Humid Regime Research Articles

Petrographic and geochemical signatures of the Upper Permian Gondwana coals: Newcastle Coal Measures, Northern Sydney Basin, Australia

This research presents an integrated approach to organic petrographical and geochemical characteristics of the Upper Permian Newcastle Coal Measures outcropping in the northern Sydney Basin, southeast Australia. Twenty-seven coal, coaly mudstone and mudstone samples were collected and analyzed by using organic petrography (maceral composition and vitrinite reflectance) techniques, Rock–Eval pyrolysis, bitumen extraction and gas chromatography - mass spectrometry (GC–MS). The obtained results indicate that the samples exhibit promising gas-prone source rock potential and contain a predominantly terrestrial in origin organic matter, with limited contribution by marine organisms. The prevalence of terrestrial organic matter is inferred by the presence of collotelinite and sporinite macerals in most of the samples and the ternary plot of C27, C28 and C29 regular steranes. Further, the low C27/C29 ratio, the cross-plots of C27/(C27 + C29) regular steranes vs. Pr/Ph ratio, the C27/C29 vs. Pr/Ph and the C24 tetracyclic/C26 tricyclic terpane ratio point also to the terrestrial origin of the organic matter. The obtained values of vitrinite reflectance, Tmax, OEP27–31 and CPI25–33, along the cross plots of 20S/(20S + 20R) versus ββ/(ββ + αα) suggest that the samples are immature and were subjected to a low burial depth. The examined samples indicate accumulation in a delta-plain environment of deposition, under fluctuating oxic/anoxic conditions, in a humid climatic zone that is characterized by dry periods, interrupting the longer-termed humid climatic regime. This research adds knowledge on the source rock potential in the northern Sydney Basin and on the environmental and climatic setting of a time interval just prior to the major Permian - Triassic climatic crisis.

Humidity-Mediated Dual Ionic-Electronic Conductivity Enables High Sensitivity in MOF Chemiresistors.

In the presence of water, the electrically conductive metal-organic framework (MOF) Cu3HHTT2 (H6HHTT = 2,3,7,8,12,13-hexahydroxy-4b1,5,10,15-tetraazanaphtho[1,2,3-gh]tetraphene) provides a conduit for proton transport, thereby becoming a dual ionic-electronic conductor. Owing to its dual conducting nature and its high density of imine and open metal sites, the MOF operates as a particularly sensitive chemiresistor, whose sensing mechanism changes with relative humidity. Thus, the interaction of NH3 gas with the MOF under low humidity promotes proton transport, which translates to high sensitivity for ammonia detection. Conversely, NO2 gas hinders proton conductivity, even under high relative humidity conditions, leading to large resistance variations in the humid regime. This dual ionic-electronic conduction-based gas sensor provides superior sensitivity compared to other conventional chemiresistors under similar conditions and highlights its potential as a platform for room-temperature gas sensors.

The mineralogy and geochemistry of the Pirashkaft bauxite, Zagros belt, Iran: New inferences on the paleo-climate at the time of formation and on the nature of the parent rock

The Pirashkaft karst type bauxite is located in north of the Paskuhak anticline, Pirashkaft region, in the Fars province (Iran). The deposit is composed of six bauxite horizons, occurring between upper Cretaceous Sarvak and Gurpy Formations, and formed in the late Turonian. Mineralogical composition includes boehmite, hematite, diaspore, kaolinite, goethite, anatase and minor minerals like, gibbsite, spinel, rutile, and kaolinite. The major oxides in the bauxite horizons mainly comprise Al2O3 (46.93–61.34 wt%), SiO2 (5.78–14.60 wt%), Fe2O3 (11.22–28.00 wt%), and TiO2 (1.66–3.03 wt%). The bauxite has a pisolitic–oolitic texture. Pisoids are mainly composed of large Al-bearing hematite cores, surrounded by layers of gibbsite or boehmite. This structure suggests that bauxite formed under a humid climatic regime, punctuated by periodic arid periods. In the Pirashkaft deposit, LREEs vary between 136.49 ppm and 928.56 ppm, whilst HREEs range from 16.48 ppm to 59.5 ppm. Positive anomalies of Ce (Ce/Ce* between 1.08 and 2.36) indicate dominant oxidizing conditions during the bauxitization process. The Eu/Eu* anomalies of the bauxite samples vary between 0.44 and 0.92, this suggesting that parent material likely derived from two geochemically distinct source rocks. Stratigraphical, mineralogical, and geochemical evidences, such as the REE distribution between the bauxitic horizons and the Sarvak marly limestone, suggest that the underlying marly carbonates were one of the sources of the Pirashkaft bauxite.

