Tree-ring Cellulose Oxygen Isotope Research Articles

Demonstration of process-based reconstruction of annual temperatures from tree ring oxygen isotope

Forecasting the global warming of the post-industrial period requires knowledge of natural variations in climatic parameters, especially temperature in preceding times. Due to its stable time resolution and known physiochemical formation process, tree ring cellulose isotope datasets have immense potential to yield climatic variability information. The first standardized site-independent temperature reconstruction model from tree-ring cellulose oxygen isotope data is demonstrated here using data from a montane site in the western Himalayas. This model does not require any statistical calibration and can be directly compared with instrumental or modelled data. The resulting temperature amplitude is dependent on moisture availability and this input is needed to modulate the reconstruction. The present work tests the possibility of input of carbon isotope discrimination as a proxy of relative humidity. This input achieved amplitude control but additional frequency components were introduced to the reconstruction.

Irrawaddy River experienced more frequent hydrological drought events with global warming: Evidence from a 400-year tree ring oxygen isotope record

Global temperature fluctuations have significantly impacted regional hydrological cycles. The Irrawaddy River (IR) is the largest river in Myanmar and has an important influence on socioeconomic conditions within its watershed and beyond. However, potential changes to the IR’s hydrological extremes under a future warming climate remain poorly understood. We reconstructed a 400-yr May–July streamflow time series for the IR using tree-ring cellulose oxygen isotopes (δ18O) and compared the variations of the hydrological extremes before and after the onset of global warming. The streamflow reconstruction shows that the IR experienced 65 extreme flood events and 67 extreme drought events during 1617–2017, with 58 extreme drought events occurred after 1850. Extreme drought events in this region have gradually increased and the frequency of extreme droughts has increased significantly since the 1850s. The occurrence of drought events in the last few decades has exceeded the natural variability. Especially, the persistent drought conditions during 2000–2017 are unprecedented compared with the record of the last 400 yr. This increase in drought events is significantly linked to the weakening of the ISM and increasing temperatures, hence the IR may experience more extreme drought events in the future under global warming.

Increased extreme drought events in south–central China since the last century：Evidence from oxygen isotope signatures preserved in tree ring cellulose

Tree-ring cellulose oxygen isotope ratios (δ18O) is a well-established proxy for hydroclimatic conditions in monsoon Asia. We reconstructed June–October relative humidity (RHJ–O) variations from 1808 to 2017, based on tree-ring cellulose δ18O data, which explain 46.2% of the actual RH variance in the Nanyue region, south–central China. Extreme wet events occurred frequently prior to the 1900s, but there have been more extreme dry events since the 1900s, apart from the late 1930s and early 1950s. Periodicity analysis revealed that the reconstructed RHJ–O records show obvious 15–30 years cycles from the 1830–1970s. The multi-decadal signals may reflect the effect of the Pacific Decadal Oscillation (PDO) on hydroclimate. In the positive PDO phase, there is drying in south–central China, which is related to a weaker East Asian summer monsoon (EASM) via the Pacific–Japan teleconnection. The decadal signal has weakened since the 1970s. In addition, the reconstructed RHJ–O record shows strong interannual variations, which may be related to the Central Pacific El Niño–Southern Oscillation (CP ENSO). During extreme CP El Niño events, there is a weaker EASM due to the Pacific–Japan teleconnection, and the study site experienced drought. Our reconstructed moisture record is characterized by a decreasing influence from the PDO and increasing influence from the CP ENSO in recent decades. Moreover, the frequency of CP ENSO events is projected to increase under anthropogenic warming. Consequently, more extreme droughts which are related to CP ENSO events may increase in the south–central China in near future.

Moisture history in the Northeast China since 1750s reconstructed from tree-ring cellulose oxygen isotope

Northeast China has suffered many serious droughts, with loss of agricultural production. A lack of long-term monitoring data has hindered our understanding of drought characteristics and mechanisms. The moisture-related history of the region was investigated by constructing a tree-ring cellulose δ18O chronology for the period 1752–2015 using samples collected from four Korean pine (Pinus koraiensis) trees in eastern NE China. Results indicate that tree-ring δ18O values are significantly correlated with summer (June–September) precipitation, relative humidity, and drought severity. The tree-ring δ18O chronology accounts for 50.7% of the observed variance in summer relative humidity and was used to reconstruct regional relative humidity levels back to 1752. Compared with previous reconstructions of drought-related changes in NE China, the reconstruction reveals more high- and low-frequency variability, with two drought periods during the 1750s–1820s and 1960s–2015, and a wet period during 1820–1960. Regional drying trends is mainly influenced by a weakened East Asia summer monsoon (EASM), with both drought periods being concurrent with high temperatures and a weak EASM. Together with the global warming trend, the increasing temperature and associated precipitation reduction in NE China indicates increasing likelihood of drought for the region in future.

