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Climate and vegetation in Hokkaido, northern Japan, since the LGM: Pollen records from core GH02-1030 off Tokachi in the northwestern Pacific
Journal of Asian Earth Sciences 40 (2011) 1102–1110
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Climate and vegetation in Hokkaido, northern Japan, since the LGM: Pollen records from core GH02-1030 off Tokachi in the northwestern Pacific Yaeko Igarashi a,⇑, Masanobu Yamamoto b, Ken Ikehara c a
Institute for Paleoenvironment of Northern Regions, Koyocho 3-7-5, Kitahiroshima 061-1134, Japan Faculty of Environmental Earth Science, Hokkaido University, Kita-10, Nishi-5, Kita-ku, Sapporo 060-0810, Japan c Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567, Japan b
a r t i c l e
i n f o
Article history: Available online 17 August 2010 Keywords: Last deglaciation Climate Vegetation Hokkaido Marine core Pollen record
a b s t r a c t 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. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The onset of warming varied in different regions during the last deglaciation (see Kiefer and Kienast (2005) for a review of the Pacific region). The island of Hokkaido, located at the northwestern margin of the Pacific Ocean, experienced slow warming during the last deglaciation. A pollen study demonstrated the southward expansion of open cold deciduous forest, during what is known as the ‘‘Kenbuchi Stadial,” in central Hokkaido Island during this period (Igarashi et al., 1993; Igarashi, 1996). An earlier study also showed several cooling events at this time on Southwestern Hokkaido (Sakaguchi, 1989). The island of Hokkaido is surrounded by the Pacific Ocean, the Sea of Okhotsk, and the Sea of Japan and is situated in a cool-temperate zone with both tropical and arctic influences. In winter, the climate of Hokkaido is governed by the winter monsoon winds, which blow from the Siberian High over
⇑ Corresponding author. Tel./fax: +81 11 373 2938. E-mail address: [email protected] (Y. Igarashi). 1367-9120/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2010.08.001
Siberia, and the air temperature is positively correlated with the Arctic Oscillation index (Yamazaki, 2004). The summer climate is governed by the relative intensities of the Okhotsk High developed in the Sea of Okhotsk and the Ogasawara High developed in the northwestern subtropical Pacific on the western flank of the North Pacific High. The development of the Okhotsk High results in a cool summer and is related to the positive mode of the Arctic Oscillation (Ogi et al., 2004). The development of the Ogasawara High results in a warm summer and is related to the La Niña state of the tropical Pacific. The mid-latitude North Pacific region contains the subarctic boundary between the subtropical Kuroshio and subarctic Oyashio currents (Fig. 1) and is sensitive to global climate changes (e.g., Chinzei et al., 1987; Isono et al., 2009). Previous studies have roughly reconstructed that the Kuroshio–Oyashio boundary shifted southward during the last glacial period and northward during the last interglacial period from 129 to 117 ka (e.g., Moore et al., 1980; Thompson and Shackleton, 1980; Chinzei et al., 1987; Harada et al., 2004). Yamamoto et al. (2005), however, demonstrated drops in alkenone-derived temperatures in core MD01-2421 off the coast of central Japan from 17 to 12 ka
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Fig. 1. Locations of the drilling sites of the cores GH02-1030 and RC14-103 (Heusser and Morley, 1985), sites of Kenbuchi Basin and Taiki, a map of the modern vegetation of Japan (after Tatewaki, 1955, and Yoshioka, 1973) and Sakhalin (after Atlas of Sakhalin, 1967) and ocean currents. Legend of vegetation. 1: boreal evergreen coniferous forest dominated with Larix, 2: boreal evergreen coniferous forest with temperate deciduous broadleaved trees, 3: cool-mixed forest, 4: temperate deciduous broadleaved forest, 5: temperate evergreen broadleaved forest.
during the last deglaciation, which was attributed to a southward shift of the summer position of the Kuroshio–Oyashio boundary due to a weaker North Pacific High and stronger Okhotsk High. These cooling intervals were not consistent with the global warming trend during the last deglaciation. In this study, we reconstructed changes in terrestrial climate based on the pollen records from a marine core taken off eastern Hokkaido and discuss the linkage of climatic variation on Hokkaido with hemispheric climatic changes, such as East Asian summer monsoon variability. Previous paleoceanographic studies of this core have examined its lithology, age-depth model, and benthic foraminifera (Ikehara et al., 2006); assemblages of benthic foraminifera (Shibahara et al., 2007); Mg/Ca ratio and oxygen isotopes of planktonic and benthic foraminifera (Sagawa and Ikehara, 2008) and alkenone sea surface temperatures and terrestrial biomarkers (Inagaki et al., 2009).
2. Materials and methods An 8.14-m-long piston core, GH02-1030, was collected from the continental slope offshore from Tokachi (1212 m water depth), eastern Hokkaido (42°13.7700 N, 144°12.5300 E), during the Geological Survey of Japan R/V Hakurei-Maru No. 2 GH02 cruise in 2002 (Fig. 1). The sediment in the core consists mainly of clayey silt. The lower part of the core is sandy silt intercalated with some thin sand layers. The uppermost and middle parts of the core are diatomaceous. Visual observation and soft X-ray radiographs revealed no clear erosional surface in the core, and even very thin sand layers were found in the lower part (Fig. 2; Ikehara et al., 2006). Accelerator mass spectrometry (AMS) 14C dates from planktonic and benthic foraminifera were established for 15 and 23 horizons, respectively, at Beta Analytic Inc. For dating, planktonic foraminif-
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least 300 fossil pollen and spores were identified per sample under a 400 optical microscope (Fig. 3).
3. Vegetation in Hokkaido Cool-mixed forest composed of boreal conifers, such as Picea jezoensis, Picea glehnii, and Abies sachalinensis, and temperate deciduous broadleaved trees such as Quercus, Ulmus, Juglans, and Carpinus, is distributed throughout most of Hokkaido (Fig. 1). In the southwestern region, temperate deciduous broadleaved forests are found, mainly composed of Fagus crenata. In contrast, boreal evergreen conifer forests that coexist with the cold deciduous conifer Larix are distributed in Sakhalin, Russian Far East. Accordingly, the vegetation in Hokkaido is characterized by intermediate vegetation from the temperate zone in eastern Honshu, the main island of Japan, and the boreal zone present in Sakhalin. Therefore, the vegetation in Hokkaido has potentially changed in response to climatic changes. Changes in the terrestrial climate and vegetation since the LGM in southern (Nakamura and Tsukada, 1960; Sakaguchi, 1989) and central Hokkaido (Nakamura, 1968; Igarashi et al., 1993; Igarashi, 1994, 1996; Igarashi et al., 2002) have been reconstructed based on terrestrial pollen data. In eastern Hokkaido, the terrestrial pollen record covers only the last 13 ka (Matsuda and Maeda, 1984; Igarashi et al., 2001; Morita, 2001a,b). Marine core RC14–103 taken from 44°020 N, 152°560 E off eastern Hokkaido in the northwest Pacific (Fig. 1; Heusser and Morley, 1985) has provided a pollen record spanning the last 90 ka, which reflects the vegetation in eastern Hokkaido.
4. Pollen analysis
Fig. 2. Columnar section of core GH02-1030 with ages of benthic and planktonic foraminifera (after Ikehara et al., 2006).
era (Neogloboquadrina pachyderma), mixed planktonic foraminifera (mainly N. pachyderma with a minor portion of Globigerina bulloides), benthic foraminifera (Uvigerina), and mixed benthic foraminifera were used (Fig. 2). The measured radiocarbon dates from planktonic foraminifera were converted to calendar ages using the program CALIB 4.4 (Stuiver et al., 1998). The averaged marine reservoir correction for the NW subarctic Pacific (R = 376 ± 46 yrs; Kuzmin et al., 2001) was used for the calculation. The sediment lithology changed from sandy mud deposited during the last glacial maximum (LGM), through diatomaceous silt in the last deglaciation and clayey silt in the early-middle Holocene, and again to diatomaceous silt in the late Holocene (Fig. 2). The existence of coarser sand grains and plant debris in the sand fraction in the LGM horizon suggests a higher terrigenous supply from the Tokachi region. For pollen analysis, 125 samples were collected from the interval between 0.3 and 6.33 m in depth (1.5–22 ka) from core GH021030. The sampling resolutions were 500 yrs/sp between 1.5 and 10 ka and 102 yrs/sp between 10 and 22 ka. Each of the 1 cm3 samples was processed using the method of Moore et al. (1991). At
Thirty-three arboreal pollen taxa, 32 non-arboreal pollen taxa, and eight spore taxa were identified. Estimated concentrations of pollen and spores range from 118 to 19,600/cm3 (Fig. 3). Percentages of arboreal pollen were calculated based on the total number of arboreal pollen, excluding Betula and Alnus to avoid the influence of their high occurrence. The percentages of Betula, Alnus, herbs, ferns, mosses, and algae were calculated based on the total number of pollen and spores (Figs. 3 and 4). The following five pollen zones were discriminated based on the characteristics of the major tree pollen assemblages.