Determination of complementary irrigation times for rainfed cultivation based on biomass optimization and soil erosion index in Yellow River Valley

Abstract Drought is the most important factor limiting the growth and production of wheat in China. Arid and semi-arid regions and high water consumption in the agricultural sector have led to various deficit irrigation strategies. The effect of the hydrological process on yield production has been evaluated in rainfed cultivation of wheat for the three climatic stations of Gansu Province, Yellow River Valley, China. A general framework was provided for rainfed cultivation of wheat in arid and semi-arid regions. Moreover, the best time and amount of complementary irrigation and its effect on increasing yield production have been evaluated using grey wolf optimization algorithm. The results showed that rainfed cultivation of wheat in a humid regime could be suggested without complementary irrigation. Conducting two complementary irrigations in semi-humid regime can increase the final yield of wheat by more than 150 kg/ha. The maximum yields in sustainable management were obtained 4,844, 4,510, and 4,408 kg/ha for Longnan, Tianshui, and Dingxi, respectively.

Precipitation Conditions Constrain the Sensitivity of Aboveground Net Primary Productivity in Tibetan Plateau Grasslands to Climate Change

Continued climate warming and precipitation fluctuations are expected to further affect aboveground net primary productivity (ANPP) across alpine grasslands, with associated implications for ecosystem functions. The spatial and temporal variability of ANPP in Tibetan Plateau (TP) grasslands and its response to temperature and precipitation were investigated in this study, based on the ANPP estimated by means of ensemble analysis of multiple machine learning models. First, the response of the spatial distribution of ANPP to variations in the precipitation gradient was nonlinear and showed an S-shaped growth pattern, which could be divided into four stages (stationary, rapid growth, slower growth, and saturation) corresponding to arid (mean annual precipitation (MAP) < 250 mm), semiarid (250 mm < MAP < 450 mm), semihumid (450 mm < MAP < 650 mm) and humid (MAP > 650 mm) precipitation regimes, respectively. Second, regional precipitation regimes affected the sensitivity of ANPP’s interannual variability to temperature and precipitation; ANPP is more sensitive to temperature in wetter areas than in dryer areas of the TP region. The results of our study suggest that in the region of Tibetan Plateau, the response of grassland ANPP variation to climate was constrained by the background precipitation regimes.

Ferns from the Arroyo Chacay flora (Huitrera Formation, Eocene) Río Negro Province, Argentina

During the Eocene, a mixed paleoflora containing austral-gondwanan and neotropical elements was established in northern Patagonia. Fossils preserving these assemblages have been recovered from the Huitrera Formation, at well-known localities as Laguna del Hunco, Pichileufu, Confluencia, Pampa de Jones and Arroyo Chacay, and show a diverse assemblage of angiosperms and conifers. The pteridophytic element, while present, is less known for these fossil floras. In this contribution, seven fern taxa based on fertile and sterile leaf compressions are described from the Huitrera Formation in the Arroyo Chacay locality. Several fern families are identified, as Osmundaceae (cf. Osmunda and Todea amissa M. Carvalho), a putative Thyrsopteridaceae (“Dicksonia” patagonica Berry), Blechnaceae (cf. Parablechnum), and Aspleniaceae (cf. Asplenium). Additionally, a taxon of unknown affinities, referred to the fossil genus Cladophlebis, is also recorded. These elements add to the total known diversity of ferns in the locality, previously represented by the Eupolypod Tapelrayen helgae M.A.Machado, E.I.Vera, Passalia et Ponce and Eupolypod incertae sedis, and the thelypteridaceous Cyclosorus sp. cf. C. interruptus. It is worth mentioning that two of the recorded taxa, T. amissa and “Dicksonia” patagonica, have been previously identified in the Huitrera Formation at other localities (Laguna del Hunco and Pichileufu, respectively), while the remaining identified taxa are new for the unit. Using the nearest living relative approach to infer ecological requirements of the recovered fossil ferns and evaluate climatic conditions supports a temperate to warm and humid regime in northern Patagonia during the Eocene, as previously postulated.

