Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan

Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan

Quaternary International xxx (2015) 1e13 Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locat...

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Quaternary International xxx (2015) 1e13

Contents lists available at ScienceDirect

Quaternary International journal homepage: www.elsevier.com/locate/quaint

Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan Yoshiki Sato a, *, Hiromi Matsuoka b, Makoto Okamura c, Kaoru Kashima d a

Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Central 7, Higashi 1-1-1, Tsukuba, Ibaraki 305-8567, Japan Research and Education Faculty, Natural Sciences Cluster, Sciences Unit, Kochi University, 2-5-1, Akebono, Kochi Kochi 780-8520, Japan Science Research Center, Disaster Prevention Section, Kochi University, 2-5-1, Akebono, Kochi Kochi 780-8520, Japan d Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, 6-10-1, Hakozaki, Higashi, Fukuoka 812-8581, Japan b c

a r t i c l e i n f o

a b s t r a c t

Article history: Available online xxx

Late Holocene environmental changes in Lake Hamana, a coastal lagoon in central Japan, were reconstructed by a diatom fossil analysis and tephra and radiocarbon dating of a lakebed sediment core (HMN08-7) with high temporal resolution. On the basis of major species composition changes in diatom assemblages, we divided the core into six zones (I to VI), and subdivided zones V and VI into 3 subzones. The environment of Lake Hamana developed in six stages that corresponded to the diatom zones: stage I (4700e4600 cal BP) was characterized by vigorous seawater inflow in an inner bay environment; during stage II (4600e4500 cal BP), a closed inner bay environment with laminated sediments formed as a result of the formation of sand barriers; stage III (4500e2650 cal BP) was characterized by a well-mixed brackish water environment caused by active mixing with riverine fresh water and, after 3500 cal BP, an enhanced inflow of seawater; during stage IV (2650e2250 cal BP), the salinity of the lake water gradually decreased owing to reduced seawater inflow; during stage V (2250 cal BP to 480 cal BP), the lake water changed from brackish to fresh, although salinity increased temporarily during the middle of the period, and the depth of the lake increased; and during Stage VI (480 cal BP to the present), an inner bay environment developed again following the AD 1498 Meio earthquake, although salinity increased temporarily from AD 1600e1750. We also identified two event deposits, EA and EB, on the basis of spikes in the abundance of minor diatom species. In EA layer (4600e4500 cal BP), Glyphodesmis williamsonii, a marine or brackish water species, was temporarily dominant, and lamination disappeared; therefore, this layer was interpreted to represent a brief episode of sediment supply from seaward, such as by a tsunami or storm surge. The EB layer (ca. 4200 cal BP), in contrast, was characterized by an increase in fresh and fresh to brackish water species, suggesting a temporary supply of allotopic riverine or lake shore sediments during a large flood event. © 2015 Elsevier Ltd and INQUA. All rights reserved.

Keywords: Lake Hamana Coastal lagoon Holocene Diatom fossil AD 1498 Meio earthquake

1. Introduction Reconstruction of paleoenvironmental changes with high temporal resolution can yield information about short-term (centennial to millennial time scale) environmental changes during the middle to late Holocene. For example, minor sea level fluctuation is a typical phenomenon of short-term environmental change and

* Corresponding author. E-mail addresses: [email protected] (Y. Sato), [email protected] (H. Matsuoka), [email protected] (M. Okamura), [email protected]. jp (K. Kashima).

caused by glacio-, hydro-, and sediment-isostastic movements through the middle to late Holocene. It was strongly related to paleoenvironmental changes in Japanese coastal areas (Umitsu, 1994; Tanabe and Ishihara, 2013; Matsubara, 2015). Generally speaking, high stand sea level of the post-glacial transgression (Jomon Transgression) around the Japanese archipelago was reached in the middle Holocene (around 6e8 ka) and after this, relative sea level generally fell, with minor fluctuations, as a result of hydro-isostatic uplift (Ota et al., 1990; Nakada et al., 1991; Umitsu, 1991; Yokoyama, 2002). For example, a minor sea level fall, relative to the present, between ca. 3 and 2 ka is known as the Yayoi Regression (Iseki, 1983; Ota et al., 1990; Umitsu, 1991; Tanabe

http://dx.doi.org/10.1016/j.quaint.2015.06.006 1040-6182/© 2015 Elsevier Ltd and INQUA. All rights reserved.

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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and Ishihara, 2013). In addition to this, catastrophic environmental changes related to earthquakes and tsunamis are also important in coastal areas located near the subduction zones where the Pacific and Philippine Sea Plates descend beneath the Eurasian Plate (Fig. 1A). Thus, examination of short-term paleoenvironmental changes in the late Holocene is expected to provide useful data for understanding the detail histories and mechanisms of the Holocene sea level fluctuation and great earthquakes.

Lakebed sediments are useful for reconstructing paleoenvironmental changes with high temporal resolution because of their successive deposition at a higher sedimentation rate compared with marine sediments. Coastal lagoons in particular are expected to contain continuous records of sea level changes and short-term events in their sediments. Many coastal lagoons occur along the coasts of the Japanese archipelago, for example, lakes Saroma, Jusan, Kasumigaura, Hamana, Nakaumi, and Shinji (Fig. 1).

Fig. 1. A: Map of the Japanese archipelago showing the locations of large coastal lagoons: lakes Saroma, Jusan, Kasumigaura, Hamana, Nakaumi, and Shinji. The base map is based on the ASTER Global Digital Elevation Model produced by the Ministry of Economy, Trade and Industry of Japan and the U.S. National Aeronautics and Space Administration. Light blue shading indicates elevations lower than 10 m, corresponding approximately to alluvial lowlands. The inset satellite images of the coastal lagoons are modified Landsat images from the U.S. Geological Survey. B: Modified Landsat image of the region around Lake Hamana. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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Holocene environmental changes of some of these coastal lagoons have been reconstructed by using geological, paleontological, and geochemical methods. These changes were presumably associated with the development of sand ridges and barriers along the coast in response to relative sea level changes and catastrophic events (Minoura et al., 1987; Matsubara, 2005). For example, Holocene environmental changes of Lake Kasumigaura, along the lower Tone River, have been reconstructed by using geological information and diatom assemblages found in the sediments (Fig. 1A; Kashima, 1990; Saito et al., 1990) as follows. An inner bay environment formed before ca. 9000 14C BP (ca. 10,000 cal BP, based on the IntCal 13.14c curve; Reimer et al., 2013). Then, as a result of the development of a flood tidal delta around the bay mouth, the inner bay 14 became enclosed around 4000e2500 C BP (ca. 4500e2500 cal BP). At Lake Shinji, along the western San'in coast facing the Sea of Japan (Fig. 1A), an inner bay environment became established before ca. 9.2 ka, in association with the post-glacial sea level rise. Environmental reconstruction based on geochemical data showed that the inner bay environment subsequently changed to a freshwater lake environment as a result of relative sea level changes, the eruption of Sanpei volcano, and avulsion of the Hii River (Nakamura, 2006; Seto et al., 2006; Yamada and Takayasu, 2006). In addition, some coastal lagoons (e.g., Lakes Jusan, Harutori, Ryujinike, and Kanigaike) have provided important information about historical seismic events (e.g., Minoura et al., 1987, 1994; Nanayama et al., 2001; Okamura and Matsuoka, 2012). At Lake Hamana, a large brackish lagoon in central Japan, geological, sedimentological, paleontological, and geochemical analyses of sediment cores from the lakebed (cores 85H1 to 85H4,

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Fig. 2) carried out by several pioneering studies (Nakai et al., 1987; Ohtsuka and Kimiya, 1987; Kashima, 1988; Saito, 1988; Ikeya et al., 1990; Matsubara, 2001) have shown that an inner bay transitioned to a brackish or freshwater lake as a result of the development of coastal sand barriers under the regressive conditions that followed the Holocene highstand (Saito, 1988; Ikeya et al., 1990; Matsubara, 2001, 2005). Morita et al. (1998) suggested on the basis of a diatom analysis of core 85H1 sediments that salinity of the lake water increased at ca. 2300 14C BP (ca. 2400 cal BP) and again at AD 1498 (after the Meio earthquake). These environmental changes were presumably induced by short-term climatic changes or tectonic movements. In addition, Honda and Kashima (1997), who analyzed diatoms in the 96HM-1C core (Fig. 2) and focused on environmental changes during the last 1000 years, also reported salinity fluctuations after the 1498 Meio earthquake. Moreover, Tsuji et al. (1998) reported the presence of five event deposits, composed of gravels and marine shell-rich layers, in lakebed sediments, which they inferred from radiocarbon ages and historical records to have been deposited ca. 3800 cal BP (3850 ± 80 14C BP, marine shell), ca. 3300 cal BP (3420 ± 90 14C BP, marine shell), in AD 1096 (Eicho earthquake), in the 13th century AD (820 ± 60 14C BP, marine shell), and in AD 1498 (Meio earthquake). The aim of this study was to reconstruct late Holocene paleoenvironments of Lake Hamana by analyzing a lakebed core with high temporal resolution and to obtain information about shortterm events useful for disaster prevention in this region. Although the previous studies cited above have provided a great deal of information about paleoenvironmental changes in this region, late Holocene paleoenvironmental changes in Lake Hamana

Fig. 2. Map showing the bathymetry of Lake Hamana, core site locations, and the geomorphology of the surrounding region. The geomorphological classification map is based on the interpretation of aerial photographs (scale 1/10,000) taken in 1962 by the Geospatial Information Authority of Japan (GSI). The bathymetric data are based on topographic maps (scale 1/25,000) made in 2007 by GSI.