Tree-ring cellulose oxygen isotopes indicate atmospheric aridity in the western Kunlun Mountains

As an important indicator of atmospheric aridity, the vapor pressure deficit (VPD) is being paid increasing attention in global change researches during recent decades. However, available proxy data with the capability to represent VPD is still scarce in the globe. Herein we demonstrated a “hidden” frequency-dependent indication of tree-ring cellulose oxygen isotope (δ18OTRC) to atmospheric aridity in the western Kunlun Mountains, Central Asia. In applying correlation and partial correlation analysis, frequency-dependent climatic drivers triggering the δ18OTRC values were detected. For the raw data with inter-decadal variability, δ18OTRC variations mainly indicated May–August precipitation (Local: r = –0.59, p < 0.001; Moisture source: r = –0.53, p < 0.001), evapotranspiration (ET) (Local: r = –0.57, p < 0.001; Moisture source: r = –0.51, p < 0.001). After a 5-year high-pass filter, the δ18OTRC series revealed highly significant correlation with May–August VPD (Local: r = 0.82, p < 0.001; Moisture source: r = 0.80, p < 0.001). The partial correlation further confirmed the strong linkages with high-frequency VPD when the impact of any additional eco-climatological variable (precipitation, temperature, ET, soil moisture 0–40 cm) was excluded. In contrast, if the effect of May–August VPD was excluded, relationships between δ18OTRC and other variables turned insignificant. Collectively, it was concluded that δ18OTRC from the western Kunlun Mountains may indicate VPD at timescales < 5 years. Our results suggest that frequency-dependent climatic significances should be considered when interpreting multi-process determined δ18OTRC as a climate-proxy.

Tree-ring oxygen isotope across monsoon Asia: Common signal and local influence

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.

Onset and maturation of Asian summer monsoon precipitation reconstructed from intra-annual tree-ring oxygen isotopes from the southeastern Tibetan Plateau

AbstractWe 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 δ18Ocreveals the onset and mature phase of the summer monsoon precipitation in this region. Analysis indicates that the δ18Ocof S1 has the strongest correlation with precipitation during the regional monsoon onset (29–33 pentads, May 21–June 10,r= −0.69), and the δ18Ocvalues for S2, S3, and S4 correlate strongly with June, July, and August precipitation, respectively. Combined δ18Ocof 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 δ18Octo reconstruct the Asian summer monsoon's intraseasonal variations.

Increased drought events in southwest China revealed by tree ring oxygen isotopes and potential role of Indian Ocean Dipole

The highlands in southwestern China experience pronounced fluctuations in the hydroclimate with profound impacts on agriculture and economics. To investigate the drought history of this region beyond instrumental records, a tree ring cellulose oxygen isotope (δ18Oc) chronology was developed for the period 1733–2013 using samples collected from six Larix trees in the low-latitude highlands (LLH) of southwestern China. The analysis revealed that δ18Oc is significantly correlated with the rainy season (May–October) precipitation and relative humidity, as well as drought severity. The δ18Oc chronology accounts for 46% of the observed variance in the rainy season precipitation and it was subsequently used to reconstruct precipitation. The reconstructed precipitation reveals an apparent drying trend since 1840, accompanied by increasingly frequent drought events since 1970. Interdecadal variability is also present, characterized with two distinct wet periods in 1740–1760 and 1800–1900 and two drier periods in 1760–1800 and 1900–2013. On the interannual timescale, the LLH precipitation was modulated collectively by the El Niño–Southern Oscillation (ENSO) and the Indian Ocean dipole (IOD). There appears to be an enhanced precipitation-IOD relationship since 1970 in response to the increase in positive-IOD events, implying an increasing likelihood of drought for the southwest China LLH.

Decreasing Indian summer monsoon on the northern Indian sub-continent during the last 180 years: evidence from five tree-ring cellulose oxygen isotope chronologies

Abstract. 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.

