Time filter

Source Type

Hayashi R.,Lake Biwa Museum | Takahara H.,Kyoto Prefectural University | Inouchi Y.,Waseda University | Takemura K.,Kyoto University | Igarashi Y.,Institute for Paleoenvironment of Northern Regions
Review of Palaeobotany and Palynology | Year: 2017

This study examined the orbital-scale vegetation response to seasonal climate changes related to the East Asian monsoon and ocean currents during the last glacial–interglacial cycle based on a new continuous pollen record from Lake Biwa, western Japan. During MIS 6, 4, and 2, pinaceous conifer forests were present in both inland and Japan Sea coastal areas around Lake Biwa, influenced by cold and dry conditions in both summer and winter. In contrast, deciduous broadleaved forests and evergreen forests grew during interglacial periods in MIS 5e and 1 under relatively warm and humid conditions in summer, as well as in winter. Fagus crenata, a tree endemic to the Japanese archipelago, was especially widely distributed during MIS 5e due in part to winter snowfall caused by warm current inflows in the Sea of Japan. During MIS 5 and 3, temperate conifer trees were dominant. During periods of low summer insolation in MIS 5, the endemic tree Cryptomeria japonica became dominant in both inland and coastal areas of the region, likely as a result of high precipitation in early summer related to southward shifts of the summer monsoon front and moderate winter climate conditions. In contrast, Sciadopitys verticillata, which is also an endemic tree, had own habitat around inland areas of western Japan during the periods of high summer insolation in MIS 5. Climate fluctuations during the glacial–interglacial cycles created several ecological niches in time and space for each endemic tree in the Japanese archipelago. © 2017 Elsevier B.V.

Tarasov P.E.,Free University of Berlin | Nakagawa T.,Northumbria University | Demske D.,Free University of Berlin | Osterle H.,Potsdam Institute for Climate Impact Research | And 11 more authors.
Earth-Science Reviews | Year: 2011

This study presents a newly compiled dataset of modern pollen and climate data from 798 sites across Japan and the Russian Far East. This comprehensive reference dataset combined with the modern analogue technique (MAT) provides a powerful tool for pollen-based reconstruction of the Quaternary Northwest Pacific climate. Pollen-derived reconstruction of the modern climate at the reference pollen-sampling sites matches well with the estimated modern climate values (R2 values vary between 0.79 and 0.95, and RMSEP values vary between 5.8 and 9.7% of the modern climatic range for all nine tested variables). The successful testing of the method encourages its application to the fossil pollen records. We used a coarse-resolution pollen record from Lake Biwa to reconstruct glacial-interglacial climate dynamics in central Japan since ~438kyr and compared it to the earlier reconstruction based on a less representative reference dataset. The current and earlier results consistently demonstrate that the coldest glacial intervals experienced pronounced cooling in winter and moderate cooling in summer, supporting the growth of cool mixed forest (COMX) where warm mixed forest (WAMX) predominates today. During the last glacial, maximum (~24kyr BP) mean temperatures of the coldest (MTCO) and warmest (MTWA) month were about -13°C (RMSEP=2.34°C) and 21°C (RMSEP=1.66°C) respectively, and annual precipitation (PANN) was about 800mm (RMSEP=158.06mm). During the thermal optimums of the interglacial intervals, the temperatures of the coldest and warmest month were above 0°C and 25°C respectively, leading to the reconstruction of WAMX and temperate conifer forest (TECO). Although both these vegetation types grow in the southern part of Japan today, WAMX requires warmer space. The presence of WAMX during marine isotope stages (MIS) 11 and 1, and its absence during MIS 9 and MIS 5 contradict the marine isotope and Antarctic ice records, suggesting that the latter two interglacials were the warmest of the last 800kyr. The apparent contradiction allows at least three different explanations including low temporal resolution of the pollen record; different trends in CO2 concentrations during 'short' and 'long' interglacials; and regional climate variability and non-linear response of different regions to the global forcing. More definitive conclusions will be possible on the basis of forthcoming high-resolution pollen records from central Japan. © 2011 Elsevier B.V.

