Abstract
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 δ
18
O 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 19
th
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 δ
18
O. However, ENSO influenced the tree-ring δ
18
O 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.
Stable isotopes in tree-ring α-cellulose are valued as environmental proxies and their use is steadily increasing; however, preparation of α-cellulose is a bottleneck in isotope analysis. Recent ...methodological breakthrough for extracting tree-ring α-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 α-cellulose from 1-mm thick tree-ring laths, in combination with fixation sheets to prevent disintegration of freeze-dried α-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 α-cellulose laths preserved distinct anatomical structure, enabling precise separation at the tree-ring boundaries. Once separated from a lath, tree-ring α-cellulose can be weighed directly into silver or tin capsules for analysis. We checked chemical purity of α-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 transform infrared spectrometry and gas chromatography. The average chemical purity of α-cellulose laths from the five species was 94.5%, similar to the chemical purity of α-cellulose prepared with the standard Jayme-Wise method. Both oxygen and carbon isotope values of α-cellulose prepared by the cross-section method also closely matched those prepared by the standard method. We conclude that, by overhauling the method of α-cellulose preparation for tree-ring isotope analysis, we increased throughput of tree-ring oxygen and carbon isotope data without sacrificing sample purity.
•We improved the complete process of α-cellulose extraction from tree rings for isotope analysis in order to enhance its throughput considerably.•Our PTFE case enabled extraction of α-cellulose from tree-ring plates as thin as 0.5–1.0mm.•Fixing freeze-dried cellulose plates onto sheets made handling of fragile cellulose plates easier.•The average purity of α-cellulose prepared with our method was 94.5%, which is similar to the standard method.
We present two new millennium-long tree-ring oxygen isotope chronologies for central and northern Japan, based on 9693 annually resolved measurements of tree-ring oxygen isotopes from 39 unearthed ...samples consisting mainly of Japanese cedar (Cryptomeria japonica). These chronologies were developed through cross-dating of tree-ring widths and δ18O data from multiple samples covering the periods 2349–1009 BCE (1341 yr) and 1412–466 BCE (947 yr) for central and northern Japan, respectively. In combination with our published chronology for central Japan, the tree-ring δ18O dataset currently available covers the past 4354 yr (2349 BCE to 2005 CE), which represents the longest annually resolved tree-ring δ18O dataset for Asia. Furthermore, the high-resolution temporal record of 14C contents independently developed by Sakurai et al. (2020) was reproduced by our 14C measurements of earlywood and latewood in annual rings for the period 667–660 BCE.
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.
The far-reaching impacts of central Pacific El Niño events on global climate differ appreciably from those associated with eastern Pacific El Niño events. Central Pacific El Niño events may become ...more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NIÑO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Niño4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Niño-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies.
Precipitation from June to August is generally used to reflect the East Asian summer monsoon (EASM) variability. However, the principal modes of the EASM rainfall are different between May–June (MJ) ...and July–August due to the seasonal march of East Asian subtropical front. Therefore, it is necessary to study them separately. In this study, we reconstruct a 167-year MJ precipitation time series using tree-ring cellulose δ
18
O that explains 46.9% of the variance in the lower Yangtze River basin, Southeast China, that extends the meteorological data back more than 100 years and makes the precipitation study at decadal scales possible. The decades with 5 or more anomalously dry or wet years are the 1880s, 1890s, and 1910s, and the 1980s and 2000s have only one anomalous year per decade. MJ precipitation shows a significantly negative relationship with absolute Niño 3.4 sea surface temperature, especially during the developing phases of El Niño-Southern Oscillation, indicating that there is less rainfall during El Niño events. However, the relationship is not uniform throughout the period. Further analyses show that it is stronger when the Pacific Decadal Oscillation is in its positive phases.
We present a 100-year oxygen isotope record from teak tree-ring cellulose (δ
18
O), originating from a site in southern Myanmar that preserves the isotopic ratios of the regional wet season’s ...rainfall. Tree-ring δ
18
O correlates strongly with regional rainfall during the months of May to October (
r
= − 0.353,
p
< 0.01). We found the tree-ring δ
18
O had clear signals of the June to September Indian Summer Monsoon (ISM) over the years 1948–1998 (
r
= − 0.53,
p
< 0.01). The δ
18
O 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 δ
18
O 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 δ
18
O 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 δ
18
O of teak. In addition, tree-ring δ
18
O also captures the signal of the Indian Ocean Dipole (IOD).
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.
•South Asian monsoon precipitation and ENSO control the common signal of 24 tree-ring oxygen isotope chronologies across Asia.•Local hydroclimate plays an important role on tree-ring oxygen isotope variations.•Combining multiple tree-ring δ18O records can increase climate signals and enhance the stability of climate signals.
Long‐term records of precipitation in Thailand are necessary to evaluate the robustness of the relationship between El Niño–Southern Oscillation (ENSO) and rainfall. This study presents a tree ...ring‐cellulose oxygen isotope (δ18O) record, based on Pinus merkusii, for the period 1804–1999 in Thailand. Response and spatial correlation analyses reveal that tree ring δ18O is significantly correlated with regional monsoon season (May–October) precipitation. Tree ring δ18O, which explains 50.1% of the variability in regional precipitation, was employed to reconstruct monsoon season rainfall back to 1804. Relatively wet periods occurred in 1809–1821, 1876–1882, 1897–1908, and 1944–1975, while the periods 1825–1850, 1913–1925, and 1979–1997 were relatively dry. During the periods 1854–1930 and 1970–1999, inter‐annual variability of precipitation was modulated by the ENSO. In contrast, the absence of this relationship between 1930 and 1970 might relate to the reduced variance of ENSO.
Tree ring δ18O that is significantly correlated with monsoon season (May–October) precipitation is employed to reconstruct monsoon season rainfall in central Thailand during the period of 1804–1999. Inter‐annual variability of monsoon precipitation was modulated by the El Niño–Southern Oscillation (ENSO), and monsoon–ENSO relationship is related to the variance of ENSO. Spatial correlations between δ18O and May–October precipitation, obtained from the CRU TS4 data set for the period 1901–1999.
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