百原 新

<title>Abstract</title>Clarifying the influences of paleoclimate changes on the disjunct distribution formation of plants allows a historical and mechanical understanding of current vegetation and biodiversity. This study investigated the influences of paleoclimate changes on the present disjunct distribution formation of <italic>Pinus koraiensis</italic> (Korean pine) using species distribution modeling. A species distribution model (SDM) was built using maximum entropy principle algorithms (MaxEnt), data from 152 occurrences of the species, and four bioclimatic variables at 2.5 arcminute (approximately 5 km) spatial resolution. The simulation revealed the excellent fit of the MaxEnt model performance, with an area under the curve (AUC) value of 0.922 and continuous Boyce index (BCI) value of 0.925 with fivefold cross-validation. The most important climatic factor was the minimum temperature of the coldest month. Suitable habitats for the species ranged between − 30.1 and − 4.1 °C. Projected suitable habitats under the Last Glacial Maximum (approximately 22,000 years ago [ka BP]: LGM) period showed wide distributions in eastern China, the southern part of the Korean Peninsula, and the Japanese Archipelago. After the mid-Holocene (approximately 6 ka BP), the suitable habitats expanded northwards in continental regions and retreated from both north and southwest of Japan. This eventually formed disjunct suitable habitats in central Japan. An increase in temperature after the LGM period caused the migration of <italic>P. koraiensis</italic> toward new, suitable habitats in continental Northeast Asia, while species in the Japanese Archipelago retreated, forming the present disjunct distributions.

© 2020 The Boreas Collegium. Published by John Wiley & Sons Ltd This study proposes a new method to detect changes of altitudinal distribution limit of a plant species based on the stomatal analysis of fossilized leaves. We use the Holocene fossil leaves of Fagus crenata (Japanese beech), a dominant deciduous tree in the cool temperate zone, from different horizons in a peat bog in Mt. Kurikoma, north Japan. Results of palaeo-CO2 concentration reconstructed from the stomatal analysis indicate palaeo-CO2 fluctuation between 317 and 352 ppmv during the Middle–Late Holocene, which was more variable and higher than Greenland and Antarctic ice-core records. This result is possibly influenced by the oceanic CO2 uptake, which increased with the strengthening of the Tsushima Warm Current during the Middle Holocene. The stomatal index (SI) variation range of fossil Fagus crenata leaves in the Middle Holocene was higher than that of the modern population at a given altitude, indicating transportation of leaves from an altitude higher than the site of fossil deposition. A decreasing trend of the SI variation range between 5000 and 2500 cal. a BP can possibly be attributed to the downward shift of the upper distribution limit of Fagus crenata from an altitude higher than or similar to the present limit to the area surrounding the fossil deposition site. This downward shift of the upper distribution limit of Fagus crenata was simultaneous with temperature and humidity decreases and correlated with the decreasing East Asian Summer Monsoon intensity and a cooling event around 4000 cal. a BP.

Stratigraphic and paleontological investigations in Mugi Town, on the Pacific coast of Shikoku Island, revealed evidence of as many as five tsunami inundations from events along the Nankai Trough between 5581 and 3640calyr BP. Nine event deposits (E1-E9) were identified in cores ranging in length from 2 to 6m, consisting of sandy and gravelly layers interbedded with organic-rich mud. Sedimentary structures in the event deposits observed by computed tomography included normal grading and sharp lower stratigraphic contacts. Event deposits E3, E6, E7, and E8 contained mainly brackish-marine diatom species, suggesting that they had been deposited during inundation by seawater. In addition, fossil diatom assemblages were markedly different above and below event deposits E3, E4, E6, and E8. For example, assemblages below event deposit E6 were dominated by a freshwater species (Ulnaria acus), whereas assemblages above it were predominantly brackish-marine (Diploneis smithii, Fallacia forcipata, and Fallacia tenera). We attributed these changes to the increase of marine influence due to coastal subsidence associated with subduction-zone earthquakes, as documented in the 1946 Showa-Nankai earthquakes. We conclude that event deposits E3, E6, and E8 and perhaps E4 and E7 were deposited by tsunamis generated by subduction zone earthquakes along the Nankai Trough. The ages of these event deposits, as constrained by ten radiocarbon ages, suggest that some of the tsunamis that impacted Mugi Town were correlated with those reported elsewhere along the Nankai Trough, thereby complementing the existing but still incomplete geological record for these events.

