記述言語：日本語   出版者・発行元：Agricultural and Forest Meteorology  

Owing to the increased need to assess global forest behavior under changing climatic conditions within a long-term context, spatial coherence in tree-ring records is of widespread interest. Spatial networks of tree growth have been widely discussed from regional to global scales, but few studies have reported stable oxygen isotopes in networks of tree rings (δ18Otree), thus impeding a comprehensive hydroclimatic interpretation of δ18Otree records over large spatial scales, i.e., isoscapes. In this study, a network of four annually resolved δ18Otree chronologies (1805–2016) was developed for Southwest China, the transitional zone of the Asian summer monsoon, to test spatial coherence in δ18Otree variations and to explore the climatic factors driving synchrony at different spatial scales. The quantitative analyses show that the four chronologies exhibit consistent annual variations, with the first principal component (PC1) accounting for 70% of the total variance, which uniformly respond to local relative humidity (RH) and precipitation δ18O during the monsoon season. This confirms the spatial coherence in δ18Otree records. Furthermore, significant inter-site correlations of local RH and precipitation δ18O are also detected, revealing that it is the regionally homogeneous year-to-year variations in the hydroclimate that should be responsible for spatial coherence. For a larger spatial perspective, spatial correlation analyses reveal that the most prominent correlations between δ18Otree and hydroclimate fields occur in the Indochina Peninsula, in which δ18Otree changes are synchronized with those in Southwest China and the synchrony temporally varies with the Indian summer monsoon (ISM) intensity, indicating that coherent δ18Otree variations are linked to ISM-related moisture transport. In addition, δ18Otree records have shown strong in-phase relationships with the natural variabilities of the ISM and El Niño-Southern Oscillation (ENSO) across interannual and interdecadal timescales over the last 150 years, suggesting that spatial coherence in δ18Otree records can be utilized to reflect the long-term history of large-scale atmospheric circulation.

DOI： 10.1016/j.agrformet.2021.108687

Web of Science

Scopus

記述言語：日本語   出版者・発行元：Quaternary Science Reviews  

Tree-ring cellulose oxygen isotope (δ18O) in monsoon Asia (MA) is affected collectively by local hydroclimate and remote oceanic-atmospheric variations. Variations of tree-ring δ18O have been widely used for quantitative reconstructions of monsoon-season precipitation, relative humidity and drought severity. However, local hydroclimate and remote large-scale circulation's influences on tree-ring δ18O has not been fully resolved. Here, we collected 24 tree-ring δ18O chronologies covering the period of 1884–1999 across a wide range of MA and investigated the common signals of these chronologies using principal component analysis. The first principal component (PC1) of the 24 tree-ring δ18O chronologies explained 25.2% of the total variances and showed significant positive correlations with the observed Asian summer monsoon oxygen isotope index (r = 0.69) during the period of 1978–1999, suggesting that a common signal of precipitation δ18O does exist in MA and that it is highly correlated with El Niño–Southern Oscillation (ENSO) (r = 0.72) and the South Asian summer monsoon precipitation (r = −0.66). South Asian summer monsoon precipitation and ENSO are the main factors controlling this common signal of tree-ring δ18O across MA. PC1 of tree-ring δ18O chronologies in MA also depicted a negative (positive) correlation with the Atlantic Multidecadal Oscillation (Pacific Decadal Oscillation), indicating the large-scale circulation influences. After removing the large-scale circulation influences on tree-ring δ18O chronologies, however, the residual tree-ring δ18O chronologies exhibit negative correlations with the regional hydroclimate, highlighting the role local hydroclimate on the individual tree-ring δ18O variations.

DOI： 10.1016/j.quascirev.2021.107156

Web of Science

Scopus

記述言語：日本語   出版者・発行元：Quaternary Research (United States)  

We present a long-term seasonal tree ring cellulose oxygen isotope (δ18Oc) time series created by analyzing four segments (S1, S2, S3, and S4) per year during the period of 1951-2009 from southeastern Tibetan Plateau. This intraseasonal δ18Oc reveals the onset and mature phase of the summer monsoon precipitation in this region. Analysis indicates that the δ18Oc of S1 has the strongest correlation with precipitation during the regional monsoon onset (29-33 pentads, May 21-June 10, r =-0.69), and the δ18Oc values for S2, S3, and S4 correlate strongly with June, July, and August precipitation, respectively. Combined δ18Oc of S2, S3, and S4 shows the most robust correlation (r =-0.82) with the mature-phase monsoon precipitation (June-July-August, JJA), passing rigorous statistical tests for calibration and verification in dendroclimatology. These results demonstrate the feasibility in using long-term intraseasonal δ18Oc to reconstruct the Asian summer monsoon's intraseasonal variations.

DOI： 10.1017/qua.2020.28

Web of Science

Scopus

記述言語：日本語   出版者・発行元：Annals of Glaciology  

We drilled an 81.2-m-long ice core in the accumulation area (5860 m a.s.l.) of Trambau Glacier in the Rolwaling region during October-November 2019. The drilling operation was conducted with a lightweight electro-mechanical drill system after two reconnaissance fieldworks in 2017 and 2018, during which two shallow firn cores were drilled with a hand auger. The drill system and ice core samples were transported by helicopters at a high elevation of 6000 m a.s.l. A further challenging issue was the ice core transportation between Nepal and Japan, as no regular commercial flight was available for the frozen samples. The addition of dry ice imported from India immediately prior to leaving Nepal allowed the ice core samples to be successfully transported to a cold room in Japan, and remain in a frozen state. Stratigraphic observations during the drilling operation suggest the drill site has been affected by melting and refreezing.