Using Holocene paleo-fire records to estimate carbon stock vulnerabilities in Hudson Bay Lowlands peatlands

Holocene fire records from charcoal are critical to understand linkages between regional climate and fire regime and to create effective fire management plans. The Hudson Bay Lowlands (HBL) of Canada is one of the largest continuous peatland complexes in the world and is predicted to be increasingly impacted by wildfire. We present three charcoal records from a bog in the western HBL and demonstrate that median fire frequency was higher in the Middle Holocene, related to warmer regional temperatures and higher evaporative demand. Holocene fire frequencies are lower than in western Canadian peatlands, supporting that the HBL lies in the transition between continental and humid boreal fire regimes. Apparent carbon accumulation rates at the site were not significantly different between the Middle and Late Holocene, suggesting that higher fire frequency and enhanced decomposition offset the potential for higher rates of biomass production. We compile records from the boreal region and demonstrate that increasing fire frequency is significantly correlated with diminishing long-term carbon accumulation rates, despite large variation in response of peatlands to fire frequency changes. Therefore, the paleo-record supports that higher fire frequencies will likely weaken the capacity of some northern peatlands to be net carbon sinks in the future.

Evolution of terminal fans in the Indo-Gangetic foreland basin: A process-response model

The present and paleo-drainage networks, depositional surfaces, fault throw, slope of the downthrown fault blocks, soil properties, sediment characteristics and published optically stimulated luminescence (OSL) ages are used to define the role of tectonics and climate in the growth of forty-five terminal fans (TFs) in the Indo-Gangetic foreland basin. Twenty-three TFs show a single exposed surface throughout, suggesting no or imperceptible breaks in sedimentation during their formation. In contrast, twenty-two TFs show multiple growth surfaces, separated by soil profiles and erosional surfaces. The available optically stimulated luminescence (OSL) dates of these depositional surfaces suggest different phases of TF growth.Tectonically triggered surface faulting altered accommodation space, slope of the substrate, and sediment supply and initiated new TF depositional cycles. The tectonically stable periods, in contrast, did not form TFs, despite the favourable humid climate conditions. Instead, the dry and humid climatic regimes, when combined with frequent surface faulting, produced and remobilized sediments more quickly, promoting TF growth. The humid climate TFs are spatially extensive (average area = 2000 km2), with clay horizons interspersed between sand facies. The dry climates TFs are smaller (average area = 1370 km2), with intervening calcrete horizons and surface salt-efflorescence. Low precipitation and inadequate sediment supply hampered the growth of these dry climate TFs. Despite a considerable period of surface exposure, the surfaces of dry climate TFs lack a well-developed soil profile.The upper Ganga Plain provides more accommodation space across the faults than the middle Ganga Plain. Accommodation space and substrate slope have little effect on TF area unless climatically triggered sediment remobilization occurs. For a given accommodation space and substrate slope, steeper sloping TFs occupy less area than lower sloping ones. Faults with throws of <5 m and substrate slopes of <2° do not form TFs; instead sediment wedges are formed across fault slope breaks.The TFs in the upper Ganga Plain show more growth surfaces than the middle Ganga Plain. The older growth surfaces are either progressively arranged across the direction of channel shift or occur as inliers in between the younger alluvium. Well-developed distributaries on the older TFs disperse sediment more readily, rather than accumulating it in proximal fan regions. However, the younger TFs, with relatively less-developed distributary channel networks, vertically stack sediments in their proximal part and occasionally transport sediment as sheet floods to their distal end regions. The combined geomorphic response of TFs to tectonic events and climatic fluctuations is, therefore, simultaneous for TF growth and stabilization.

Age, depositional history, and paleoclimatic setting of Early Cretaceous dinosaur assemblages from the Sao Khua Formation (Khorat Group), Thailand

We describe the sedimentology, geochronology, and geochemistry of the Early Cretaceus Sao Khua Formation of the Khorat Basin, northeastern Thailand, and report a temporal range adjustment for its dinosaurian assemblage. Facies analysis and architectural studies reveal that sedimentation occurred within a floodplain setting fed by large meandering bedload-rich channels. Interfluve areas comprised freshwater lakes and emergent areas subject to pedogenic modification. Multiple paleosol types are identified and geochemistry is indicative of a stable humid subtropical climate regime. Based on radiometric dating of detrital zircons (via LA-ICP-MS), we interpret that the middle part of the Sao Khua Formation was deposited no later than 133.8 (±1.8) Ma (late Valanginian), and grain ages collected from the overlying lowermost Phu Phan Fm constrain sedimentation of the upper part of the Sao Khua Formation to no earlier than 132.4 (±2.0) Ma (early Hauterivian). In consideration of the Early Cretaceous regional tectonic framework, we interpret that youthful igneous zircon grains are derived from the adjacent South China-Vietnam South Borneo Volcanic Arc. We establish that the entombed dinosaur biota (including members of the Ornithomimosauria, Spinosauridae, Megaraptora, and Somphospondylia) is ~5–9 million years older than previously recognized and that these records are among the oldest known globally for these clades. Constraining the age of the Sao Khua Formation indicates that the shift from sauropod-dominated, ornithischian depauperate ecosystems of the Sao Khua Formation to iguanodontian-rich ecosystems of the Khok Kruat Formation occurred sometime between the early Hauterivian and Aptian on the Khorat Plateau.