大阪府泉佐野市の大阪層群最下部の炭質層，および同枚方市の大阪層群上部，Ma8海成粘土層より産出した3点の子嚢菌類の化石について，形態的特徴を観察した．その結果，子座および子嚢殻の形態的特徴に基づき，これらは現生の分類群であるクロコブタケ属との類似性が示された．また，これら3点の化石の子嚢殻と子嚢胞子の形態にはそれぞれ違いが認められ，これらは異なる分類群である可能性が示唆された．

Fossil plant assemblages play a critical role in paleoenvironment estimation, especially for the Cenozoic. However, the extent that the fossil assemblage reflects the source forest is difficult to estimate. The comparison between modern assemblages and their subfossil assemblages shows a significant difference, indicating that the transportation of plant organs can affect the accuracy of paleoenvironment analysis. In this study, we aim to detect leaf transport based on stomatal frequency (stomatal index and stomatal density) variation of 30 fossilized Fagus crenata leaves from the Sayama Formation (1.54–1.66 Ma). We distinguished the sun and shade morphotype of fossil leaves by using undulation index and calculated stomatal frequency variation of only sun fossil leaves. Considering the stomatal index variation of fossil Fagus crenata leaves, the paleo-pCO2 variation in a warm period between 1.54 Ma and 1.66 Ma was estimated as ca. 35.0 to 39.6 pa. Based on this paleo-pCO2 variation, altitudinal transportation range of the Early Pleistocene fossil Fagus crenata leaves was estimated at over 1000 m. We presume that leaves of Fagus crenata in the fossil assemblage possibly had come from a wide range of altitudes near the fossil site during the Early Pleistocene. This provides an example of altitudinal transportation of plants before their deposition, which suggests a consideration when reconstructing the palaeovegetation and palaeoclimate from fossil assemblages.

Crocodylians are ectothermic animals, and their past distribution has been greatly influenced by changing climate since their Cretaceous origin. The Pliocene-Pleistocene witnessed a contraction of the crocodylian latitudinal ranges due to rapid cooling with superimposed pronounced orbital-scale climate oscillations. However, a chronologically-continuous record of the geographically marginal populations of crocodylians is yet to be provided for this time interval, and crocodylian response to such climatic changes is poorly known. This study describes a partial crocodylian skeleton from the Middle Pleistocene of Osaka, Japan, diagnosed as Toyotamaphimeia cf. machikanensis, on the basis of character comparisons, including ontogenetic skull shape change, and consideration of the reconstruction error in the holotype of T. machikanensis. Pliocene-Pleistocene record of fossil crocodylians in the Kinki, Tokai, and Kanto districts of Japan extends from ~3.5 Ma to ~0.3 Ma. The paleotemperature estimates for the crocodylian-bearing horizons indicate that late Early–Middle Pleistocene crocodylians in the Kinki district of Japan were living near their lower thermal limit. During the glacial periods, they might have moved to the southern extremity of Japan or locally became extinct from Japan, while re-expanding their range after the end of glacial periods.

Among the Early Pleistocene fluvial sediments in Japan that yield plant macrofossils, the Uonuma Group in the Niigata sedimentary basin provides the most continuous profile without any conspicuous hiatuses and is therefore suitable for high-resolution reconstructions of environmental and vegetation histories based on tephro-and magneto-stratigraphy. Based on the species composition of plant macrofossil assemblages, along with previously reported results on sedimentary environments and pollen records, we performed a reconstruction of changes in paleovegetation and paleotemperatures between MIS 63 and 53. Macrofossil assemblages identified from 33 samples include 89 arboreal and 88 herbaceous taxa in total, of which 9 taxa are extinct from Japan. Assemblages from the peat deposits in fluvial backmarshes during glacial stages are composed mainly of wetland herbaceous plants, whereas those from the sandy channel-fill deposits are characterized by a higher diversity in life forms and habitat preferences. During the interval from MIS 63 to 53, paleotemperatures fluctuated between a coldest-month mean temperature of -4.6 degrees C and - 0.9 degrees C and between a mean annual temperature of 6.6 degrees C and 11.0 degrees C, which is within the present range for cool-temperate, deciduous broad-leaved forests in Japan. MIS 60 was the coldest of the glacial stages with temperatures nearly equivalent to those during the last glacial maximum. Major plant extinctions in and around MIS 60 were not recorded in the sedimentary basin in response to the temperature decline. The relatively indistinct floral changes in and around MIS 60 are attributed to easier recovery of flora by migration from glacial refugia in the southern basins after termination of the glacial stage. Interglacial temperatures during MIS 57, 55, and 53 were higher than during MIS 63, 61, and 59. The presence of a maritime environment during the interglacial periods between MIS 57 and 53 may have resulted from a greater extent of marine transgression and heat provided by the Tsushima Warm Current flowing into the Sea of Japan after MIS 59. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.

