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.
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.
We reconstructed fluctuations in the East Asian monsoon and vegetation in the Japan Sea region since the middle Pliocene based on pollen data obtained from sediments collected by the Integrated Ocean ...Drilling Program off the southwestern coast of northern Japan. Taxodiaceae conifers Metasequoia and Cryptomeria and Sciadopityacere conifer Sciadopitys are excellent indicators of a humid climate during the monsoon. The pollen temperature index (Tp) can be used as a proxy for relative air temperature. Based on changes in vegetation and reconstructed climate over a period of 4.3 Ma, we classified the sediment sequence into six pollen zones. From 4.3 to 3.8 Ma (Zone 1), the climate fluctuated between cool/moist and warm/moist climatic conditions. Vegetation changed between warm temperate mixed forest and cool temperate conifer forest. The Neogene type tree Carya recovered under a warm/moist climate. The period from 3.8 to 2.5 Ma (Zone 2) was characterized by increased Metasequoia pollen concentration. Warm temperate mixed forest vegetation developed under a cool/moist climate. The period from 2.5 to 2.2 Ma (Zone 3) was characterized by an abrupt increase in Metasequoia and/or Cryptomeria pollen and a decrease in warm broadleaf tree pollen, indicating a cool/humid climate. The Zone 4 period (2.2–1.7 Ma) was characterized by a decrease in Metasequoia and/or Cryptomeria pollen and an increase in cool temperate conifer Picea and Tsuga pollen, indicating a cool/moist climate. The period from 1.7 to 0.3 Ma (Zone 5) was characterized by orbital-scale climate fluctuations. Cycles of abrupt increases and decreases in Cryptomeria and Picea pollen and in Tp values indicated changes between warm/humid and cold/dry climates. The alpine fern Selaginella selaginoides appeared as of 1.6 Ma. Vegetation alternated among warm mixed, cool mixed, and cool temperate conifer forests. Zone 6 (0.3 Ma to present) was characterized by a decrease in Cryptomeria pollen. The warm temperate broadleaf forest and cool temperate conifer forest developed alternately under warm/moist and cold/dry climate. Zone 2 corresponded to a weak Tsushima Current breaking through the Tsushima Strait, and the beginning of orbital-scale climatic changes at 1.7 Ma during Zone 5 corresponded to the strong inflow of the Tsushima Current into the Japan Sea during interglacial periods (Gallagher et al., 2015).
•Identification of East Asian monsoon (EAM) during the last 4.3 million years based on pollen Taxodiaceae•Abrupt increase of Taxodiaceae at around 1.7 Ma•Orbital-scale fluctuations of EAM since 1.7 Ma
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.
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•Pollen records from Lake Biwa have recorded vegetation fluctuations since MIS 6.•Regional vegetation patterns based on long-core pollen records are shown.•Vegetation responses to changes in monsoons and ocean currents were determined.•Endemic trees had own habitats in glacial–interglacial climate oscillations.•Orbital-scale climate fluctuations created ecological niches in time and space.
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.
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 (40–2300m 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 700–1500m, 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.
•Palynomorphs on the shelf-slope off Hokkaido were mainly transported from the adjacent land by local wind and floods•Palynomorphs concentrate highly in 700–1500m depth which correspond to higher silt, clay and oxygen minimum zone•Redistribution of palynomorphs is attributed according to their grain sizes rather than better preservation of palynomorphs•Pollen transportation with south-westerly wind is 10% of all palynomorphs
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.
The burning of trees and grasses produces charred particles, such as charcoal and soot, that can be transported over long distances via winds and rivers to coastal, deltaic, and ocean environments, ...where they are preserved in sediments. Charcoal contained in sediments has been widely used as a proxy for biomass burning and human activities as well as climate change. Charcoal and soot in Cenozoic marine sediments at Integrated Ocean Drilling Program (IODP) Expedition (Exp.) 346 Site U1423 were measured to examine the regional history of biomass burning in East Asia. Charcoal and soot were measured as elemental carbon (EC) in coarse (> 2 μm) and fine (< 2 μm) fractions using grain size separation by repeated settling followed by application of a thermal optical transmittance (TOT) method. Organic carbon (OC) was also quantified during the process. EC and OC in both coarse and fine fractions are higher from 0 to 1.8 Ma and lower from 1.8 to 4.3 Ma but have large variations, which suggest more frequent or intense biomass burning since 1.8 Ma. Terrestrial biomass and precipitation could be major controls on the EC supply. Fine EC varies independently from coarse EC, which suggests a remote origin of fine EC. Large increases in terrestrial vegetation cover have led to high-temperature burning, which is associated with interglacial stages.
