Global and Planetary Change最新文献

Based on the Shidi-1 drill core, this paper presents new and highly time resolved carbon isotope data (δ¹³C_carb) for the Early Ordovician through Early Silurian of the Yangtze Platform, South China. Five carbon isotopic shifts (C1-C5) through the late Tremadocian to the Katian have been recognized in the Shidi-1 drill core recordings. Together with previously published isotope data, a composite carbon isotope curve for the Yangtze platform, permits the identification of a continuous Ordovician carbon isotope trend with five prominent carbon isotope shifts; including the TSICE, the Late Tremadocian positive Isotopic Carbon Excursion (LTICE, named herein), the Late Floian Rise, the MDICE and the Pagoda Isotopic Carbon Excursion (PICE, named herein). The identification and documentation of these anomalies further strengthen the regional and global correlation of the Ordovician succession on the Yangtze platform. The long-term trend in carbon isotopes indicates that organic carbon burial increased gradually throughout the Great Biodiversification Event (GOBE). A tipping point is also marked by the Dapingian-Darriwilian border, which is followed by a notable shift in the environment and creatures in the middle Darriwilian.

The oceanic oxygenation from the Ediacaran to the early Cambrian (ca. 635–520 Ma) has been commonly linked with the radiation or innovation of early metazoans. However, in this period, the spatio-temporal changes in redox states have not been well constrained for shallow seawater that is proposed to be potential habitats for most metazoans. Here, we report new iodine (I) concentration and Cerium anomaly (Ce/Ce*) data from two Ediacaran–Cambrian carbonate successions in South China. Combined with published data, the new database provides more insights into the evolution of shallow-water redox states on the continental margin. Overall low I/(Ca + Mg) (0.07–1.092 μmol/mol) and high Ce/Ce* (0.64–0.91) indicate frequent presence of low oxygen waters on the Yangtze margin in the early-middle Ediacaran (ca. 635–575 Ma). The initial increases of shallow-water oxygen levels occur from the middle Ediacaran (< ca. 575 Ma), coincident with the rise of the Ediacara biota. However, large variabilities of I/(Ca + Mg) (0.003–4.53) and Ce/Ce* (0.1–0.92) through different sections from the late Ediacaran to the early Cambrian (ca. 575–520 Ma) suggest highly dynamic redox states on both spatial and temporal scales before the Cambrian explosion in a narrow sense. The new I/(Ca + Mg) and Ce/Ce* data bolster the case that the Ediacaran–Cambrian oceans have much lower oxygenation levels than recent fully oxygenated oceans, and frequent redox fluctuations in habitats may have stimulated the early animal innovations.

Methane seepage has been extensively observed in various continental margin settings. It has profound effects on the marine redox environment and the molybdenum (Mo) cycles in marine sediments. Therefore, there has been much recent attention on the redox-sensitive behavior of Mo in methane seepage environments. However, the characteristics of the Mo isotope composition in the cold-seep system remain poorly understood. In this study, we performed geochemical analyses, including Mo content and isotope composition, on sediment samples (core QDN-MS6) from the “Haima” cold-seep deposit area in the South China Sea. The analysis reveals a significant concentration of authigenic pyrite in the mid-section of QDN-MS6 core (373–403 cm). Moreover, the δ³⁴S value in this interval is notably elevated with high total sulfur/total organic carbon ratio. Additionally, the sediments in the mid-section exhibits substantial enrichment in Mo (enrichment factors of Mo ranging from 5.29 to 39.32). This implies that the sediments in the mid-section are influenced by sulfate-driven anaerobic oxidation of methane. Most notably, the sediments in the mid-section displayed distinct low δ⁹⁸Mo values (with an average of −0.7‰). After careful consideration, we ruled out the influence of organic matter, an oxic environment, a weakly sulfidic environment, and incomplete removal of thiopolybdate as contributing factors. Based on δ⁵⁶Fe-Fe/Al ratios, (Mo–U) enrichment factors, and As enrichment factors, we propose that the “benthic Fe-Mn redox shuttle process” is the primary cause of the observed light δ⁹⁸Mo signatures in sediments. This newly identified mechanism sheds light on Mo isotope cycling in methane seepage environments and enhances our understanding of the Mo isotope cycling process.