4.1. Zone T1 (6.4–4 m in depth; 22–17 ka) Zone T1 is characterized by the highest percentages of Picea, Larix, and Pinus over the last 22 ka in the Tokachi region. Tsuga, Abies, Betula, and Alnus are the subdominant taxa. Herbs such as Gramineae, Cyperaceae, Artemisia, and ferns such as monolete types and Selaginella selaginoides are relatively abundant. S. selaginoides grows presently in the grassland of the alpine zone at elevations greater than 1500 m a.s.l. in Hokkaido and northern Honshu (Ohwi, 1975).
4.2. Zone T2 (4–2.02 m in depth; 17–10 ka) Compared with Zone T1, Zone T2 is characterized by an increase in Betula and Alnus and a decrease in Picea, Larix, and S. selaginoides. Betula abundance reaches a maximum (50%) at 11.5 ka. Cool-temperate broadleaved trees, such as Quercus, Carpinus/Ostrya, and Juglans/Pterocarya, increase slightly.
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Fig. 3. Major arboreal pollen diagram from core GH02-1030, off Tokachi.
Fig. 4. Non arboreal pollen and spore diagram from core GH02-1030, off Tokachi.
4.3. Zone T3 (2.02–0.3 m in depth; 10–0.5 ka)
5. Modern pollen spectra and vegetation of Sakhalin
Quercus begins to increase after 10 ka and reaches a maximum at 6.4 ka. Other cool-temperate trees also increase in abundance up to modern proportions. In contrast, Larix disappears at 8.5 ka. Herbs and ferns sharply decrease, and a sudden significant drop in Quercus abundance occurs at 8 ka.
In Hokkaido, Larix pollen was highly abundant from the last glacial to the early Holocene. Larix then disappeared until 6–8 ka in Hokkaido (Igarashi et al., 2002). The discovery of the megafossil Larix gmelinii (Yano, 1970) clearly showed that the Larix pollen originated from this species. Presently, L. gmelinii is distributed in
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Sakhalin, South Kuriles, Kamchatka Peninsula, and northeastern Siberia (Schmidt, 1992). The present vegetation in Sakhalin consists of boreal forest, occurring in sub-maritime and maritime climates. The main vegetation type on Sakhalin is P. jezoensis forest mixed with A. sachalinensis and L. gmelinii (Kudo, 1924). The deciduous conifer L. gmelinii is present with Pinus pumila on the lowlands, mountains, and mires in the north. In central and southern Sakhalin, Larix grows on mires and sand dunes, with some cool-temperate broadleaved trees mixed with Picea–Abies forest (Fig. 1; Krestov, 2003). To reconstruct the paleovegetation in the Tokachi region, we compared the pollen spectra of core GH02-1030 with those from surface samples in the natural vegetation of Sakhalin. The surface samples were collected from 31 mires in Sakhalin (Igarashi, 2008; Fig. 5). They were separated into five groups, based on the
characteristics of tree pollen assemblages (Fig. 6). Picea occurs in high percentages in all groups, and Larix shows irregular changes. Conversely, relative Abies abundance is highest in the south (Group A), and decreases toward the north. Abies and cool-temperate broadleaved trees almost disappear in the north (Group E). Pinus occurs in highest percentages in the north (Group E). Relative Betula abundance is greatest in Group B, which is connected with the fact that sampling sites were located along the road; after road construction, Betula trees typically grow as pioneer groups. Meteorological data from six observatory sites in Sakhalin and Hokkaido are shown in Table 1. 6. Climate conditions of the Tokachi region based on pollen composition In Zone T1 (LGM), open boreal forest dominated by Picea and Larix developed on the plain in the present continental shelf area of the Tokachi margin. Abies, Tsuga, Pinus, and temperate broadleaved trees developed as minor components. Tsuga pollen is found in all zones in core GH02-1030; however Tsuga trees are not found naturally in Hokkaido and Sakhalin today. As Tsuga pollen is not transported a long distance by the wind (Igarashi, 1979, 1987), the presence of Tsuga pollen in all zones of the core suggests that Tsuga trees were able to, and did, grow in Hokkaido at least from 22 ka until recent. The pollen spectra in Zone T1 can be correlated with those of Group C based on ratios of conifer pollen. At Nogliki station in the Group C area (Fig. 5), the mean temperature for August was 14.4 °C and the annual precipitation was 613 mm (Table 1), which are 4–5 °C lower and 400 mm lower than values at Taiki station, Tokachi (Fig. 1), respectively. Within Zone T2 (last deglaciation), Betula forest developed. Subdominant components Pinus, Larix, Tsuga, and Abies decreased in relative abundance, while temperate broadleaved trees such as Quercus, Ulmus, and Juglans slightly increased. A decrease in the proportion of conifers and an increase in temperate broadleaved trees indicate that climate became less cold and slightly wetter than in the Zone T1 interval. The pollen spectra of Zone T2 can be correlated with those of Group B. At Poronaisk station in the Group B area (Fig. 5), the mean temperature for August was 15.9 °C and annual precipitation was 747 mm (Table 1), which are 3 °C lower and about 300 mm lower than values at Taiki station, respectively. In Zone T3, cool-mixed forest dominated by Quercus mixed with minor Picea, Abies, and temperate broadleaf trees developed. The climate became the same as the present. At 8 ka, Quercus abruptly decreased over a short time period (260 years). The importance of Quercus in the vegetation increased again and reached a maximum at 6.4 ka. The decrease in the abundance of Quercus at 8 ka is associated with the decline in the summer temperature. This cool event could be correlated with the 8.2 ka event (Prasad et al., 2009), which is recognized globally. 7. Comparison with pollen data from marine and inland cores
Fig. 5. Locations of sampling site collected surface samples in Sakhalin.
We compared the pollen record from core GH02-1030 with that from marine core RC104-103, which was taken 600 km off eastern Hokkaido, northwestern Pacific and covers the last 90 ky (Fig. 1; Heusser and Morley, 1985). The pollen record since the LGM in core RC104-103 is generally the same as that from core GH021030. One difference is the over-representation of Pinus pollen in core RC104-103. This is probably due to preferential transportation of Pinus pollen by wind to remoter areas, as this pollen is easily carried by wind (Aario, 1940). The other difference is the lack of Larix pollen, even during the LGM. Larix pollen is not easily transported
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Fig. 6. Major pollen diagram from surface samples in Sakhalin.
Table 1 Meteorological data of Kenbuchi, Taiki and regions in Sakhalin where surface samples were corrected. Data sources: Japan Meteorological Association Hokkaido Branch, 1982; Chuoh Kishoudai, 1942. Site
Location
a.s.l. (m)
Mean temp. of January (°C)
Mean temp. of August (°C)
Annual temp.