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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were not examined in detail, in part owing to the relatively low temporal resolution of the data. Because tsunami deposits occurred both before and after 3000 14C BP (ca. 3200 cal BP) along the Nankai Trough (Tsuji et al., 1998; Komatasubara and Fujiwara, 2007), it is expected that some short-term environmental also changes occurred before 3000 14C BP (ca. 3200 cal BP). To reconstruct the late Holocene environments of Lake Hamana, we carried out geological and paleontological analyses of lakebed sediments from core HMN08-7, collected in the central part of the lake, and examined the major developmental stages of the lake's history, as well as the occurrence of short-term environmental changes. 2. Regional settings 2.1. Limnology Lake Hamana, along the Enshu-nada coast, Shizuoka Prefecture, central Japan, has an area of approximately 65.0 km2; thus, it is the tenth largest lake, and the fifth largest coastal lagoon, in Japan (Figs. 1 and 2; National Astronomical Observatory of Japan (2013)). The intricately indented lakeshore is approximately 114 km long. The average water depth of the lake is 4.8 m, but the lake is much deeper in its northern (approximately 10e12 m depth) than in its southern (approximately 2e3 m depth) part, and the lakebed slopes steeply downward from east to west. The bottom in the southern part of the lake consists of sandy deposits, which on the basis of their geomorphological and depositional features are interpreted as a flood tidal delta that formed during the middle to late Holocene (Saito, 1988; Ikeya et al., 1990). At present, Lake Hamana is brackish and mesotrophic with low transparency (Secchi depth 1.3 m; National Astronomical Observatory of Japan (2013)). The tidal range is largest in the inlet and it decays landward to approximately 25% of the maximum (Mazda, 1999). The annual mean tidal range in 2013 measured at the Maisaka tidal gauge, located on the southeastern shore of the lake (Fig. 2), was 124.0 cm (mean high tide, 297.7 cm; mean low tide, 173.7 cm; Japan Meteorological Agency, 2014). Deformation of the lake inlet by a typhoon in AD 1953 and subsequent coastal stabilization works constructed from AD 1954 to AD 1973 caused the salinity of the lake water to increase gradually from approximately 20 to 28 [psu], on average, until the 1980s (Mazda, 1984; Suzuki, 2003). Since then, salinity has been stable or has fluctuated slightly around the high value of 28.55 (Suzuki, 2003). Salinity is highest in the inlet and decreases landward. Vertical structures of salinity and temperature in the lake are quite different seasonally; in summer, density stratification is strongly developed (higher salinity and colder temperatures in lower water layers), whereas in winter stratification is weak or homogeneous conditions prevail (Mazda, 1999). The strong summer stratification is caused by the large amount of fresh water supplied to the surface water layer by the abundant rainfall (approximately 150e250 mm/month in summer; National Astronomical Observatory of Japan (2013)) in the northern lake basin. As a result of this stratification, a low dissolved oxygen layer develops at the bottom of the lake. 2.2. Geomorphology Lake Hamana is surrounded by mountains, hills, and terraces. The mountains and hills distributed along its northern to northwestern shores consist mainly of Mesozoic chert of the Chichibu belt (Isomi and Inoue, 1972; Sugiyama, 1991). Three well-developed middle to late Pleistocene terraces are distributed along its eastern and western shores, from oldest to youngest, the Tenpakubara, Kamoe, and Mikatagahara terraces (Isomi and Inoue, 1972; Muto,

1987; Sugiyama, 1991; Koike and Machida, 2001; Nakashima et al., 2008). The Tenpakubara terrace stretches along the western shore to the Atsumi Peninsula and consists of Atsumi Group sediments, which are characterized by cyclic depositional sequences of the transgressive estuary system (mud covering sand gravels) to regressive strand plain system (sandy deposits) associated with glacioeustatic sea level changes in the middle Pleistocene (Hiroki and Kimiya, 1990; Nakashima et al., 2008). The middle to upper part of Atsumi Group has been dated tephrostratigraphically to Marine Isotope Stage (MIS) 9e11 (Nakashima et al., 2008). The Kamoe and Mikatagahara terraces are distributed along the eastern shore of Lake Hamana. The Kamoe terrace, which is exposed only at the southern margin of the Mikatagahara terrace, consists of three fining-upward sedimentary cycles and an overlying deltaic fan gravel bed deposited by the paleo-Tenryu River during the regressive stage following MIS 7c (Sugiyama, 1991). The extensive Mikatagahara terrace has a southward gradient and consists of deltaic gravel beds deposited by the paleo-Tenryu River that overlie the Kamoe terrace or the Yamasaki mud bed (Sugiyama, 1991). It is inferred to be a riverine terrace that formed during the regressive stage following MIS 5e (Muto, 1987; Sugiyama, 1991). The southern margins of these terraces were eroded during the post-glacial Jomon transgression, forming sea cliffs. Seaward of the sea cliffs, some wave-cut benches have been buried by Holocene sediments (Matsubara, 2004). Alluvial lowlands of various shapes and sizes, including drowned-type lowlands (Umitsu, 1994), have developed in valleys in the mountains, hills, and terraces around the lake and along the Enshu-nada Coast. Morphological differences among the alluvial lowlands suggest that they were formed by distinctive geological and geomorphological processes. In addition, some narrow segments of the valleys reflect differences in the hardness of the rocks through which the streams and rivers flow. Sato et al. (2011) and Fujiwara et al. (2013b) have studied middle to late Holocene environmental changes of the Rokkengawa and Miyakodagawa alluvial lowlands (Fig. 2). South of Lake Hamana along the Enshu-nada coast, six coastal sand barriers (including sandy beach ridges and sand dunes), called beach ridge (BR) I to VI following Matsubara (2001, 2007), protect the inlet to the lake. Although the six distinct sand barriers can be recognized easily on the eastern side of Lake Hamana, they merge into just three barriers on the western side (Matsubara, 2001). BR VI, which is distributed along the present shoreline, is an aeolian sand dune that has been much affected by human activity during the recent historical period. Between pairs of beach ridges are welldeveloped inter-ridge marshes. The Tenryu Lowland is distributed east of the Pleistocene terraces, and natural levees are well developed along the Tenryu and Magome rivers. Some levees and back marshes in central Hamamatsu City have been subjected to extensive artificial alterations (Fig. 2). 2.3. Tectonic movements Because the Nankai Trough, where the northwestward-moving Philippine Sea plate is subducting beneath the Eurasian plate (Fig. 1), is offshore of the Lake Hamana region, tectonic activity is relatively high in this area. Historical documents record severe damage caused by repeated huge earthquakes generated along the Nankai Trough (e.g., Ishibashi, 1984; Yata, 2009). For example, the AD 1498 Meio earthquake apparently caused profound geomorphological deformation around Lake Hamana (Shizuoka Prefecture, 1996; Yata, 2005; Fujiwara et al., 2013a). Before the Meio earthquake, the Hamana River flowed from the lake to the Enshu-nada Coast. Then, tectonic movement or tsunami currents at the time

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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of the earthquake opened up the present lake inlet. A geological survey has identified some late Holocene tsunami deposits on the alluvial lowlands around the lake (Fujiwara et al., 2006, 2013b). Although accurate measurements of co-seismic displacements have not been made, geodetic data indicate the possibility of coseismic subsidence in the lake area. Kato and Tsumura (1979), who have monitored interseismic deformation using tidal gauges, reported that the accumulation of tectonic stresses has led to interseismic uplift (Kato and Tsumura, 1979; CMDC, 2014). The estimated annual uplift rate around Lake Hamana is approximately 2.85 mm/yr (CMDC, 2014). Furthermore, Sagiya (2007) analyzed recent geodetic data and reported a regional pattern of interseismic uplift from Nagoya city to Kakegawa city and of subsidence from Kakegawa city to Numazu city. If much of the cumulative stress inferred by these studies were to be released during an earthquake, the total deformation that has occurred during the interseismic period would be reversed by co-seismic subsidence. The late Pleistocene terraces record the cumulative uplift over a period on the order of 105 yr. The cumulative vertical displacement and slip rate have been estimated to be 52e70 m and 0.16e0.22 m/ kyr, respectively, based on the distribution height and formation age of the Tenpakubara terrace (Sugiyama, 1991; Koike and Machida, 2001). 3. Materials and methods

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3.4. Diatom analysis A total of 320 subsamples were taken from the core sediments at 1.0 cm (mainly), or 0.5 or 2.0 cm at joint gaps, intervals for diatom analyses. The uppermost part of the core, 0e28 cm depth, was not subsampled. Diatom analyses were carried out according to the method of Kosugi (1993). Each subsample (~1 g) was transferred into centrifuge tubes with around 5% H2O2 solution and maintained at 40e50  C for at least 3 h to remove organic matter. After this acid treatment, the diatom fossil concentration of the treated subsample solution was adjusted with distilled water for easier counting the diatom fossils. Then the solution was transferred to a glass slide and allowed to dry. After drying, the glass slide was mounted using Mount medium (Wako Pure Chemical Industries Ltd., Japan). At least 300 individual diatoms or identifiable parts were counted under an optical microscope at 1000 magnification. Diatom identification and nomenclature are based on Hustedt (1930a, 1930b, 1959, 1961e1966), Krammer and Lange-Bertalot (1986, 1988, 1991a, 1991b), Watanabe (2005), and Kobayashi (2006). We referred to Kashima (1986), Kosugi (1988), and Ando (1990) for the habitats of the diatoms. Diatom zones are divided by using stratigraphically constrained cluster analysis (CONISS; Grimm, 1987) based on square-root transformation of data.