In this study, we employ biological, geochemical and mineral, and physical proxies to quantitatively and semi-quantitatively reconstruct regional paleoclimate variations in China over the past ∼21 thousand years (ka). We have constructed state-of-the-art transfer functions between proxies and climatic variables in East Asia, revealing substantial paleoclimate variability, and demonstrate significant diversity of paleoclimate variations in regions of China over the past ∼21 ka. Compared with observational data between 1961 and 1990, averaged mean annual temperature (MAT) was ∼5 °C (3–8 °C) lower during the Last Glacial Maximum (LGM, ∼21 ± 3 ka), and ∼ 2 °C (1–3 °C) higher during Holocene Optimum (HO, ±9 ka) in China; while averaged mean annual precipitation (MAP) and averaged summer precipitation varied between 30 and 150%, with enhanced seasonality during the warmer Holocene (8–5 ka). Our quantitative and semi-quantitative paleoclimate reconstructions reveal both similarities and contrasts with previous studies of regional temperature and precipitation variability. The most remarkable paleoclimate variability is recorded in the transitional zone between the humid monsoon and arid desert regions of central and northern China. We conducted a dynamic downscaling paleoclimate simulation with a regional climate model (RegCM4), using the output from the fully-forced transient simulation of the global climate (TraCE-21 K) as the prescribed boundary conditions, to simulate regional climate changes at high spatial resolution in China over the past ∼21 ka. The results improve paleoclimate simulations at regional scales, but reveal differences in comparison with TraCE-21 K, thereby highlighting uncertainties in the simulation modeling. Moreover, we compare proxy-based paleoclimate reconstructions and the output of TraCE-21 K to identify inconsistencies in relation to regional paleoclimate variations, and confirm a generally consistent warming trend in MAT from the LGM to the HO followed by a cooling trend during the late Holocene. An overall increase in both annual and summer precipitation is observed from LGM to Holocene. This general paleoclimate pattern is likely to have been driven by northern hemisphere ice volume and atmospheric greenhouse gas concentrations (GHGs) during the last deglaciation, and boreal summer insolation during the Holocene. This study represents the first attempt to use multi sources and large datasets of proxy reconstructions and numerical simulations to evaluate regional paleoclimate variability in China since the LGM. Our research provides a comprehensive overview of climate change over the past 21 ka and underscores the critical importance of conducting high-resolution simulations and quantitative paleoclimate studies. This approach is essential for deciphering patterns of paleoclimate change that are currently poorly defined.

Paleoclimate change can be quantified by modelling the paleoglacier extents at well-dated moraines. However, previous studies typically use paleo-precipitation changes derived from climate proxies in other locations to constrain paleo-temperature changes. This approach may lead to significant uncertainties due to the lack of a physical basis and spatial-temporal representativeness. To address this issue, we developed a two-step approach to better constrain the paleo-temperature and precipitation changes. The first step is to identify all potential scenarios for temperature-precipitation changes using a coupled glacial-mass-balance and ice-flow model. In the second step, we incorporate a physics-based parameter k, reflecting the sensitivity of precipitation and temperature change, to determine the most probable temperature-precipitation change. We demonstrate our new approach by reconstructing paleoclimate changes of two valley glaciers in the Bhutanese Himalaya (BH). This approach derives a set of temperature reductions of −4.14 °C, −4.08 °C, −0.93 °C, −0.33 ∼ −0.57 °C, and − 0.31 ∼ −0.52 °C, with their corresponding precipitation decreases of 21.4%, 21.0%, 5.2%, 1.7–3.3%, and 1.6–3.0% relative to the present, during the Last Glacial Maximum, Heinrich event 1, Younger Dryas, Neoglacial, and Little Ice Age in BH, respectively. The reconstructed cold and dry climates in BH are consistent with the paleoclimate reconstructions across the Tibetan Plateau, but our approach improved the accuracy of regional paleoclimate reconstructions. These results suggest that temperature change dominates the glacial fluctuations in BH, with additional influences from solar insolation, oceanic and atmospheric circulation changes, and volcanic eruptions.