DOI： 10.1017/aog.2021.15

Web of Science

Scopus

記述言語：日本語   出版者・発行元：Climate of the Past  

Oxygen isotope ratios (δ18O) of tree-ring cellulose are a novel proxy for summer hydroclimate in monsoonal Asia. In central Japan, we collected 67 conifer wood samples, mainly Chamaecyparis obtusa, with ages encompassing the past 2600 years. The samples were taken from living trees, archeological wood, architectural wood, and buried logs. We analyzed stable isotope ratios of oxygen (δ18O) and hydrogen (d2H) in tree-ring cellulose in these samples (more than 15 000 rings in total) without using a pooling method and constructed a statistically reliable treering cellulose δ18O time series for the past 2500 years. However, there were distinct age trends and level offsets in the δ18O record, and cellulose δ18O values showed a gradual decrease as an individual tree matures. This suggested it is difficult to establish a cellulose δ18O chronology for lowfrequency signals by simple averaging of all the δ18O time series data. In addition, there were opposite age trends in the cellulose δ2H, and δ2H gradually increased with tree age. There were clear positive correlations in the short-periodicity variations between δ18O and δ2H, probably indicating a common climate signal. A comparison of the δ18O and δ2H time series in individual trees with tree-ring width suggested that the opposite age trends of δ18O and δ2H are caused by temporal changes in the degree of post-photosynthetic isotope exchange with xylem water (physiological effect), accompanied by changes in stem growth rate that are influenced by human activity in the forests of central Japan. Based on the assumptions that cellulose δ18O and δ2H vary positively and negatively with constant proportional coefficients due to climatological and physiological effects, respectively, we solved simultaneous equations for the climatological and physiological components of variations in tree-ring cellulose δ18O and δ2H in order to remove the age trend. This enabled us to evaluate the climatic record from cellulose δ18O vari ations. The extracted climatological component in the cellulose δ18O for the past 2600 years in central Japan was well correlated with numerous instrumental, historical, and paleoclimatological records of past summer climate at various spatial and temporal scales. This indicates that integration of tree-ring cellulose δ18O and δ2H data is a promising method to reconstruct past summer climate variations on annual to millennial timescales, irrespective of the growth environment. However, analytical and statistical methods need to be improved for further development of this climate proxy.

DOI： 10.5194/cp-16-2153-2020

Web of Science

Scopus

記述言語：日本語   出版者・発行元：Journal of Hydrology  

The Asian Summer Monsoon system (ASM) affects a large population in the monsoonal Asia. Previous studies have thoroughly discussed the temporally unstable response of tree-ring oxygen isotope (δ18O) to the regional climate variables and ocean–atmosphere interaction modes, however, the response to the ASM remains ambiguous. In this study, an annually resolved tree-ring δ18O chronology is developed from eastern Yunnan-Guizhou Plateau, in the transitional zone of the ASM. Based on the results from response analyses, the climatic controls of tree-ring δ18O is considered to be the moisture-related variables of the monsoon season. Spatial correlations suggest that in the study area, the water vapor is mainly originated from the Bay of Bengal and transported by the Indian Summer Monsoon (ISM). Furthermore, the temporal stability in relationships between the tree-ring δ18O and the ISM variability are explored. Our findings suggest that on interannual to decadal timescales, the tree-ring δ18O is significantly anti-correlated, but temporally unstable with respect to the ISM. The strength of interannual relationship is affected by the ISM intensity, which is modulated by the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) variability. Moreover, the strength of decadal relationship is associated with the phase shift of the Pacific Decadal Oscillation (PDO). Additionally, the decreasing trend of tree-ring δ18O after the late 1970 s that diverges from the simultaneous normal level of the ISM is caused by the isotopically-depleted trend in upstream precipitation of the moisture source. The opposite patterns of correlations between the tree-ring δ18O and the ENSO and IOD in recent decades demonstrate that the regional hydroclimate in the study region has been undergoing significant secular variations that are characterised by an increasing effect of the IOD and a decreasing effect of the ENSO. The findings from this study further improve our understanding of the tree-ring δ18O response to the ASM, at multi-time scales, and shed light on the impact of the ASM on regional hydroclimate variability, across the transitional zone of the ASM.

DOI： 10.1016/j.jhydrol.2020.125522

Web of Science

Scopus

記述言語：日本語   出版者・発行元：Scientific Reports  

A 338-year oxygen isotope record from teak tree-ring cellulose collected from Mae Hong Son province in northwestern Thailand was presented. The tree-ring series preserves the isotopic signal of the regional wet season rainfall and relative humidity. Tree-ring δ18O correlates strongly with regional rainfall from May to October, showing coherent variations over large areas in Southeast Asia. We reconstructed the summer monsoon season (May to October) rainfall based on a linear regression model that explained 35.2% of the actual rainfall variance. Additionally, we found that in the 19th century, there was a remarkable drought during many years that corresponded to regional historic drought events. The signals of the June to September Indian summer monsoon (ISM) for the period between 1948 and 2009 were clearly found. Spatial correlations and spectral analyses revealed a strong impact of the El Niño-Southern Oscillation (ENSO) on tree-ring δ18O. However, ENSO influenced the tree-ring δ18O more strongly in the 1870–1906, 1907–1943, and 1944–1980 periods than in the 1981–2015 period, which corresponded to periods of weaker and stronger ISM intensity.