4. Results

3.1. Core HMN08-7

4.1. Sediments

Piston core HMN08-7 of lakebed sediment was obtained on 28 September 2008 (Okamura et al., 2009) from the central part of Lake Hamana (latitude 34 440 55.2000 N, longitude 137 340 02.6400 E; water depth, approxmately10 m; Fig. 2). At present, the bottom around the HMN08-7 core site is muddy (Ikeya et al., 1990). 3.2. Radiocarbon dating Seven radiocarbon ages on bulk organic sediments in the core were obtained by the accelerator mass spectrometry method at Geo-Science Laboratory Co. Ltd., Japan (Table 1). All radiocarbon ages were calibrated by using CALIB7.0 software (Stuiver et al., 2014) and the IntCal13.14c dataset (Reimer et al., 2013), because all samples were presumed to consist of terrestrial materials.

Core HMN08-7 is 348 cm long (Fig. 3). From 348 to 335 cm depth, the sediments consist of grayish mud. Well-developed grayish and brownish-red laminae alternate from 335 to 323 cm depth (Fig. 4A). A massive mud layer (323e315 cm) is overlain by an interval of weak, coarse laminae (315e295 cm depth; Fig. 4B and C). The sediments above 295 cm depth consist of massive mud; active bioturbation was recognized in the interval from 210 to 113 cm depth (Fig. 4E) and the interval from 113 to 64 cm depth contains many shell fragments (Fig. 4F). The boundary between these two layers is gradual and obscure. Two thin volcanic ash layers are intercalated at 265 and 263e261 cm depth within the massive mud layer, along with a thin fine-sand layer at 288e285 cm depth (Figs. 3 and 4D). The boundaries separating each of these layers from the massive mud layer are gradual, and there are no sharp

Table 1 Radiocarbon dating results. Seven radiocarbon ages were measured by the accelerator mass spectrometry method with a 2s error range and calibrated using CALIB7.0 (Stuiver et al., 2014). C age (yr BP, 1s)

Depth (cm)

Sample materials

14

78e81 111e114 199e202 216e220 280 290.5e293 324e326

Organic Organic Organic Organic Organic Organic Organic

1100 1030 1800 2190 4440 4040 4090

sediments sediments sediments sediments sediments sediments sediments

± ± ± ± ± ± ±

40 40 40 30 30 30 30

3.3. Tephras Tephra layers, that is, volcanic ashes and scoria, are key beds for determining sedimentation ages in the Japanese archipelago (Machida and Arai, 2003). We visually observed tephra beds, and the refractive indices of the main heavy minerals and volcanic glass shards were measured by the MAIOT (Measuring Actual Immersion Oil Temperature) method (Furusawa, 1995) at Furusawa Geological Survey Co. Ltd., Japan.

Calibrated age (cal BP, 2s)

Probability (%)

Lab. No. (Beta-)

930e1085 900e1010 1610e1825 2130e2310 4955e5075 4425e4580 4515e4650

97.7 84.6 99.8 100.0 55.5 97.7 69.6

251570 251571 251572 333478 334352 333480 333481

depositional facies changes to suggest the presence of an erosional surface. The top ~25 cm of the core is very soft and has a distinct hydrogen sulfide gas smell. 4.2. Age model We constructed an age model for the HMN08-7 core from the radiocarbon ages and tephra beds (Fig. 3B, Table 1). The lower tephra layer (265 cm depth) contained pumice-type and bubble-

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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Fig. 3. Photographs of core HMN08-7, diagram of the geological column, and age model. A: Photographs of the core. The numbers at the top and bottom of each column indicate depth beneath the lakebed (cm). B: Diagram of the geological column and the age model constructed from the radiocarbon ages (Table 1) and tephra layers. The dashed line above 199 cm depth is a modified accumulation curve estimated from the depth and age of the boundary associated with the 1498 Meio earthquake.

Fig. 4. Soft X-ray images of the lakebed core samples. A: 343e328 cm depth, strong laminae overlying massive mud. B: 323e308 cm depth, a weak, coarsely laminated interval above a massive mud layer; C: 306e291 cm depth, weak, coarse laminae; D: 289e274 cm depth, the EB layer within the massive mud layer; E: 127e112 cm depth, active bioturbation in massive mud; F: 107e92 cm depth, massive mud. Dark areas (Dk) in B, C, and D are where subsamples were removed.

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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wall-type volcanic glasses with some heavy minerals. The refractive indices of the volcanic glasses, pyroxenes, and hornblendes were estimated to be 1.501e1.503, 1.705e1.708, and 1.669e1.679, respectively. These indices coincide with those of the Amagi-Kawagodaira Pumice [Kg], which erupted around 3126e3145 cal BP (Shimada, 2000; Machida and Arai, 2003) from Kawagodaira volcano, Izu Peninsula, central Japan (Fig. 1). Both the analysis result and the tephra's stratigraphic position in the core are consistent with its identification as Kg tephra. From the tephra catalogue and stratigraphy in the region around the study area (Ikeya et al., 1990; Morita et al., 1998; Machida and Arai, 2003) and the core stratigraphy, we inferred that the upper tephra layer (263e261 cm depth) is Fuji-Osawa scoria [Os], which erupted at 2.5e2.8 ka from Mt. Fuji, central Japan (Machida and Arai, 2003). The radiocarbon ages show an age reversal at 280 cm depth, which we attributed to reworking of the sediments. Therefore, we did not use the radiocarbon date from this depth as an age control point in the final age model (Fig. 3B). According to the age model, it is estimated by extrapolation that core HMN08-7 records the lake environment from ca. 4700 cal BP to the present. 4.3. Diatom fossil assemblages The distribution of diatoms, based on their relative abundances, in core HMN08-7 is shown in Fig. 5. On the basis of changes in diatom assemblages, we divided the core into six diatom zones, zones I to VI in ascending order. We also subdivided zones V and VI into three subzones each, designated a to c in ascending order. Finally, we identified two layers, one in zone II and one in zone III, called EA and EB, respectively, containing unusual diatom fossil assemblages. 4.3.1. Zone I (depth: 348e339 cm) Zone I, in the lowest part of the core, is in massive mud sediments (Fig. 3). This zone is characterized by abundant brackish and marine water species, including outer bay indicators such as Thalassiosira sp., which accounted for around 10%e20% of total diatoms in zone I. Inner bay indicators such as Cyclotella striata are rare in this zone. Other marine to brackish water species, such as Diploneis pseudovalis, Diploneis smithii, Rhaphoneis surirella, Glyphodesmis williamsonii, Dimeregramma minor, and Opephora martyi, though present in only minor amounts, are more abundant in this zone than in the overlying zones. 4.3.2. Zone II (depth: 338e296 cm) Zone II approximately corresponds to both the well-developed and weakly laminated sediments and wedging massive mud layer. In this zone, Cyclotella striata, a significant indicator of a brackish lake environment (Kashima, 1988, 2001), abruptly increases, reaching a relative abundance of approximately 40%. The abundances of Thalassiosira sp. and Thalassionema nitzschioides are similar to those in zone I, ~10%e15% and ~10%, respectively, whereas the abundance of Cocconeis scutellum, a benthic marine to brackish water species, increased by about 10%e15% compared with its abundance in zone I. The EA layer, in the middle part of this diatom zone (322e321 cm depth), is characterized by a spike in the relative abundance of Glyphodesmis williamsonii. This spike coincides with the lower boundary of the massive mud layer that separates the two laminated sediment intervals. In the muddy sediments just above this spike, Paralia sulcata and T. nitzschioides increase in abundance, each accounting for ~5%e10% of total diatoms, becoming slightly more abundant than in the sediments below the spike.

