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Material balance in manganese nodule formation (north central Pacific)
et Cosmochimiea Ann Vol.46,pp.693to 695 (9 PcrgsmmPrcgsLtd.1982. Printed in U.S.A. Go&mica
NOTE
Material balance in manganese nodule formation (North Central Pacific) V. MARCHIG and H. GUNDLACH Federal Institute for Geosciences and Natural Resources P.O. Box 51 01 53, D-3000 Hannover, Germany (Received February 3, 198 1; accepted in revised form December 2, 198 1) Abstract-All data necessary to calculate the metal balance for Mn nodules in a well-investigated area of the North Central Pacific are now available. The nodules lie on porous siliceous ooze, and receive more than 96% of their metal content from the underlying ooze by diagenetic mobilisation. Only a very small portion of the metal contained in the sediment has to be mobilised to form the nodules. which explains why the expected depletion of metals from the sediments has never been demonstrated. manganese nodules in the so-called manganese nodule belt in the North Central Pacific grow on a very porous substrate of radiolarian ooze. In previous papers (Gundlach et al., 1979; Marchig and Gundlach, 1976a,b; 1979a,b; 1981; Marchig et al., 1979; Schnier et al., 1977, 1980), we have shown that diagenetic remobilisation takes place within this sediment type and that this diagenetic remobilisation is an important factor in the supply of metals for the growth of the manganese nodules. In particular, Mn, Ni, Cu, and Zn are supplied to the nodules by means of diagenetic remobilisation within the sediment column, i.e. by means of pore water transport. Diagenetic remobilisation takes place in the upper part of the sediment column, and in most cases occurs within the top 20-30 cm. The supply of metals to the manganese nodules in this area through diagenetic processes from below strongly outweighs the supply from sea water (i.e. hydrogenous supply). One objection, used frequently in the discussion on the predominance of diagenetic remobilisation, is the fact that there is no marked depletion of metals in the sediment substratum on which manganese noduies are growing, compared to other sediment areas not covered with manganese nodules. Recently, following very extensive investigation of a manganese nodule field in the radiolarian ooze area, we obtained sufficient data for a quantitative calculation of the amount of metals needed for the growth of manganese nodules. Samples of various kinds were gathered in the nodule field during cruise 13/ 1 of the German research vessel Valdivia in 1976. The area studied is 200 n.m. X 200 n.m. with the central coordinates of 9”OS’N and 148”45’W. The deep-sea plain covered with radiolarian ooze has an average water depth of 5 100 to 5200 m and is interrupted by three sea-mounts with elevations of 600 to 1000 m above the deep-sea plain. The following data about this field are available: THE
693
a. As the initiation time of the growth of manganese nodules the hiatus between Early Miocene and Late Pliocene was suggested (Beiersdorf and Wolfart, 1974; v. Stackelberg, 1979). v. Stackelberg (1979) also calculated the size of manganese nodules from this area knowing their average growth rate and the time of growth, and found it in a good accordance with the actual average size of nodules in the area. For the following calculation, we approximated the time of initiation of manganese nodules to be the boundary from Miocene to Pliocene, i.e. 7 million years ago (Geological Society of London, 1964). b. The average rate of sedimentation is 3.8 mm/ 1000 years (Heye, 1976; Meyer, 1977). This means a sediment column of 26.6 m was deposited in 7 million years. This thick sediment cover is not preserved everywhere and might have been partly removed by deep-sea currents. Since only the top 30 cm of sediment are involved in nodule formation, it is immaterial whether part of the sediment was removed. c. The specific weight of the wet sediment is 1.14 g/cm3 (average water content of 63.9% Meyer, 1977). For the following calculation the specific weight of dry sediment was used, as chemical analyses refer to the dry sediment. d. The average population density of manganese nodules on the sea floor (on the sediment surface) is 9.5 kg/m” (Marchig and Gundlach, 1979b). e. The average composition of the nodules is 21.7% Mn, 1.01% Ni, 0.75% Cu, 0, 103% Zn (Marchig and Gundlach, 1979b). f. The sediment has an average composition of 0.48% Mn, 195 ppm Ni, 639 ppm Cu, 212 ppm Zn (Marchig et al., 1979) as shown in Table 1. g. Manganese nodules in abyssal plains have linear growth rates which are approximately three times higher than those from manganese nodules on seamounts ( 15 mm/ lo6 years and 5 mm/lo”