A preliminary study on teak tree ring cellulose δ18O from northwestern Thailand: the potential for developing multiproxy records of Thailand summer monsoon variability

Thailand monsoon is located in the transition zone between the Indian and western North Pacific monsoons. Assuredly, proxy climate data from this area could improve our understanding of the nature of Asian monsoon. Tree rings and stalagmites from this area are two potential materials for high-resolution paleoclimate reconstructions. However, a comprehensive understanding of these multiproxy records is still a challenge. In this study, a 76-year tree ring cellulose oxygen isotope value (δ18O) of a teak tree from northwestern Thailand was developed to test its climatic significance and potential for multiproxy climate reconstruction. The results indicate that the interannual variability of cellulose δ18O can be interpreted as a proxy of rainfall in the early monsoon season (May to July rainfall) as well as a proxy of relative humidity. Comparisons with speleothem proxies from the same locality and tree ring records from wider geographical areas provide a basis for developing a multiproxy approach. The results from a teleconnection analysis reveal that the El Nino-Southern Oscillation (ENSO) is an important climate mode that impacts monsoon rainfall in Thailand. High-quality proxy records covering recent decades are critically important not only to improve proxy data calibrations but also to provide a better understanding of teleconnections within the modern atmosphere. Preliminary findings demonstrated the potential of tree ring stable isotopes from Thai teak to develop multiproxy climate reconstruction.

Early summer precipitation in the lower Yangtze River basin for AD 1845–2011 based on tree-ring cellulose oxygen isotopes

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 δ18O 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 Nino 3.4 sea surface temperature, especially during the developing phases of El Nino-Southern Oscillation, indicating that there is less rainfall during El Nino 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.

Hydroclimate reconstruction in central Japan over the past four centuries from tree-ring cellulose δ18O

The East Asian summer monsoon is an important part of the Earth's climate system that is characterized by variations in the strength and expansion of the summer rain band. Rainfall reconstructions in China have revealed changing patterns of rainfall during the Little Ice Age (LIA), but limited hydroclimate reconstruction around Japan have hindered detailed understanding of physical processes associated with the atmospheric system in the western North Pacific. Here, we report relative humidity variations in the Meiyu/Baiu season from 1600–1959 CE by using tree-ring cellulose oxygen isotopes from central Japan; this is the first record of the LIA from the easternmost regions of the East Asian monsoon domain. Our data suggest that the wettest period occurred around 1780–1880 CE corresponding to the final stage of the LIA. This shift was concurrent with sea surface temperature negative (positive) anomalies around the Philippines (off eastern Japan). We suggest that meridional atmospheric circulation was weak during the last stage of the LIA.

Sampling strategy and climatic implication of tree-ring cellulose oxygen isotopes of Hippophae tibetana and Abies georgei on the southeastern Tibetan Plateau.

The tree-ring cellulose oxygen isotopes (δ18O) for four trees of Hippophae tibetana and four trees of Abies georgei growing in different locations around the terminal moraine in Xincuo from 1951 to 2010 were measured to explore its potential for reconstructing climatic variations in the southeastern Tibetan Plateau. The mean and standard deviation of tree-ring δ18O at different heights do not have significant differences, and there are no significant differences in the mean and standard deviation of tree-ring δ18O between trees near the brook and trees at the top of moraine, indicating that we can collect samples for tree-ring δ18O analysis regardless of sampling heights and that the micro-environment does not affect tree-ring δ18O significantly. The mean inter-series correlations of cellulose δ18O for A. georgei/H. tibetana are 0.84/0.93, and the correlation between δ18O for A. georgei and H. tibetana is 0.92. The good coherence between inter-tree and inter-species cellulose δ18O demonstrates the possibility of using different species to develop a long chronology. Correlation analysis between tree-ring δ18O and climate parameters revealed that δ18O for A. georgei/H. tibetana had negative correlations (r = -0.62/r=-0.69) with relative humidity in July-August, and spatial correlation revealed that δ18O for A. georgei/H. tibetana reflected the regional Standardized Precipitation Evapotranspiration Index (29°-32° N, 88°-98° E). In addition, tree-ring δ18O in Xincuo has a significant correlation with tree-ring δ18O in Bhutan. The results indicate that cellulose δ18O for A. georgei and H. tibetana in Xincuo is a good proxy for the regional hydroclimate.

Negligible local-factor influences on tree ring cellulose δ18O of Qilian juniper in the Animaqing Mountains of the eastern Tibetan Plateau

Tree ring cellulose oxygen isotopes (δ18O) were measured on 21 trees of Qilian juniper from the Animaqing Mountains, Tibetan Plateau, to investigate intra- and inter-tree variability, potential juvenile and elevation effects and climatic implications. There are no significant differences in mean and standard deviation of tree ring δ18O values at different heights in individual trees. Tree ring δ18O values from different directions show a high degree of coherence. The mean and standard deviation for vertical and circumferential δ18O time series are very similar, and δ18O data from different heights and directions are highly correlated (r > 0.88). The δ18O values of young trees are lower than those of old trees in the first 10 years of tree growth. Tree ring δ18O data from five different altitudes are highly correlated (r > 0.88) and share similar climatic signals. As such, an altitude effect on tree ring δ18O is not observed. Our results indicate that samples from one site, regardless of sampling height, direction or altitude, can be used to reconstruct a long-term δ18O record. Tree ring δ18O data from the Animaqing Mountains show a significant negative correlation (r = −0.67; p < 0.001) with May–July regional precipitation and appear to be a promising proxy for precipitation reconstruction.

