, 1990᎐1995: emission 6.185 PgCryear; atm. increase 2.930 PgCryear; and difference 3.255 PgCryear.
䢇
䢇
Thus, the annual emission is rising rather steadily, while the atmospheric increase varies approximately 3.160 PgCryear. In the budget of anthropogenic CO 2 in the atmosphere for 1980᎐1989 presented by Dyrssen and Turner Ž1994. the numbers were 5.4" 0.5 for the emission and 3.2" 0.2 PgCryear for the accumulation in the atmosphere. 4. Global sinks In the treatments of global ocean data the effect of wind speed on the CO 2 gas transfer according to Wanninkhof Ž1992. was used in several contributions at the Tsukuba meeting of the 2nd International Symposium on ‘CO2 in the Oceans’. Based on two million measurements for the P CO 2 in surface waters and available temperature and wind speed data ŽTakahashi et al., 1999. arrived at the 1990 numbers in Table 1. Negative values indicate that the ocean is a sink for atmospheric CO 2 . Around the equator CO 2 is released Ž0.719 PgCryear.. The global ocean sink is 1.151 PgCryear according to Table 1. This is only 19.1% of the emitted 6.0355 PgCryear for the 1985᎐1995 decade. The value of 1.151 is within the value of 1.6" 0.7 PgCryear presented
at the Tsukuba meeting by ŽGruber and Keeling, 1999.. The sink of 1.151 Pg for 1990 calculated by ŽTakahashi et al., 1999. is only a fraction of the CO 2 exchange with the ocean surface mixed layer Žestimated depth of 270 m. which is approximately 270 PgCryear according to Machta. The CO 2 exchange with the living land phytomass was approximately 56 PgCryear according to Machta. At the Tsukuba meeting Gruber and Keeling presented a table with the flux values 87 PgCryear Žatm. into oc. and 23 PgCryear for the flux with terrestrial biosphere. One should notice that the land area of the Northern Hemisphere Žapprox. 99 = 10 6 km2 . is larger than the land area of the Southern Hemisphere Žapprox. 48 = 10 6 km2 .. The industrial belt where most of the CO 2 is emitted extends over 30⬚ to 60⬚N in the Northern Hemisphere. The emission during 1990᎐1995 was 6.185 PgCryear. This amount should be compared with the increase in atmospheric CO 2 of 2.930 PgCryear Ž47.4%.. This number is calculated from the mean increase in the atmospheric concentration of CO 2 during 1990 to 2000 of 1.4 ppmvryear Ž354᎐368 ppmv.. Dyrssen and Wedborg Ž1982. have calculated the increase in total dissolved inorganic carbon ŽTDIC. for the range 250᎐400 ppmv at 0⬚ and 25⬚ and a salinity of 35 and total alkalinity ŽTA. of 2325 molrkg. A mean value of TDIC of 52 molrkg Žor 0.052= 1.03 molrm3 . for an increase of CO 2 of 280 to 375 ppmv may be used in order to calculate an input of 0.828 PgCryear for an increase of 1.4
Table 1 Net sea-air CO 2 fluxes for the global oceans ŽTakahashi et al., 1999. a Latitudes o
N. of 50 N 50o N᎐14o N 14o N᎐14o S 14o S᎐50o S S. of 50o S Total Uptake Ž%. Area Ž106 km2 . a
Pacific
Atlantic
Indian
y5 y309 q538 y252
y356 y257 q83 y162
q18 q98 y298
y692 60 72.7 Ž22.4%.
y182 16 52.7 Ž16.3%.
y28 2 153.5 Ž47.4%.
The numbers are given in TgCryear for 1990 ŽTg, teragram s 10 12 g..
Southern
Global
y249 y249 22 44.9 Ž13.9%.
y361 y548 q719 y712 y249 y1151 100 323.9 Ž100%.