Precipitation (mm)
Pollen group
Okha Nogliki Poronisk Dolinsk Kenbuchi Taiki
53°350 N,143°E 51°500 N,143°100 E 49°220 N,143°480 E 47°200 N,142°500 E 44°080 N,142°220 E 42°300 N,143°160 E
15 17 4 35 131 92
19 19.1 17.6 13.9 9.8 8.2
14 14.4 15.9 17.2 22.1 19
0.25 0.45 0 2 5.7 5.6
546 613 747 884.1 1301.6 1021
E C, D B A
long distances by wind (Erdman, 1969) and is thus not likely to occur in marine core RC104-103. We also compared the pollen record from core GH02-1030 with that from a terrestrial boring core from the Kenbuchi Basin in central Hokkaido (Fig. 1). At the Kenbuchi Basin, six pollen zones, K1– K6, were discriminated covering the last 37 ky (Fig. 7; after Igarashi et al., 1993; Igarashi, 1996). The vegetation in Zone K1 consists of boreal forest dominated by Picea coexisting with Pinus, Larix and Abies as minor components. Pollen spectra in Zone K1 are correlated with those of Group A. At Dolinsk station in Group A area, the mean temperature for August is 17.2 °C, and annual precipitation is 884.1 mm (Table 1), about 5 °C cooler and 400 mm lower than at present respectively. In Zone K2, open cold deciduous forest dominated by Larix and Pinus with diverse herbaceous taxa, Cyperaceae, and dominant S. selaginoides developed in the Kenbuchi Basin at the LGM. Picea, Abies, and cool-temperate broadleaved trees coexisted to some extent. The pollen spectra of Zone K-2 can be correlated with those of Group D. At Nogliki station in the Group D area, the mean temperature for August for this zone was 14.4 °C and the annual precipitation was 613 mm (Table 1), which were about 8 °C lower and 700 mm drier, respectively, than those at Kenbuchi. Zone K2 can be correlated with Zone T1 in core GH02-1030 based on radiocarbon ages. During Zone K3, open boreal forest dominated by Picea developed. Pollen spectra from Zone K3 can be correlated with those
of Group A. Temperatures were about 5 °C lower, and it was 400 mm drier than at present day Kenbuchi Basin. The climate in Zone K3 became warmer and moister than in Zone K2. Zone K3 represents an interstadial during the last deglaciation. The open cold deciduous forest dominated by Larix and Pinus developed again during Zone K4 where Abies was remarkably scarce. Pollen spectra of Zone K4 can be correlated with Group E and/or the far north. At Okha station in the Group E area, the mean temperature for August was 14 °C, and the annual precipitation was 546 mm, which were at least 8 °C lower and 750 mm drier, respectively, than in present day Kenbuchi. The cooling event during Zone K4 was called as the ‘‘Kenbuchi Stadial” (Igarashi et al., 1993; Igarashi, 1996). In Zone K5, cold deciduous forest dominated by Larix, Pinus, and Picea developed, whereas Larix and Pinus began to decrease upward. Pollen spectra from K5 can be correlated with those of Group D. Compared with the climate at Nogliki in the Group D area, the mean temperature for August was about 7–8 °C lower and 700 mm drier, respectively, than at Kenbuchi. During Zone K6 cool-mixed forest mainly composed of Quercus and Abies developed under a warm/moist climate. At about 8 ka, Quercus abruptly decreased over a short time period. This decrease in Quercus abundance can also be correlated with the 8-ka event, which is recognized globally. The comparison between core GH02-1030 and the boring core in the Kenbuchi Basin demonstrates that the difference in temper-
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Fig. 7. Sammarized pollen diagram for Kenbuchi Basin, central Hokkaido.
ature and precipitation during the deglaciation was much larger in inland Hokkaido than in the maritime area of the Pacific coast (Fig. 8). Presently, the August temperature at Taiki in the Tokachi region is 3 °C lower than that in the Kenbuchi Basin in central Hokkaido (Table 1); conversely, during the deglaciation, the August temperature at Taiki was 1.5–2 °C warmer than at Kembuchi Basin except for the interstadial (Zone K3).
In the present-day Tokachi region, the warm air masses coming from the south in summer and the cold ocean surface water in the Oyashio area create advection fogs, lowering summer air temperatures in this area. During the early stages of deglaciation, a weaker summer monsoon (Nakagawa et al., 2005; Igarashi and Oba, 2006) may have dampened the formation of fogs, resulting in predominantly sunny weather and warmer than present temperatures in the Tokachi region.
Fig. 8. Climate in the LGM and the last deglaciation in Tokachi region and Kenbuchi Basin.
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8. Discussion and conclusion Vegetation in the Tokachi region during the last deglaciation was characterized by the development of Betula forest. In present-day Hokkaido, there are six species of the genus Betula. Discrimination of these six species based on the shape and size of pollen is impossible. We speculate that the Betula species that flourished during Zone T2 periods (17–10 ka) in the Tokachi region was Betula ermanii. At present, B. ermanii is distributed in the lowlands of the Kamchatka Peninsula through the southern Kuril Islands to eastern Hokkaido along the Pacific margin (Itoh, 1982). On the Kamchatka Peninsula, B. ermanii forest is well developed from 0 to 400 m a.s.l. around the Pacific Ocean under the maritime climate influenced by the Pacific, with small seasonal fluctuations in temperature and high annual precipitation resulting in heavy snowfall and a short growing season (Kojima, 1994). These facts suggest that B. ermanii was the dominant Betula species in the Tokachi region during the last deglaciation. During the last deglaciation, the Kuroshio–Oyashio boundary shifted to the south, and as a result, the water temperature off Tokachi dropped to its lowest point (Inagaki et al., 2009). In contrast, pollen records from core MD01-2421 taken off the coast of central Japan in the northwestern Pacific (Igarashi and Oba, 2006) and from Lake Suigetsu in central Japan (Nakagawa et al., 2005) indicate an abrupt onland warming at 15 ka. This sudden warming corresponds to an abrupt negative shift in oxygen isotopes found in Chinese stalagmites (Wang et al., 2001), suggesting a strengthening of the East Asian summer monsoon. Colder ocean water and a strengthened summer monsoon after 15 ka may have resulted in the formation of advection fogs, lowering summer temperatures and decreasing the seasonal temperature difference in the Tokachi district, which is similar to the modern climate conditions on the Kamchatka Peninsula. Acknowledgements We would like to express deep thanks to two reviewers whose comments were helpful. One reviewer, Dr. Pavel Tarasov, gave us particularly good suggestions about vegetation in East Asia, which were much appreciated. We also express our heart-felt thanks to the captain, crew, and on-board scientists of the GH02 cruise of R/V Hakurei-Maru No. 2. References Aario, L., 1940. Waldgrenzen und subrezente pollenspektren in Petsamo Lappland. Annales Academiae Scientiarum Fenniae, Series A 54, 1–120. Chinzei, K., Fujioka, K., Kitazato, H., Koizumi, I., Oba, T., Oda, M., Okada, H., Sakai, T., Tanimura, Y., 1987. Postglacial environmental change of the Pacific Ocean off the coasts of central Japan. Marine Micropaleontology 11, 273–291. Erdman, G., 1969. Handbook of Palynology. Munksgaard, Copenhagen. 486pp. Harada, N., Ahagon, N., Uchida, M., Murayama, M., 2004. Northward and southward migrations of frontal zones during the past 40 kyr in the Kuroshio–Oyashio transition area. Geochemistry, Geophysics, Geosystems 5, Q09004. Heusser, E.L., Morley, J.J., 1985. Pollen and radiolarian records from deep-sea core RC14-103: climatic reconstructions of northeast Japan and northwest Pacific for the last 90,000 years. Quaternary Research 24, 60–72. Igarashi, Y., 1979. Pollen incidence and wind transport in central Hokkaido (I). Journal of the Faculty of Science, Hokkaido University Series IV19, 257–264. Igarashi, Y., 1987. Pollen incidence and wind transport in central Hokkaido (II). Research Bulletins of the College Experiment Forests, Faculty of Agriculture, Hokkaido University 44, 477–506. Igarashi, Y., 1994. Quaternary forest and climate history of Hokkaido, Japan, from marine sediments. Quaternary Science Reviews 13, 335–344. Igarashi, Y., 1996. A lateglacial climatic reversion in Hokkaido, Northeast Asia, inferred from the Larix pollen record. Quaternary Science Reviews 15, 989–995. Igarashi, Y., 2008. Climate and vegetation changes since 40,000 years BP in Hokkaido and Sakhalin. In: International Symposium on Human Ecosystem Changes in the Northern Circum Japan Sea Area (NCJSA) in Late Pleistocene, Tokyo University, Japan, pp. 27–41. Igarashi, Y., Oba, T., 2006. Fluctuations in the East Asian monsoon over the last 144 ka in the northwest Pacific based on a high-resolution pollen