Large earthquakes along the Kuril subduction zone in northern Japan are known to have caused damaging tsunami, although there is a little information on historical earthquakes and tsunami in this ...area because no documents exist before the 19th century that might refer to tsunami events. To determine the likely timing and size of future events we need information on their recurrence intervals and to do this for the prehistoric past we have investigated sediments located in the Kiritappu marsh in eastern Hokaido that we interpret as laid down by tsunami. Using reliable multiple lines of evidence from sedimentological, geomorphological, micropaleontological, and chronological results, we identify 13 tsunami sands. Two of these lie within a peat bed above a historical tephra, Ta-a (AD 1739); the upper one probably corresponds to the AD 1843 Tempo Tokachi-oki earthquake (
M 8.2) tsunami, and the lower to either the AD 1952 Tokachi-oki earthquake (
M 8.2) tsunami or the AD 1960 Chilean earthquake (
M 9.5) tsunami. Underlying are 11 prehistoric tsunami sand beds (nine large sand beds and two smaller sand beds) deposited during the past 4000 years. Because of the wide spatial distribution of the large sand beds, and inundation distances inland of between 1200 to 3000 m, we suggest that they record unusually large tsunamis along the Kuril subduction zone. According to our analyses, these tsunami sands were derived from the coastal area and, although they do not show clear graded bedding, they commonly have gradational upper boundaries and erosional bases and include internal sedimentary structures such as plane beds, dunes, and current ripples, reflecting bedload transportation. Based on our results we calculate the recurrence interval of unusually large earthquakes (probably
M 8.6) along the Kuril subduction zone as about 365–553 years and estimate the youngest large event to have occurred in the 17th century.
Accurate reconstruction of late-Quaternary vegetation cover is necessary for better understanding of past vegetation dynamics, the role of vegetation feedbacks in glacial–interglacial climate ...variations, and for validating vegetation and climate models. In this paper over 1700 surface-pollen spectra from the former Soviet Union, Mongolia, northern China, and northern Japan together with data from the Advanced Very High Resolution Radiometer (AVHRR) were used to calibrate modern-analogue method for quantitatively reconstructing past woody cover from fossil pollen data. The AVHRR-based estimates of woody cover percentages within a 21
×
21 km window around pollen sampling sites were attributed to the respective modern pollen spectra. Reconstructions of modern woody cover using the pollen data and best-modern-analogues (BMA) method matched well to the original AVHRR-based estimates, for both total woody cover (
r
2
=
0.77) and its fractions, including broad-leaved (
r
2
=
0.66), needle-leaved (
r
2
=
0.79), deciduous (
r
2
=
0.60) and evergreen (
r
2
=
0.76) woody cover. Discrepancies in the pollen–AVHRR cross-validation may be caused by long-distance transport of arboreal pollen, patchy forest distributions, underrepresentation of
Larix and
Populus in pollen records, and errors in the AVHRR classification. The generally strong correlations encourage application of the modern-analogue approach for reconstructing late-Quaternary variations in vegetation cover from northern Asian fossil pollen records. At the last glacial maximum (LGM: ∼
21,000 cal yr BP), areas presently occupied by boreal forest were much more open, suggesting a reduction in total woody cover to below 20% at most modern forest sites. Pollen records from northern and central Siberia suggest a rather quick spread of tree and shrub vegetation after 15,000 cal yr BP, presumably in response to increased summer insolation. Woody cover histories are spatially variable in the modern forest-steppe, where tree growth is largely controlled by the ratio of annual actual over potential evapotranspiration which serves as an index of moisture availability. In northwestern Mongolia, woody cover percentages decreased between ∼
9000 and 5000 cal yr BP and again between 2000 and 1000 cal yr BP and may be linked to shifts in intensity of the Pacific monsoon. In contrast, pollen data from the Kazakhstan forest-steppe (where atmospheric precipitation is associated with the Atlantic westerly flow) suggest that woody cover density reached modern levels only during the last millennium.
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