DOI： 10.1038/s41598-020-66001-0

Web of Science

Scopus

PubMed

記述言語：日本語   出版者・発行元：Theoretical and Applied Climatology  

We present a 100-year oxygen isotope record from teak tree-ring cellulose (δ18O), originating from a site in southern Myanmar that preserves the isotopic ratios of the regional wet season’s rainfall. Tree-ring δ18O correlates strongly with regional rainfall during the months of May to October (r = − 0.353, p < 0.01). We found the tree-ring δ18O had clear signals of the June to September Indian Summer Monsoon (ISM) over the years 1948–1998 (r = − 0.53, p < 0.01). The δ18O has a significant and negative correlation with the minimum temperature in September and has a significant positive correlation with maximum temperature in November and December. The study found that δ18O has a significant positive correlation with the difference between the maximum temperature and the minimum temperature (DTR) in August to October. Based on our results, it can be concluded that tree-ring δ18O in teak in southern Myanmar is controlled by the amount of rainfall during the monsoon season and the temperature in the November and December. Spatial correlation and spectral analyses revealed a strong impact of the El Niño-Southern Oscillation (ENSO) on tree-ring δ18O of teak. In addition, tree-ring δ18O also captures the signal of the Indian Ocean Dipole (IOD).

DOI： 10.1007/s00704-019-03036-y

Web of Science

Scopus

DOI： 10.1007/978-3-030-29684-1_14

記述言語：英語  

DOI： 10.1016/j.scitotenv.2019.06.268

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s00484-017-1365-6

Scopus

PubMed

記述言語：英語  

DOI： 10.1016/j.scitotenv.2019.01.186

PubMed

記述言語：日本語   掲載種別：研究論文（大学，研究機関等紀要）  

DOI： 10.1029/2018GL081458

DOI： 10.1016/j.dendro.2019.125626

DOI： 10.5026/jgeography.128.49

CiNii Research

記述言語：日本語   出版者・発行元：Dendrochronologia  

The oxygen isotopic composition (δ18O) of tree-ring cellulose has been recognized as a powerful tool for dendroclimatological and dendrochronological investigations in Asia. Only a few studies of cellulose δ18O so far published, however, have been conducted in Indonesia, and the spatial coherence of cellulose δ18O has yet to be clarified. In this study we measured cellulose δ18O of teak (Tectona grandis) collected from four sites on Java Island to evaluate the similarity between the different teak δ18O values and the potential for using teak δ18O both as a climate proxy and as a tool for cross-dating. Cellulose δ18O time series of Javanese teaks were found to be significantly correlated in all of the comparisons between sites, even between sites separated by a distance as great as 400 km. While significant correlations did not appear in the ring width data between our samples (expressed population signal (EPS) = 0.64; Rbar = 0.23; sample depth = 10), they were found between the cellulose δ18O values (EPS = 0.89; Rbar = 0.58; sample depth = 10). These results suggest that teak δ18O variations have higher spatial coherence and might be a useful tool for cross-dating. A significant negative correlation was observed between cellulose δ18O and the relative humidity/precipitation during the rainy season, indicating that the cellulose δ18O of Javanese teak is an effective proxy for relative humidity/precipitation during the rainy season. Cellulose δ18O was found to be positively correlated with precipitation during the dry season preceding the growing season, whereas it showed no correlations with the temperature and Palmer Drought Severity Index (PDSI), the key constraints of δ18O on the Indochina Peninsula.

DOI： 10.1016/j.dendro.2018.09.010

Web of Science

Scopus

記述言語：英語  

DOI： 10.1080/10256016.2018.1495203

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Copernicus GmbH  

We have constructed a regional tree-ring cellulose oxygen isotope (δ18O) record for the northern Indian sub-continent based on two new records from northern India and central Nepal and three published records from northwestern India, western Nepal and Bhutan. The record spans the common interval from 1743 to 2008 CE. Correlation analysis reveals that the record is significantly and negatively correlated with the three regional climatic indices: all India rainfall (AIR
r = -0.5, p &lt
0.001, n = 138), Indian monsoon index (IMI
r = -0.45, p &lt
0.001, n = 51) and the intensity of monsoonal circulation (r = -0.42, p &lt
0.001, n = 51). The close relationship between tree-ring cellulose δ18O and the Indian summer monsoon (ISM) can be explained by oxygen isotope fractionation mechanisms. Our results indicate that the regional tree-ring cellulose δ18O record is suitable for reconstructing high-resolution changes in the ISM. The record exhibits significant interannual and long-term variations. Interannual changes are closely related to the El Niño-Southern Oscillation (ENSO), which indicates that the ISM was affected by ENSO in the past. However, the ISM-ENSO relationship was not consistent over time, and it may be partly modulated by Indian Ocean sea surface temperature (SST). Long-term changes in the regional tree-ring δ18O record indicate a possible trend of weakened ISM intensity since 1820. Decreasing ISM activity is also observed in various high-resolution ISM records from southwest China and Southeast Asia, and may be the result of reduced land-ocean thermal contrasts since 1820 CE.

DOI： 10.5194/cp-14-653-2018

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1007/s00382-018-4212-5

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier B.V.  

