Tree-rings stable isotope (δ18O and δ2H) based 368 years long term precipitation reconstruction of South Eastern Kashmir Himalaya.

The hydroclimatic variability in Kashmir Himalaya is influenced by the western disturbances and the Indian Summer Monsoon. To investigate long-term hydroclimatic variability, 368 years tree-ring oxygen and hydrogen isotope ratios (δ18O and δ2H) extending from 1648 to 2015 CE were analysed. These isotopic ratios are calculated using five core samples of Himalayan silver fir (Abies pindrow) collected from the south-eastern region of Kashmir valley. The relationship between the long and short periodicity components of δ18O and δ2H suggested that physiological processes had a minimum effect on the tree-ring stable isotopes in Kashmir Himalaya. The δ18O chronology was developed based on the average of five-individual tree-ring δ18O time series covering the time span of 1648-2015 CE. The climate response analysis revealed the strongest and most significant negative correlation between tree ring δ18O and precipitation amount from the previous year's December to current year's August (D2Apre). The reconstructed D2Apre (D2Arec) explains precipitation variability from 1671 to 2015 CE and is supported by historical and other proxy-based hydroclimatic records. The reconstruction has two distinguishing features: first, it is characterized by stable wet conditions during the last phase of Little Ice Age (LIA) i.e., from 1682 to 1841 CE; and second, the southeast Kashmir Himalaya had experienced drier conditions as compared to recent and historical period with intense pluvial events since 1850. The present reconstruction shows, there have been more extreme dry events than extreme wet events since 1921. A tele-connection is observed between D2Arec and Sea Surface Temperature (SST) of the Westerly region.

The modulation of Pacific Decadal Oscillation on ENSO-East Asian summer monsoon relationship over the past half-millennium.

Monsoon precipitation affects natural and social systems in East Asia, one of the most densely populated regions in the world. Monsoon precipitation variability is strongly influenced by El Niño-Southern Oscillation (ENSO) and may be related to the phase of the Pacific Decadal Oscillation (PDO). However, a collective understanding of the long-term PDO-ENSO-monsoon relationship remains limited because related studies are almost exclusively based on short instrumental records. Although paleoclimate proxies for PDO and ENSO are currently available, there is a lack of high-quality proxies for East Asian summer monsoon (EASM) precipitation. Moreover, the strengthening of the ENSO-EASM relationship since the 1970s has raised the question of anthropogenic impact. Reconstructing EASM precipitation is thus crucial to understanding its variability under natural and anthropogenic forcings. In this study, we addressed these challenges using tree ring oxygen isotopes of red cypress (Chamaecyparis formosensis Matsum), a long-lived endemic tree species in Taiwan. We developed an annual-resolved and well-validated EASM precipitation proxy from 1533 CE to 2011 which explained 49 % of the variance in instrumental precipitation. In comparison with multiple paleoclimate proxies, we revealed that PDO persistently modulated the ENSO-EASM relationship over the past half-millennium. The ENSO-EASM relationship was enhanced during the positive PDO phases and dynamically weakened during the negative PDO phases, notably in the early-17th, 18th, and early to mid-20th centuries. The strengthened relationship since the 1970s concurred with an unusually high PDO and ENSO and fell within its natural variability. Nevertheless, as the amplitude of the PDO is predicted to weaken under warming, the modulation effects may become less predictable.

Delayed warming in Northeast China: Insights from an annual temperature reconstruction based on tree-ring δ18O.