years according to Heye, 1978). Krishnaswamt et al. (1979) suggest that alpha track dating, on which our data are based. lead to some errors in growth rate determination due to the contamination by contemporary sediment filling nodule cracks. As for the following calculation only the ratio of two average values is used; the eventual error of the method does not significantly change our statement. As the linear growth of the nodules from the abyssal plain is three times higher than the linear growth of nodules on seamounts, the volume of abyssal plain nodules is enlarging 27 times faster than the volume of seamount nodules. The seamounts are sediment-free outcrops of basalt. Thus, no diagenetic remobilisation from sediment can take place there. The nodules on the seamounts are products of purely hydrogenous supply (from the seawater), and the nodules in the abyssal plains are formed by combination of hydrogenous and diagenetic supply. From this, it is concluded that less than 4% of the supply of manganese nodules in the investigated abyssal plain is of hydrogenous origin, the rest being supplied by diagenetic remobilisation. The following data:
calculations
can be made with these
The average sediment cover of 26.6 m in the investigated area, deposited within the last 7 million years account for 10,900 kg of dry sediment per m* on the ancient (prior to nodule formation) sea floor. Such a sediment column of 1 m* base and of 26.6 m height contains
(A) 52.3 kg Mn, 2.13 kg Ni, 6.97 kg Cu, 2.31 kg Zn On the top of this sediment column, i.e. on the recent sea floor 9.5 kg manganese nodules are growing. More than 96% of this growth results from diagenetic remobilisation from the sediment (Schnier et al., 1977; Schnier et al., 1980; Heye and Marchig, 1977; Heye, 1978). These nodules (again calculated over the surface of 1 m’) contain
(B)
2.06 kg Mn, 0.096 kg Ni, 0.071 kg Cu, 0.0098 kg Zn. Taking into account that 96% of the material needed for the growth of manganese nodules was extracted from the sediment, the sediment would be depleted of
(C) 3.78% of its Mn content 4.32% of its Ni content 0.98% of its Cu content 0.41% of its Zn content. Using the figures under (f), a comparison of the average sediment content before and after the diagenetic remobilisation is shown in Table 1.
1,
iable
element
:,omparison )jf the me1 contents in the sedimerit before and after diagenet-r %-emobiiisation (i.e. ?55 at imetals dire to nodL. $2 formationj.
sediment before diagenetic remobilisation _I_.-_______
Mn (%) Ni (wm) Cu (wm) Zn (wm)
0.50 203 645 213
sediment after diagenetic remobilisation ~. ~__.__. 0.4E 195 639 212
From these figures, it becomes clear why the diagenetic depletion of metals in deep-sea sediments, which plays such an important role in the formation of manganese nodules, could not be detected in the past. An additional calculation was performed using 4 million years as the time of growth of manganese nodules (end of the hiatus, Stackelberg pers. comm.). A sediment column of 15.2 m is obtained (see b) containing 29.9 kg Mn, 1.22 kg Ni, 3.98 kg Cu, and 1.32 kg Zn (see a). Due to the supply of manganese nodules, the sediment would be depleted of 6.98% of its Mn content, 7.87% of its Ni content, 1.78% of its Cu content, and 0.74% of its Zn content (see c). The sediment before diagenetic remobilisation would then have the following chemical composition: 0.5 1% Mn, 210 ppm Ni, 650 ppm Cu, and 214 ppm Zn (d). Comparing these data with the results calculated for a period of 7 million years (Table 1), it can be seen that errors in this order of magnitude do not change our conclusions.