Takahara H.,Kyoto Prefectural University | Igarashi Y.,Institute for Paleoenvironment of Northern Regions | Hayashi R.,Kyoto Prefectural University | Kumon F.,Shinshu University | And 5 more authors.
Quaternary Science Reviews | Year: 2010

High-resolution pollen records from Taiwan, Japan and Sakhalin document regional vegetation changes during Dansgaard-Oeschger (D-O) cycles during the last glacial. During the period from the cold phase (GS 18/19) to warm phase (D-O 19), the biome shift from temperate conifer forest to cold/cool conifer forest in Japan and from subtropical forest to temperate deciduous/conifer forest in Taiwan. The vegetation in D-O 17, cool mixed forest in central Japan, temperate deciduous broadleaf forest in western Japan and subtropical forest in Taiwan, indicates warm condition but not wet in all area. These vegetation changes lead to biome shift from MIS (Marine Isotope Stage) 4 to MIS 3. The abundance of Cryptomeria japonica and Fagus crenata in D-O 12 and D-O 8 indicates wet conditions brought by the strong summer monsoon through the Islands and high snowfall brought by the inflow of the Tsushima Warm Current into the Sea of Japan. The registration of other D-O warming events in MIS 3, although reflected by shifts in the abundance of key species, is not sufficient to produce changes in biomes. Development of cold deciduous forest in HS (Heinrich events) 1 in Sakhalin, Hokkaido and central Japan was conspicuous and was much larger than that in YD. Vegetation response in YD was small scale and within the same biome in the East Asian Islands. In D-O 1 at the termination of the last glacial, the same taxa that developed in the early Holocene, cold evergreen needleleaf trees in northern region, temperate deciduous broadleaf trees in central and western Japan, and warm-temperate evergreen trees in Taiwan, increased. © 2009 Elsevier Ltd.

Igarashi Y.,Institute for Paleoenvironment of Northern Regions | Zharov A.E.,Subsidiary Joint Stock Company RN Shelf Far East
Quaternary International | Year: 2011

Pollen data from marine isotope stage (MIS) 3 to the early Holocene in Kenbuchi, central Hokkaido, and Khoe, central-west Sakhalin, were reviewed and the climate and vegetation compared. Changes in climate and vegetation during the examined time period in the two regions resembled each other, except for latitudinal differences in forest composition. During MIS 3, cold evergreen needle-leaf forests expanded under a cool, moist climate. The climate then rapidly changed to cool and dry around the MIS 3/MIS 2 boundary. MIS 2 was characterized by millennial-scale variability in climate. Heinrich event 2 (H2, 24-21 ka), the last glacial maximum (LGM), and H1 (between 17 and 13 ka) were characterized by the dominance of Larix and Pinus in cold deciduous forests. In Kenbuchi, grassland composed of alpine elements developed. In both regions, climate was coldest and driest during H1. The Bölling-Allerød interstadial (14-12 ka) was characterized by a maritime climate with an abundance of Betula in the coastal region. The Younger Dryas (11.5 ka) was a minor event in East Asia. During the Pre-Boreal period (around 12 ka), cold evergreen needle-leaf (Picea-Betula) forest and mixed (Quercus-Abies) forest developed in two different regions under a warm, moist climate. © 2011 Elsevier Ltd and INQUA.

Igarashi Y.,Institute for Paleoenvironment of Northern Regions | Yamamoto M.,Hokkaido University | Noda A.,Japan National Institute of Advanced Industrial Science and Technology | Ikehara K.,Japan National Institute of Advanced Industrial Science and Technology | Katayama H.,Japan National Institute of Advanced Industrial Science and Technology
Marine Geology | Year: 2015

Hokkaido Island in northern Japan is located in a cool temperate to boreal climate zone influenced by summer monsoons and typhoons during summer-autumn, while its eastern area is influenced by the subarctic Oyashio Current. Palynomorph (pollen and spores) distribution was investigated in surface sediments from the shelf and slope (40-2300. m water depth) in the offshore area of Tokachi Plain, central-eastern Hokkaido Island. The objective of this study was to examine the source, transportation, and deposition of palynomorphs in marine environments. The majority of palynomorphs were transported from the Tokachi coastal plain by both strong local winds from the mountain areas during the spring-summer and the floods caused by heavy monsoon and typhoon rainfall. Approximately 10% of all palynomorphs were transported from both southwest and west areas by the wind. Palynomorph transportation by the Oyashio Current could not be discriminated because the same vegetation is present in Hokkaido and the islands in upper streams of the Oyashio Current. The total grain abundance was dependent on water depth. High concentrations were observed at depths of 700-1500. m, which is a region associated with high levels of fine silt and clay, suggesting that the transportation and deposition of palynomorphs are controlled by their grain sizes. This study supported a strong correlation between the distribution of sediments and the concentration of palynomorphs. © 2015 Elsevier B.V.