Global warming has had an unprecedented impact on environmental changes and thus human life in mid-high latitude regions. As one of the areas most affected by global warming, Northeast China has suffered from a series of ecological crises, including warming-induced water deficits, permafrost thaw, and extended growing seasons. The change in annual average temperature (annual T) variations in Northeast China since the Industrial Revolution are still not fully understood, mainly because of the lack of long-term instrumental data and high-resolution annual T reconstructions. Here, we present the first annual T reconstruction (r = -0.683, p < .001, n = 60) for 1818-2012 in Northeast China, which may also be the first temperature reconstruction based on tree-ring δ18O in China. The reconstruction is significantly related to temperature variations over mid-high latitude Eurasia and agree (p < .01) with several long-term hydroclimatic reconstructions in the surrounding area. When the internal variability in the reconstruction was high, the decadal to multidecadal cycles were significant. Further analysis found that the reconstruction was mainly affected by the East Asian Summer Monsoon (EASM) and North Atlantic Oscillation (NAO). The reconstruction was significantly negatively correlated with several time series of annual T in the Northern Hemisphere, which showed that there is a substantial difference in annual T between Northeast China and other regions of the Northern Hemisphere. The difference mainly existed before the 1950s. From the 1850s to the 1950s, the annual T in Northeast China decreased slightly. However, extreme warming began in the 1950s in Northeast China, and this warming has been unprecedented during the past two centuries. If the warming trend since the 1950s continues, then it will lead to devastating disasters to forest and permafrost ecosystems in Northeast China.

A 338-year tree-ring oxygen isotope record from Thai teak captures the variations in the Asian summer monsoon system.

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.

Specific response of earlywood and latewood δ18O from the east and west of Mt. Qomolangma to the Indian summer monsoon.

This study reports the earlywood and latewood δ18O time series from two hemlock sites located to the east (EQ) and west (WQ) of Mt. Qomolangma (Everest) in the Himalaya. The latewood δ18O series from both sites were highly consistent, whereas the earlywood δ18O values for the two sites show variations over the investigation period. Climate response analysis revealed that the dominant control on latewood δ18O values at both sites was the precipitation amounts of the middle/peak periods of upstream Indian Summer Monsoon (ISM). However, for EQ- and WQ-Earlywood, the main controls were precipitation amounts during the early and middle phases of the upstream ISM, respectively. The upstream amount effect could have accounted for earlywood and latewood δ18O variance. Combined with moisture transport models, we found that source water incorporated into latewood at both sites was derived mainly from the Bay of Bengal and Arabian Sea during middle/peak ISM precipitation. However, during the early ISM, the high ridges of Mt. Qomolangma may block most of the moisture that originates from the Bay of Bengal, which results in a stronger signal of early ISM being recorded in EQ-Earlywood δ18O. The influence of the ISM on WQ-Earlywood is delayed until the middle ISM.

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.

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.

Evaluation of the effect of the 2011 Tsunami on coastal forests by means of multiple isotopic analyses of tree-rings.

The March 2011 Mega-Tsunami in eastern Japan damaged at different degrees the black pine (Pinus thunbergii) forests along the coast. In order to evaluate the recovery of black pine four years later, tree-ring samples from 9 trees for the period 2002-2014 were analyzed for ring growth and stable isotopes (δ13C, δ15N and δ18O). The results showed that annual tree-ring width decreased approximately 70 % from the year 2011 to 2014 compared to the period previous to the tsunami (2002-2010). The multiple isotopic analyses showed that the reduction in growth was caused by soil salinity that prompted stomatal closure and an abrupt increase of tree-ring δ13C. Sea water deposition in the soil did not affect tree-ring δ18O values. Two years after the tsunami, decreasing tree-ring δ13C values caused by apparently photosynthetic recovery did not translate into radial tree-growth, indicating a possible shift in carbon allocation to foliage and mainly roots as a defense mechanism to sodium toxicity. The dual δ13C-δ18O model explains neither the limited growth nor the subsequent recovery in δ13C. Similarly tree-ring δ15N indicated that there was no difference in nitrogen availability before and after the tsunami, suggesting that nutrients were not a limitation but rather soil salinity.

Seasonal changes of δD and δ18O in tree-ring cellulose of Quercus crispula suggest a change in post-photosynthetic processes during earlywood growth.