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analysis of IMAGES core MD01-2421. Quaternary Science Reviews 25, 1447– 1459. Igarashi, Y., Igarashi, T., Daimaru, H., Yamada, O., Miyagi, T., Matsushita, K., Hiramatsu, K., 1993. Vegetation history of Kenbuchi Basin and Furano Basin in Hokkaido, North Japan, since 32,000 yrs BP. The Quaternary Research 32, 89– 105. Igarashi, Y., Igarashi, T., Endo, K., Yamada, O., Nakagawa, M., Sumita, M., 2001. Vegetation history since the Late Glacial of Habomai Bog and Ochiishi Cape Bog, Nemuro Peninsula, eastern Hokkaido, north Japan. Japanese Journal of Historical Botany 10, 67–79. Igarashi, Y., Murayama, M., Igarashi, T., Higake, T., Fukuda, M., 2002. History of Larix forest in Hokkaido and Sakhalin, northeast Asia since the Last Glacial. Acta Palaeontologica Sinica 41, 524–533. Ikehara, K., Ohkushi, K., Shibahara, A., Hoshiba, M., 2006. Change of bottom water conditions at intermediate depths of the Oyashio region, NW Pacific over the past 20,000 yrs. Global and Planetary Change 53, 78–91. Inagaki, M., Yamamoto, M., Igarashi, Y., Ikehara, K., 2009. Biomarker records from Core GH02-1030 off Tokachi in the northwestern Pacific over the last 23,000 years; environmental changes during the last deglaciation. Journal of Oceanography 65, 847–858. Isono, D., Yamamoto, M., Irino, T., Oba, T., Murayama, M., Nakamura, T., Kawahata, H., 2009. The 1500-year climate oscillation in the mid-latitude North Pacific during the Holocene. Geology 37, 591–594. Itoh, K., 1982. Ecosystems of Hokkaido-based on LANDSAT images. Japan Foundation for Shipbuilding Advancement, 32pp. (in Japanese). Kiefer, T., Kienast, M., 2005. Patterns of deglacial warming in the Pacific Ocean: a review with emphasis on the time interval of Heinrich event. Quaternary Science Reviews 24, 1063–1081. Kojima, S., 1994. Vegetation and environment of Betula ermanii forest on the Kamchatka Peninsula. Japanese Journal of Ecology 44, 49–59. Krestov, P.V., 2003. Forest vegetation of Easternmost Russia (Russian Far East). In: Kolbekll, J., Srutek, M., Box, E.O. (Eds.), Forest Vegetation of Northeast Asia. Kluwer Academic Publishers, Dordrecht, pp. 93–180. Kudo, Y., 1924. Vegetation in North Sakhalin. Sagaren Gunseibu, Santo Press Co., Sapporo. 295 p (in Japanese). Kuzmin, Y.V., Burr, G.S., Jull, A.J.T., 2001. Radiocarbon reservoir correction ages in the Peter the Great Gulf, Sea of Japan, and eastern coast of the Kunasir, Southern Kuriles (Northwestern Pacific). Radiocarbon 43, 477–481. Matsuda, I., Maeda, Y., 1984. Pollen analysis of the Holocene Sediments in Western Mire of Cape Notoro Historical Remains, Onbetsu-cho Shiranukagun, Hokkaido. Cape Notoro, Onbetsu-cho Education Committee, pp. 147–152 (in Japanese). Moore, T.C., Burkle, L.L., Geitzenauer, K., Luz, B., Molina-Cruz, A., Robertson, J.H., Sachs, H., Sancetta, C., Thiede, J., Thompson, P., Wenkam, C., 1980. The reconstruction of sea surface temperatures in the Pacific Ocean of 18,000 B. P. Marine Micropaleontology 5, 215–247. Moore, P.D., Webb, J.A., Collinson, M.E., 1991. Pollen Analysis. Blackwell Scientific Publications, Oxford. 216pp.. Morita, Y., 2001a. Vegetation history of Yururi Island in easternmost Hokkaido since the Late Glacial. Japanese Journal of Historical Botany 10, 81–89 (in Japanese with English abstract). Morita, Y., 2001b. Vegetation history in Nemuro Peninsula since the Late Pleistocene. Vegetation Science 18, 39–41 (in Japanese with English abstract). Nakagawa, T., Kitagawa, H., Yasuda, Y., Tarasov, P.E., Gotanda, K., Sawai, Y., 2005. Pollen/event stratigraphy of the varved sediment of Lake Suigetsu, central Japan from 15,701 to 10,217 SG vyr BP (Suigetsu varve years before present): description, interpretation, and correlation with other regions. Quaternary Science Reviews 24, 1691–1701. Nakamura, J., 1968. Palynological aspects of the Quaternary in Hokkaido. Research reports of the Kochi University 17, 39–51 (in Japanese with English abstract). Nakamura, J., Tsukada, M., 1960. Palynological aspect of the Quaternary in Hokkaido. I. The Oshima Peninsula (1). Research Reports of the Kochi University 9, 1–22 (in Japanese with English abstract). Ogi, M., Tachibana, Y., Yamazaki, K., 2004. The connectivity of the winter North Atlantic Oscillation (NAO) and the summer Okhotsk High. Journal of the Meteorological Society of Japan 82, 905–913. Ohwi, J., 1975. Flora of Japan. Shibundo, Tokyo. 244. Prasad, S., Witt, A., Kienel, U., Dulski, P., Bauer, E., Yancheva, G., 2009. The 8.2 ka event: evidence for seasonal differences and the rate of climate change in western Europe. Global and Planetary Change 67, 218–226. Sagawa, T., Ikehara, K., 2008. Intermediate water ventilation change in the subarctic northwest Pacific during the last deglaciation. Geophysical Research Letters 35, L24702. doi:10.1029/2008GL035133. Sakaguchi, Y., 1989. Some pollen records from Hokkaido and Sakhalin. Bulletin of the Department of Geography University of Tokyo (21), 1–17. Schmidt, C.W., 1992. Around the world with Larix: an introduction. Ecology and management of Larix forests: a look ahead. In: Proceedings of an International Symposium, Whitefish, Montana, USA 6, 6–18. Shibahara, A., Ohkushi, K., Kennett, J.P., Ikehara, K., 2007. Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: a benthic foraminiferal perspective. Paleoceanography 22, PA3213. doi:10.1029/2005PA001234. Stuiver, M., Reimer, P.J., Bard, E., Beck, J.W., Burr, G.S., Hughen, K.A., Kromer, B., McCormac, G., van der Plicht, J., Spurk, M., 1998. INTCAL 98 radiocarbon age calibration, 24000-0 cal BP. Radiocarbon 40, 1041–1083.
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Tatewaki, M., 1955. Pan-mixed Forest Zone. Hoppo-Ringyo 7, 240–243 (in Japanese). Thompson, P.R., Shackleton, N.J., 1980. North Pacific paleoceanography: late Quaternary coiling variations of planktonic foraminifer Neogloboquadrina pachyderma. Nature 287, 829–833. Wang, Y.J., Cheng, H., Edwards, R.L., An, Z.S., Wu, J.Y., Shen, C.C., Dorale, J.A., 2001. A high-resolution absolute-dated late Pleistocene monsoon record from Hulu Cave, China. Science 294, 2345–2348. Yamamoto, M., Suemune, R., Oba, T., 2005. Equatorward shift of the subarctic boundary in the northwestern Pacific during the last deglaciation. Geophysical Research Letters 32, L05609. doi:10.1029/2004GL021903.
Yamazaki, K., 2004. The Arctic Ocean, ‘‘Kisyokenkyu” Note, vol. 206. The Meteorological Society of Japan, Tokyo, 181pp (in Japanese). Yano, M., 1970. Larix gmelini from the Pleistocene deposits in Hokkaido, Japan. The Journal of the Geological Society of Japan 76, 205–214 (in Japanese with English abstract). Yoshioka, K., 1973. Phytogeography. Kyouritsu Shuppan. 84pp (in Japanese).
