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The deepest living foraminifera, Challenger Deep, Mariana Trench
Marine Micropaleontology 42 (2001) 95±97
www.elsevier.nl/locate/marmicro
Micronote
The deepest living foraminifera, Challenger Deep, Mariana Trench K. Akimoto a,*, M. Hattori b, K. Uematsu c, C. Kato d b
a Department of Earth Sciences, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan Deep Sea Research Department, Japan Marine Science and Technology Center, 2-15, Natsushima-cho Yokosuka, Kanagawa 237-0061, Japan c Marine Work Japan Co. Ltd., 2-15, Natsushima-cho Yokosuka, Kanagawa 237-0061, Japan d The DEEPSTAR Group, Japan Marine Science and Technology Center, 2-15, Natsushima-cho Yokosuka, Kanagawa 237-0061, Japan
Received 5 February 1999; revised 27 November 2000; accepted 8 December 2000
1. Introduction The paleobathymetry of the Mariana Trench during Cenozoic time has been reconstructed based on benthic foraminiferal biostratigraphy obtained on Legs 125 and 126 (Izu-Bonin Arc) of the Ocean Drilling Program (ODP). The accuracy of such paleobathymetrical estimates depends on the depth distributions of benthic foraminifers in the modern trench area. Here in the Challenger Deep of the Mariana Trench we discovered living agglutinated foraminifera. Three studies revealed the distribution of benthic foraminiferal thanatocoenoses in trenches around Japan (Thompson, 1980: Japan Trench, Inoue, 1989: Japan Trench and Nankai Trough, Kaiho and Nishimura, 1992: Ogasawara Trench). Thompson (1980) studied benthic foraminiferal assemblages in the depth interval from 3300 to 7400 m in the Japan Trench, and recognized a boundary between the abyssal and hadal zones at a depth of 6000 m. Thus, data on the benthic assemblage below 7400 m is not yet available. * Corresponding author. Present address: Center for Marine Environment Studies, Kumamoto University, Kurokami, 2-39-1, Kumamoto 860-8555, Japan. E-mail address: [email protected] (K. Akimoto).
In addition, the above three papers did not identify whether or not specimens were living because the samples were not stained. The deepest record of live foraminifera around Japan, which was reported by Matoba (1976), is at 2000 m water depth on the continental slope of the Japan Trench with water temperatures below 2.68C and salinity of 34.5½. The Challenger Deep (10,924 m water depth) is located in the southwest portion of the Mariana Trench at the boundary between the Paci®c and Philippine Sea plates. On 23rd dive of ROV `KAIKO' (March 4, 1996) at 14085.85 0 E, 118259 0 N, depth of 10,897 m, sediment samples were collected using an Eckman Barge sampler (Fig. 1). The temperature, salinity and water-pressure at the sampling station was 2.68C, 34.7½ and 11.13 KB, respectively. The subsample we examined was 54 ml in volume and lay above a substrate of pelagic red clay. The mud content of this sample was 96% of the dry weight and the total sample was 16.788 g dry weight. Grains more than 0.063 mm in diameter were mainly diatom fragments and radiolarian tests. This sample was washed on a 0.063 mm (250-mesh) sieve screen and stained with rose Bengal to detect living specimens (Walton, 1952). All specimens of benthic foraminifers larger than
0377-8398/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0377-839 8(01)00012-3
96
K. Akimoto et al. / Marine Micropaleontology 42 (2001) 95±97 Table 1 List of benthic foraminifers in the Mariana Trench Species
Fig. 1. Index map of the western Paci®c Ocean showing trenches and the collection site.
