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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. Source


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. Source


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. Source


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. Source


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. Source

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