Igarashi Y.,Institute for Paleoenvironment of Northern Regions | Yamamoto M.,Hokkaido University | Ikehara K.,Geological Survey of Japan
Journal of Asian Earth Sciences | Year: 2011

Vegetation and climate since the LGM in eastern Hokkaido were investigated based on a pollen record from marine core GH02-1030 from off Tokachi in the northwestern Pacific. We also examined pollen spectra in surface samples from Sakhalin to compare and understand the climatic conditions of Hokkaido during the last glacial period. Vegetation in the Tokachi region in the LGM (22-17. ka) was an open boreal forest dominated by Picea and Larix. During the last deglaciation (17-10. ka), vegetation was characterized by abundant Betula. In the Kenbuchi Basin, central Hokkaido, a remarkable increase of Larix and Pinus occurred in the LGM and the last deglaciation, which was assigned as the " Kenbuchi Stadial." Comparison of climatic data between the core GH02-1030 and that of Kenbuchi Basin demonstrates that variations in temperature and precipitation were larger in inland Hokkaido than in the maritime area of the Pacific coast. During the LGM in the Tokachi region, the August mean temperature was about 5°C lower, and annual precipitation was about 40% lower than today. In the Kenbuchi Basin, central Hokkaido, the August mean temperature was about 8°C lower, and annual precipitation was half that of today. During the last deglaciation, August mean temperatures were about 3°C lower, and annual precipitation was about 30% lower than today in the Tokachi region. In the Kenbuchi Basin, August mean temperatures were about 5-8°C lower, and annual precipitation was about 40-60% lower than today. Cold ocean water and a strengthened summer monsoon after 15. ka may have resulted in the formation of advection fogs, reduced summer temperatures, and a decrease in the seasonal temperature difference in the Tokachi district, which established favorable maritime conditions for Betula forests. © 2010 Elsevier Ltd.

Igarashi Y.,Institute for Paleoenvironment of Northern Regions
Quaternary International | Year: 2013

Hokkaido is classified into five regions based on climatic features: the Japan Sea coast, the Pacific coast, the Okhotsk Sea coast, the inland region, and southwest Hokkaido. Holocene vegetation and climate changes at twelve sites selected from these regions are reviewed and compared. On the Japan Sea coast, Picea and Quercus pollen fluctuated at millennial scale, matching with pulses of the Tsushima Current revealed from diatom-based temperature reconstructions in the Japan Sea. A marine core obtained from off the Pacific coast revealed a maritime climate through increasing Betula pollen percentages during the last deglaciation and early Holocene. In summer, dense sea fog resulting from the Oyashio Cold Current and Ogasawara High caused a maritime climate on the Pacific coast. Pollen percentages of Betula ermanii, which is well adapted to the maritime climate in Northeast Asia, increased during this period. Vegetation changes on the Okhotsk Sea coast and in inland regions were similar, indicating similar climatic changes. In these regions, Quercus forests have been distributed steadily since 8000 BP under a warm and moist climate, except for the northern coast, at the Sea of Okhotsk, where Picea and Abies increased slightly since 2000 BP. In southwest Hokkaido, Quercus began to increase 1000 years earlier than in other regions. Fagus crenata migrated from Honshu Island to southernmost Hokkaido around 6000 BP and reached the current northern limit around 1000 BP. The period during which Quercus pollen percentages increased is recognized in almost all regions at around 8000-9000 BP. However, local factors, such as river flooding and local strong winds, also influenced the vegetation changes. Comparison of the vegetation changes in three neighboring regions of Northeast Asia indicate abrupt warming at around 8000-9000 BP and cooling at 2500 BP common to all regions, suggesting global climatic changes. © 2012 Elsevier Ltd and INQUA.

Igarashi Y.,Institute for Paleoenvironment of Northern Regions
Quaternary International | Year: 2016

In the process of reviewing pollen data from Hokkaido and Sakhalin, three facts were confirmed. 1) The climate was revised to one colder than the Last Glacial Maximum (LGM) during the last deglaciation in the last glacial period, called the Kenbuchi Stadial, which was related to the southward shift of the summer position of the Kuroshio-Oyashio sea current boundary, which affected not only northern Hokkaido but also eastern Hokkaido and northwestern Sakhalin. 2) From marine isotope stage 3-8000 Cal. yr BP, grassland and mire that developed in Hokkaido were characterized by expanded spikemoss, which grows in snowpatch grassland and mire in the alpine zone of Hokkaido and northern Honshu today. 3) During the LGM, thermokarst depressions, so-called "alas," likely formed in eastern Hokkaido along the Sea of Okhotsk based on the yield of the aquatic plants Menyanthes and Botryococcus in LGM sediments. © 2016 Elsevier Ltd and INQUA.

Loading Institute for Paleoenvironment of Northern Regions collaborators
Loading Institute for Paleoenvironment of Northern Regions collaborators