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Climate and vegetation in Hokkaido, northern Japan, since the LGM: Pollen records from core GH02-1030 off Tokachi in the northwestern Pacific Yaeko Igarashi a,⇑, Masanobu Yamamoto b, Ken Ikehara c a
Institute for Paleoenvironment of Northern Regions, Koyocho 3-7-5, Kitahiroshima 061-1134, Japan Faculty of Environmental Earth Science, Hokkaido University, Kita-10, Nishi-5, Kita-ku, Sapporo 060-0810, Japan c Geological Survey of Japan, AIST, Tsukuba, Ibaraki 305-8567, Japan b
a r t i c l e
i n f o
Article history: Available online 17 August 2010 Keywords: Last deglaciation Climate Vegetation Hokkaido Marine core Pollen record
a b s t r a c t 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. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The onset of warming varied in different regions during the last deglaciation (see Kiefer and Kienast (2005) for a review of the Pacific region). The island of Hokkaido, located at the northwestern margin of the Pacific Ocean, experienced slow warming during the last deglaciation. A pollen study demonstrated the southward expansion of open cold deciduous forest, during what is known as the ‘‘Kenbuchi Stadial,” in central Hokkaido Island during this period (Igarashi et al., 1993; Igarashi, 1996). An earlier study also showed several cooling events at this time on Southwestern Hokkaido (Sakaguchi, 1989). The island of Hokkaido is surrounded by the Pacific Ocean, the Sea of Okhotsk, and the Sea of Japan and is situated in a cool-temperate zone with both tropical and arctic influences. In winter, the climate of Hokkaido is governed by the winter monsoon winds, which blow from the Siberian High over
⇑ Corresponding author. Tel./fax: +81 11 373 2938. E-mail address: [email protected] (Y. Igarashi). 1367-9120/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jseaes.2010.08.001
Siberia, and the air temperature is positively correlated with the Arctic Oscillation index (Yamazaki, 2004). The summer climate is governed by the relative intensities of the Okhotsk High developed in the Sea of Okhotsk and the Ogasawara High developed in the northwestern subtropical Pacific on the western flank of the North Pacific High. The development of the Okhotsk High results in a cool summer and is related to the positive mode of the Arctic Oscillation (Ogi et al., 2004). The development of the Ogasawara High results in a warm summer and is related to the La Niña state of the tropical Pacific. The mid-latitude North Pacific region contains the subarctic boundary between the subtropical Kuroshio and subarctic Oyashio currents (Fig. 1) and is sensitive to global climate changes (e.g., Chinzei et al., 1987; Isono et al., 2009). Previous studies have roughly reconstructed that the Kuroshio–Oyashio boundary shifted southward during the last glacial period and northward during the last interglacial period from 129 to 117 ka (e.g., Moore et al., 1980; Thompson and Shackleton, 1980; Chinzei et al., 1987; Harada et al., 2004). Yamamoto et al. (2005), however, demonstrated drops in alkenone-derived temperatures in core MD01-2421 off the coast of central Japan from 17 to 12 ka
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Fig. 1. Locations of the drilling sites of the cores GH02-1030 and RC14-103 (Heusser and Morley, 1985), sites of Kenbuchi Basin and Taiki, a map of the modern vegetation of Japan (after Tatewaki, 1955, and Yoshioka, 1973) and Sakhalin (after Atlas of Sakhalin, 1967) and ocean currents. Legend of vegetation. 1: boreal evergreen coniferous forest dominated with Larix, 2: boreal evergreen coniferous forest with temperate deciduous broadleaved trees, 3: cool-mixed forest, 4: temperate deciduous broadleaved forest, 5: temperate evergreen broadleaved forest.
during the last deglaciation, which was attributed to a southward shift of the summer position of the Kuroshio–Oyashio boundary due to a weaker North Pacific High and stronger Okhotsk High. These cooling intervals were not consistent with the global warming trend during the last deglaciation. In this study, we reconstructed changes in terrestrial climate based on the pollen records from a marine core taken off eastern Hokkaido and discuss the linkage of climatic variation on Hokkaido with hemispheric climatic changes, such as East Asian summer monsoon variability. Previous paleoceanographic studies of this core have examined its lithology, age-depth model, and benthic foraminifera (Ikehara et al., 2006); assemblages of benthic foraminifera (Shibahara et al., 2007); Mg/Ca ratio and oxygen isotopes of planktonic and benthic foraminifera (Sagawa and Ikehara, 2008) and alkenone sea surface temperatures and terrestrial biomarkers (Inagaki et al., 2009).
2. Materials and methods An 8.14-m-long piston core, GH02-1030, was collected from the continental slope offshore from Tokachi (1212 m water depth), eastern Hokkaido (42°13.7700 N, 144°12.5300 E), during the Geological Survey of Japan R/V Hakurei-Maru No. 2 GH02 cruise in 2002 (Fig. 1). The sediment in the core consists mainly of clayey silt. The lower part of the core is sandy silt intercalated with some thin sand layers. The uppermost and middle parts of the core are diatomaceous. Visual observation and soft X-ray radiographs revealed no clear erosional surface in the core, and even very thin sand layers were found in the lower part (Fig. 2; Ikehara et al., 2006). Accelerator mass spectrometry (AMS) 14C dates from planktonic and benthic foraminifera were established for 15 and 23 horizons, respectively, at Beta Analytic Inc. For dating, planktonic foraminif-
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least 300 fossil pollen and spores were identified per sample under a 400 optical microscope (Fig. 3).
3. Vegetation in Hokkaido Cool-mixed forest composed of boreal conifers, such as Picea jezoensis, Picea glehnii, and Abies sachalinensis, and temperate deciduous broadleaved trees such as Quercus, Ulmus, Juglans, and Carpinus, is distributed throughout most of Hokkaido (Fig. 1). In the southwestern region, temperate deciduous broadleaved forests are found, mainly composed of Fagus crenata. In contrast, boreal evergreen conifer forests that coexist with the cold deciduous conifer Larix are distributed in Sakhalin, Russian Far East. Accordingly, the vegetation in Hokkaido is characterized by intermediate vegetation from the temperate zone in eastern Honshu, the main island of Japan, and the boreal zone present in Sakhalin. Therefore, the vegetation in Hokkaido has potentially changed in response to climatic changes. Changes in the terrestrial climate and vegetation since the LGM in southern (Nakamura and Tsukada, 1960; Sakaguchi, 1989) and central Hokkaido (Nakamura, 1968; Igarashi et al., 1993; Igarashi, 1994, 1996; Igarashi et al., 2002) have been reconstructed based on terrestrial pollen data. In eastern Hokkaido, the terrestrial pollen record covers only the last 13 ka (Matsuda and Maeda, 1984; Igarashi et al., 2001; Morita, 2001a,b). Marine core RC14–103 taken from 44°020 N, 152°560 E off eastern Hokkaido in the northwest Pacific (Fig. 1; Heusser and Morley, 1985) has provided a pollen record spanning the last 90 ka, which reflects the vegetation in eastern Hokkaido.
4. Pollen analysis
Fig. 2. Columnar section of core GH02-1030 with ages of benthic and planktonic foraminifera (after Ikehara et al., 2006).
era (Neogloboquadrina pachyderma), mixed planktonic foraminifera (mainly N. pachyderma with a minor portion of Globigerina bulloides), benthic foraminifera (Uvigerina), and mixed benthic foraminifera were used (Fig. 2). The measured radiocarbon dates from planktonic foraminifera were converted to calendar ages using the program CALIB 4.4 (Stuiver et al., 1998). The averaged marine reservoir correction for the NW subarctic Pacific (R = 376 ± 46 yrs; Kuzmin et al., 2001) was used for the calculation. The sediment lithology changed from sandy mud deposited during the last glacial maximum (LGM), through diatomaceous silt in the last deglaciation and clayey silt in the early-middle Holocene, and again to diatomaceous silt in the late Holocene (Fig. 2). The existence of coarser sand grains and plant debris in the sand fraction in the LGM horizon suggests a higher terrigenous supply from the Tokachi region. For pollen analysis, 125 samples were collected from the interval between 0.3 and 6.33 m in depth (1.5–22 ka) from core GH021030. The sampling resolutions were 500 yrs/sp between 1.5 and 10 ka and 102 yrs/sp between 10 and 22 ka. Each of the 1 cm3 samples was processed using the method of Moore et al. (1991). At
Thirty-three arboreal pollen taxa, 32 non-arboreal pollen taxa, and eight spore taxa were identified. Estimated concentrations of pollen and spores range from 118 to 19,600/cm3 (Fig. 3). Percentages of arboreal pollen were calculated based on the total number of arboreal pollen, excluding Betula and Alnus to avoid the influence of their high occurrence. The percentages of Betula, Alnus, herbs, ferns, mosses, and algae were calculated based on the total number of pollen and spores (Figs. 3 and 4). The following five pollen zones were discriminated based on the characteristics of the major tree pollen assemblages.