REFERENCES Beiersdorf H. and Wolfart R. (1974) Sedimentologischbiostratigraphische Untersuchungen an Sedimenten aus dem zentralen Pazifischen Ozean. Meeresrechnik 5,192198. Geological Society Of London (1964) The Phanerozoic time-scale. In A Symposium dedicated to Professor Arthur Holmes. Quart. Jour. Geol. Sot. London. 120, suppl., pp. 260-262. Gundlach H., Marchig V. and Schnier C. (1979) Woher stammen die Metalle in den Manganknollen? In Proc. Marine Rohstoffgewinnung, 7. Seminar Meerestechnik TU Clausthal/TU Berlin (ed. P. Halbach), pp. 46-82. Verlag GlUckauf Essen. Heye D. (1976) Geophysikalische Untersuchungen an Knollen und Sedimenten.-Manganknollen. In Wissenschaftsfahrt VA 13/l, Fahrtberichte 51-53, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hannover. Heye D. (1978) Growth conditions of manganese nodules. Comparative studies of growth rate, magnetization, chemical composition and internal structure. Progress in Oceanography
7, 163-239.
MANGANESE
NODULE FORMATION
Heye D. and Marchig V. (1977) Relationship between the growth rate of manganese nodules from the Central Pacific and their chemical constitution. Marine Geology 23, Ml9-M25. Krishnaswami S., Cochran J. K., Turekian K. K. and Sarin M. M. (1979) Time scales of deep-sea ferro-manganese nodule growth bases on “‘Be and alpha track distributions and their relation to uranium decay series measurements. In La genke des nodules de mango&e, pp. 251-260, Colloques Internationaux du CNRS No. 289, Paris. Marchig V. and Gundlach H. (1976a) Ein Hinweis auf die At&sung des Mangans innerhalb des Sediments als Materialquelle fur die Bildung von Manganknollen (vorlaufige Mitteilung). Geol. Jahrbuch D16, 79-83. Marchig V. and Gundlach H. (1976b) Zur Geochemie von Manganknollen und ihrer Umgebung. Vergleich Manganknollen zu Manganmikroknollen. Interocean 76 Dtlsseldorf, KongreBberichtswerk Vol. I., pp. 59-67, Seehafen-Verlag Hamburg. Marchig V. and Gundlach H. (1979a) Diagenetic changes in the radiolarian oozes of the Central Pacific and their influence on the growth of manganese nodules. In La genbe des nodules de manganbe, pp. 55-60. Colloques Internationaux du CNRS No. 289, Paris. Marchig V. and Gundlach H. (1979b) Changes in the chemical composition of some Pacific manganese nodules during their growth. In Marine Geology and Oceanography of the Pacific Manganese Nodule Province (eds.
695
J. L. Bischoff and D. Z. Piper), pp. 729-746, Plenum Press. Marchig V. and Gundlach H. (1981) Separation of iron from manganese and growth of manganese nodules as a consequence of diagenetic ageing of radiolarians. Marine Geology 40, M35-M43. Marchig V., Gundlach H. and Schnier C. (1979) Verhalten von Radiolarienschalen aus dem Zentralpazifik bei der Diaaenese. Geol. Rundschau 68. 1037-1053. Meye; H. (1977) Untersuchungen liber Beziehungen zwischen Sedimenten und Manganknollen im zentralen Pazifik SE von Hawaii. Ph.D. Thesis, Tech. Univ. Braunschweig. Schnier C., Gundlach H. & Marchig V. (1977) Trace elements in pore water and sea water in the radiolarian ooze area of the Central Pacific as related to the genesis of manganese nodules. Proc. 3rd Internat. Symp. Environm. Geochem. Vol. 3, pp. 859-867, WolfenbUttel. Schnier C., Marchig V. and Gundlach H. (1980) The chemical composition of sea water and pore water in the manganese nodules area of the Central Pacific. Abstracts 26th International Geoloaical Conaress. D. 1006. Paris 1980. Stackelberg U. v. (1919) Sedimentatibn, hiatuses and development of manganese nodules: Valdivia Site VA 13/ 2, northern Central Pacific. In Marine Geology and Oceanography of the Pacific Manganese Nodule Province (eds. J. L. Bischoff and D. Z. Piper), pp. 559-586,
Plenum Press.