Dendrochronological analysis using the oxygen isotope composition (18O/16O) of cellulose was performed to reveal the age of an ancient rock avalanche that scattered huge granitic rock clasts on the bank of the Dondokosawa River in the east of Mount Hououzan, the Akaishi Range, central Japan. The samples for dating were disc-cut wood logs or increment cores of Japanese cypress (Chamaecyparis obtusa (Sieb. &amp
Zucc.) Endl.) and Hemlock tree (Tsuga sp.) buried in lacustrine sediments. Cellulose was extracted directly from tree-ring cross-sectional thin wood plates. Cellulose rings of each disc were sampled and their oxygen isotope ratios were measured with a pyrolysis-type elemental analyser and an isotope ratio mass spectrometer. We compared the inter-annual variations in oxygen isotope ratios of cellulose for samples with those of a 470-year-long tree-ring δ18O chronology (AD450–919) independently constructed from Japanese cypress. The estimated death year of the barkless Japanese cypress is around AD885, and that of the barked hemlock tree is AD888. If the rock avalanche was induced by strong ground motion from a large earthquake, these ages are relevant to a large historical earthquake that occurred in this area. The candidates are the AD 887 Goki-Shichido Earthquake (Ninna Earthquake), which was one of the gigantic ocean-trench earthquakes documented along the Suruga and Nankai Troughs off central Japan, and another large intraplate earthquake remotely triggered by this ocean-trench earthquake.

DOI： 10.1016/j.quageo.2017.12.004

Scopus

記述言語：日本語   掲載種別：研究論文（大学，研究機関等紀要）  

記述言語：日本語   掲載種別：研究論文（大学，研究機関等紀要）  

DOI： 10.2343/geochemj.2.0543

DOI： 10.1002/joc.5859

記述言語：日本語   出版者・発行元：公益社団法人 日本雪氷学会／日本雪工学会  

DOI： 10.14851/jcsir.2018.0_180

CiNii Research

CiNii Research

CiNii Research

DOI： 10.3759/tropics.MS17-09

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1080/16000889.2017.1391663

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.gloplacha.2017.08.009

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：NATURE PUBLISHING GROUP  

Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850-2014. Global temperature composites show a remarkable degree of coherence between high-and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.
(TABLE)
Since the pioneering work of D'Arrigo and Jacoby1-3, as well as Mann et al. 4,5, temperature reconstructions of the Common Era have become a key component of climate assessments6-9. Such reconstructions depend strongly on the composition of the underlying network of climate proxies10, and it is therefore critical for the climate community to have access to a community-vetted, quality-controlled database of temperature-sensitive records stored in a self-describing format. The Past Global Changes (PAGES) 2k consortium, a self-organized, international group of experts, recently assembled such a database, and used it to reconstruct surface temperature over continental-scale regions11 (hereafter, ` PAGES2k-2013').
This data descriptor presents version 2.0.0 of the PAGES2k proxy temperature database (Data Citation 1). It augments the PAGES2k-2013 collection of terrestrial records with marine records assembled by the Ocean2k working group at centennial12 and annual13 time scales. In addition to these previously published data compilations, this version includes substantially more records, extensive new metadata, and validation. Furthermore, the selection criteria for records included in this version are applied more uniformly and transparently across regions, resulting in a more cohesive data product.
This data descriptor describes the contents of the database, the criteria for inclusion, and quantifies the relation of each record with instrumental temperature. In addition, the paleotemperature time series are summarized as composites to highlight the most salient decadal-to centennial-scale behaviour of the dataset and check mutual consistency between paleoclimate archives. We provide extensive Matlab code to probe the database-processing, filtering and aggregating it in various ways to investigate temperature variability over the Common Era. The unique approach to data stewardship and code-sharing employed here is designed to enable an unprecedented scale of investigation of the temperature history of the Common Era, by the scientific community and citizen-scientists alike.

DOI： 10.1038/sdata.2017.88

Web of Science

記述言語：日本語   掲載種別：研究論文（研究会，シンポジウム資料等）  

記述言語：朝鮮語   掲載種別：研究論文（学術雑誌）  

DOI： 10.5658/WOOD.2017.45.5.661

Scopus

記述言語：日本語   出版者・発行元：一般社団法人日本地球化学会  

<p>本州の中部及び近畿地方の多数の地点から得られた、様々な時代の約70個体の長樹齢(百～九百年)の木材年輪試料から、年層毎にセルロースを抽出して酸素同位体比を測定し、過去2600年間に及ぶ高精度の酸素同位体比クロノロジーを完成させると共に、同時に測定した水素同位体比と組み合わせることで、酸素同位体比に含まれる樹齢効果を理論的に削除し、純粋に気候(降水量)変動の成分のみを計算することに成功した。その方法の詳細、及び得られた成果の気候学的、歴史学的、考古学的意義について紹介する。</p>