The partial pressure of atmospheric CO₂ (pCO₂) significantly influences global climate change and biological evolution through geological history. Boron isotopic composition (δ¹¹B) in carbonates has been used to reconstruct the paleo-pH of seawater, providing insight into atmospheric pCO₂ levels. However, the fidelity of δ¹¹B records in marine carbonates due to diagenesis remains uncertain. Here, to understand how diagenetic processes influence B isotopic records in marine carbonates, we examined B concentrations and δ¹¹B values of modern corals (from Hainan Island), unconsolidated shallow pushcores (Jiuzhang A and Jiuzhang B from Nansha Islands, South China Sea), and a long drillcore (XK-1 from Xisha Islands, South China Sea) covering the Late Miocene to Holocene periods. Our coral samples show a uniform δ¹¹B range (20.16 ± 0.85%), consistent with previously published values for modern corals in other open oceans. The δ¹¹B values of the unlithified carbonate sediments from Jiuzhang A and B pushcores vary within a narrow range (18.70 ± 0.84%), yielding pH and CO₂ concentrations consistent with the range between modern and pre-industrial values. Since we did not observe any statistically significant covariations between traditionally established diagenetic proxies (such as δ¹³C, δ¹⁸O, Mn/Sr, and Al/Ca) and δ¹¹B values for non-dolomitized samples in the XK-1 drillcore, we suggest that δ¹¹B values of bulk limestones are not significantly affected by typical diagenesis (meteoric, mixed-diagenetic, and marine diagenetic processes), likely due to limited post-depositional recrystallization of our study carbonates. In contrast, dolomitization significantly decreases δ¹¹B values of bulk carbonates, rendering dolomites unsuitable as archives for reconstructing seawater δ¹¹B_borate values. Our study supports that marine limestone with limited recrystallization or dolomitization have the potential to record ambient seawater pH values with high resolution. The established secular seawater pH variations based on XK-1 δ¹¹B records provide information about ocean acidification over the past 5.1 million years.

Pelagic fishes are a key trophic component of the Southern Ocean ecosystem. However, understanding the spatial and temporal changes in geographic distribution patterns of pelagic fishes in the context of climate change remains limited. This research applied the MaxEnt model to project the distributions of current and future (2100s) suitable habitats for ten major pelagic fish species in the Southern Ocean (two scenarios: RCP4.5 and RCP8.5). Results suggested that the current spatial distribution of pelagic fishes is significantly correlated with their realized niche and that global warming will lead to significant changes in the spatial distribution of pelagic fishes in the Southern Ocean. Model predictions showed that eight out of ten pelagic fish species are likely to face a significant reduction in their ranges of suitable habitats under the RCP8.5 scenario by the 2100s. Except for the Bathylagus antarcticus, all of the other nine species were predicted to migrate toward South Pole by the 2100s. In addition, the community composition of pelagic fishes also may change significantly, mostly because of species loss. The results of this study clarify the impact of climate change on pelagic fishes in the Southern Ocean, and provide theoretical support for sustainable management and conservation efforts of these pelagic fishes.