4.1. Zone T1 (6.4–4 m in depth; 22–17 ka) Zone T1 is characterized by the highest percentages of Picea, Larix, and Pinus over the last 22 ka in the Tokachi region. Tsuga, Abies, Betula, and Alnus are the subdominant taxa. Herbs such as Gramineae, Cyperaceae, Artemisia, and ferns such as monolete types and Selaginella selaginoides are relatively abundant. S. selaginoides grows presently in the grassland of the alpine zone at elevations greater than 1500 m a.s.l. in Hokkaido and northern Honshu (Ohwi, 1975).
4.2. Zone T2 (4–2.02 m in depth; 17–10 ka) Compared with Zone T1, Zone T2 is characterized by an increase in Betula and Alnus and a decrease in Picea, Larix, and S. selaginoides. Betula abundance reaches a maximum (50%) at 11.5 ka. Cool-temperate broadleaved trees, such as Quercus, Carpinus/Ostrya, and Juglans/Pterocarya, increase slightly.
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Fig. 3. Major arboreal pollen diagram from core GH02-1030, off Tokachi.
Fig. 4. Non arboreal pollen and spore diagram from core GH02-1030, off Tokachi.
4.3. Zone T3 (2.02–0.3 m in depth; 10–0.5 ka)
5. Modern pollen spectra and vegetation of Sakhalin
Quercus begins to increase after 10 ka and reaches a maximum at 6.4 ka. Other cool-temperate trees also increase in abundance up to modern proportions. In contrast, Larix disappears at 8.5 ka. Herbs and ferns sharply decrease, and a sudden significant drop in Quercus abundance occurs at 8 ka.
In Hokkaido, Larix pollen was highly abundant from the last glacial to the early Holocene. Larix then disappeared until 6–8 ka in Hokkaido (Igarashi et al., 2002). The discovery of the megafossil Larix gmelinii (Yano, 1970) clearly showed that the Larix pollen originated from this species. Presently, L. gmelinii is distributed in
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Sakhalin, South Kuriles, Kamchatka Peninsula, and northeastern Siberia (Schmidt, 1992). The present vegetation in Sakhalin consists of boreal forest, occurring in sub-maritime and maritime climates. The main vegetation type on Sakhalin is P. jezoensis forest mixed with A. sachalinensis and L. gmelinii (Kudo, 1924). The deciduous conifer L. gmelinii is present with Pinus pumila on the lowlands, mountains, and mires in the north. In central and southern Sakhalin, Larix grows on mires and sand dunes, with some cool-temperate broadleaved trees mixed with Picea–Abies forest (Fig. 1; Krestov, 2003). To reconstruct the paleovegetation in the Tokachi region, we compared the pollen spectra of core GH02-1030 with those from surface samples in the natural vegetation of Sakhalin. The surface samples were collected from 31 mires in Sakhalin (Igarashi, 2008; Fig. 5). They were separated into five groups, based on the
characteristics of tree pollen assemblages (Fig. 6). Picea occurs in high percentages in all groups, and Larix shows irregular changes. Conversely, relative Abies abundance is highest in the south (Group A), and decreases toward the north. Abies and cool-temperate broadleaved trees almost disappear in the north (Group E). Pinus occurs in highest percentages in the north (Group E). Relative Betula abundance is greatest in Group B, which is connected with the fact that sampling sites were located along the road; after road construction, Betula trees typically grow as pioneer groups. Meteorological data from six observatory sites in Sakhalin and Hokkaido are shown in Table 1. 6. Climate conditions of the Tokachi region based on pollen composition In Zone T1 (LGM), open boreal forest dominated by Picea and Larix developed on the plain in the present continental shelf area of the Tokachi margin. Abies, Tsuga, Pinus, and temperate broadleaved trees developed as minor components. Tsuga pollen is found in all zones in core GH02-1030; however Tsuga trees are not found naturally in Hokkaido and Sakhalin today. As Tsuga pollen is not transported a long distance by the wind (Igarashi, 1979, 1987), the presence of Tsuga pollen in all zones of the core suggests that Tsuga trees were able to, and did, grow in Hokkaido at least from 22 ka until recent. The pollen spectra in Zone T1 can be correlated with those of Group C based on ratios of conifer pollen. At Nogliki station in the Group C area (Fig. 5), the mean temperature for August was 14.4 °C and the annual precipitation was 613 mm (Table 1), which are 4–5 °C lower and 400 mm lower than values at Taiki station, Tokachi (Fig. 1), respectively. Within Zone T2 (last deglaciation), Betula forest developed. Subdominant components Pinus, Larix, Tsuga, and Abies decreased in relative abundance, while temperate broadleaved trees such as Quercus, Ulmus, and Juglans slightly increased. A decrease in the proportion of conifers and an increase in temperate broadleaved trees indicate that climate became less cold and slightly wetter than in the Zone T1 interval. The pollen spectra of Zone T2 can be correlated with those of Group B. At Poronaisk station in the Group B area (Fig. 5), the mean temperature for August was 15.9 °C and annual precipitation was 747 mm (Table 1), which are 3 °C lower and about 300 mm lower than values at Taiki station, respectively. In Zone T3, cool-mixed forest dominated by Quercus mixed with minor Picea, Abies, and temperate broadleaf trees developed. The climate became the same as the present. At 8 ka, Quercus abruptly decreased over a short time period (260 years). The importance of Quercus in the vegetation increased again and reached a maximum at 6.4 ka. The decrease in the abundance of Quercus at 8 ka is associated with the decline in the summer temperature. This cool event could be correlated with the 8.2 ka event (Prasad et al., 2009), which is recognized globally. 7. Comparison with pollen data from marine and inland cores
Fig. 5. Locations of sampling site collected surface samples in Sakhalin.
We compared the pollen record from core GH02-1030 with that from marine core RC104-103, which was taken 600 km off eastern Hokkaido, northwestern Pacific and covers the last 90 ky (Fig. 1; Heusser and Morley, 1985). The pollen record since the LGM in core RC104-103 is generally the same as that from core GH021030. One difference is the over-representation of Pinus pollen in core RC104-103. This is probably due to preferential transportation of Pinus pollen by wind to remoter areas, as this pollen is easily carried by wind (Aario, 1940). The other difference is the lack of Larix pollen, even during the LGM. Larix pollen is not easily transported
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Fig. 6. Major pollen diagram from surface samples in Sakhalin.
Table 1 Meteorological data of Kenbuchi, Taiki and regions in Sakhalin where surface samples were corrected. Data sources: Japan Meteorological Association Hokkaido Branch, 1982; Chuoh Kishoudai, 1942. Site
Location
a.s.l. (m)
Mean temp. of January (°C)
Mean temp. of August (°C)
Annual temp.