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4.3.3. Zone III (depth: 295e257 cm) Zone III is in massive muddy sediments. The top of this zone is bounded by the Os tephra layer. The relative abundance of Cyclotella striata in zone III is around 20%, which is lower than its abundance in zone II. Although planktonic brackish to marine species such as C. striata are dominant in zone III, the abundances of Staurosira construens, a fresh to brackish water species, and of Cocconeis scutellum, a benthic brackish to marine species, increased slightly from zone II. The upper part of this zone, above 275 cm depth, includes an obvious peak in the relative abundance of the outer bay indicator Thalassiosira sp. in the 275e272 cm depth interval. Above this interval, its relative abundance gradually decreases. The EB layer, at 288e283 cm depth, is distinguished by gradual increases in fresh and fresh to brackish water species such as S. construens, Fragilaria spp., and Aulacoseira ambigua. The EB layer mainly corresponds to the thin sandy sediment layer, 288e285 cm depth. 4.3.4. Zone IV (depth: 256e222 cm) Zone IV is in massive humic mud overlying the Os layer. In this zone, brackish to marine water species are much less abundant than in zone III, and it includes fresh to brackish water and freshwater species. The abundances of Thalassiosira sp., Paralia sulcata, and Thalassionema nitzschioides, marine planktonic species, decrease from about 5% to 10% in zone III to almost 0%. In addition, the abundances of Cyclotella striata and Cocconeis scutellum decline gradually upward in the zone, from ~25% to ~5% and from ~25% to ~0%, respectively. In contrast, Staurosira construens, a fresh to brackish tychoplanktonic species, and Fragilaria spp., a freshwater species, increase gradually upward, replacing C. striata and C. scutellum. Staurosira construens, in particular, becomes dominant, accounting for ~35% of diatoms, in the upper part of this zone. 4.3.5. Zone V (depth: 221e105 cm) Zone V is in the massive muddy sediments. This zone is dominated by freshwater species such as Fragilaria spp., Aulacoseira granulata, and Aulacoseira ambigua. Marine species are low, except for minor Cyclotella striata. We subdivided this zone into four parts, zones V-a, V-b, V-c, and V-d, according to the abundance of Staurosira construens, which is high in V-b and V-d, but lower in V-a and V-c. Zone V-a, 221e151 cm depth, is characterized by high abundances of Fragilaria spp. and A. ambigua, with Fragilaria spp. being more abundant in the lower part of this subzone than in the upper part. Aulacoseira granulata increases gradually upward. In zone V-b, 150e127 cm depth, S. construens is dominant, and the abundance of A. ambigua drastically decreases compared with its abundance in zone V-a. Cyclotella striata is also slightly more abundant than in zone V-a, reaching ~2%. Zone V-c, 126e111 cm depth, is dominated mainly by A. granulata and A. ambigua. Zone V-d, 110e105 cm depth, is characterized by higher percentages of C. striata and S. construens, reaching ~15%, than lower zones and persistence of freshwater and brackish water species, A. granulata, A. ambigua and S. construens. 4.3.6. Zone VI (depth: 104e28 cm) Zone VI roughly corresponds to a grayish muddy layer with many shell fragments. This zone is characterized by renewed dominance of brackish to marine species and the near absence of freshwater species. In particular, Cyclotella striata, Cocconeis scutellum, Diploneis pseudovalis, and Paralia sulcata increase in abundance abruptly from zone V. In the lowest part of this zone, however, Aulacoseira granulata and Staurosira construens still

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Fig. 5. Fossil diatom assemblages in core HMN08-7 shown alongside the geological column (as in Fig. 3B but vertically expanded). The dendrogram on the right-hand side of the diagram was obtained by a stratigraphically constrained cluster analysis (CONISS; Grimm, 1987) based on square-root transformation of the data. The estimated dates, shown at each diatom zone boundary, were inferred from the age model (cal BP, except for the boundary between zones V and VI).

account for approximately 10%e20% and 20% of diatoms, respectively. We subdivided this zone into three subzones on the basis of the relative abundance of Cyclotella striata. In zone VI-a (104e80 cm depth), Cyclotella striata is the dominant species ranging from 14.5% to 54.9% in relative abundance, and C. scutellum and D. pseudovalis account for around 10%e20% and 5%e10% of diatoms, respectively. In zone VI-b (79e61 cm depth) Thalassionema nitzschioides and Thalassiosira sp. are more abundant than in the other subzones. Zone VI-c (60e28 cm depth) is dominated by C. striata, and the abundances of C. scutellum, Thalassiosira sp., and D. pseudovalis are similar to those in zone VI-a.

5. Discussion 5.1. Environmental changes inferred from diatom assemblages We used the diatom zones to reconstruct late Holocene environmental changes of Lake Hamana by associating each diatom zone with a stage in the development of the lake (Fig. 6). 5.1.1. Stage I (ca. 4700e4600 cal BP) In the lowest diatom zone, which deposited during ca. 4700e4600 cal BP inferred from the age model (Fig. 3), the low abundance of inner bay environment indicators such as Cyclotella striata (Kosugi, 1988) suggests that coastal sand barriers had not yet

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Fig. 6. Summary of the reconstructed late Holocene environmental changes around Lake Hamana. Environmental changes in the alluvial lowlands are those reconstructed by Sato et al. (2011, 2013). Eruption ages of the Kg and Os tephra are based on Machida and Arai (2003). The estimated eustatic curve during the late Holocene is from Fleming et al. (1998). Relative sea level curves A and B are for the region around Ise Bay (Fig. 1A; calibrated after Umitsu (1992) using IntCal 13.14c) and around the Tokyo lowland (Tanabe and Ishihara, 2013), respectively.

developed enough close off the bay from the ocean and allow a brackish lake or a coastal lagoon environment to develop. Because Thalassiosira sp. and Diploneis smithii, which are indicators of an outer bay environment (Kosugi, 1988) were more abundant than C. striata, we infer the active exchange of seawater between the ocean and the core site, which corresponding to the inner bay environment with large seawater discharge before 4200 14C BP (ca. 4650 cal BP) suggested by Morita et al. (1998) (Fig. 6). In addition, the abundances of Opephora martyi, Glyphodesmis williamsonii, Dimeregramma minor, and Rhaphoneis surirella are comparatively high. As these species are indicators of sandy tidal flats (Kosugi, 1988), we infer that seawater transported allotopic sediments, including diatoms, to the site from a tidal flat and flood/ebb tidal delta. The period from 4700 to 4000 cal BP corresponds to a sea level highstand. Saito (1988) suggested that at this time there was an active barrier system south of the core site (Fig. 6). According to Saito (1988), BR I, the most inland beach ridge, was still partly submerged and prograding landward. Hence, the reconstructed environment inferred from diatom assemblage is strongly supported by the sedimentological information. 5.1.2. Stage II (ca. 4600e4500 cal BP) This stage corresponds to the zone II and occurred around 4600e4500 cal BP inferred from the age model (Fig. 3). The dominance of Cyclotella striata and the laminated lake bottom sediments deposited during this period suggest that a brackish lake or lagoon environment formed ca. 4600 cal BP. At this time, the core site was well protected from the open ocean, and a brackish lake or lagoon environment was reducing. Because Cyclotella striata increased abruptly at the bottom of zone II, the brackish lake or lagoon environment must have formed rapidly around 4600 cal BP. We suggest that the change from an open bay to a closed inner bay environment, brackish lake or lagoon, was probably caused by the

development of coastal sand barriers that drastically reduced the exchange of seawater between the bay and the open ocean. However, because the percentage of Thalassiosira sp. was almost the same in zones I and II, some inflow of seawater into the bay continued to occur during stage II. In the protected inner bay environment, strong density stratification probably developed, which led to the deposition of laminated sediments under reducing conditions. The estimated formation of a brackish lake or lagoon environment ca. 4600 cal BP is consistent with the findings of Morita et al. (1998), who, on the basis of their diatom analysis, reported a reduction in salinity after ca. 4200 14C BP (ca. 4650 cal BP). The diatom species in the inner bay sediments (zone I) in the present study are almost the same as those reported by Morita et al. (1998), but their age model was not based on calibrated radiocarbon ages or tephras. If we modify their age model by roughly calibrating it against the radiocarbon and tephra ages inferred from the IntCal13.14c curve (Reimer et al., 2013), the change to a brackish lake or lagoon environment can be estimated to have occurred ca. 4700e4600 cal BP. Thus, the timing of this environmental change is similar between core HMN08-7 and the core studied by Morita et al. (1998), suggesting that both studies are describing the same transition. 5.1.3. Stage III (ca. 4500e2650 cal BP) This stage corresponds to the zone III and occurred around 4500e2650 cal BP inferred from the age model (Fig. 3). The decreasing abundance of Cyclotella striata and massive muddy sediments during this period indicate a well-mixed brackish water environment. Cyclotella striata is replaced mainly by benthic species such as Staurosira construens and Cocconeis scutellum. Higher taxonomical diversity indicates that active mixing of riverine freshwater and high-salinity marine water in a brackish lake or lagoon. In addition, above 275 cm depth, which estimated after ca.