Global Flash Drought Analysis: Uncertainties From Indicators and Datasets

AbstractFlash Drought (FD) has garnered much attention in recent years, with significant advancements in the indicators applied for identifying these rapidly intensifying events. However, the difference in existing FD definitions and methodologies among research communities and the choice of different data sources underscores the importance of addressing the uncertainties associated with the global FD characteristics and their drivers. This study compares two key FD indicators derived based on evaporative stress ratio (ESR) and root‐zone soil‐moisture (RZSM) using three different data sources to investigate the uncertainties in global FD frequency and intensity (speed), and the influencing drivers. The results suggest that such disparities are significant in the two FD indicators across different climate regions of the globe. The results highlight varying spatial drivers of FD frequency, intensity, and their evolution, potentially linked to background aridity. Changes in precipitation, temperature, vapor pressure deficit, and soil‐temperature coupling play an important role with a cascading (concurrent) impact on the evolution of FD based on RZSM (ESR). The relationship between ESR and RZSM fails to explain most of the variance in each of these indicators specific to the FD episodes, especially in the transitional and humid climate regimes. Overall, the results highlight the necessity of more nuanced methodologies for deriving FD indicators that can efficiently couple the rapid soil‐moisture depletion rates in deeper layers with changes in atmospheric evaporative demand which has direct implications on vegetation health.

Improved spring temperature reconstruction using earlywood blue intensity in southeastern China

AbstractBecause instrumental observations are too short to fully represent long‐term natural variability, high‐resolution temperature proxy records are essential to understanding past climate and assessing current climate variability in the context of long‐term patterns. In the subtropics, progress in this field has been hampered by a relative lack of long and truly temperature‐sensitive proxy records. In this study, we provide an assessment of the dendroclimatic potential of blue intensity (BI) and ring‐width (RW) measurements from two hot/humid Pinus massoniana sites in China. Our results show that RW exhibits a significant (p &lt; .05) response to precipitation over a hydrological year (previous November to October) and to temperature over the winter–spring season (January to March). We find the earlywood blue intensity parameter to be the most robust parameter for reconstruction purposes; over the 1916–2015 period, it explains 36% of regional‐scale spring season (March–May) temperature variance. Strong agreements between the current reconstruction and observed temperature over a large area of southeastern China implied that our reconstruction exhibited high reliability and large spatial representation. As expected, our reconstructed temperature data are directly correlated with El Niño–Southern Oscillation. These results suggest that there is great potential to use BI to advance our understanding of temperature variability in regions hot and humid climate regimes. However, more studies are needed to understand (1) which subtropical tree species will be appropriate for use and (2) how to overcome biases from differential staining between sapwood and heartwood.

A Multivariate Flash Drought Indicator for Identifying Global Hotspots and Associated Climate Controls

AbstractThe significant impact of flash droughts (FDs) on society can vary based on a combination of FD characteristics (event counts, mean severity, and rate of intensification), which is largely unexplored. We employed root‐zone soil‐moisture for 1980–2018 to calculate the FD characteristics and integrated them to formulate a novel multivariate FD indicator for mapping the global FD hotspot regions. The potential influence of climate characteristics (i.e., anomalies, aridity, and evaporative fractions) and land‐climate feedbacks on the evolution of multivariate FD indicator is investigated. Our results indicate that precipitation is the primary driver of FD evolution, while the effect of temperature, vapor pressure deficit, and land‐climate interaction varies across the climate divisions after the onset of the events. The magnitude of multivariate FD indicator decreases with increased climate aridity, and it is significant in the global humid regimes, underscoring the importance of water and energy supply as limiting factors regulating FD‐risk.