Precipitation (mm)
Pollen group
Okha Nogliki Poronisk Dolinsk Kenbuchi Taiki
53°350 N,143°E 51°500 N,143°100 E 49°220 N,143°480 E 47°200 N,142°500 E 44°080 N,142°220 E 42°300 N,143°160 E
15 17 4 35 131 92
19 19.1 17.6 13.9 9.8 8.2
14 14.4 15.9 17.2 22.1 19
0.25 0.45 0 2 5.7 5.6
546 613 747 884.1 1301.6 1021
E C, D B A
long distances by wind (Erdman, 1969) and is thus not likely to occur in marine core RC104-103. We also compared the pollen record from core GH02-1030 with that from a terrestrial boring core from the Kenbuchi Basin in central Hokkaido (Fig. 1). At the Kenbuchi Basin, six pollen zones, K1– K6, were discriminated covering the last 37 ky (Fig. 7; after Igarashi et al., 1993; Igarashi, 1996). The vegetation in Zone K1 consists of boreal forest dominated by Picea coexisting with Pinus, Larix and Abies as minor components. Pollen spectra in Zone K1 are correlated with those of Group A. At Dolinsk station in Group A area, the mean temperature for August is 17.2 °C, and annual precipitation is 884.1 mm (Table 1), about 5 °C cooler and 400 mm lower than at present respectively. In Zone K2, open cold deciduous forest dominated by Larix and Pinus with diverse herbaceous taxa, Cyperaceae, and dominant S. selaginoides developed in the Kenbuchi Basin at the LGM. Picea, Abies, and cool-temperate broadleaved trees coexisted to some extent. The pollen spectra of Zone K-2 can be correlated with those of Group D. At Nogliki station in the Group D area, the mean temperature for August for this zone was 14.4 °C and the annual precipitation was 613 mm (Table 1), which were about 8 °C lower and 700 mm drier, respectively, than those at Kenbuchi. Zone K2 can be correlated with Zone T1 in core GH02-1030 based on radiocarbon ages. During Zone K3, open boreal forest dominated by Picea developed. Pollen spectra from Zone K3 can be correlated with those
of Group A. Temperatures were about 5 °C lower, and it was 400 mm drier than at present day Kenbuchi Basin. The climate in Zone K3 became warmer and moister than in Zone K2. Zone K3 represents an interstadial during the last deglaciation. The open cold deciduous forest dominated by Larix and Pinus developed again during Zone K4 where Abies was remarkably scarce. Pollen spectra of Zone K4 can be correlated with Group E and/or the far north. At Okha station in the Group E area, the mean temperature for August was 14 °C, and the annual precipitation was 546 mm, which were at least 8 °C lower and 750 mm drier, respectively, than in present day Kenbuchi. The cooling event during Zone K4 was called as the ‘‘Kenbuchi Stadial” (Igarashi et al., 1993; Igarashi, 1996). In Zone K5, cold deciduous forest dominated by Larix, Pinus, and Picea developed, whereas Larix and Pinus began to decrease upward. Pollen spectra from K5 can be correlated with those of Group D. Compared with the climate at Nogliki in the Group D area, the mean temperature for August was about 7–8 °C lower and 700 mm drier, respectively, than at Kenbuchi. During Zone K6 cool-mixed forest mainly composed of Quercus and Abies developed under a warm/moist climate. At about 8 ka, Quercus abruptly decreased over a short time period. This decrease in Quercus abundance can also be correlated with the 8-ka event, which is recognized globally. The comparison between core GH02-1030 and the boring core in the Kenbuchi Basin demonstrates that the difference in temper-
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Fig. 7. Sammarized pollen diagram for Kenbuchi Basin, central Hokkaido.
ature and precipitation during the deglaciation was much larger in inland Hokkaido than in the maritime area of the Pacific coast (Fig. 8). Presently, the August temperature at Taiki in the Tokachi region is 3 °C lower than that in the Kenbuchi Basin in central Hokkaido (Table 1); conversely, during the deglaciation, the August temperature at Taiki was 1.5–2 °C warmer than at Kembuchi Basin except for the interstadial (Zone K3).
In the present-day Tokachi region, the warm air masses coming from the south in summer and the cold ocean surface water in the Oyashio area create advection fogs, lowering summer air temperatures in this area. During the early stages of deglaciation, a weaker summer monsoon (Nakagawa et al., 2005; Igarashi and Oba, 2006) may have dampened the formation of fogs, resulting in predominantly sunny weather and warmer than present temperatures in the Tokachi region.
Fig. 8. Climate in the LGM and the last deglaciation in Tokachi region and Kenbuchi Basin.
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8. Discussion and conclusion Vegetation in the Tokachi region during the last deglaciation was characterized by the development of Betula forest. In present-day Hokkaido, there are six species of the genus Betula. Discrimination of these six species based on the shape and size of pollen is impossible. We speculate that the Betula species that flourished during Zone T2 periods (17–10 ka) in the Tokachi region was Betula ermanii. At present, B. ermanii is distributed in the lowlands of the Kamchatka Peninsula through the southern Kuril Islands to eastern Hokkaido along the Pacific margin (Itoh, 1982). On the Kamchatka Peninsula, B. ermanii forest is well developed from 0 to 400 m a.s.l. around the Pacific Ocean under the maritime climate influenced by the Pacific, with small seasonal fluctuations in temperature and high annual precipitation resulting in heavy snowfall and a short growing season (Kojima, 1994). These facts suggest that B. ermanii was the dominant Betula species in the Tokachi region during the last deglaciation. During the last deglaciation, the Kuroshio–Oyashio boundary shifted to the south, and as a result, the water temperature off Tokachi dropped to its lowest point (Inagaki et al., 2009). In contrast, pollen records from core MD01-2421 taken off the coast of central Japan in the northwestern Pacific (Igarashi and Oba, 2006) and from Lake Suigetsu in central Japan (Nakagawa et al., 2005) indicate an abrupt onland warming at 15 ka. This sudden warming corresponds to an abrupt negative shift in oxygen isotopes found in Chinese stalagmites (Wang et al., 2001), suggesting a strengthening of the East Asian summer monsoon. Colder ocean water and a strengthened summer monsoon after 15 ka may have resulted in the formation of advection fogs, lowering summer temperatures and decreasing the seasonal temperature difference in the Tokachi district, which is similar to the modern climate conditions on the Kamchatka Peninsula. Acknowledgements We would like to express deep thanks to two reviewers whose comments were helpful. One reviewer, Dr. Pavel Tarasov, gave us particularly good suggestions about vegetation in East Asia, which were much appreciated. We also express our heart-felt thanks to the captain, crew, and on-board scientists of the GH02 cruise of R/V Hakurei-Maru No. 2. References Aario, L., 1940. Waldgrenzen und subrezente pollenspektren in Petsamo Lappland. Annales Academiae Scientiarum Fenniae, Series A 54, 1–120. Chinzei, K., Fujioka, K., Kitazato, H., Koizumi, I., Oba, T., Oda, M., Okada, H., Sakai, T., Tanimura, Y., 1987. Postglacial environmental change of the Pacific Ocean off the coasts of central Japan. Marine Micropaleontology 11, 273–291. Erdman, G., 1969. Handbook of Palynology. Munksgaard, Copenhagen. 486pp. Harada, N., Ahagon, N., Uchida, M., Murayama, M., 2004. Northward and southward migrations of frontal zones during the past 40 kyr in the Kuroshio–Oyashio transition area. Geochemistry, Geophysics, Geosystems 5, Q09004. Heusser, E.L., Morley, J.J., 1985. Pollen and radiolarian records from deep-sea core RC14-103: climatic reconstructions of northeast Japan and northwest Pacific for the last 90,000 years. Quaternary Research 24, 60–72. Igarashi, Y., 1979. Pollen incidence and wind transport in central Hokkaido (I). Journal of the Faculty of Science, Hokkaido University Series IV19, 257–264. Igarashi, Y., 1987. Pollen incidence and wind transport in central Hokkaido (II). Research Bulletins of the College Experiment Forests, Faculty of Agriculture, Hokkaido University 44, 477–506. Igarashi, Y., 1994. Quaternary forest and climate history of Hokkaido, Japan, from marine sediments. Quaternary Science Reviews 13, 335–344. Igarashi, Y., 1996. A lateglacial climatic reversion in Hokkaido, Northeast Asia, inferred from the Larix pollen record. Quaternary Science Reviews 15, 989–995. Igarashi, Y., 2008. Climate and vegetation changes since 40,000 years BP in Hokkaido and Sakhalin. In: International Symposium on Human Ecosystem Changes in the Northern Circum Japan Sea Area (NCJSA) in Late Pleistocene, Tokyo University, Japan, pp. 27–41. Igarashi, Y., Oba, T., 2006. Fluctuations in the East Asian monsoon over the last 144 ka in the northwest Pacific based on a high-resolution pollen