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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3500 cal BP from the age model, Thalassiosira sp., an indicator of an outer bay environment (Kosugi, 1988), increased, suggesting that the inflow of seawater increased at that time. Cyclotella striata and Cocconeis scutellum were as abundant after 3500 cal BP as before. Therefore, it is reasonable to infer that the oceanic species Thalassiosira sp. was transported by seawater inflow from the Pacific into a brackish lake or lagoon. 5.1.4. Stage IV (ca. 2650e2250 cal BP) This stage corresponds to the zone IV. After the eruption of the Os tephra about 2650 cal BP, salinity around the core site declined continuously until ca. 2250 cal BP inferred from the age model (Fig. 3). First, the absence of any diatom indicator of an outer bay environment indicates that seawater inflow to the core site ceased about this time. During the early part of this stage, however, salinity was still high enough for Cyclotella striata to be a dominant species. In zone IV, the clear upward decrease of C. striata and Cocconeis scutellum together with an upward increase in Staurosira construens suggests that salinity gradually declined from 2650 to 2250 cal BP. The minor presence of freshwater diatom species also implies that the surface water was gradually becoming fresher. After the Kg and the Os tephra falls, environmental changes occurred gradually around the core site. It was reported previously based on paleontological analyses of sediment cores that the lake water became fresh around 3000 14C BP (ca. 3200 cal BP), after the Kg and the Os tephra falls (Kashima, 1988; Kojima, 1989; Ikeya et al., 1990; Morita et al., 1998). In the present study, however, we found that the lake remained brackish for a while after deposition of the Os tephra. Therefore, we inferred that the seawater inflow decreased just after the Os tephra fall, and the gradual transitions in the diatom assemblages reflect increasing dilution with freshwater. However, brief increases of freshwater species such as Aulacoseira granulata, Aulacoseira ambigua, and Achnanthes minutissima in the middle of the stage, suggest the occurrence of some short-term reductions in salinity at that time. In addition, the abundance of C. striata increases briefly at the top of zone IV. Morita et al. (1998) inferred from changes in the abundances of A. granulata and C. striata that the water changed from fresh to brackish at ca. 2300 cal BP (ca. 2400 cal BP). Although the environmental change inferred in this study is much smaller, it may correspond to the temporary formation of a brackish lake described by Morita et al. (1998). 5.1.5. Stage V (ca. 2250 cal BP to ca. 480 cal BP) This stage corresponds to the zone V. The environment of the core site changed from a brackish to a freshwater lake in ca. 2250 cal BP based on the age model (Fig. 3). Most diatoms after this date are freshwater species, and only a few brackish to marine species were identified. In addition, active bioturbation of the muddy sediments indicates that along with the salinity reduction, density stratification was absent and bottom conditions were oxidative. Moreover, the upward increase of Aulacoseira granulata, an indicator of fresh water (Ando, 1990), and upward decrease of Fragilaria spp., a fresh to brackish tychoplanktonic species, imply the existence of a lake that was gradually becoming deeper. Because Staurosira construens, a fresh to brackish water species, is the dominant species in zone V-b, salinity may have increased temporarily during the middle of stage V, that is, between ca. 1300 and 1150 cal BP according to our age model. This freshwater lake probably persisted until the AD 1498 Meio earthquake. Previous studies reported an environmental change in the lakebed sediments from a freshwater lake at the time of the Meio earthquake (Honda and Kashima, 1997; Morita et al., 1998) to a brackish environment afterward. In the present study, we identified a boundary between a brackish water and a freshwater

environment at 111 cm below the lake bottom, that is, between zones V-c and V-d. Above this boundary, there is no evidence of a freshwater environment. Therefore, the boundary between zones V-c and V-d probably corresponds to the Meio earthquake. Our age model for core HMN08-7 (Fig. 3) shows an age of around 1000 cal BP, about 500 yr before the AD 1498 Meio earthquake, for the boundary between brackish and freshwater environments. We attribute this discrepancy to reworked dead carbon from the 78e81 cm and 111e114 cm depth intervals being used for radiocarbon samples. Hence, the age model above 199 cm was modified based on the depth and age of the boundary associated with the 1498 Meio earthquake (a dashed line shown in Fig. 3). The boundary between the brackish water and freshwater environments does not correspond to the lithological boundary between humic and non-humic mud at 113 cm below the lake bottom. We attribute this discrepancy between the diatom zones and lithology to bioturbation, or possibly to an environmental change in the coastal lowlands. The gradual change of the depositional facies and shell-rich deposits above zone V-d suggests that freshwater diatom species were transported by bioturbation from the lower sediment layer. In addition, in the coastal lowlands around Lake Hamana, an environmental change from freshwater marsh to tidal flats was likely associated with the Meio earthquake, and this change probably reduced the amount of organic material entering Lake Hamana. Because the coastal lowlands were directly affected by tides, the reduction in organic material occurred before the salinity decrease at the core site. After the 1498 Meio earthquake, the occurrence of both freshwater and brackish water species in zone V-d along with C. striata, a marine species, suggests that the salinity in Lake Hamana increased gradually. The modified accumulation curve suggests that this salinity gradually increasing phase probably continued until ca. 480 cal BP (Fig. 3). 5.1.6. Stage VI (after ca. 480 cal BP) Stage VI probably began after the AD 1498 Meio earthquake, estimated to be ca. 480 cal BP. The dominance of Cyclotella striata throughout zone VI indicates that a brackish lake or coastal lagoon environment re-developed after the earthquake and has lasted to the present day. Bioturbation is rare in the core sediment during this period, which suggests that the reductive environment occurred in the lake bottom as a result of density stratification accompanying the increase in salinity. After ca. 480 cal BP, fluctuating inflows of seawater are suggested by fluctuations in the abundance of the outer bay indicator Thalassiosira sp. (Kosugi, 1988). Zone VI-b, in particular, is characterized by a high relative abundance of Thalassiosira sp. and a decrease in the abundance of C. striata. This assemblage change probably reflects an increase of seawater inflow and increasing salinity. If the sedimentation rate from the Meio earthquake to the present has been constant (about 0.45 mm/yr), then zone VI-b covers the period from approximately 100 to 250 yr after the earthquake (i.e., AD 1600e1750). Honda and Kashima (1997) reported a similar environmental change around the same time (ca. AD 1700e1850) characterized by an abundance of Thalassiosira sp. and Thalassionema nitzschioides. Honda and Kashima (1997) also reported an increase in salinity just after the Meio earthquake, but we could not recognize this increase in our data. 5.2. Event deposits 5.2.1. EA layer The diatom assemblages and depositional facies of the EA layer during stage II (when the core site was in a closed inner bay environment), as well as its extreme thinness, suggest a short-term

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event. The main diatom species in this layer is Glyphodesmis williamsonii, a brackish to marine water species that is an indicator sandy tidal flats (Kosugi, 1988). Moreover, except in the EA layer, this species is quite rare in the core, and the diatom assemblages above and below the layer are dominated by planktonic species. It is therefore unlikely that the layer represents sandy tidal flats formed at the core site as a result of relative sea level fluctuations. It is more reasonable to infer that G. williamsonii diatom valves were transported from coastal sandy tidal flats by some short-term event. An environmental change is also apparently associated with the deposition of the EA layer. Above the layer, Thalassiosira sp. and Thalassionema nitzschioides are slightly more abundant than below, and the EA layer separates laminated from massive muddy sediment, which suggests an environmental change from reducing to oxidative. This finding suggests that after deposition of the EA layer, seawater flowed more readily into the inner bay so that the environment became temporarily oxidative. Transferred diatom species from seaward and increased seawater inflow imply that drastic geomorphological changes around the southern part of the lake occurred in association with a strong current flow from seaward. Sandy tidal flats, the presumed source of G. williamsonii, were widely distributed at this time south of the core site (Ikeya et al., 1990). Furthermore, coastal sand barriers were distributed between the bay and the ocean. Therefore, it is likely that a strong current from seaward, such as a tsunami and storm surge, struck the coast in this region, eroding the sandy tidal flats and partly destroying the coastal sand barriers. If this current was caused by a tsunami, then related seismic subsidence might have caused greater landward penetration of a saltwater wedge as well as an increase in water depth. It is likely that this event deposit has not been recognized previously around Lake Hamana. According to our age model, this event occurred between ca. 4600 and 4500 cal BP. Although Tsuji et al. (1998) and Okamura et al. (2009) have already reported the presence of some event deposits dating to after ca. 4 ka in the Lake Hamana area, they cannot be linked to the EA event, which occurred before 4 ka. The EA layer is thus an important addition to the longterm record of event deposits in and around Lake Hamana. 5.2.2. EB layer The EB layer (288e283 cm), which was deposited during stage III, contained relatively high percentages of fresh and fresh to brackish species, such as Aulacoseira granulata, Fragilaria spp., and Cocconeis placentula. However, the main components of the diatom assemblage of zone III, Cyclotella striata, Cocconeis scutellum, and Thalassiosira sp., are as abundant in the EB layer as in other parts of the zone. In addition, the thin sandy deposits composing this layer suggest that it was deposited more rapidly than the other core sediments. Therefore, we infer that the fresh and fresh to brackish water diatom species are allotopic fossils transported from coastal freshwater environments such as marshes or ponds. The diatom assemblages and depositional facies above and below the EB layer are almost the same, indicating that the deposition of this layer was not associated with subsidence and coastal deformation. Moreover, there is no evidence for any episodic current from seaward, such as an increase in indicator species of outer bay and tidal flat environments. Therefore, the fresh and fresh to brackish water species were likely transported from landward by a riverine flood event. The upper part of the EB layer (i.e., 285e283 cm depth) overlies the thin fine-sand layer (Figs. 3e5). The diatom assemblages in this part showed a gradual increase in brackish to marine species and a decrease in freshwater and fresh to brackish water species upward. Moreover, the depositional facies and soft X-ray photo showed no difference between the upper part of the EB layer and the massive