A Review of two Middle Jurassic Theropod Tracksites Discovered in the 1980s from Sichuan Basin

Tracks from two sites in the Middle Jurassic Xintiangou Formation in the Wuma Village area, Wuhuang Township, Zizhong have been known and intermittently studied and excavated since the 1980s. The track-bearing surfaces were exposed by a combination of natural weathering and deliberate excavation by residents in a rural agricultural area. The surfaces were used as “threshing floors” for the processing of agricultural crops in an area subject to weathering under a humid sub-tropical climatic regime. Despite the negative effects of weathering on the quality of track preservation, the sites are historically significant in Chinese ichnology as the type areas for many controversially named theropod ichnotaxa. Subsequent researchers challenged the ichnotaxonomy as provincial and over-split, suggesting that many of the tracks, belong to well-known Lower Jurassic ichnogenera. The present study reviews these two sites, providing new information, and confirming that the tracks belong to the ichnogenera Grallator, Eubrontes and Kayentpus which are typical of the globally widespread Lower Jurassic tetrapod biochron. This suggests the Middle Jurassic ichnofauna in Sichuan is like Lower Jurassic ichnofaunas elsewhere. Previous efforts to transfer the ichnospecies to globally, better-known ichnogenera were important in reducing ichnogenus diversity, but did not reduce ichnosepcies diversity. Herein the ichnotaxa are reviewed and it is shown that the ichnospecies names have no utility for comparative study or in assessing assemblage diversity, or biochron composition. It is therefore proposed that the multiple ichnospecies names proposed based on tracks from these two localities can mostly be accommodated under the labels Grallator isp. indet., and Eubrontes isp. indet.

Latest Cretaceous (Maastrichtian) climate of the Koryak Upland of North-East Russia based on a quantitative analysis of a palaeo-polar flora

We describe fossil plant assemblages from the late Maastrichtian Kakanaut Formation of the Koryak Upland, North-East of Russia, which represent a high (75oN) palaeolatitude flora. The flora contains about 40 species, including liverworts, horsetails, ferns, cycadophytes, ginkgos, conifers and angiosperms. Angiosperms and conifers predominate and, unusually, the flora contains typical Cretaceous taxa admixed with elements that are more characteristic of the Paleocene. Reconstruction of the palaeoclimate in the Kakanaut area was made using the Climate Leaf Analysis Multivariate Program (CLAMP) employing a recently developed calibration that yields 23 different climate variables. Analysis was made based on 21 morphotypes of woody dicotyledonous plants from the Kakanaut flora. The analysis indicated a mean annual temperature of 12.2 ± 2.0 °C, a warmest month mean temperature of 20.6 ± 2.5 °C, a coldest month mean temperature of 4.8 ± 3.2 °C. The growing season lasted approximately 7 months, during which there was almost 1 m of precipitation. This and other indicators (relative humidity, vapour pressure deficit and potential evapotranspiration) all suggest a year-round humid regime. The winter temperatures suggest occasional mild frosts in this near sea level setting, so that at higher elevations freezing conditions would have been more persistent. These results throw new light on the living and breeding conditions of diverse latest Cretaceous Arctic dinosaur populations as represented by numerous skeletal and egg remains associated with the plants.

Using Blue Intensity from drought-sensitive Pinus sylvestris in Fennoscandia to improve reconstruction of past hydroclimate variability

High-resolution hydroclimate proxy records are essential for distinguishing natural hydroclimate variability from possible anthropogenically-forced changes, since instrumental precipitation observations are too short to represent the whole spectrum of natural variability. In Northern Europe, progress in this field has been hampered by a relative lack of long and truly moisture-sensitive proxy records. In this study, we provide the first assessment of the dendroclimatic potential of Blue Intensity (BI) and partial ring-width measurements (latewood and earlywood width series) from a network of cold and drought-prone Pinus sylvestris L. sites in Sweden. Our results show that all tree-ring parameters and sites share a clear and strong sensitivity to warm-season precipitation. The ΔBI parameter, in particular, shows considerable potential for hydroclimate reconstructions, here permitting a cross-validated precipitation reconstruction capable of explaining 56% (1901–2010 period) of regional-scale warm-season high-frequency precipitation variance. Using ΔBI as an alternative to ring-width improves the predictive skill with nearly a 20 percentage points increase in explained variance, reduces signal instability over time as well as allows a broader seasonal window (May–July) to be reconstructed. Additionally, we found that earlywood BI also reflect a positive late winter through early summer temperature signal. These findings emphasize that tree-rings, and in particular wood density parameters such as from BI, are capable of providing fundamental information to advance our understanding of hydroclimate variability in regions with a cool and rather humid climate regime that traditionally has been overlooked in studies of past droughts. Increasing the spatio-temporal coverage of hydroclimate records in northern Europe, and taking full advantage of the opportunities offered by the wood densitometric properties should be considered a research priority.