0.125 mm were picked from the dried sample under a binocular microscope. 2. Results Ninety-one individuals of agglutinated foraminifers were obtained, and are identi®ed as four species (Fig. 2; Table 1). Living Lagenammina dif¯ugiformis (four individuals) occur in this assemblage, indicating that some agglutinated foraminifers can inhabit areas under 11.13 KB water-pressure. Lagenammina dif¯ugiformis (42 individuals) and Rhabdammina abyssorum (27 individuals) dominate while Hormosina globulifera (nine individuals) was subordinate in the thanatocoenoses of benthic foraminifers (Table 1). These species are found in the Neogene trench-®ll deposits (Akimoto, 1991,
Living Lagenammina dif¯ugiformis (Brady)
4
Total number of living individuals
4
Dead Hormosina globulifera (Brady) Lagenammina dif¯ugiformis (Brady) Reophax guttifer Brady Rhabdammina abyssorum Sars Miscellaneous agglutinated foraminifers
9 42 3 27 6
Total number of dead individuals
87
Total number of benthic foraminifers
91
1994; Kaiho, 1992). L. dif¯ugiformis and R. abyssorum are abundant, but H. globulifera is absent from assemblages in the depth interval between 3000 and 7400 m in the modern Northwest Paci®c Ocean (Inoue, 1989; Thompson, 1980). H. globulifera, whose tests preserve poorly but consititute about 10% of individuals in the assemblage in the Challenger Deep, can be used as a paleobathymetrical indicator in Neogene pelagic sediments. The grains formed by the tests of Lagenammina dif¯ugiformis and Rhabdammina abyssorum were analyzed by EDS and SEM. The tests of both species mainly consisted of anorthite grains. They did not contain diatom fragments or radiolarian tests, which were the other major grains in the sediments. Olivine and augite grains comprised only minimal portions of the tests of R. abyssorum. These two species intentionally selected and collected the speci®ed size of anorthite grains.
Acknowledgements We would like to thank the crews of the R/V Kairei and ROV Kaiko. We acknowledge the valuable comments on our manuscript by Dr Dhugal J. Lindsay of Japan Marine Science and Technology Center (JAMSTEC) and Dr Jere H. Lipps of the University of California.
K. Akimoto et al. / Marine Micropaleontology 42 (2001) 95±97
97
Fig. 2. Scanning electron microscope photograph. Scale bars indicate 50 mm. 1. Hormosina globulifera Brady. 2. Reophax guttifer Brady. 3. Lagenamminadif¯ugifor (Brady). 4. Rhabdammina abyssorum Sars.
References Akimoto, K., 1991. Paleoenvironmental studies of the Nishiyatsushiro and Shizukawa groups, south Fossa-Magna region. Sci. Rep. Tohoku Univ., 2nd Ser. 61 (1), 1±102. Akimoto, K., 1994. Cenozoic benthic foraminiferal biostratigraphy, paleobathymetry, paleoenvironments and paleoceanography of the New Hebrides Island Arc and North D'Entrecasteaux Ridge area, Vanuatu, southwest Paci®c Ocean. Proceedings of Ocean Drilling Program, Scienti®c Results, 134, 265±291. Inoue, Y., 1989. Northwest Paci®c foraminifera as paleoenvironmental indicators. Sci. Rep. Inst. Geosci., Univ. Tsukuba, Sec. B (Geol. Sci.) 10, 57±162. Kaiho, K., 1992. Eocene to Quaternary benthic foraminifers and paleobathymetry of the Izu-Bonin Arc, Legs 125 and 126. Proceedings of the Ocean Drilling Program, Scientiftc Results, 126, 285±310.
Kaiho, K., Nishimura, A., 1992. Distribution of Holocene benthic foraminifers in the Izu-Bonin Arc. Proceedings of the Ocean Drilling Program, Scienti®c Results, 126, 311±320. Matoba, Y., 1976. Recent foraminiferal assemblages off Sendai, Northeast Japan. In: Schafer, C.T., Pelletier, B.R. (Eds.), The First International Symposium on Benthic foraminifera of Continental Margins. Part A, Ecology and Biology. Maritime Sediments Special Publication 1, Halifax, Nova Scotia, Canada, pp. 205±220. Thompson, P.R., 1980. Foraminifers from Deep Sea Drilling Project sites 434, 435, and 436, Japan Trench. Initial Reports Deep Sea Drilling Project 56±57, 775±807. Walton, W.R., 1952. Techniques for recognition of living foraminifera. Cushman Found. Foram. Res., Contr. 3 (2), 56±60.