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mud layer above 283 cm depth (Fig. 4D). Thus, after its deposition, the lower part of the EB layer was covered by finer sediments containing freshwater and fresh to brackish water diatom species. According to our age model, this event occurred around 4200 cal BP. The sedimentation rate between 293e290.5 cm and 263e261 cm depth, an interval that includes the EB layer, was much smaller compared with that of the intervals above and below. Although it is possible that the flooding event associated with deposition of the EB layer eroded the lake floor, we could identify neither an erosional surface nor a depositional facies change related to the EB layer (Fig. 4D). Therefore, we inferred that the smaller sedimentation rate was probably caused not by erosion during the event associated with the EB layer but by an environmental change that occurred at ca. 4500 cal BP. 5.3. Environmental changes around 3 ka After ca. 3 ka, freshwater environments became widespread in the Lake Hamana region, affecting both the lake itself and the surrounding coastal lowlands (Fig. 6). In particular, after the Os tephra event, the salinity of Lake Hamana declined gradually and a freshwater environment formed. In addition, around 3400 cal BP, just before the Kg tephra event, freshwater marshes occupied the Rokkengawa lowland along the southeastern shore of the lake (Sato et al., 2011; Fujiwara et al., 2013b), and freshwater marshes formed in inter-ridge environments (BR IeII and BR IIIeIV) around 3200 cal BP (Sato et al., 2013). The timing and similarity of these environmental changes suggest that BR IV emerged around 3 ka and sheltered the lake and coastal lowlands. The freshwater environments after ca. 3 ka in and around Lake Hamana are characterized by greater stability than before. During stages IV and V, the salinity of Lake Hamana declined gradually and the environment changed to a freshwater pond/marsh. The freshwater environment was maintained in the lake until the Meio Earthquake, except for a slight salinity increase between ca. 1300 and 1150 cal BP, although in the coastal lowlands, freshwater ponds/marshes persisted until the present (Fig. 6). In contrast, salinity fluctuated frequently before 3 ka, and in the Hamana Lake area an inner bay environment alternated with a brackish lagoon, while tidal flats alternated with a freshwater marsh environment in the surrounding lowlands (Fig. 6, Sato et al., 2011, 2013; Fujiwara et al., 2013b). This difference in stability between before and after ca. 3 ka indicates that development of the BR IV made sea water difficult to inundate to inland area associated with deformation and subsidence of beach ridges, such as from storms, tsunamis, and earthquakes, than before 3 ka. Along the Japanese coast, numerous sand barriers and beach ridges formed and emerged around ca. 3 ka, including around Hokkaido (Ohira, 1995), the Kujukuri Strand Plain (Moriwaki, 1979), and Suruga Bay (Matsubara, 1989, 2000). These environmental changes were caused by relative sea level fall associated with the Yayoi Regression (Fig. 6; Matsubara, 2000, 2015). Around Ise Bay, approximately 80 km west of Lake Hamana (Fig. 1A), sea level was around 3 m below the present level in this period (Fig. 6; Umitsu, 1992). These data indicate that the environmental changes around 3 ka around Lake Hamana was also attributed to the minor sea level fall during the Yayoi Regression. 6. Conclusions Our detailed diatom fossil analysis and tephra and radiocarbon dating of core HMN08-7 from the lakebed of Lake Hamana revealed environmental changes from 4700 cal BP with high temporal resolution. The conclusions of this study are as follows:

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

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1. Six stages reflecting stepwise environmental changes were reconstructed as follows: stage I (4700e4600 cal BP), seawater inflow was vigorous in an inner bay; stage II (4600e4500 cal BP), a closed inner bay environment due to the formation of sand barriers; stage III (4500e2650 cal BP), a wellmixed brackish environment resulted from active mixing with riverine freshwater and, after 3500 cal BP, the enhanced inflow of seawater; stage IV (2650e2250 cal BP), a gradual salinity decrease due to reduced seawater inflow; stage V (2250 cal BP to 480 cal BP), a freshwater lake which deepened during the middle of the period and temporarily became more salty; and stage VI (480 cal BP), redevelopment of an inner bay environment after the AD 1498 Meio earthquake with fluctuation of lake water salinity. 2. Two event deposits, EA and EB, were inferred from spikes in minor diatom species. We inferred that EA represented a shortterm event during which sediment was supplied from seaward, such as by a tsunami or storm surge. EB layer appears to consist of allotopic sediments supplied temporarily from rivers or the lake shore, such as during a huge flood. 3. After ca. 3000 cal BP, salinity gradually decreased and a freshwater lake formed in the area of Lake Hamana, and similar changes occurred at the same time in the coastal alluvial lowlands in the region. These environmental changes were probably related to the formation of BR IV, which was presumably formed associated with the Yayoi Regression. Acknowledgements We sincerely appreciate Associate Professor Yusuke Okazaki of Kyushu University, Dr. Osamu Fujiwara of the National Institute of Advanced Industrial Science and Technology (AIST), and Dr. Satoshi Ishikawa of Nagoya University for their constructive discussion of our study. We are deeply grateful to Dr. Satoshi Ishiguro of the National Institute for Environmental Studies (NIES) and Dr. Susumu Tanabe of AIST for their help in creating some of our figures. This study was partially funded by a Grant-in-Aid for JSPS Fellows (Project Number 11J03774) and the Research Concerning Interaction between the Tokai, Tonankai, and Nankai Earthquakes Project of the Ministry of Education, Culture, Sports, Science and Technology of Japan. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.quaint.2015.06.006. References1 Ando, K., 1990. Environmental indicators based on freshwater diatom assemblages and its application to reconstruction of paleo-environments. Annals of the Tohoku Geographical Association (Tohoku Chiri) 42, 73e88 (in Japanese, with English abstract). * CMDC [Coastal Movements Data Center], 2014. Crustal Deformation Estimated from Tidal Gauge of Japanese Tidal Stations (accessed 22.05.14.) (in Japanese). http://cais.gsi.go.jp/cmdc/center/annualgra.html. Fleming, K., Johnston, P., Zwartz, D., Yokoyama, Y., Lambeck, K., Chappell, J., 1998. Refining the eustatic sea-level curve since the Last Glacial Maximum using farand intermediate-field sites. Earth and Planetary Science Letters 163, 327e342. Fujiwara, O., Komatsubara, J., Takada, K., Shishikura, M., Kamataki, T., 2006. Temporal development of a Late Holocene strand plain system in the Shirasuka area along Western Shizuoka Prefecture on the Pacific coast of Central Japan. Journal of Geography (Chigaku-zasshi) 115 (5), 569e581 (in Japanese, with English abstract).

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*English translation from the original written in Japanese.