Гидротермические особенности биотопов степной и лесной растительности Приокско-Террасного заповедника

The growth of steppe plant species (so called “Oka flora” in the Prioksko-Terrasny Reserve) in the forest zone is a botanical phenomenon. To understand the mechanisms of such biogeographic anomalies’ formation, comparative studies of steppe communities’ habitats and zonal forest vegetation are important. In the article, for the first time on the original experimental material, an assessment of the humidity and hydrothermal regime of steppe communities’ habitat, its difference from biotopes of neighboring meadow and forest ecosystems, within the alien zone has been carried out. It is shown that the biotope of steppe vegetation has distinct differences from biotopes of other vegetation types of the reserve. The humid regime of meadow-steppe associations and the neighboring pine forest during the growing season is determined only by atmospheric precipitation, in contrast to the biotopes of other types of vegetation, in which the influence of upper water is noticeable. The most significant influence of the upper water was observed on the middle terraces of the Oka River (Rodnikovaya Polyana). Steppe vegetation of the Doly tract is formed in conditions of a “temperature trap” and lack of moisture during critical periods of spring and early autumn. The increase in summer temperatures and the duration of the summer period in the Moscow oblast’s southern part, as well as repeated droughts in the second half of summer and early autumn contribute to the preservation and expansion of the steppe area in the south of Moscow oblast.

Chlorite weathering linked to magnetic enhancement in Red Clay on the Chinese Loess Plateau

Magnetic parameters are widely used in the loess-palaeosol sequence tracing Quaternary climate change on the Chinese Loess Plateau (CLP). However, the climatic implication and magnetic enhancement mechanism in aeolian Red Clay on the CLP is still debated. Chlorite is a common Fe-bearing silicate in Red Clay and it is easily to be weathered. The transformation of weakly magnetic ferrihydrite, a product in chlorite weathering process, into strongly magnetic iron oxides has been linked to magnetic enhancement in many soils. Here, we present a complete chlorite weathering record within the Red Clay sequence through a detailed mineralogical investigation, from a 125-m thick eolian Red Clay deposit in the Chaona section (~8.1 to 2.6 Ma) of the central CLP to explore the link between changes in chlorite geochemical composition and magnetic susceptibility enhancement and regional climate. The results suggest a concomitant evolution of chlorite Fe content and magnetic susceptibility, indicating that Fe released from chlorite brucite-like interlayers, which induced ferrihydrite formation, is responsible for the enhanced magnetic susceptibility in the CLP Red Clay deposits. Moreover, the results also show that the chlorite Fe content exhibited a stepwise decrease, with two accelerated stages at ~6.2 Ma and ~3.6 Ma. The post-6.2 Ma evolution of chlorite Fe content is related to increased precipitation caused by phased enhancement of the East Asian summer monsoon (EASM). Our study also suggests that changes in chlorite chemical composition and crystallinity linked to soil weathering are useful proxies in tracing past weathering intensity and climate change within arid-less humid regime.

Stochastic projection of precipitation and wet and dry spells over Pakistan using IPCC AR5 based AOGCMs

Abstract Stochastic projections of precipitation amount, number of wet days and precipitation per wetday from 25 IPCC AR5 based AOGCMs under RCP4.5 and RCP8.5 are carried out in all climate regimes of Pakistan. In arid climate regime, the ensemble average annual precipitation is projected to decrease by about 5.56%, 3.43%, 4.94% during 2011–2030 (T1), 2046–2065 (T2), 2080–2099 (T3), relative to baseline period (TB) respectively, under RCP4.5, whereas average annual precipitation in semi-arid (humid) climate regime, is projected to increase by about 8.40% and 8.02% (2.12% and 2.61%) during T2 and T3, relative to TB, respectively. Under RCP8.5, the average annual precipitation is projected to decrease in arid climate regime during T1 and increase in semi-arid and humid climate regimes during T2 and T3, relative to TB. There is a projected increase (decrease) in precipitation during T2 (T3) in all climate regimes, relative to T1. Under RCP4.5 (RCP8.5), precipitation on wetdays in arid climate regime is projected to be 7.84 (7.64), in semi-arid climate regime it is projected to be 10.78 (10.96) and in humid climate regime it is projected to be 13.67 (13.95) mm wetday−1, during T1. During T2, precipitation per wet day in arid climate regime is projected to be 7.86 (7.83), in semi-arid climate regime it is projected to be 11.32 (11.55), and in humid climate regime it is projected to be 14.40 (14.73) mm wetday−1 under RCP4.5 (RCP8.5). Overall, under both RCPs, the average annual precipitation and number of wetdays in Pakistan are projected to progressively decrease, whereas precipitation per wetday in Pakistan is projected to progressively increase, all relative to TB.