DOI： 10.14862/geochemproc.64.0_15

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER HEIDELBERG  

Compared with annual tree-ring cellulose delta (18) O, intra-annual cellulose delta (18) O has potential to reconstruct precipitation with higher resolution and stronger signal intensity.
Annual tree-ring cellulose oxygen isotope values (delta O-18) of Fokienia hodginsii provide a promising proxy of monsoon-season precipitation in Southeast China. Measuring intra-annual cellulose delta O-18 values may reveal the seasonal variability of precipitation and the associated climate influences. Here, we examine intra-annual variation of cellulose delta O-18 values in Fokienia hodginsii and Cryptomeria fortune from Fujian Province, Southeast China. Both species exhibited considerable intra-annual variations in cellulose delta O-18 (range similar to 6 aEuro degrees) with a consistent pattern of enriched values near the annual ring boundary and depleted values in the central portion of the ring. Seasonal patterns in the tree-ring delta O-18 values generally followed changes in precipitation delta O-18 values. Compared with annual tree-ring cellulose delta O-18, intra-annual cellulose delta O-18 has potential to reconstruct precipitation with higher resolution and stronger signal intensity. July tree-ring cellulose delta O-18 is significantly correlated (r = -0.58, p &lt; 0.05) with July precipitation, and June-August tree-ring cellulose delta O-18 and annual tree-ring cellulose delta O-18, respectively, explain 52 and 41 % of the actual variance of April-August precipitation. In addition, May-October cellulose delta O-18 values during El Nio years are higher than in La Nia years, and April to October rainfall is lower in El Nio years than in La Nia years. Combining the significant correlations between inter-annual cellulose delta O-18 values and sea surface temperatures in the central tropical Pacific, our results support the hypothesis that El Nio-Southern Oscillation affects tree-ring cellulose delta O-18 in Southeast China by modulating seasonal precipitation.

DOI： 10.1007/s00468-015-1320-2

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2015JD023610

Web of Science

記述言語：日本語   掲載種別：研究論文（大学，研究機関等紀要）  

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Hydrology  

A tree-ring δ18O chronology for the period 1828-2000 was developed from four Pinus merkusii trees, to find a reliable proxy for reconstructing precipitation in northwest Thailand. Inter-tree δ18O correlations were high during the entire period (r=0.57-0.79). The tree-ring δ18O chronology shows significant negative correlations with regional July-October precipitation during the period 1901-2000 (r=-0.62) and with July-October river flow (r=-0.54), and is in good agreement with a shorter tree-ring δ18O chronology from living Pinus kesiya in northwest Thailand. The spatial correlation analysis between tree-ring δ18O and regional July-October precipitation also support that the tree-ring δ18O of P. merkusii is a promising proxy to reconstruct precipitation in northwest Thailand. The tree-ring δ18O-based July-October reconstruction, which accounts for 37.6% of the precipitation variance, shows a close relationship with El Niño-Southern Oscillation (ENSO) during the period 1871-2000, with the exception of during the past two decades; the exception may be related to the southeastward shift of the descending limb of Walker circulation and increased frequency of central Pacific ENSO.

DOI： 10.1016/j.jhydrol.2015.02.037

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

To investigate climate variability in Asia during the last millennium, the spatial and temporal evolution of summer (June-July-August; JJA) temperature in eastern and south-central Asia is reconstructed using multi-proxy records and the regularized expectation maximization (RegEM) algorithm with truncated total least squares (TTLS), under a point-by-point regression (PPR) framework. The temperature index reconstructions show that the late 20th century was the warmest period in Asia over the past millennium. The temperature field reconstructions illustrate that temperatures in central, eastern, and southern China during the 11th and 13th centuries, and in western Asia during the 12th century, were significantly higher than those in other regions, and comparable to levels in the 20th century. Except for the most recent warming, all identified warm events showed distinct regional expressions and none were uniform over the entire reconstruction area. The main finding of the study is that spatial temperature patterns have, on centennial time-scales, varied greatly over the last millennium. Moreover, seven climate model simulations, from the Coupled Model Intercomparison Project Phase 5 (CMIP5), over the same region of Asia, are all consistent with the temperature index reconstruction at the 99 % confidence level. Only spatial temperature patterns extracted as the first empirical orthogonal function (EOF) from the GISS-E2-R and MPI-ESM-P model simulations are significant and consistent with the temperature field reconstruction over the past millennium in Asia at the 90 % confidence level. This indicates that both the reconstruction and the simulations depict the temporal climate variability well over the past millennium. However, the spatial simulation or reconstruction capability of climate variability over the past millennium could be still limited. For reconstruction, some grid points do not pass validation tests and reveal the need for more proxies with high temporal resolution, accurate dating, and sensitive temperature signals, especially in central Asia and before AD 1400.

DOI： 10.1007/s10584-015-1413-3

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人日本地球化学会  

Oxygen isotope ratios (δ18O) of tree-ring cellulose in pine (Pinus densiflora) and oak (Quercus serrate and Quercus variabilis) growing in central Japan from 1970 to 2011 share a common inter-annual variance among different cores in a tree, different trees in a species, and different species in a forest. The high mean correlation between the two radii (r = 0.738) of individual trees and the mean standard deviation of two measurements for the same year from the two radii of eight trees (σ = 0.361‰) reveals the reliability and representativeness of single cores. The significant correlation (r = 0.667, p < 0.01) between pine and oak cellulose δ18O suggests that δ18O in tree-ring cellulose is controlled by common external factors, and that it is possible to establish a unique δ18O chronology using different tree species. The δ18O values of tree-ring cellulose in pine and oak trees are negatively correlated with precipitation from June to August (correlation coefficients are -0.679 for pine and -0.583 for oak), which is attributable to the precipitation amount effect, mainly caused by the stagnant rain front (Baiu) in early summer and typhoons in late summer in this region. The δ18O values are negatively correlated with relative humidity from April to September for pine (r = -0.632, p < 0.01), and in June and July for oak (r = -0.437, p < 0.01); these correlations probably reflect different lengths of the growing season. Multiple regression analysis reveals that tree-ring δ18O values of pine and oak in this region are largely governed by summer precipitation. Relative humidity does not appear to greatly affect tree-ring δ18O of oak, in contrast to pine, which may be interpreted in terms of differences in leaf morphology and/or cellulose synthesis processes. Our results indicate that δ18O values of tree-ring cellulose can provide a potential crossdating tool, irrespective of the physiological differences between gymnosperms and angiosperms. In central Japan, tree-ring δ18O values of both pine and oak can act as reliable proxies of June-August precipitation, while pine trees tend to exhibit more potential for reconstruction of relative humidity.