Fujiwara, O., Ono, E., Yata, T., Umitsu, M., Sato, Y., Heyvaert, V.M.A., 2013a. Assessing the impact of 1498 Meio earthquake and tsunami along the Enshu-nada coast, central Japan using coastal geology. Quaternary International 308e309, 4e12. Fujiwara, O., Sato, Y., Ono, E., Umitsu, M., 2013b. Researches on tsunami deposits using sediment cores: 3.4 ka tsunami deposit in the Rokken-gawa Lowland near Lake Hamana, Pacific Coast of Central Japan. Journal of Geography (Chigaku Zasshi) 122 (2), 308e322 (in Japanese, with English abstract). Furusawa, A., 1995. Identification of tephra based on statistical analysis of refractive index and morphological classification of volcanic glass shards. Journal of the Geological Society of Japan 101 (2), 123e133 (in Japanese, with English abstract). Grimm, E.C., 1987. CONISS: a FORTRAN 77 program for stratigraphically constrained cluster analysis by the mothod of incremental sum of squares. Conputer Geosience 13, 13e35. Hiroki, Y., Kimiya, K., 1990. The development of barrier-island and strand-plain systems with the glacio-eustatic sea-level change in the Pleistocene Atsumi Group, central Japan. Journal of the Geological Society of Japan 96 (10), 805e820 (in Japanese, with English abstract). Honda, S., Kashima, K., 1997. Paleo-environmental changes during the last 1,000 years from lake deposits at Lake Hamana, central Japan. LAGUNA 4, 69e76 (in Japanese, with English abstract). Hustedt, F., 1930a. Bacillariophyta (Diatomeae). In: Pacchers, A., Gustav, Fischer (Eds.), Die Süsswasser-Flora Mitteleuropas Heft 10. Jena (in German). € Hustedt, F., 1930b. Die Kieselalgen : Deutschlands, Osterreichs und der Schweiz €nder Europas sowie der angrenzenden unter Berücksichtigung der übrigen La Meeresgebiete. Dr. L, Rabenhorst's Kryptogamen-Flora von Deutschland, € Osterreich und der Schweiz, VII Band, 1. Teil (reprinted 1977). Otto Koeltz, Koenigstein (in German). € Hustedt, F., 1959. Die Kieselalgen : Deutschlands, Osterreichs und der Schweiz unter Berucksichtigung der ubrigen Lander Europas sowie der angrenzenden Meer€ esgebiete. Dr. L, Rabenhorst's Kryptogamen-Flora von Deutschland, Osterreich und der Schweiz, VII Band, 2. Teil (reprinted 1977). Otto Koeltz, Koenigstein, Germany (in German). € Hustedt, F., 1961e1966. Die Kieselalgen: Deutschlands, Osterreichs und der Schweiz €nder Europas sowie der angrenzenden unter Berucksichtigung der übrigen La Meeresgebiete. Dr. L, Rabenhorst's Kryptogamen-Flora von Deutschland, € Osterreich und der Schweiz, VII Band, 3. Teril (reprinted 1977). Otto Koeltz, Koenigstein, Germany (in German). Ikeya, N., Wada, H., Akutsu, H., Takahashi, M., 1990. A Report on Stratigraphy, Lithofacies and Geological Age of the Holocene Sediments along the East Coast of Hamana-ko. Geoscience Reports of Shizuoka University 11, pp. 171e179 (in Japanese, with English abstract). * Iseki, H., 1983. Alluvial Lowland. University of Tokyo Press, Tokyo (in Japanese). Ishibashi, K., 1984. Coseismic vertical crustal movements in the Suruga Bay region. Quaternary Research (Daiyonki-kenkyu) 23 (2), 105e110 (in Japanese, with English abstract). Isomi, H., Inoue, M., 1972. Geology of the Hamamatsu District e Quadrangle Series Scale 1:50,000 Kyoto (11) No. 59. Geological Survey of Japan, Kawasaki (in Japanese). * Japan Meteorological Agency, 2014. Annual Tide Record of Tidal Gauges. http:// www.data.jma.go.jp/kaiyou/db/tide/gaikyo/nenindex.php (accessed 21.01.15.) (in Japanese). Kashima, K., 1986. Holocene succession of diatom fossil assemblages in alluvium, and those relation to paleogeographical changes. Geographical Review of Japan 59A (7), 383e403 (in Japanese, with English abstract). Kashima, K., 1988. Holocene paleo-environmental succession in Lake Hamana presumed by diatom analysis. Journal of Research Group of Clastic Sediments in Japan 5, 95e107. Kashima, K., 1990. Holocene environmental change in some brackish lakes in Japan, presumed by fossil and sedimentary analyses of lake sediments. Journal of the Sedimentological Society of Japan 32, 31e32. Kashima, K., 2001. Salinity changes during the Late Holocene at coastal brackish lakes in Japan. LAGUNA 8, 1e14 (in Japanese, with English abstract). Kato, T., Tsumura, K., 1979. Vertical Land movement in Japan as deduced from tidal record, (1951e1978). Bulletin of the Earthquake Research Institute 54, 559e628 (in Japanese, with English abstract). Kobayashi, H. (Ed.), 2006. H. Kobayashi's Atlas of Japanese Diatoms Based on Electron Microscopy. Uchida Rokakuho Publishing, Tokyo, p. 531 (in Japanese). Koike, K., Machida, H. (Eds.), 2001. Atlas of Quaternary Marine Terraces in the Japanese Islands. University of Tokyo Press, Tokyo (in Japanese). Kojima, N., 1989. Dinoflagellate Cyst analysis of Holocene sediments from Lake Hamana in Central Japan. Transactions and Proceedings of the Palaeontological Society of Japan New Series 155, 197e211. Komatsubara, J., Fujiwara, O., 2007. Overview of Holocene Tsunami deposits along the Nankai, Suruga, and Sagami Troughs, Southwest Japan. Pure and Applied Geophysics 164, 493e507. Kosugi, M., 1988. Classification of living diatom assemblages as the indicator of environments, and its application to reconstruction of paleoenvironments. Quaternary Research (Daiyonki-kenkyu) 27 (1), 1e20 (in Japanese, with English abstract). Kosugi, M., 1993. Diatom. In: Japan Association of Quaternary Research (Ed.), A Handbook of Quaternary Research, vol. 2. University of Tokyo Press, Tokyo, pp. 245e252 (in Japanese). Krammer, K., Lange-Bertalot, H., 1986. Bacillariophyceae, 1. Teil: Naviculaceae. In: Ettle, H., Gerloff, J., Heynig, H., Mollenhauer, D. (Eds.), Süsswasserflora von Mitteleuropa, Band 2/1. Fischer Verlag, Stuttgart, New York (in German).

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006

Y. Sato et al. / Quaternary International xxx (2015) 1e13 Krammer, K., Lange-Bertalot, H., 1988. Bacillariophyceae, 2. Teil: Bacillariophyceae, Epithemiaceae, Surirellaceae. In: Ettl, H., Gerloff, J., Heynig, H., Mollenhauer, D. (Eds.), Süsswasserflora von Mitteleuropa, Band 2/2. Fischer Verlag, Stuttgart, New York (in German). Krammer, K., Lange-Bertalot, H., 1991a. Bacillariophyceae, 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In: Ettle, H., Gerloff, J., Heynig, H., Mollenhauer, D. (Eds.), Süsswasserflora von Mitteleuropa, Band 2/3. Fischer Verlag, Stuttgart, Jena (in German). Krammer, K., Lange-Bertalot, H., 1991b. Bacillariophyceae, 4. Teil: Achnanthaceae. In: Ettle, H., Gartner, G., Gerloff, J., Heynig, H., Mollenhauer, D. (Eds.), Süsswasserflora von Mitteleuropa, Band 2/4. Fischer Verlag, Stuttgart, Jena (in German). Machida, H., Arai, F., 2003. Atlas of Tephra in and Around Japan. University of Tokyo Press, Tokyo (in Japanese). Matsubara, A., 1989. Geomorphic development of barriers in the Coastal Lowlands during the Holocene e a case study of the lowlands along the Suruga Bay, Central Japan-. Geographical Review of Japan 62A (2), 160e183 (in Japanese, with English abstract). Matsubara, A., 2000. Holocene geomorphic development of coastal barriers in Japan. Geographical Review of Japan 73A (5), 409e434 (in Japanese, with English abstract). Matsubara, A., 2001. Coastal barriers in Hamana Lake and the Hamamatsu lowland. The Hiyoshi Review of Social Sciences, Keio University 11, 20e32 (in Japanese). Matsubara, A., 2004. Sedimentary environment around archaeological sites in the Hamamatsu lowland. The Hiyoshi Review of Social Sciences, Keio University 14, 35e52 (in Japanese). Matsubara, A., 2005. Processes in Holocene development of coastal ridges in Japan. The Hiyoshi Review of Social Sciences, Keio University 15, 73e90. Matsubara, A., 2007. Relationships between geomorphic development of coastal ridges and human activities: a case study of the Hamamatsu and Haibara lowlands. The Hiyoshi Review of Social Sciences, Keio University 18, 1e13 (in Japanese). Matsubara, A., 2015. Holocene Geomorphic Development of Coastal Ridges in Japan. Keio University Press Inc., Tokyo. Mazda, Y., 1984. Year-to-year change in water exchange characteristics in a semienclosed bay, Lake Hamana. Journal of the Oceanographical Society of Japan 40, 199e206. * Mazda, Y., 1999. Wonders of Lake Hamana e Nature and Hydrological Dynamics e Shizuoka Shimbun Pub., Shizuoka (in Japanese). Minoura, K., Nakaya, S., Sato, Y., 1987. Traces of tsunami recorded in lake deposits Examples from Jusan, Shiura-mura, Aomori. Journal of the Seismological Society of Japan 2nd series Zisin 40, 183e196 (in Japanese, with English abstract). Minoura, K., Nakaya, S., Uchida, M., 1994. Tsunami deposits in a lacustrine sequence of the Sanriku coast, northeast Japan. Sedimentary Geology 89, 25e31. Morita, H., Kashima, K., Takayasu, K.,1998. Paleoenvironmental changes of Lake Hamana and Lake Shinji during the Last 10,000 years, inferred by diatom assemblages from lake core sediments. LAGUNA 5, 47e53 (in Japanese, with English abstract). Moriwaki, H., 1979. The Landform evolution of the Kujukuri Coastal Plain, Central Japan. Quaternary Research (Daiyonki-kenkyu) 18 (1), 1e16 (in Japanese, with English abstract). Muto, T., 1987. Geology of the Mikatagahara and Iwatabara Terraces, in the lower Tenryugawa River area, Japan e an interpretation from the present dissected alluvial fan. Journal of the Geological Society of Japan 93 (4), 259e273. Nakada, M., Yonekura, N., Lambeck, K., 1991. Late Pleistocene and Holocene sealevel changes in Japan: implications for tectonic histories and mantle rheology. Palaeogeography, Palaeoclimatology, Palaeoecology 85, 107e122. Nakai, N., Ohishi, S., Kuriyama, T., 1987. Application of 14C-dating to sedimentary geology and climatology : sea-level and climate change during the Holocene. Nuclear Instruments and Methods in Physics Research B29, 228e231. Nakamura, T., 2006. Holocene sea level changes and Paleogeography of the Central part of the San-in District, Japan. Quaternary Research (Daiyonki-kenkyu) 45 (5), 407e420 (in Japanese, with English abstract). Nakashima, R., Mizuno, K., Furusawa, A., 2008. Depositional age of the Middle Pleistocene Atsumi Group in Atsumi Peninsula, central Japan, based on tephra correlation. Journal of the Geological Society of Japan 114 (2), 70e79 (in Japanese, with English abstract). Nanayama, F., Makino, A., Satake, K., Furukawa, R., Yokoyama, Y., Nakagawa, M., 2001. Twenty tsunami envet deposits in the past 9000 years along the Kuril subduction zone identified in Lake Harutori-ko, Kushiro City, eastern Hokkaido, Japan. Annual Report on Active Fault and Paleoearthquake Researches 1, 233e249 (in Japanese, with English abstract). National Astronomical Observatory of Japan (Ed.), 2013. Chronological Scientific Tables 2014 (Rika Nenpyo). Maruzen Publishing, Tokyo (in Japanese). Ohira, A., 1995. Holocene evolution of Peatland and paleoenvironmental changes in the Sarobetsu lowland, Hokkaido, Northern Japan. Geographical Review of Japan 68A (10), 695e712 (in Japanese, with English abstract). Ohtsuka, K., Kimiya, K., 1987. Paleolimnological Environment and Sedimentary Processes of Hamana Lake, Central Japan e Preliminary Results of Sedimentary Facies Analysis of the Lake Floor Boring Samples. Geoscience Reports of Shizuoka University 13, pp. 113e145 (in Japanese, with English abstract).