Geochemical characteristics of Early Cretaceous marine oil shale from the Changshe Mountain area in the northern Qiangtang Basin, Tibet: Implications for palaeoweathering, provenance, tectonic setting, and organic matter accumulation

The Early Cretaceous Shengli River–Changshe Mountain marine oil shale belt, located in the northern Qiangtang Basin, Tibet, is estimated to be the largest marine oil shale resource in China. However, its palaeoweathering, provenance, and tectonic setting during the depositional history have received little interest. In this paper, 19 outcrop marine oil shale samples from the ChangsheMountain (CSM) area were studied to investigate the provenance, palaeoclimate, palaeoweathering, and tectonic setting during the marine oil shale deposition. The total organic carbon and organic sulphur contents of the CSM oil shales range from 2.2% to 13.44% and 0.19% to 1.08%, respectively. The CSM oil shale samples contain abundant carbonate (e.g., calcite and dolomite), quartz, and clay minerals. The clay minerals of the CSM oil shale samples is dominated by illite and then by smectite. Other minerals, including haematite, apatite, pyrite, baryte, and celestite, were also identified by scanning electron microscope–energy‐dispersive X‐ray spectrometer. The total rare earth element (∑REE) contents of the oil shales range from 9.01 to 105.96 ppm (average 57.56 ppm), close to the average REE contents of U.S. coals. The REE contents in oil shale samples are mainly controlled by terrigenous input. The CSM oil shales show LREE‐enriched, HREE‐depleted, with the LREE/HREE ratios ranging from 5.12 to 10.18, negative Eu anomalies (0.56–0.84) and slightly negative Ce anomalies (0.87–1.05). The chemical index of alteration values of the CSM oil shales range from 67 to 76 (average 73), indicating a moderate chemical weathering condition. Sr/Cu and Rb/Sr ratios suggest the CSM oil shales were mainly deposited under a warm and humid climate regime. Sr/Ba ratios, ranging from 0.54 to 7.84, suggest a palaeoenvironment with fluctuant salinity. Major element, trace element, and REE relationships indicate that the CSM oil shales are mainly from the felsic and intermediate igneous rocks. The REE distribution patterns of the CSM oil shales are similar to the Late Triassic Nadi Kangri felsic volcanic rocks in the Qiangtang Basin, indicating that the CSM oil shale may be derived from the Late Triassic volcanic rocks and the oil shales were mainly formed in rift tectonic setting. Favourable preservation condition (e.g., warmer palaeoclimate, higher palaeosalinity, and dysoxic to anoxic water column environment) could be the main controlling factor for organic matter accumulation.

The changing role of fire in conifer-dominated temperate rainforest through the last 14,000 years

Climate, fire and vegetation dynamics are often tightly coupled through time. Here, we use a 14 kyr sedimentary charcoal and pollen record from Lake Osborne, Tasmania, Australia, to explore how this relationship changes under varying climatic regimes within a temperate rainforest ecosystem. Superposed epoch analysis reveals a significant relationship between fire and vegetation change throughout the Holocene at our site. Our data indicates an initial resilience of the rainforest system to fire under a stable cool and humid climate regime between ca. 12–6 ka. In contrast, fires that occurred after 6 ka, under an increasingly variable climate regime wrought by the onset of the El Niño-Southern Oscillation (ENSO), resulted in a series of changes within the local rainforest vegetation that culminated in the replacement of rainforest by fire-promoted Eucalypt forest. We suggest that an increasingly variable ENSO-influenced climate regime inhibited rainforest recovery from fire because of slower growth, reduced fecundity and increased fire frequency, thus contributing to the eventual collapse of the rainforest system.