www.elsevier.nl/locate/marmicro
Micronote
The deepest living foraminifera, Challenger Deep, Mariana Trench K. Akimoto a,*, M. Hattori b, K. Uematsu c, C. Kato d b
a Department of Earth Sciences, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan Deep Sea Research Department, Japan Marine Science and Technology Center, 2-15, Natsushima-cho Yokosuka, Kanagawa 237-0061, Japan c Marine Work Japan Co. Ltd., 2-15, Natsushima-cho Yokosuka, Kanagawa 237-0061, Japan d The DEEPSTAR Group, Japan Marine Science and Technology Center, 2-15, Natsushima-cho Yokosuka, Kanagawa 237-0061, Japan
Received 5 February 1999; revised 27 November 2000; accepted 8 December 2000
1. Introduction The paleobathymetry of the Mariana Trench during Cenozoic time has been reconstructed based on benthic foraminiferal biostratigraphy obtained on Legs 125 and 126 (Izu-Bonin Arc) of the Ocean Drilling Program (ODP). The accuracy of such paleobathymetrical estimates depends on the depth distributions of benthic foraminifers in the modern trench area. Here in the Challenger Deep of the Mariana Trench we discovered living agglutinated foraminifera. Three studies revealed the distribution of benthic foraminiferal thanatocoenoses in trenches around Japan (Thompson, 1980: Japan Trench, Inoue, 1989: Japan Trench and Nankai Trough, Kaiho and Nishimura, 1992: Ogasawara Trench). Thompson (1980) studied benthic foraminiferal assemblages in the depth interval from 3300 to 7400 m in the Japan Trench, and recognized a boundary between the abyssal and hadal zones at a depth of 6000 m. Thus, data on the benthic assemblage below 7400 m is not yet available. * Corresponding author. Present address: Center for Marine Environment Studies, Kumamoto University, Kurokami, 2-39-1, Kumamoto 860-8555, Japan. E-mail address: [email protected] (K. Akimoto).
In addition, the above three papers did not identify whether or not specimens were living because the samples were not stained. The deepest record of live foraminifera around Japan, which was reported by Matoba (1976), is at 2000 m water depth on the continental slope of the Japan Trench with water temperatures below 2.68C and salinity of 34.5½. The Challenger Deep (10,924 m water depth) is located in the southwest portion of the Mariana Trench at the boundary between the Paci®c and Philippine Sea plates. On 23rd dive of ROV `KAIKO' (March 4, 1996) at 14085.85 0 E, 118259 0 N, depth of 10,897 m, sediment samples were collected using an Eckman Barge sampler (Fig. 1). The temperature, salinity and water-pressure at the sampling station was 2.68C, 34.7½ and 11.13 KB, respectively. The subsample we examined was 54 ml in volume and lay above a substrate of pelagic red clay. The mud content of this sample was 96% of the dry weight and the total sample was 16.788 g dry weight. Grains more than 0.063 mm in diameter were mainly diatom fragments and radiolarian tests. This sample was washed on a 0.063 mm (250-mesh) sieve screen and stained with rose Bengal to detect living specimens (Walton, 1952). All specimens of benthic foraminifers larger than
0377-8398/01/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0377-839 8(01)00012-3
96
K. Akimoto et al. / Marine Micropaleontology 42 (2001) 95±97 Table 1 List of benthic foraminifers in the Mariana Trench Species
Fig. 1. Index map of the western Paci®c Ocean showing trenches and the collection site.
