Synchronous multi-decadal climate variability of the whole Pacific areas revealed in tree rings since 1567

Oceanic and atmospheric patterns play a crucial role in modulating climate variability from interannual to multi-decadal timescales by causing large-scale co-varying climate changes. The brevity of the existing instrumental records hinders the ability to recognize climate patterns before the industrial era, which can be alleviated using proxies. Unfortunately, proxy based reconstructions of oceanic and atmospheric modes of the past millennia often have modest agreements with each other before the instrumental period, raising questions about the robustness of the reconstructions. To ensure the stability of climate signals in proxy data through time, we first identified tree-ring datasets from distant regions containing coherent variations in Asia and North America, and then interpreted their climate information. We found that the multi-decadal covarying climate patterns of the middle and high latitudinal regions around the northern Pacific Ocean agreed quite well with the climate reconstructions of the tropical and southern Pacific areas. This indicates a synchronous variability at the multi-decadal timescale of the past 430 years for the entire Pacific Ocean. This pattern is closely linked to the dominant mode of the Pacific sea surface temperature (SST) after removing the warming trend. This Pacific multi-decadal SST variability resembles the Interdecadal Pacific Oscillation

An increase in the biogenic aerosol concentration as a contributing factor to the recent wetting trend in Tibetan Plateau

A significant wetting trend since the early 1980s in Tibetan Plateau (TP) is most conspicuous in central and eastern Asia as shown in the instrumental data and the long-term moisture sensitive tree rings. We found that anomalies in the large-scale oceanic and atmospheric circulations do not play a significant role on the wetting trend in TP. Meanwhile, the weak correlation between local temperature and precipitation suggests that the temperature-induced enhancement of the local water cycle cannot fully explain the wetting trend either. This may indicate the presence of nonlinear processes between local temperature and precipitation. We hypothesize that the current warming may enhance the emissions of the biogenic volatile organic compounds (BVOC) that can increase the secondary organic aerosols (SOA), contributing to the precipitation increase. The wetting trend can increase the vegetation cover and cause a positive feedback on the BVOC emissions. Our simulations indicate a significant contribution of increased BVOC emissions to the regional organic aerosol mass and the simulated increase in BVOC emissions is significantly correlated with the wetting trend in TP.Peer reviewe

Clay mineralogy indicates a mildly warm and humid living environment for the Miocene hominoid from the Zhaotong Basin, Yunnan, China

Global and regional environmental changes have influenced the evolutionary processes of hominoid primates, particularly during the Miocene. Recently, a new Lufengpithecus cf. lufengensis hominoid fossil with a late Miocene age of ~6.2 Ma was discovered in the Shuitangba (STB) section of the Zhaotong Basin in Yunnan on the southeast margin of the Tibetan Plateau. To understand the relationship between paleoclimate and hominoid evolution, we have studied sedimentary, clay mineralogy and geochemical proxies for the late Miocene STB section (~16 m thick; ca. 6.7–6.0 Ma). Our results show that Lufengpithecus cf. lufengensis lived in a mildly warm and humid climate in a lacustrine or swamp environment. Comparing mid to late Miocene records from hominoid sites in Yunnan, Siwalik in Pakistan, and tropical Africa we find that ecological shifts from forest to grassland in Siwalik are much later than in tropical Africa, consistent with the disappearance of hominoid fossils. However, no significant vegetation changes are found in Yunnan during the late Miocene, which we suggest is the result of uplift of the Tibetan plateau combined with the Asian monsoon geographically and climatically isolating these regions. The resultant warm and humid conditions in southeastern China offered an important refuge for Miocene hominoids

Increased Variability of Thailand\u27s Chao Phraya River Peak Season Flow and Its Association With ENSO Variability: Evidence From Tree Ring δ\u3csup\u3e18\u3c/sup\u3eO

We present a statistically robust reconstruction of Thailand\u27s Chao Phraya River peak season streamflow (CPRPF) that spans the 202 years from 1804 to 2005 CE. Our reconstruction is based on tree ring δ18O series derived from three Pinus merkusii sites from Laos and Thailand. The regional δ18O index accounts for 57% of the observed variance of CPRPF. Spatial correlation and 21‐year running correlation analyses reveal that CPRPF is greatly influenced by regional precipitation variations associated with the El Niño–Southern Oscillation (ENSO). Periods of enhanced and reduced ENSO activity are associated with strong and weak ENSO‐streamflow correlation, respectively. At the longer timescale, the Pacific Decadal Oscillation (PDO) appears to modulate the ENSO‐streamflow correlations, with the most extreme flood events along the Chao Phraya River occurring during periods of increased frequency of La Niña events that coincide with extended cold phases of the PDO. The CPRPF reconstruction could aid management planning for Thailand\u27s water resources