D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
ppmvryear and a mixed depth of 270 m w1.4Ž0.052 = 1.03r95.270 = 323.9= 10 12 = 12x. If a somewhat lower value is chosen for the depth of the mixed layer Ž d . the input will be lowered by dr270. Thus, it is possible to calculate the net transfer of CO 2 into the oceans and the land vegetation for the period of 1990 to 2000 as follows: 䢇
䢇
䢇
Annual emission of CO 2 , 6.185 PgC. Annual accumulation in the atmosphere, 2.930 PgC. Annual sinks, 3.255 PgC Ž51%.. Net uptake by the oceans for 1990, 1.151 PgC. Solubility pump into the mixed layer, 0.828 PgCryear. Residual input Že.g. by rivers., 0.323 PgCryear. Annual uptake by land phytomass, 3.255y 1.151s 2.104 PgCryear.
The further diffusion of the CO 2 input into the deeper waters Žcf. Feely et al., 1999. is not considered in this rough calculation, nor is the formation of dense water masses, e.g. in the Northeast Atlantic Ocean Žcf. Tait et al., 1999.. The vertical exchange of seawater between the mixed layer and the deep ocean involves less CO 2 than the exchange between the troposphere and the mixed layer. The exchange is, however, large enough to restore nitrogen and phosphorus lost by the fallout from the biological production. The transfer of organic nitrogen to nitrate in the deep ocean NH 3 Ž org. q 2O 2 « Hqq NO 3y qH 2 O affects both the oxygen concentration and the alkalinity. One way to correct for the further transport of carbon into the deep ocean is to use the residence time of the deep water. Machta, ŽAyres et al., 1999. used 1600 years, but the average value is probably closer to 1000 years. 5. The biocycling-perturbations by man 5.1. Land Even if the CO 2 exchange with the land vegetation is in the order of 100 PgCryear an annual
5
input of 6 PgC is not a negligible quantity. Machta’s, ŽAyres et al., 1999. plain approach with a long term storage time of 40 years and a short term storage time of 2 years may be revised and extended, but its simplicity is beneficial. It is reasonable that an increase of the atmospheric concentration stimulates the growth on land, especially as man has introduced irrigation and improved the fertilizers by balancing nitrate, urea and ammonium, using soluble forms of phosphate and adding limestone, magnesium, cobalt, copper, zinc and molybdenum. Within the industrial belt acid rain has damaging effects, but it brings back ammonia that has evaporated from farmlands and nitrate originating from NO x in exhaust gases. Part of the organic matter produced on land is brought to the sea as dissolved and particulate organic matter in rivers, runoff and sewage and waste water pipes Žcf. Aumont et al., 1999.. A river inflow of 1 Sv Ž10 6 m3rs. into the mixed layer with 10.2 gCrm3 would explain an input of inorganic and organic carbon of 0.323 PgCryear. 5.2. Ocean The solubility pump, i.e. the increase of CO 2 ŽTDIC. in the mixed layer, is increasing with the atmospheric concentration as calculated above. Since the main carbonate equilibrium is the autoprotolysis of the major species HCOy 3 2HCO 3ym CO 2 q H 2 O q CO 32 y the increase of the atmospheric CO 2 concentration from 280 to 368 ppmv has only slightly shifted the equilibrium. TDIC Žsum of conc. of CO 2 , 2y . H 2 CO 3 , HCOy has been increased 3 and CO 3 by 48 molrkg from the pre-industrial time around 1750 to year 2000. This has lowered the pH by approximately 0.1 unit, which is negligible in relation to the effects of the carbohydrate production in the euphotic zone and decomposition below this zone together with the production of biogenic calcite. This might shift the pH between 8.5 and 7.5. Since the carbohydrate production is approximately 4᎐5 times larger than the calcite production the surface Žeuphotic.