Research into the geographical distribution of temperate tree refugia and their associated environmental conditions during glacial stages is necessary to understand the processes by which the present vegetation and plant distributions developed. On the basis of pollen and plant macrofossil assemblages deposited in a small valley in a hill in the northern Kanto district in central Japan, we reconstructed the local and regional vegetation changes in and around the distribution range limit of temperate broadleaf trees during the latest stage of marine isotope stage (MIS) 3 (36.2-32.8 ka) and around the late stage of the last glacial maximum (LGM) (23.4-16.6 ka). During the latest stage of MIS 3, the local and regional vegetation in and around the hill was composed of temperate deciduous broadleaf forest dominated by Quercus subgen. Lepidobalanus and mixed with pinaceous conifers. The proportion of deciduous broadleaf trees in the regional vegetation increased during recurring warm and humid phases that were correlated with Greenland D-O 7, 6, and 5 warming events. During the LGM, coniferous forests composed of Picea jezoensis var. hondoensis, Tsuga diversifolia, Abies veitchii, and Betula ermanii, which are major components of the present subalpine forests in central and western Japan, expanded in hilly and mountain zones in central Japan. Refugia of temperate broadleaf trees existed at altitudes up to that of the study site and were limited to mesic places along the valley bottom. At the termination of the LGM around 18.8 ka, a biome shift to mixed coniferous and deciduous broadleaf forest dominated by Betula occurred in and around the study site. The expansion of deciduous broadleaf trees at ca. 19 ka, which has also been recognized in other localities in central Japan, may have been triggered by an increase in precipitation during the stage wherein summer insolation became greater. The temperate broadleaf trees that have been distributed in hilly-zone refugia were sensitive to warming at the termination of the LGM. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.

Reconstruction of the magnitude and frequency of past floods is important for assessments of flood risk. However, there have been few reconstructions of past flood activity based on long-term continuous records from a single fluvial system and thus suitable for comparison with other paleoclimate proxies. Consequently, the influence of climate change on flood activity remains unclear. Floodplain peat beds can be preserved for long periods of geologic time; they also contain both elastic sediments from overbank flooding and organic material produced in situ, both of which are important inputs for geologic reconstructions. In this study, we examined 24 cores from the Ishikari lowland, northern Japan, to find out if temporal changes of loss on ignition (LOI) of peat can provide a record of flood magnitude and frequency and to investigate the influence of regional climate change on flood activity. Our plant macrofossil analyses, the distribution of characteristic LOI depth profiles, and sedimentary facies suggest that the LOI of peat increases when the magnitude and frequency of floods decreases, which in turn suggests that temporal changes of LOI in peat might be useful as a proxy for past flood activity. Our results indicate that increases in the LOI of peat deposited near the Ishikari River at ca. 5500-5000 and 4000-3500 cal BP may correspond to weakened activities of the East Asian summer monsoon (EASM) and El Nino-Southern Oscillation (ENSO). Furthermore, our analyses show that an increase in flood activity of the Ishikari River during 1400-1300 cal BP may be related to a decrease in ENSO activity. However, temporal changes of the LOI of peat formed near a tributary of the Ishikari River did not correlate with these climate changes. Our results suggest that the past flood activity of rivers with large watersheds reflects regional climate change, because the extensive precipitation that induces flooding of such rivers is generally associated with regional climate systems such as the EASM and ENSO, whereas this association is not necessarily the case for rivers with small watersheds.