Reconstruction of soil water oxygen isotope values from tree ring cellulose and its implications for paleoclimate studies

Abstract We present here a rationale for estimation of soil water oxygen isotope values ( δ sw ) from tree ring cellulose oxygen isotope data and examine, for the first time, its ( δ sw ) efficacy as a tool to obtain paleoclimate information. We analyzed pre-dated tree ring cellulose samples collected from a site at Western Himalaya for oxygen isotopes, used similar dataset of overlapping time period from 12 different locations across the world, reconstructed δ sw for 1901–2004 CE, compared the data with available observations and examined implications of this technique. Our study shows (a) good agreement in spatial ranges between observed and estimated δ sw data suggesting its suitability for a representative parameter, and (b) reconstructed δ sw largely depend on soil moisture content modulated by regional evaporation regimes. Considering a growing importance of measurement of recycled soil moisture and its ensuing role in rainfall amount, a method to reconstruct soil moisture isotope as presented in this work will enable application of land hydrological models to the past.

Inter- and intra-annual tree-ring cellulose oxygen isotope variability in response to precipitation in Southeast China

Key message Compared with annual tree-ring cellulose δ18O, intra-annual cellulose δ18O has potential to reconstruct precipitation with higher resolution and stronger signal intensity.

Interpreting species‐specific variation in tree‐ring oxygen isotope ratios among three temperate forest trees

Although considerable variation has been documented in tree-ring cellulose oxygen isotope ratios (δ(18)O(cell)) among co-occurring species, the underlying causes are unknown. Here, we used a combination of field measurements and modelling to investigate the mechanisms behind variations in late-wood δ(18) O(cell) (δ(18)O(lc)) among three co-occurring species (chestnut oak, black oak and pitch pine) in a temperate forest. For two growing seasons, we quantified among-species variation in δ(18)O(lc), as well as several variables that could potentially cause the δ(18)O(lc) variation. Data analysis based on the δ(18) O(cell) model rules out leaf water enrichment (Δ(18)O(lw)) and tree-ring formation period (Δt), but highlights source water δ(18) O (δ(18) O(sw)) as an important driver for the measured difference in δ(18)O(lc) between black and chestnut oak. However, the enriched δ(18)O(lc) in pitch pine relative to the oaks could not be sufficiently explained by consideration of the above three variables only, but rather, we show that differences in the proportion of oxygen exchange during cellulose synthesis (p(ex)) is most likely a key mechanism. Our demonstration of the relevance of some species-specific features (or lack thereof) to δ(18)O(cell) has important implications for isotope based ecophysiological/paleoclimate studies.

Oxygen isotopes as a valuable tool for measuring annual growth in tropical trees that lack distinct annual rings

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‰ and 9‰, 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 δ18O. 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.

Oxygen isotope signatures preserved in tree ring cellulose as a proxy for April–September precipitation in Fujian, the subtropical region of southeast China

AbstractA tree ring cellulose oxygen isotope (δ18O) chronology for the period 1870–2011 was established using samples from four Fokienia hodginsii trees with the aim of exploring the potential to use tree ring δ18O records to reconstruct climatic variations in Fujian, a subtropical region of southeast China. We believe that this is the first tree ring δ18O chronology from this area. Response analysis revealed that tree ring δ18O is significantly correlated with precipitation between April and September, relative humidity between August and October, and the Palmer drought severity index between April and October. Our δ18O chronology accounts for 37.4% (24.6%) of actual variation in precipitation between April and September during the period from 1951 to 2011 (1901 to 2011). Spatial correlation analysis revealed that tree ring cellulose δ18O is a suitable proxy for reconstructing April–September precipitation in Fujian, as well as in parts of Guangdong and Jiangxi, southeast China. In addition, significant correlations between δ18O chronology and the Indian summer monsoon index show that large‐scale atmosphere circulation also influences tree ring δ18O. Comparisons between the tropical Pacific sea surface temperature (SST) and tree ring δ18O, during the period from 1895 to 2009, indicate that the tropical Pacific SST is positively correlated with tree ring δ18O in the study region over the last 110 years, except between 1920 and 1960. Reduced El Niño–Southern Oscillation (ENSO) variance from 1920 to 1960 may result in collapsed relationship between tree ring δ18O in Fujian and tropical Pacific SST.