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D.W. Dyrssen r The Science of the Total En¨ ironment 277 (2001) 1᎐6
waters are always supersaturated with respect to the chemogenic formation of calcite. However, the magnesium and sulfate ions hamper this formation. The phytoplankton production is the basis for the marine life in the upper ocean. This life secretes organic material Ždetritus. into deeper waters together with plankton shells of calcite Žforaminipheres and pteropodes.. Since fish feed on plankton overfishing is diminishing the secretion. The surface waters are refertilized by the consumption of the primary photosynthetic production and in the sub-polar waters by vertical mixing in the mixed layer which brings back the nitrate and phosphate for new production. Man is also perturbing the calcium cycle. Kremling and Wilhelm Ž1997. have measured an increase of calcium in Baltic waters. The action of acid rain and an increase of the atmospheric CO 2 concentration and organic matter on Central European limestone may explain this CaCO 3 Ž s . q Hq« Ca2qq HCO 3y CaCO 3 Ž s . q CO 2 Ž g. q H 2 O « Ca2qq 2HCO 3y CaCO 3 Ž s . q CH 2 O Ž org. q O 2 « Ca2qq 2HCO 3y . The carbonate dissolution approach suggested by Caldeira and Rau , at the Tsukuba meeting, in order to sequester CO 2 will also increase the flux of CaŽHCO 3 . 2 into the oceans. Iron is brought into the sea by rivers in the form of ironŽII. Žmainly Fe 2q . which is then retained in the coastal zones as FeOOH wironŽIII. hydroxidex. The plankton production in the open sea may, therefore, suffer from iron deficiency. Also polar waters close to the Antarctic continent may at times suffer from a shortage of iron ŽHannon et al., 1999.. It has, therefore, been suggested to increase the production by fertilizing the ocean with iron Žcf. Watson et al., 1999.. This could be done with leaking gyre floats filled with a solution of ironŽII. sulfate or, as was suggested at the Tsukuba meeting, with a water-soluble glass containing ironŽII. ŽHirose et al., 1999..
It has also been suggested to increase the removal of CO 2 by forming CO 2 ŽH 2 O.5.75 clathrates at depth. An experiment at 3650 m was presented at the Tsukuba meeting ŽBrewer et al., 1999.. In the long run such clathrates would react with biogenic calcite at the sediment surface CaCO 3 Ž s . q CO 2 Ž H 2 O . 5.75 Ž s . « Ca2qq 2HCO 3y q4.75H 2 O. Eddy diffusion will then slowly bring back calcium and hydrogen carbonate to surface waters. Considering the scale of the natural processes and the huge changes of land vegetation the perturbations by adding iron and forming clathrates might be rather small. It seems better to go easy on the burning of fossil fuels until reliable climate models have been worked out. Saving coal and oil and using gas is one way to produce energy with less CO 2 and air pollution. An industrial process to remove CO 2 might, in some cases, prove to be less costly than to check certain uses of fossil fuels. References Aumont O, Orr JC, Monfray PC, Ludwig W, Probst J-L, 1999:18-13. Ayres RU, Button K, Nijkump P. Global Aspects of the Environment. Cheltenham, UK: Edward Elgar, 1999. Brewer PG, Friederich G, Pelzer ET, Orr F Jr, 1999:22-12. Caldeira K, Rau GH, 1999:22-13. Chierici M, Drange H, Anderson LG, Johannessen T, 1999:21-03. Dyrssen D, Wedborg M. Mar Chem, 1982:183. Dyrssen D, Turner DR. In: Paul J, Pradier C-M, editors. Carbon Dioxide Chemistry: Environmental issues. London: The Royal Society of Chemistry, 1994:405. Feely RA, Sabine CL, Key RM, Peng T-S, Wanninkhof R, 1999:20-01. Gruber W, Keeling CD, 1999:20-11. Hannon E, Lancelot C, Stoll M, De Baar H, 1999:19-13. Hirose N, Watanuki A, Kitao S, Sennon Y, 1999:P-05. Kremling K, Wilhelm G. Mar Pollut Bull 1997;34:763. Tait KK, Gershey RM, Jones EP, 1999:20-03. Takahashi T, Wanninkhof RH, Feely RA, Weiss RF, Weiss, Chipman DW, Bates N, Olafsson J, Sabine C, Sutherland SC, 1999:18-01. Wanninkhof R. J Geophys Res 1992;97:7373 19-01. Watson AJ, Jickells TD, Maher BA, 1999:21-01.