1109
analysis of IMAGES core MD01-2421. Quaternary Science Reviews 25, 1447– 1459. Igarashi, Y., Igarashi, T., Daimaru, H., Yamada, O., Miyagi, T., Matsushita, K., Hiramatsu, K., 1993. Vegetation history of Kenbuchi Basin and Furano Basin in Hokkaido, North Japan, since 32,000 yrs BP. The Quaternary Research 32, 89– 105. Igarashi, Y., Igarashi, T., Endo, K., Yamada, O., Nakagawa, M., Sumita, M., 2001. Vegetation history since the Late Glacial of Habomai Bog and Ochiishi Cape Bog, Nemuro Peninsula, eastern Hokkaido, north Japan. Japanese Journal of Historical Botany 10, 67–79. Igarashi, Y., Murayama, M., Igarashi, T., Higake, T., Fukuda, M., 2002. History of Larix forest in Hokkaido and Sakhalin, northeast Asia since the Last Glacial. Acta Palaeontologica Sinica 41, 524–533. Ikehara, K., Ohkushi, K., Shibahara, A., Hoshiba, M., 2006. Change of bottom water conditions at intermediate depths of the Oyashio region, NW Pacific over the past 20,000 yrs. Global and Planetary Change 53, 78–91. Inagaki, M., Yamamoto, M., Igarashi, Y., Ikehara, K., 2009. Biomarker records from Core GH02-1030 off Tokachi in the northwestern Pacific over the last 23,000 years; environmental changes during the last deglaciation. Journal of Oceanography 65, 847–858. Isono, D., Yamamoto, M., Irino, T., Oba, T., Murayama, M., Nakamura, T., Kawahata, H., 2009. The 1500-year climate oscillation in the mid-latitude North Pacific during the Holocene. Geology 37, 591–594. Itoh, K., 1982. Ecosystems of Hokkaido-based on LANDSAT images. Japan Foundation for Shipbuilding Advancement, 32pp. (in Japanese). Kiefer, T., Kienast, M., 2005. Patterns of deglacial warming in the Pacific Ocean: a review with emphasis on the time interval of Heinrich event. Quaternary Science Reviews 24, 1063–1081. Kojima, S., 1994. Vegetation and environment of Betula ermanii forest on the Kamchatka Peninsula. Japanese Journal of Ecology 44, 49–59. Krestov, P.V., 2003. Forest vegetation of Easternmost Russia (Russian Far East). In: Kolbekll, J., Srutek, M., Box, E.O. (Eds.), Forest Vegetation of Northeast Asia. Kluwer Academic Publishers, Dordrecht, pp. 93–180. Kudo, Y., 1924. Vegetation in North Sakhalin. Sagaren Gunseibu, Santo Press Co., Sapporo. 295 p (in Japanese). Kuzmin, Y.V., Burr, G.S., Jull, A.J.T., 2001. Radiocarbon reservoir correction ages in the Peter the Great Gulf, Sea of Japan, and eastern coast of the Kunasir, Southern Kuriles (Northwestern Pacific). Radiocarbon 43, 477–481. Matsuda, I., Maeda, Y., 1984. Pollen analysis of the Holocene Sediments in Western Mire of Cape Notoro Historical Remains, Onbetsu-cho Shiranukagun, Hokkaido. Cape Notoro, Onbetsu-cho Education Committee, pp. 147–152 (in Japanese). Moore, T.C., Burkle, L.L., Geitzenauer, K., Luz, B., Molina-Cruz, A., Robertson, J.H., Sachs, H., Sancetta, C., Thiede, J., Thompson, P., Wenkam, C., 1980. The reconstruction of sea surface temperatures in the Pacific Ocean of 18,000 B. P. Marine Micropaleontology 5, 215–247. Moore, P.D., Webb, J.A., Collinson, M.E., 1991. Pollen Analysis. Blackwell Scientific Publications, Oxford. 216pp.. Morita, Y., 2001a. Vegetation history of Yururi Island in easternmost Hokkaido since the Late Glacial. Japanese Journal of Historical Botany 10, 81–89 (in Japanese with English abstract). Morita, Y., 2001b. Vegetation history in Nemuro Peninsula since the Late Pleistocene. Vegetation Science 18, 39–41 (in Japanese with English abstract). Nakagawa, T., Kitagawa, H., Yasuda, Y., Tarasov, P.E., Gotanda, K., Sawai, Y., 2005. Pollen/event stratigraphy of the varved sediment of Lake Suigetsu, central Japan from 15,701 to 10,217 SG vyr BP (Suigetsu varve years before present): description, interpretation, and correlation with other regions. Quaternary Science Reviews 24, 1691–1701. Nakamura, J., 1968. Palynological aspects of the Quaternary in Hokkaido. Research reports of the Kochi University 17, 39–51 (in Japanese with English abstract). Nakamura, J., Tsukada, M., 1960. Palynological aspect of the Quaternary in Hokkaido. I. The Oshima Peninsula (1). Research Reports of the Kochi University 9, 1–22 (in Japanese with English abstract). Ogi, M., Tachibana, Y., Yamazaki, K., 2004. The connectivity of the winter North Atlantic Oscillation (NAO) and the summer Okhotsk High. Journal of the Meteorological Society of Japan 82, 905–913. Ohwi, J., 1975. Flora of Japan. Shibundo, Tokyo. 244. Prasad, S., Witt, A., Kienel, U., Dulski, P., Bauer, E., Yancheva, G., 2009. The 8.2 ka event: evidence for seasonal differences and the rate of climate change in western Europe. Global and Planetary Change 67, 218–226. Sagawa, T., Ikehara, K., 2008. Intermediate water ventilation change in the subarctic northwest Pacific during the last deglaciation. Geophysical Research Letters 35, L24702. doi:10.1029/2008GL035133. Sakaguchi, Y., 1989. Some pollen records from Hokkaido and Sakhalin. Bulletin of the Department of Geography University of Tokyo (21), 1–17. Schmidt, C.W., 1992. Around the world with Larix: an introduction. Ecology and management of Larix forests: a look ahead. In: Proceedings of an International Symposium, Whitefish, Montana, USA 6, 6–18. Shibahara, A., Ohkushi, K., Kennett, J.P., Ikehara, K., 2007. Late Quaternary changes in intermediate water oxygenation and oxygen minimum zone, northern Japan: a benthic foraminiferal perspective. Paleoceanography 22, PA3213. doi:10.1029/2005PA001234. Stuiver, M., Reimer, P.J., Bard, E., Beck, J.W., Burr, G.S., Hughen, K.A., Kromer, B., McCormac, G., van der Plicht, J., Spurk, M., 1998. INTCAL 98 radiocarbon age calibration, 24000-0 cal BP. Radiocarbon 40, 1041–1083.
1110
Y. Igarashi et al. / Journal of Asian Earth Sciences 40 (2011) 1102–1110
Tatewaki, M., 1955. Pan-mixed Forest Zone. Hoppo-Ringyo 7, 240–243 (in Japanese). Thompson, P.R., Shackleton, N.J., 1980. North Pacific paleoceanography: late Quaternary coiling variations of planktonic foraminifer Neogloboquadrina pachyderma. Nature 287, 829–833. Wang, Y.J., Cheng, H., Edwards, R.L., An, Z.S., Wu, J.Y., Shen, C.C., Dorale, J.A., 2001. A high-resolution absolute-dated late Pleistocene monsoon record from Hulu Cave, China. Science 294, 2345–2348. Yamamoto, M., Suemune, R., Oba, T., 2005. Equatorward shift of the subarctic boundary in the northwestern Pacific during the last deglaciation. Geophysical Research Letters 32, L05609. doi:10.1029/2004GL021903.
Yamazaki, K., 2004. The Arctic Ocean, ‘‘Kisyokenkyu” Note, vol. 206. The Meteorological Society of Japan, Tokyo, 181pp (in Japanese). Yano, M., 1970. Larix gmelini from the Pleistocene deposits in Hokkaido, Japan. The Journal of the Geological Society of Japan 76, 205–214 (in Japanese with English abstract). Yoshioka, K., 1973. Phytogeography. Kyouritsu Shuppan. 84pp (in Japanese).