Fossil benthic foraminifera from sediment core S1 of Lake Shinji, western Japan

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1 LAGUNA LAGUNA 14 p Hugo Coops 5 Fossil benthic foraminifera from sediment core S1 of Lake Shinji, western Japan Hiroyuki Takata 1, Kazuyoshi Yamada 1, Kota Katsuki 2, Keiko Yamaguchi 3, Yasushi Miyamoto 4, Daisuke Nakayama 1 and Hugo Coops 5 Abstract: Fossil benthic foraminifera from a sediment core taken from central Lake Shinji, western Japan, were investigated as an indicator of paleoenvironmental change in the Shinjiko-Nakaumi lake system during the 20th century. A transition from dominance of Haplophragmoides canariensis to that of Ammonia beccarii forma 1 occurred in the middle 20th century. This faunal association and its transition are similar to those observed in previous studies of Lake Shinji and the Ohashi River. This faunal transition might be affected by not only environmental change in Lake Shinji but also that in the Ohashi River. Keywords: Lake Shinji, fossil benthic foraminifera, faunal transition in the 20th century Haplophragmoides canariensis Ammonia beccarii type A. beccarii Ammonia event COD Nomura cm Research Center for Coastal Lagoon Environments, Shimane University, 1060 Nishikawatsu, Matsue , Japan. Division Earth Environmental Systems, Pusan National University, Pusan , Korea. Life and Environmental Science, Shimane University, 1060 Nishikawatsu, Matsue , Japan. Tottori Prefectural Institute of Public Health and Environmental Science, Tottori , Japan. Institute for Inland Water Management and Waste Water Treatment RIZA, P.O.Box 17, 8200 AA Lelystad, Netherlands. 1

2 2 Hugo Coops ; km m psu S1a S1b S1a S1b 21 cm 17 cm 1 S1a S1b 210 S1a 1 cm 3 70 S1b ' ' ' ' ' ' 35 Sakai Strait 34' A Core S1 Hii River Lake Shinji B Ohashi River Lake Nakaumi Ihnashi River Photo Lithology Description black mud Sea of Japan dark grey mud dark grey mud with lamination 1 A S1a, S1b B S1b Fig. 1. A Location of sediment cores S1a and S1b, B Columnar section of core S1b ' 35 25' X 1 cm S1a 63 μm 500 m 500 µm μm 50

3 S1 3 1 S1b Table 1. Pb-210 activity used for age estimation in core S1b depth Pb-210 (total) Pb-214 Pb-210 (excess) (cm) (dpm / g) (dpm / g) (dpm / g) / / / / / / / / / / / / Sampei et al S1a S1b 10 mg mol l FISON CHNS E.A BBOT 2, 5-bis- 5-tert-butyl-benzoxanzol-2yl -thiophen S1b Pb ; Pb ex 214 Pb 210 Pb 214 Pb S1b Pb ex 2 S1b 5.18 mm yr 210 Yamamuro and Kanai mm yr 3 Pb (ex) (dpm / g) Mass depth (g / cm ) 0 5 Sedimentation rate: (cm / yr) R = S1b 210 Pb ex Fig Pb ex activity in core S1b. S1a S1b S1a S1a S1b 3 S1a S1b cm S1a S1b cm cm S1a cm S1b cm S1b S1a 50 S1a cm cm Haplophragmoides canariensis d Orbigny Ammonia beccarii Linné forma 1 Miliammina fusca Brady Haynesina sp. 0.5 cm Elphidium somaense, Miliolinella spp., Uvigerinella glabra

4 4 Hugo Coops 2. S1a Table 2. Occurrence of fossil benthic foraminifera in core S1a Ammonia beccarii (Linne) forma Haplophragmoides canariensis (d'orbigny) 2 2 Elphidium excavatum (Terquem) forma selseyensis 1 Haynesina sp. Miliammina fusca (Brady) Trochammina hadai Uchio 6 Total Split Sample weight (g) Ammonia beccarii (Linne) forma Haplophragmoides canariensis (d'orbigny) Elphidium excavatum (Terquem) forma selseyensis Haynesina sp Miliammina fusca (Brady) Trochammina hadai Uchio Total Split Sample weight (g) Core S1B Core S1A Estimated age (AD) Water Total sulfur Water Total sulfur Estimated age (AD) 3 S1a S1b 2 S1b Fig. 3. Change in water and total sulfur of cores S1a and S1b. The sediment cores can be correlated at two horizons based on these indices. The chronology shown here was based on these correlations and the average sedimentation rate of core S1b. Nomura, 2003 S1 0.5 cm

5 S Ammonia beccarii forma 1 (# / g) Haplophragmoides canariensis (# / g) ~1990 ~1980 ~1970 ~ S1a Fig. 4. Stratigraphic change in characteristic benthic foraminifera in core S1a. cm H. canariensis cm A. beccarii forma cm A. beccarii forma 1 S1a 1995 SI-4, 5 S1b S1a S1 2 S1a H. canariensis A. beccarii forma ; 1990 H. canariensis 1933 Ammonia beccarii type 1 A. beccarii forma H. canariensis A. beccarii forma H. canariensis A. beccarii forma COD 1980 Nomura and Seto, 1992 ; 2000 H. canariensis H. canariensis H. canariensis A. beccarii forma 1 Yamamuro and Kanai Ammonia COD

6 6 Hugo Coops 1. S1a Plate 1. Scanning electron micrographs of benthic foraminifera from core S1a. Scale bar=100 μm. 1a c. Ammonia beccarii Linné forma 1 2a, b. Haplophragmoides canariensis d Orbigny 3a, b. Haynesina sp. no Pb 137Cs 46: : Nomura, R Assessing the roles of artificial vs. natural impacts on brackish lake environments: southwestern Japan. The Journal of the Geological Society of Japan, 109: Ammonia event 2005 LAGUNA 5: Nomura, R. and Seto, K Benthic foraminifera

7 S1 7 from brackish Lake Nakaumi, San-in District, southwestern Honshu, Japan. In: Ishizaki, K. and Saito, T. eds., Centenary of Japanese Micropaleontology. Terra Scientific Publishing Company, Tokyo, pp : : Sampei, Y., Matsumoto, E., Kamei, T. and Tokuoka, T Sulfur and organic carbon relationship in sediment from coastal brackish lakes in the Shimane peninsula district, southwest Japan. Geochemical Journal, 31: : : : Yamamuro, M. and Kanai, Y A 200-year record of natural and anthropogenic changes in water quality from coastal lagoon sediments of Lake Shinji, Japan. Chemical Geology, 218:

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