NOTE
Material balance in manganese nodule formation (North Central Pacific) V. MARCHIG and H. GUNDLACH Federal Institute for Geosciences and Natural Resources P.O. Box 51 01 53, D-3000 Hannover, Germany (Received February 3, 198 1; accepted in revised form December 2, 198 1) Abstract-All data necessary to calculate the metal balance for Mn nodules in a well-investigated area of the North Central Pacific are now available. The nodules lie on porous siliceous ooze, and receive more than 96% of their metal content from the underlying ooze by diagenetic mobilisation. Only a very small portion of the metal contained in the sediment has to be mobilised to form the nodules. which explains why the expected depletion of metals from the sediments has never been demonstrated. manganese nodules in the so-called manganese nodule belt in the North Central Pacific grow on a very porous substrate of radiolarian ooze. In previous papers (Gundlach et al., 1979; Marchig and Gundlach, 1976a,b; 1979a,b; 1981; Marchig et al., 1979; Schnier et al., 1977, 1980), we have shown that diagenetic remobilisation takes place within this sediment type and that this diagenetic remobilisation is an important factor in the supply of metals for the growth of the manganese nodules. In particular, Mn, Ni, Cu, and Zn are supplied to the nodules by means of diagenetic remobilisation within the sediment column, i.e. by means of pore water transport. Diagenetic remobilisation takes place in the upper part of the sediment column, and in most cases occurs within the top 20-30 cm. The supply of metals to the manganese nodules in this area through diagenetic processes from below strongly outweighs the supply from sea water (i.e. hydrogenous supply). One objection, used frequently in the discussion on the predominance of diagenetic remobilisation, is the fact that there is no marked depletion of metals in the sediment substratum on which manganese noduies are growing, compared to other sediment areas not covered with manganese nodules. Recently, following very extensive investigation of a manganese nodule field in the radiolarian ooze area, we obtained sufficient data for a quantitative calculation of the amount of metals needed for the growth of manganese nodules. Samples of various kinds were gathered in the nodule field during cruise 13/ 1 of the German research vessel Valdivia in 1976. The area studied is 200 n.m. X 200 n.m. with the central coordinates of 9”OS’N and 148”45’W. The deep-sea plain covered with radiolarian ooze has an average water depth of 5 100 to 5200 m and is interrupted by three sea-mounts with elevations of 600 to 1000 m above the deep-sea plain. The following data about this field are available: THE
693
a. As the initiation time of the growth of manganese nodules the hiatus between Early Miocene and Late Pliocene was suggested (Beiersdorf and Wolfart, 1974; v. Stackelberg, 1979). v. Stackelberg (1979) also calculated the size of manganese nodules from this area knowing their average growth rate and the time of growth, and found it in a good accordance with the actual average size of nodules in the area. For the following calculation, we approximated the time of initiation of manganese nodules to be the boundary from Miocene to Pliocene, i.e. 7 million years ago (Geological Society of London, 1964). b. The average rate of sedimentation is 3.8 mm/ 1000 years (Heye, 1976; Meyer, 1977). This means a sediment column of 26.6 m was deposited in 7 million years. This thick sediment cover is not preserved everywhere and might have been partly removed by deep-sea currents. Since only the top 30 cm of sediment are involved in nodule formation, it is immaterial whether part of the sediment was removed. c. The specific weight of the wet sediment is 1.14 g/cm3 (average water content of 63.9% Meyer, 1977). For the following calculation the specific weight of dry sediment was used, as chemical analyses refer to the dry sediment. d. The average population density of manganese nodules on the sea floor (on the sediment surface) is 9.5 kg/m” (Marchig and Gundlach, 1979b). e. The average composition of the nodules is 21.7% Mn, 1.01% Ni, 0.75% Cu, 0, 103% Zn (Marchig and Gundlach, 1979b). f. The sediment has an average composition of 0.48% Mn, 195 ppm Ni, 639 ppm Cu, 212 ppm Zn (Marchig et al., 1979) as shown in Table 1. g. Manganese nodules in abyssal plains have linear growth rates which are approximately three times higher than those from manganese nodules on seamounts ( 15 mm/ lo6 years and 5 mm/lo”