DOI： 10.2343/geochemj.2.0336

Web of Science

Scopus

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Stable isotopes in tree-ring alpha-cellulose are valued as environmental proxies and their use is steadily increasing; however, preparation of alpha-cellulose is a bottleneck in isotope analysis. Recent methodological breakthrough for extracting tree-ring alpha-cellulose directly from tree-ring cross-sectional laths drastically increased the throughput of tree-ring isotope data. In this paper, we evaluate our recently designed "cross-section" method. This method employs polytetrafluoroethylene (PTFE) cases, enabling direct extraction of alpha-cellulose from 1-mm thick tree-ring laths, in combination with fixation sheets to prevent disintegration of freeze-dried alpha-cellulose laths. Perforated PTFE cases are easily producible at an affordable cost. They are made of commonly available lab consumables in catalogs and do not require specially made PTFE parts. Freeze-dried alpha-cellulose laths preserved distinct anatomical structure, enabling precise separation at the tree-ring boundaries. Once separated froma lath, tree-ring alpha-cellulose can beweighed directly into silver or tin capsules for analysis. We checked chemical purity of alpha-cellulose prepared by the cross-section method from five tree species (larch, pine, spruce, beech, and oak). Residual lignin and hemicellulose contents were quantitatively assessed by Fourier transforminfrared spectrometry and gas chromatography. The average chemical purity of alpha-cellulose laths from the five species was 94.5%, similar to the chemical purity of alpha-cellulose prepared with the standard Jayme-Wise method. Both oxygen and carbon isotope values of alpha-cellulose prepared by the cross-section method also closely matched those prepared by the standard method. We conclude that, by overhauling the method of alpha-cellulose preparation for tree-ring isotope analysis, we increased throughput of tree-ring oxygen and carbon isotope data without sacrificing sample purity. (c) 2014 The Authors. Published by Elsevier B.V.

DOI： 10.1016/j.chemgeo.2014.11.019

Web of Science

記述言語：日本語   出版者・発行元：一般社団法人日本地球化学会  

日本語版はありません。

DOI： 10.14862/geochemproc.61.0_190

CiNii Research

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：GEOCHEMICAL SOC JAPAN  

Some trees from tropical areas lack visually detectable and consistent annual growth rings. As such, we have measured the radial variation of cellulose oxygen isotopes in trees that grow in seasonally dry forests of Northern Laos to explore the possibility if this method can be used for the identification of annual rings. One disk from a 7-year-old Styrax tonkinensis (S. tonkinensis) in plantation and two cores from two Ficus semicordata var. semicordata (F. semicordata) in forests were examined. High-resolution cellulose oxygen isotopes of S. tonkinensis and F. semicordata show clear cycles with amplitudes of 5 parts per thousand and 9 parts per thousand, respectively. To further test if the oxygen isotope cycles that we observed are annual or not, a tree ring cellulose oxygen isotope model is employed. Input data of the model are relative humidity and modeled precipitation delta O-18. The modeling results independently support our detection of oxygen isotope annual cycles. Therefore, we conclude that tree ring cellulose oxygen isotopes have great potential to identify annual rings in tropical trees, which typically lack distinct annual rings in the context of seasonal climate.

DOI： 10.2343/geochemj.2.0312

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1002/2013JD019803

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Climate Dynamics  

We develop a summer temperature reconstruction for temperate East Asia based on a network of annual tree-ring chronologies covering the period 800-1989 C.E. The East Asia reconstruction is the regional average of 585 individual grid point summer temperature reconstructions produced using an ensemble version of point-by-point regression. Statistical calibration and validation tests indicate that the regional average possesses sufficient overall skill to allow it to be used to study the causes of temperature variability and change over the region. The reconstruction suggests a moderately warm early medieval epoch (ca. 850-1050 C.E.), followed by generally cooler 'Little Ice Age' conditions (ca. 1350-1880 C.E.) and 20th century warming up to the present time. Since 1990, average temperature has exceeded past warm epochs of comparable duration, but it is not statistically unprecedented. Superposed epoch analysis reveals a volcanic forcing signal in the East Asia summer temperature reconstruction, resulting in pulses of cooler summer conditions that may persist for several years. Substantial uncertainties remain, however, particularly at lower frequencies, thus requiring caution and scientific prudence in the interpretation of this record. © 2012 Springer-Verlag Berlin Heidelberg.