Temperature reconstructions for the last 1.74-Ma on the eastern Tibetan Plateau based on a novel pollen-based quantitative method

Terrestrial palaeo-temperature data are of great value in improving our understanding of past climate and they provide a basis for evaluating climate simulations. Such data are, however, poorly constrained for long time-scales. In addition to the scarcity of high-quality continuous time-series, finding proxies with a clear response to past temperature changes and developing appropriate reconstruction methods are major challenges. We present a new and robust method – Locally-weighted Weighted-average partial least squares (LW-WAPLS) to reconstruct quantitative temperature changes based on a high-resolution 1.74-Ma pollen record from the Zoige Basin on the eastern Tibetan Plateau, where the vegetation today is mainly controlled by temperature. The reconstructed mean annual (MAT) and warmest month (MTWM) temperatures reveal a general cooling trend with two major shifts at ~1.54 and 0.62 Ma BP, and regular glacial-interglacial variability ranging from ~ − 4 to 2 °C and from 8 to 16 °C, respectively. They indicate ~4–5 °C (MAT) and ~ 5–6 °C (MTWM) magnitudes of glacial-interglacial temperatures. Both statistical and ecological evaluations validate the reliability of the reconstructions. The reconstructions provide important insights into the spatial aspects of long-term terrestrial temperature change. LW-WAPLS shows advantages over both the traditional modern analogue technique and non-linear transfer-function methodologies such as WAPLS for reconstructing the broad-scale climate changes for the Zoige Basin, by combining the strength of both methods. The LW-WAPLS approach potentially provides a robust tool to develop pollen-based climate reconstructions over long time-scales

New paleomagnetic data from the central Tethyan Himalaya refine the size of Greater India during the Campanian

Knowledge of the size of Greater India is critical to deciphering the geodynamic processes of the India-Asia collision, as the size of this landmass primarily determines the amount of continental subduction and crustal shortening. Recently, paleomagnetic data revealed the rapid drift of a Himalayan microcontinent (i.e., the Tibetan Himalaya) during ca. 75–61 Ma, which resulted in a triple-stage India-Asia collision scenario. This scenario implies a relatively small Greater India at 75 Ma (Late Cretaceous), but this hypothesis is only based on one high quality Campanian paleomagnetic pole from the eastern part of the Tethyan Himalaya. Here we report comprehensive petrographic, rock magnetic and paleomagnetic studies on Upper Cretaceous oceanic affinity red beds (CORBs) of the Chuangde Formation from the central part of the Tethyan Himalaya at 83.6°E longitude. These CORBs are characterized by multi-component magnetizations carried dominantly by detrital hematite, which retains a primary remanent magnetization. Accordingly, the high temperature magnetization components (585−690°C) were isolated by high-resolution thermal demagnetization. The new paleomagnetic data provide, after applying an inclination shallowing correction, a Campanian paleopole of 43.3°N/258.3°E, which places the central part of the Tethyan Himalaya at a paleolatitude of 16.7° ± 1.8°S at ca. 75 Ma. Comparison of this paleolatitude with the expected paleolatitude of India, using its apparent polar wander path, shows that the N-S extent of central Greater India was ∼910 km during the middle Campanian. Our paleomagnetic data are in agreement with balanced cross section reconstructions and seismologic interpretations of the India-Asia collision zone and provide additional support for the North India Sea hypothesis. The improved estimate of the size of Greater India has several implications for Indian continental crust behavior and results in an updated reconstruction of the India-Asia collision system in the Campanian

Evolution of vegetation and climate variability on the Tibetan Plateau over the past 1.74 million years

The Tibetan Plateau exerts a major influence on Asian climate, but its long-term environmental history remains largely unknown. We present a detailed record of vegetation and climate changes over the past 1.74 million years in a lake sediment core from the Zoige Basin, eastern Tibetan Plateau. Results show three intervals with different orbital- and millennial-scale features superimposed on a stepwise long-term cooling trend. The interval of 1.74–1.54 million years ago is characterized by an insolation-dominated mode with strong ~20,000-year cyclicity and quasi-absent millennial-scale signal. The interval of 1.54–0.62 million years ago represents a transitional insolation-ice mode marked by ~20,000- and ~40,000-year cycles, with superimposed millennial-scale oscillations. The past 620,000 years are characterized by an ice-driven mode with 100,000-year cyclicity and less frequent millennial-scale variability. A pronounced transition occurred 620,000 years ago, as glacial cycles intensified. These new findings reveal how the interaction of low-latitude insolation and high-latitude ice-volume forcing shaped the evolution of the Tibetan Plateau climate.publishedVersio