In this study, the joint effects of the El Niño-Southern Oscillation (ENSO) and Arctic Oscillation (AO) on winter net surface heat flux (Q_net) anomalies over the tropical Indian Ocean (TIO) are investigated for the 1979/1980–2017/2018 period. The results show that, in multisource datasets, the Q_net pattern for El Niño plus positive AO cases is the most robust. The major feature of Q_net is dominated by a significant dipole pattern, with oceanic heat gain anomalies appearing over the southeastern TIO and oceanic heat loss near the western TIO. Analysis of the flux components shows that the Q_net anomalies are mainly contributed by changes in latent heat flux and shortwave radiation (Q_LHF and Q_SWR), which are tightly associated with the regional atmospheric and oceanic conditions. In association with positive AO, northerly wind anomalies on the eastern flanks of a low-level anomalous anticyclone in the Arabian Sea enhance the intertropical convergence zone (ITCZ) in the western TIO. Meanwhile, the El Niño-related SST warming occurs in the western TIO. Both enhanced ITCZ and anomalous SST warming favour in situ increased low and middle cloud cover and a reduced Q_SWR. Furthermore, under El Niño's effect, a low-level anomalous anticyclone located in the southeastern TIO leads to a positive Q_LHF through decreased near-surface wind speed and increased near-surface air humidity. As a result, a dipole Q_net pattern tends to be observed for the combination of El Niño and positive AO.

Mongolia's ecosystem has suffered severe damage due to factors such as global warming, population growth, and land management change. In this regard, Mongolia's dust (MD) events have significantly impacted the social and economic development of both local and surrounding areas. The transport of MD significantly impacts the dust concentrations in China, and should not be ignored. To address this issue, we conducted a study on the MD emission and its contribution to East Asia using the Weather Research and Forecasting model coupled to Chemistry (WRF-Chem) model coupled with dynamic dust sources. The results shows that the WRF-Chem model with dynamic dust source effectively improves numerical simulations. The spatiotemporal distribution of simulated aerosol optical depth (AOD) is in good agreement with the observations. Compared to March, scarcer snow cover and higher surface temperature in April and May lead to higher dust source function and more dust emission flux. Moreover, we further demonstrated the impact of MD contribution on dust concentration over East Asia. Specifically, MD is responsible for approximately 25% of dust emissions, 23.1% of dust loading and 14.1% of dust transport flux at 500 hPa in the spring over East Asia. This study not only fills a scientific gap in understanding MD emissions but also enhances prediction and early warning capabilities for dust storms in China.

Stable oxygen isotopes records (δ¹⁸O) in tree-rings are commonly used to assess the response of trees to environmental variability being a valuable tool for studying past climate at different temporal and spatial scales. This is particularly relevant in semi-arid regions like the southern Tropical Andes, where ongoing environmental changes coincide with a rapidly increasing demand for hydrological resources, presenting a challenge for ecosystem dynamics and water resource management. In this study, we aim to determine the main spatio-temporal variability of a new network of δ¹⁸O Polylepis tarapacana chronologies during the last century, and their relationships with hydroclimate and tropical circulation at local to subcontinental scales throughout the Tropical Andes. For this purpose, we develop six δ¹⁸O P. tarapacana tree-ring chronologies across a 450 km latitudinal moisture gradient in the southern Tropical Andes adjacent to the Atacama Desert, covering the period 1900–2007. Results show a clear latitudinal gradient in the δ¹⁸O values across the network and significant relationships are observed with other δ¹⁸O tree-ring chronologies in Tropical South America, demonstrating clear regional climate influences at a subcontinental scale. A principal component analysis of the δ¹⁸O tree-ring chronologies demonstrate a strong regional environmental signal contained in the network, exhibiting a main temporal pattern (PC1 δ¹⁸O) that explains 63% of the total variance during the period 1900–2007. Comparisons between PC1 δ¹⁸O and environmental variables showed significant negative relationships with precipitation and soil moisture, and positive relationships with temperature and vapor pressure deficit (VPD) during summer when the South American monsoon occurs. The main δ¹⁸O tree-ring network signal clearly records tropical atmospheric and circulation patterns across South America. The easterly wind flux conditions from the Amazon basin favor lower δ¹⁸O values, and the PC1 δ¹⁸O exhibit significant positive correlations with VPD across the entire Tropical Andes and the northern portion of the Amazon basin, and as well as outgoing longwave radiation across the southern Tropical Andes and part of the Amazon basin. The close relationships between the regional signals from our δ¹⁸O tree-ring network with the previously mentioned parameters, highlight the potential to develop future hydroclimatic-related reconstructions with these δ¹⁸O records to assess climate variability and change across the Tropical Andes.