DOI： 10.1007/s00382-012-1611-x

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Palaeogeography, Palaeoclimatology, Palaeoecology  

We present here a chronology of tree ring cellulose δ18O for the period 1588-2002 based on individual measurements of seven Fokienia hodginsii trees growing in northern Laos. Response function analysis of meteorological data revealed that this oxygen isotope chronology has a significant negative correlation with monsoon season precipitation, the water level of the Mekong River, and the Palmer drought severity index (PDSI). Our reconstructed monsoon season PDSI, which accounts for 41.5% of PDSI variance, showed that wetter phases occurred during the periods AD 1660-1695 and AD 1705-1790, that the main drier periods were AD 1630-1660, AD 1900-1940, and AD 1954-2002, and that there has been a trend of decreasing moisture during the monsoon season over the last 200years. A reduction in monsoon activity can also be seen in various tree ring oxygen isotope records from the Himalaya, Tibet Plateau, and Southeast Asia. Rising sea surface temperatures over the tropical Pacific and Indian Ocean could be responsible for this reduction in the Asian summer monsoon. By combining proxies sensitive to the El Niño-Southern Oscillation (ENSO) in northern Laos and Vietnam, we were able to reconstruct the annual multivariate ENSO index (MEI) and local ENSO event history, and so improve our understanding of long-term variations in ENSO and its influences on Southeast Asia. •The long δ18O chronology built just by tree ring oxygen isotopes was robust.•ENSO event history during the last 400years was reconstructed in Southeast Asia.•Reduction of Asian monsoon activity during the last 200years was found. © 2013 Elsevier B.V..

DOI： 10.1016/j.palaeo.2013.06.025

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research Atmospheres  

We developed a 50-year tree ring δ18O chronology for each of three tree species (Juniperus indica, Larix griffithii, and Picea spinulosa) using a total of 12 trees (four trees per species) from the Bhutan Himalaya. Despite originating from different species sampled at two different altitudes, the δ18O chronologies are highly correlated with one another (r = 0.76-0.89). Response analyses reveal that tree ring δ18O values are controlled mainly by summer precipitation, irrespective of species. Based on these results, a robust 269-year δ18O chronology was established to reconstruct the amount of May-September precipitation based on data from four larch trees. Our tree ring δ18O data show significant correlations with those from other regions of the Himalaya and the Tibetan Plateau, indicating that common signals related to monsoon activity are recorded in the data. However, at centennial timescales, our data from Bhutan show normal conditions during the 20th century, whereas records from sites in western Nepal and the southern/eastern Tibetan Plateau show weakening trends in monsoon intensity during the last 100-200 years; the weakening trends may be the result of a reduction in the meridional sea surface temperature gradient in the Indian Ocean during this time. At continental scales, the tree ring records show that areas more from ocean basins are particularly sensitive to reduced monsoon circulation. Correlation analyses suggest that the El Niño-Southern Oscillation (ENSO) plays an important role in modulating summer precipitation. However, the teleconnected relationship disappears during the period 1951-1970, coinciding with a negative phase of the Pacific Decadal Oscillation (PDO), implying interdecadal modulation of the PDO on the influence of the ENSO on precipitation in Bhutan. Key Points Tree ring delta-18O data are strongly correlated among different species No delta-18O trends in Bhutan since 1900 but inland data show reduced rainfall Link between delta-18O data and ENSO disappears when PDO is in negative phase ©2013. American Geophysical Union. All Rights Reserved.

DOI： 10.1002/jgrd.50664

Web of Science

Scopus

記述言語：英語   出版者・発行元：NATURE PUBLISHING GROUP  

DOI： 10.1038/ngeo1834

Web of Science

記述言語：日本語   出版者・発行元：Nature Geoscience  

Past global climate changes had strong regional expression. To elucidate their spatio-temporal pattern, we reconstructed past temperatures for seven continental-scale regions during the past one to two millennia. The most coherent feature in nearly all of the regional temperature reconstructions is a long-term cooling trend, which ended late in the nineteenth century. At multi-decadal to centennial scales, temperature variability shows distinctly different regional patterns, with more similarity within each hemisphere than between them. There were no globally synchronous multi-decadal warm or cold intervals that define a worldwide Medieval Warm Period or Little Ice Age, but all reconstructions show generally cold conditions between ad 1580 and 1880, punctuated in some regions by warm decades during the eighteenth century. The transition to these colder conditions occurred earlier in the Arctic, Europe and Asia than in North America or the Southern Hemisphere regions. Recent warming reversed the long-term cooling; during the period ad 1971-2000, the area-weighted average reconstructed temperature was higher than any other time in nearly 1,400 years.

DOI： 10.1038/NGEO1797

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1177/0959683611430338

Web of Science

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research Atmospheres  

A tree ring δ18O chronology is developed for the past 300years (1705-2004) using 6 cypress trees from northern Vietnam to reconstruct long-term hydroclimatic variations in the summer monsoon season. To the best of our knowledge, this is the first well-replicated tree ring δ18O chronology from Southeast Asia, as well as the longest yet produced. Response analyses reveal that tree ring δ18O is significantly correlated with temperature, precipitation, and the Palmer Drought Severity Index (PDSI) during the period May-October, with highest correlation to the PDSI. Our δ18O chronology accounts for 44% of the PDSI variance, and is in good agreement with a 52-year tree ring δ18O chronology from northern Laos (r=0.77), indicating that regional hydroclimatic signals are well recorded in the δ18O data. Spatial correlation analyses with global sea surface temperatures suggest that the tropical Pacific plays an important role in modulating hydroclimate over the study region. Further, the δ18O chronology correlates significantly with El Nio-Southern Oscillation (ENSO)-related indices, and is therefore used to reconstruct the annual Multivariate ENSO Index. Because previously published ENSO reconstructions are based mainly on proxy records originating from North America and/or the tropical Pacific, the future development of a tree ring δ18O network from mainland Southeast Asia could lead to an independent and more robust reconstruction of ENSO variability. © 2012 American Geophysical Union. All Rights Reserved.