years according to Heye, 1978). Krishnaswamt et al. (1979) suggest that alpha track dating, on which our data are based. lead to some errors in growth rate determination due to the contamination by contemporary sediment filling nodule cracks. As for the following calculation only the ratio of two average values is used; the eventual error of the method does not significantly change our statement. As the linear growth of the nodules from the abyssal plain is three times higher than the linear growth of nodules on seamounts, the volume of abyssal plain nodules is enlarging 27 times faster than the volume of seamount nodules. The seamounts are sediment-free outcrops of basalt. Thus, no diagenetic remobilisation from sediment can take place there. The nodules on the seamounts are products of purely hydrogenous supply (from the seawater), and the nodules in the abyssal plains are formed by combination of hydrogenous and diagenetic supply. From this, it is concluded that less than 4% of the supply of manganese nodules in the investigated abyssal plain is of hydrogenous origin, the rest being supplied by diagenetic remobilisation. The following data:
calculations
can be made with these
The average sediment cover of 26.6 m in the investigated area, deposited within the last 7 million years account for 10,900 kg of dry sediment per m* on the ancient (prior to nodule formation) sea floor. Such a sediment column of 1 m* base and of 26.6 m height contains
(A) 52.3 kg Mn, 2.13 kg Ni, 6.97 kg Cu, 2.31 kg Zn On the top of this sediment column, i.e. on the recent sea floor 9.5 kg manganese nodules are growing. More than 96% of this growth results from diagenetic remobilisation from the sediment (Schnier et al., 1977; Schnier et al., 1980; Heye and Marchig, 1977; Heye, 1978). These nodules (again calculated over the surface of 1 m’) contain
(B)
2.06 kg Mn, 0.096 kg Ni, 0.071 kg Cu, 0.0098 kg Zn. Taking into account that 96% of the material needed for the growth of manganese nodules was extracted from the sediment, the sediment would be depleted of
(C) 3.78% of its Mn content 4.32% of its Ni content 0.98% of its Cu content 0.41% of its Zn content. Using the figures under (f), a comparison of the average sediment content before and after the diagenetic remobilisation is shown in Table 1.
1,
iable
element
:,omparison )jf the me1 contents in the sedimerit before and after diagenet-r %-emobiiisation (i.e. ?55 at imetals dire to nodL. $2 formationj.
sediment before diagenetic remobilisation _I_.-_______
Mn (%) Ni (wm) Cu (wm) Zn (wm)
0.50 203 645 213
sediment after diagenetic remobilisation ~. ~__.__. 0.4E 195 639 212
From these figures, it becomes clear why the diagenetic depletion of metals in deep-sea sediments, which plays such an important role in the formation of manganese nodules, could not be detected in the past. An additional calculation was performed using 4 million years as the time of growth of manganese nodules (end of the hiatus, Stackelberg pers. comm.). A sediment column of 15.2 m is obtained (see b) containing 29.9 kg Mn, 1.22 kg Ni, 3.98 kg Cu, and 1.32 kg Zn (see a). Due to the supply of manganese nodules, the sediment would be depleted of 6.98% of its Mn content, 7.87% of its Ni content, 1.78% of its Cu content, and 0.74% of its Zn content (see c). The sediment before diagenetic remobilisation would then have the following chemical composition: 0.5 1% Mn, 210 ppm Ni, 650 ppm Cu, and 214 ppm Zn (d). Comparing these data with the results calculated for a period of 7 million years (Table 1), it can be seen that errors in this order of magnitude do not change our conclusions.