13

Okamura, M., Matsuoka, H., 2012. Nankai Earthquake recurrences from tsunami sediment. KAGAKU 82 (2), 182e191 (in Japanese). Okamura, M., Matsuoka, H., Furuno, H., 2009. Two-types seismic events recorded in Lake Hamana, Shizuoka Prefecture, Japan. In: Japan Geoscience Union Meeting 2009, Japan Geoscience Union, Tokyo. T225-P004. Ota, Y., Umitsu, M., Maatsushima, Y., 1990. Recent Japanese research on relative sea level changes in the Holocene and related problems e review of studies between 1980 and 1988. Quaternary Research (Daiyonki-kenkyu) 29 (1), 31e48 (in Japanese, with English abstract). Reimer, P.J., Bard, E., Bayliss, A., Beck, J.W., Blackwell, P.G., Bronk Ramsey, C., Buck, C.E., Cheng, H., Edwards, R.L., Friedrich, M., Grootes, P.M., Guilderson, T.P., Haflidason, H., Hajdas, I., Hatte, C., Heaton, T.J., Hoffmann, D.L., Hogg, A.G., Hughen, K.A., Kaiser, K.F., Kromer, B., Manning, S.W., Niu, M., Reimer, R.W., Richards, D.A., Scott, E.M., Southon, J.R., Staff, R.A., Turney, C.S.M., van der Plicht, J., 2013. IntCal13 and Marine13 radiocarbon age calibration curves, 0e50,000 years cal BP. Radiocarbon 54, 1869e1887. Sagiya, I., 2007. Crustal uplift in the western Shizuoka Prefecture associated with the 1944 Tonankai earthquake and a splay fault model. In: Japan Geoscience Union Meeting 2007, Japan Geoscience Union, Tokyo. S151-S006. Saito, Y., 1988. Barrier systems as a recorder of Holocene sea-level changes and problems on reconstruction of their Paleogeography in the early Holocene: example from Lake Hamana, Central Japan. Journal of Research Group of Clastic Sediments in Japan 5, 109e132 (in Japanese, with English Abstract). Saito, Y., Inouchi, Y., Yokota, S., 1990. Coastal lagoon evolution influenced by Holocene sea-level changes, Lake Kasumigaura, central Japan. Memoirs of the Geological Society of Japan 36, 103e118 (in Japanese, with English abstract). Sato, Y., Fujiwara, O., Ono, E., Umitsu, M., 2011. Environmental change in coastal lowlands around the Lake hamana during the Middle to Late Holocene. Geographical Review of Japan 84 (3), 258e273 (in Japanese, with English abstract). Sato, Y., Fujiwara, O., Ono, E., 2013. Late Holocene environmental changes of the inter-ridge marshes in the western Hamamatsu strand plain. In: Japan Geoscience Union Meeting 2013, Japan Geoscience Union, Tokyo. HQR24-P13. Seto, K., Nakatake, M., Sato, T., Katsuki, K., 2006. East diversion event of the Hii River and its influence on sedimentary environments in Lake Shinji. Quaternary Research (Daiyonki-kenkyu) 45 (5), 375e390 (in Japanese, with English abstract). Shimada, S., 2000. Eruption of the Amagi-Kawagodaira volcano and paleoenvironments in the Late and Latest Jomon Periods around the Izu Peninsula. Quaternary Research (Daiyonki-kenkyu) 39 (2), 151e164 (in Japanese, with English abstract). History of shizuoka prefecture, separated. In: Shizuoka Prefecture (Ed.), 1996. History of Natural Disasters, vol. 2. Shizuoka Prefecture, Shizuoka (in Japanese). Stuiver, M., Reimer, P.J., Reimer, R.W., 2014. CALIB 7.0. http://calib.qub.ac.uk/calib/ (accessed 15.10.13.). Sugiyama, Y., 1991. The Middle Pleistocene deposits in the Atsumi Peninsula and along the east coast of Lake Hamana, Tokai district e sedimentary cycles formed by the glacio-eustatic sea-level change and their correlations to the contemporaneous deposits in the Kanto and Kinki districts. Bulletin of the Geological Survey of Japan 42 (2), 75e109 (in Japanese, with English abstract). Suzuki, K., 2003. Analysis on the variation of salinity in Lake Hamana e 1. Bulletin of the Shizuoka Prefectural Fisheries Experiment Station 38, 1e6 (in Japanese). Tanabe, S., Ishihara, Y., 2013. Evolution of the Uppermost Alluvial in the Tokyo and Nakagawa Lowlands, Kanto Plain, central Japan: response to the “Yayoi regression”. Journal of the Geological Society of Japan 119 (5), 350e367 (in Japanese, with English Abstract). * Tsuji, Y., Okamura, M., Matsuoka, H., Murakami, Y., 1998. Study of tsunami traces in lake floor sediment of Lake Hamana. Historical Earthquakes (Rekishi-Jishin) 14, 101e113 (in Japanese). Umitsu, M., 1991. Holocene sea-level changes and coastal evolution in Japan. Quaternary Research (Daiyonki-kenkyu) 30 (3), 187e196. Umitsu, M., 1992. Holocene deltaic sequence in the Kiso River delta, Central Japan. Journal of the Sedimentological Society of Japan 36, 47e56. http://dx.doi.org/10. 14860/jssj1972.36.47 (in Japanese, with English abstract). Umitsu, M., 1994. Late Quaternary Environment and Landform Evolution of Riverine Coastal Lowlands. Kokon-Shoin Pub., Tokyo (in Japanese). Watanabe, T. (Ed.), 2005. Picture Book and Ecology of the Freshwater Diatoms. Uchida Rokakuho Publishing Co., Tokyo, ISBN 978-4753640478 (in Japanese). Yamada, K., Takayasu, K., 2006. Paleoenvironmental variability during the Holocene in the Area of Izumo Plain e Lake Shinji based on the results of sedimentary cores. Quaternary Research (Daiyonki-kenkyu) 45 (5), 391e405. http://dx.doi. org/10.4116/jaqua.45.391 (in Japanese, with English abstract). Yata, T., 2005. The damages by tsunami in Meiou-Toukai earthquake in 1498 and the suffering in Anotsu in the Middle Ages. Historical Earthquakes (Rekishi-Jishin) 20, 9e12 (in Japanese, with English abstract). Yata, T., 2009. Large Earthquakes Occurred in Medieval Period Recorded in Japanese History. Yoshikawa-kobunkan, Tokyo, ISBN 978-4642056649 (in Japanese). Yokoyama, Y., 2002. Global ice volume during the Last Glacial and human migrations. Journal of Geography (Chigaku-zasshi) 111 (6), 883e899. http://dx.doi. org/10.5026/jgeography.111.6_883 (in Japanese, with English abstract).

Please cite this article in press as: Sato, Y., et al., Late Holocene environmental changes of coastal lagoon inferred from a fossil diatom analysis of sediment core from Lake Hamana, central Japan, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.06.006