0.125 mm were picked from the dried sample under a binocular microscope. 2. Results Ninety-one individuals of agglutinated foraminifers were obtained, and are identi®ed as four species (Fig. 2; Table 1). Living Lagenammina dif¯ugiformis (four individuals) occur in this assemblage, indicating that some agglutinated foraminifers can inhabit areas under 11.13 KB water-pressure. Lagenammina dif¯ugiformis (42 individuals) and Rhabdammina abyssorum (27 individuals) dominate while Hormosina globulifera (nine individuals) was subordinate in the thanatocoenoses of benthic foraminifers (Table 1). These species are found in the Neogene trench-®ll deposits (Akimoto, 1991,
Living Lagenammina dif¯ugiformis (Brady)
4
Total number of living individuals
4
Dead Hormosina globulifera (Brady) Lagenammina dif¯ugiformis (Brady) Reophax guttifer Brady Rhabdammina abyssorum Sars Miscellaneous agglutinated foraminifers
9 42 3 27 6
Total number of dead individuals
87
Total number of benthic foraminifers
91
1994; Kaiho, 1992). L. dif¯ugiformis and R. abyssorum are abundant, but H. globulifera is absent from assemblages in the depth interval between 3000 and 7400 m in the modern Northwest Paci®c Ocean (Inoue, 1989; Thompson, 1980). H. globulifera, whose tests preserve poorly but consititute about 10% of individuals in the assemblage in the Challenger Deep, can be used as a paleobathymetrical indicator in Neogene pelagic sediments. The grains formed by the tests of Lagenammina dif¯ugiformis and Rhabdammina abyssorum were analyzed by EDS and SEM. The tests of both species mainly consisted of anorthite grains. They did not contain diatom fragments or radiolarian tests, which were the other major grains in the sediments. Olivine and augite grains comprised only minimal portions of the tests of R. abyssorum. These two species intentionally selected and collected the speci®ed size of anorthite grains.
Acknowledgements We would like to thank the crews of the R/V Kairei and ROV Kaiko. We acknowledge the valuable comments on our manuscript by Dr Dhugal J. Lindsay of Japan Marine Science and Technology Center (JAMSTEC) and Dr Jere H. Lipps of the University of California.
K. Akimoto et al. / Marine Micropaleontology 42 (2001) 95±97
97
Fig. 2. Scanning electron microscope photograph. Scale bars indicate 50 mm. 1. Hormosina globulifera Brady. 2. Reophax guttifer Brady. 3. Lagenamminadif¯ugifor (Brady). 4. Rhabdammina abyssorum Sars.
References Akimoto, K., 1991. Paleoenvironmental studies of the Nishiyatsushiro and Shizukawa groups, south Fossa-Magna region. Sci. Rep. Tohoku Univ., 2nd Ser. 61 (1), 1±102. Akimoto, K., 1994. Cenozoic benthic foraminiferal biostratigraphy, paleobathymetry, paleoenvironments and paleoceanography of the New Hebrides Island Arc and North D'Entrecasteaux Ridge area, Vanuatu, southwest Paci®c Ocean. Proceedings of Ocean Drilling Program, Scienti®c Results, 134, 265±291. Inoue, Y., 1989. Northwest Paci®c foraminifera as paleoenvironmental indicators. Sci. Rep. Inst. Geosci., Univ. Tsukuba, Sec. B (Geol. Sci.) 10, 57±162. Kaiho, K., 1992. Eocene to Quaternary benthic foraminifers and paleobathymetry of the Izu-Bonin Arc, Legs 125 and 126. Proceedings of the Ocean Drilling Program, Scientiftc Results, 126, 285±310.
Kaiho, K., Nishimura, A., 1992. Distribution of Holocene benthic foraminifers in the Izu-Bonin Arc. Proceedings of the Ocean Drilling Program, Scienti®c Results, 126, 311±320. Matoba, Y., 1976. Recent foraminiferal assemblages off Sendai, Northeast Japan. In: Schafer, C.T., Pelletier, B.R. (Eds.), The First International Symposium on Benthic foraminifera of Continental Margins. Part A, Ecology and Biology. Maritime Sediments Special Publication 1, Halifax, Nova Scotia, Canada, pp. 205±220. Thompson, P.R., 1980. Foraminifers from Deep Sea Drilling Project sites 434, 435, and 436, Japan Trench. Initial Reports Deep Sea Drilling Project 56±57, 775±807. Walton, W.R., 1952. Techniques for recognition of living foraminifera. Cushman Found. Foram. Res., Contr. 3 (2), 56±60.