Leaf photosynthetic and post-photosynthetic processes modulate the isotope ratios of tree-ring cellulose. Post-photosynthetic processes, such as the remobilization of stored starch in early spring, are important to understanding the mechanisms of xylem formation in tree stems; however, untangling the isotope ratio signals of photosynthetic and post-photosynthetic processes imprinted on tree rings is difficult. Portions of carbon-bound hydrogen and oxygen atoms are exchanged with medium water during post-photosynthetic processes. We investigated the δD and δ18O values of tree-ring cellulose using Quercus crispula Blume trees in two different habitats to evaluate seasonal changes in the exchange rate (f-value) of hydrogen or oxygen with medium water, and examined the associations of the post-photosynthetic processes. Theoretically, if the f-value is constant, δD and δ18O would be positively correlated due to meteorological factors, while variation in the f-value will create a discrepancy and weak correlation between δD and δ18O due to the exchange of carbon-bound hydrogen and oxygen with medium water. The values of δD decreased drastically from earlywood to latewood, while those of δ18O increased to a peak and then decreased toward the latewood. The estimated seasonal f-value was high at the beginning of earlywood and decreased toward the latewood. The post-photosynthetic processes associated with changes in the f-value were the remobilization of stored starch and triose cycling during cellulose synthesis because of the shortage of photo-assimilates in early spring. Although we did not evaluate relevant physiological parameters, the seasonal pattern of δD and δ18O in tree-ring cellulose of Q. crispula was clear, suggesting that the dual isotope (δD and δ18O) approach can be used to reveal the resource allocation mechanisms underlying seasonal xylem formation.

Recent enhancement of central Pacific El Niño variability relative to last eight centuries.

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.

Synchronized Northern Hemisphere climate change and solar magnetic cycles during the Maunder Minimum.

The Maunder Minimum (A.D. 1645-1715) is a useful period to investigate possible sun-climate linkages as sunspots became exceedingly rare and the characteristics of solar cycles were different from those of today. Here, we report annual variations in the oxygen isotopic composition (δ(18)O) of tree-ring cellulose in central Japan during the Maunder Minimum. We were able to explore possible sun-climate connections through high-temporal resolution solar activity (radiocarbon contents; Δ(14)C) and climate (δ(18)O) isotope records derived from annual tree rings. The tree-ring δ(18)O record in Japan shows distinct negative δ(18)O spikes (wetter rainy seasons) coinciding with rapid cooling in Greenland and with decreases in Northern Hemisphere mean temperature at around minima of decadal solar cycles. We have determined that the climate signals in all three records strongly correlate with changes in the polarity of solar dipole magnetic field, suggesting a causal link to galactic cosmic rays (GCRs). These findings are further supported by a comparison between the interannual patterns of tree-ring δ(18)O record and the GCR flux reconstructed by an ice-core (10)Be record. Therefore, the variation of GCR flux associated with the multidecadal cycles of solar magnetic field seem to be causally related to the significant and widespread climate changes at least during the Maunder Minimum.

Behaviors of the "raman spectroscopic signature of life" in single living fission yeast cells under different nutrient, stress, and atmospheric conditions.

Time- and space-resolved Raman spectra of mitochondria in single living fission yeast cells have been measured under various nutrient, stress, and atmospheric conditions. A focus is placed on the behavior of the Raman band located at 1602 cm(-1), which sensitively reflects the metabolic activity in mitochondria and which has been called by us the "Raman spectroscopic signature of life". Addition of nutrients increases the intensity of this band by approximately 1.5 times, confirming its correlation with the metabolic activity in mitochondria. The spectra of cells cultured under 100% N(2), 100% O(2), and N(2)/O(2) (V(N2):V(O2) congruent with approximately = 4:1) atmospheres have been measured for both (16)O(2) and (18)O(2). Yeast cells have been found to lose their metabolic activity after the culture under 100% N(2) and 100% O(2) atmospheres. Cells cultured under a N(2)/(16)O(2) ((16)O(2) = 20%) atmosphere show strong "Raman spectroscopic signature of life". No (18)O isotopic shift has been found for the wavenumber 1602 cm(-1), indicating that the origin of this signature is neither O(2) nor an O-containing small molecule. Addition of H(2)O(2) causes a quick decrease of the "Raman spectroscopic signature of life", followed by the cis-trans isomerization in the unsaturated phospholipid chain. The "Raman spectroscopic signature of life" has thus been proved to be a reliable real-time and in vivo indicator for monitoring the metabolic activity in living cells.