DOI： 10.1029/2012JD017749

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Geophysical Research Atmospheres  

A tree ring cellulose δ18O chronology of Fokienia hodginsii from 1951 to 2002 is established by four cores from four different trees to explore its potential for reconstructing climatic variations in northern Laos. This chronology is the first tree ring δ18O chronology from Laos as well as the first for this species. We compare variations of tree ring cellulose δ18O and ring width between cores. The results suggest that the δ18O time series are more strongly correlated between different trees than ring width time series are. In addition, correlation analysis shows a significantly negative correlation between tree ring cellulose δ18O and the May-October Palmer Drought Severity Index (PDSI), while the tree ring width indices have a poor correlation with PDSI. The spatial correlation analysis between tree ring cellulose δ18O and global sea surface temperature and the time series correlation analysis between tree ring cellulose δ18O and the Multivariate El Niño-Southern Oscillation (ENSO) Index (MEI) during the investigated period (1951-2002) reveal that ENSO has an important effect on tree ring cellulose δ18O in Laos. Our results indicate that the tree ring cellulose δ18O of Fokienia hodginsii is a promising proxy to reconstruct PDSI in Southeast Asian countries, such as Laos, and to discuss their teleconnections with global atmospheric circulations such as ENSO. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2011JD016694

Web of Science

Scopus

記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Forest Research  

We have developed a 247-year ring-width chronology of Betura ermanii Cham. growing in an open canopy forest close to the tree line at a coastal site in southern Kamchatka. Climatic response analyses revealed that the ring width was primarily controlled by July-August temperature. The regression models that we used for statistical reconstruction passed the stringent calibration-verification tests used in dendroclimatology, resulting in the first quality-controlled tree-ring reconstruction for southern Kamchatka. The reconstructed temperature shows a cool period from the 1830s to the 1880s, followed by gradual warming until ca. 1940, then a cooling trend extending to the 1970s, and finally a warming trend continuing to the present. Spatial correlation analyses with sea surface temperature in the North Pacific indicated that the seas surrounding the Kamchatka peninsula play a role in modulating temperature variations in the study area whereas the effects of the Pacific Decadal Oscillation are relatively weak. © 2010 The Japanese Forest Society and Springer.

DOI： 10.1007/s10310-010-0183-z

Web of Science

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1073/pnas.0910827107

Web of Science

PubMed

記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.dendro.2009.05.005

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

We present here the first statistically calibrated and verified tree-ring reconstruction of climate from continental Southeast Asia. The reconstructed variable is March-May (MAM) Palmer Drought Severity Index (PDSI) based on ring widths from 22 trees (42 radial cores) of rare and long-lived conifer, Fokienia hodginsii (Po Mu as locally called) from northern Vietnam. This is the first published tree ring chronology from Vietnam as well as the first for this species. Spanning 535 years, this is the longest cross-dated tree-ring series yet produced from continental Southeast Asia. Response analysis revealed that the annual growth of Fokienia at this site was mostly governed by soil moisture in the pre-monsoon season. The reconstruction passed the calibration-verification tests commonly used in dendroclimatology, and revealed two prominent periods of drought in the mid-eighteenth and late-nineteenth centuries. The former lasted nearly 30 years and was concurrent with a similar drought over northwestern Thailand inferred from teak rings, suggesting a "mega-drought" extending across Indochina in the eighteenth century. Both of our reconstructed droughts are consistent with the periods of warm sea surface temperature (SST) anomalies in the tropical Pacific. Spatial correlation analyses with global SST indicated that ENSO-like anomalies might play a role in modulating droughts over the region, with El Nio (warm) phases resulting in reduced rainfall. However, significant correlation was also seen with SST over the Indian Ocean and the north Pacific, suggesting that ENSO is not the only factor affecting the climate of the area. Spectral analyses revealed significant peaks in the range of 53.9-78.8 years as well as in the ENSO-variability range of 2.0 to 3.2 years.

DOI： 10.1007/s00382-008-0454-y

Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER TOKYO  

We developed a 378-year tree-ring-width chronology based on 110 core samples from 55 individual trees of Larix gmelinii (Rupr.) Rupr. growing in a wide open forest close to the tree line in the Kronotsky National Park. Reflecting strong climatic control over tree growth not only within the study area but also more extensively over central Kamchatka, our chronology was well correlated with those from other larch sites. Response analysis with 10-day mean temperature revealed that the ring width was primarily controlled by the temperature of early summer, i.e., of late May through late June (40 days). While the regression models for a formal reconstruction failed to pass stringent verification tests commonly used in dendroclimatology, the relationship between tree growth and climate was statistically significant and credible. We therefore used our chronology as a proxy of early summer temperature. The chronology shows a cool period from the 1660s until the 1680s, followed by gradual warming until ca. 1800, then by a slight cooling trend extending to ca. 1910, and a warming trend continuing up to the present, with decadal fluctuations throughout the chronology. The warming trend found in our chronology over the twentieth century is generally consistent with the ones commonly appearing in higher latitudes.

DOI： 10.1007/s10310-009-0123-y

Web of Science