REFERENCES Beiersdorf H. and Wolfart R. (1974) Sedimentologischbiostratigraphische Untersuchungen an Sedimenten aus dem zentralen Pazifischen Ozean. Meeresrechnik 5,192198. Geological Society Of London (1964) The Phanerozoic time-scale. In A Symposium dedicated to Professor Arthur Holmes. Quart. Jour. Geol. Sot. London. 120, suppl., pp. 260-262. Gundlach H., Marchig V. and Schnier C. (1979) Woher stammen die Metalle in den Manganknollen? In Proc. Marine Rohstoffgewinnung, 7. Seminar Meerestechnik TU Clausthal/TU Berlin (ed. P. Halbach), pp. 46-82. Verlag GlUckauf Essen. Heye D. (1976) Geophysikalische Untersuchungen an Knollen und Sedimenten.-Manganknollen. In Wissenschaftsfahrt VA 13/l, Fahrtberichte 51-53, Bundesanstalt fur Geowissenschaften und Rohstoffe, Hannover. Heye D. (1978) Growth conditions of manganese nodules. Comparative studies of growth rate, magnetization, chemical composition and internal structure. Progress in Oceanography
7, 163-239.
MANGANESE
NODULE FORMATION
Heye D. and Marchig V. (1977) Relationship between the growth rate of manganese nodules from the Central Pacific and their chemical constitution. Marine Geology 23, Ml9-M25. Krishnaswami S., Cochran J. K., Turekian K. K. and Sarin M. M. (1979) Time scales of deep-sea ferro-manganese nodule growth bases on “‘Be and alpha track distributions and their relation to uranium decay series measurements. In La genke des nodules de mango&e, pp. 251-260, Colloques Internationaux du CNRS No. 289, Paris. Marchig V. and Gundlach H. (1976a) Ein Hinweis auf die At&sung des Mangans innerhalb des Sediments als Materialquelle fur die Bildung von Manganknollen (vorlaufige Mitteilung). Geol. Jahrbuch D16, 79-83. Marchig V. and Gundlach H. (1976b) Zur Geochemie von Manganknollen und ihrer Umgebung. Vergleich Manganknollen zu Manganmikroknollen. Interocean 76 Dtlsseldorf, KongreBberichtswerk Vol. I., pp. 59-67, Seehafen-Verlag Hamburg. Marchig V. and Gundlach H. (1979a) Diagenetic changes in the radiolarian oozes of the Central Pacific and their influence on the growth of manganese nodules. In La genbe des nodules de manganbe, pp. 55-60. Colloques Internationaux du CNRS No. 289, Paris. Marchig V. and Gundlach H. (1979b) Changes in the chemical composition of some Pacific manganese nodules during their growth. In Marine Geology and Oceanography of the Pacific Manganese Nodule Province (eds.
695
J. L. Bischoff and D. Z. Piper), pp. 729-746, Plenum Press. Marchig V. and Gundlach H. (1981) Separation of iron from manganese and growth of manganese nodules as a consequence of diagenetic ageing of radiolarians. Marine Geology 40, M35-M43. Marchig V., Gundlach H. and Schnier C. (1979) Verhalten von Radiolarienschalen aus dem Zentralpazifik bei der Diaaenese. Geol. Rundschau 68. 1037-1053. Meye; H. (1977) Untersuchungen liber Beziehungen zwischen Sedimenten und Manganknollen im zentralen Pazifik SE von Hawaii. Ph.D. Thesis, Tech. Univ. Braunschweig. Schnier C., Gundlach H. & Marchig V. (1977) Trace elements in pore water and sea water in the radiolarian ooze area of the Central Pacific as related to the genesis of manganese nodules. Proc. 3rd Internat. Symp. Environm. Geochem. Vol. 3, pp. 859-867, WolfenbUttel. Schnier C., Marchig V. and Gundlach H. (1980) The chemical composition of sea water and pore water in the manganese nodules area of the Central Pacific. Abstracts 26th International Geoloaical Conaress. D. 1006. Paris 1980. Stackelberg U. v. (1919) Sedimentatibn, hiatuses and development of manganese nodules: Valdivia Site VA 13/ 2, northern Central Pacific. In Marine Geology and Oceanography of the Pacific Manganese Nodule Province (eds. J. L. Bischoff and D. Z. Piper), pp. 559-586,
Plenum Press.