Global and Planetary Change最新文献

Summer precipitation over the Mongolian Plateau (MP) has experienced a consistent decline in recent decades. While the influence of atmospheric wave train on this reduction in precipitation has been recognized in prior studies, this study delves deeper into the physical mechanisms and quantifies the contributions of the internal atmosphere and oceanic variations to the diminishing precipitation utilizing a comprehensive 100-member ensemble simulations from the Max Planck Institute Earth System Model (MPI-ESM). Results show that the ensemble-mean precipitation in MP exhibits a positive trend and cannot explain the observed results. The precipitation trends vary significantly among individual ensemble members, highlighting the pivotal role of internal variability. The leading EOF mode of precipitation trends among ensemble members exhibits uniform variations. Further investigations reveal that the internal summer precipitation in MP is affected by the internal atmospheric circulation, the remote influence of the North Atlantic Dipole sea surface temperature (SST) anomalies, and Pacific Decadal Oscillation-like SST patterns. An eastward-propagating Rossby wave originating from the North Atlantic dipole SST anomalies provides the anomalous large-scale circulation that influences summer precipitation. The PDO contributes to reinforcing the anticyclonic anomaly over the MP. Additionally, the uncertainty of precipitation trends in MPI-ESM can be reduced by 13% through removing the internal atmospheric wave train-related precipitation variation, while oceanic factors only contribute about 7% uncertainty of precipitation variations. Our insights enhance the understanding of the physical drivers behind summer precipitation variability in the MP and effectively quantify the uncertainties stemming from internal variability.

Burial of terrigenous organic carbon in marine sediments serves as a net sink for atmospheric CO₂ and therefore regulates global climate on geologic time scales. Woody debris is an important carrier of terrigenous organic carbon, but its burial in deep-sea sediments has been rarely reported. Here, woody debris from the last glacial sediments in the southern South China Sea was used for analyzing its abundance, organic carbon content, and organic carbon stable isotopes, in order to elucidate the burial of deep-sea woody debris and its contribution to carbon cycling. The woody debris presents the higher abundance (0.15 ± 0.14%) during the last glacial 14.3–20.8 cal ka BP while woody debris is lacking during the 2.0–14.3 cal ka BP, suggesting increased woody-debris burial during the last glaciation. The woody debris shows the constant organic carbon content (27.9%) and stable isotope value (−27.6‰) during the last glaciation, indicating its same C3 plant source. Combining woody-debris abundance, organic carbon content, and other published data, the last glacial burial of C3 plants in the southern South China Sea was estimated to have sequestered 0.39 ± 0.39 Gt carbon, contributing 3 ± 3‰ to the atmospheric CO₂ reduction during the last glaciation. If similar magnitude can be identified in other low-latitude seas, the increased burial of C3 plants in deep-sea sediments could efficiently reduce the atmospheric CO₂ during the last glaciation. This study proposes the glacial burial and interglacial absence of woody debris in the deep sea as a new carbon sequestration mechanism in the glacial carbon cycle.

Mercury (Hg) is a volatile metal of international concern due to its toxicity, with a large atmospheric emission and transport capacity. The biogeochemical cycle of Hg is sensitive to changes in climate, yet our understanding of the specific impact of climatic factors on the Hg cycle remains limited. Here we use a multi-proxy framework, supported by AMS ¹⁴C dating, to interpret climatic events in South-Eastern Australia from ∼18,000 years to 6500 years before present from the sediments of Blue Lake in Australia's alpine region. By combining Hg analysis with Antarctic temperature records and iTRACE climate model outputs, carbon-to‑nitrogen ratios (C:N), macroscopic charcoal, and pollen analysis, we find Hg records within Blue Lake's sediments primarily reflect changes in the catchment as a result of a changing climate. The increase in Hg concentrations began with the onset of the Holocene, following a glacial period during which the region was predominantly rocky, relatively barren, and likely covered by ice and snow. The strong relationship between Hg and organic matter in our record indicates that soil development in the watershed post de-glaciation was a predominant driver of Hg concentration and deposition in Blue Lake. An increase in precipitation and temperature in the Holocene contributed to an increase in nutrients and organic matter, further increasing Hg concentration in Blue Lake. A primary challenge in modern Hg research, particularly in the context of climate change, involves distinguishing changes in Hg levels resulting from human activities from those driven by climatic variations. Our pre-anthropogenic data highlight the long-term interrelationships among climate dynamics, soil processes, and ecological transformations within lake catchments on the geochemical cycle of Hg. These connections should be factored into strategies aimed at mitigating Hg increases in lake sediments resulting from global warming.

In July 2021, a devastating flood occurred in the Ahr Valley, in western Germany, which caused 134 fatalities and extreme economic damage. Because gauges were destroyed during the flood or were undersized, peak discharge could not be measured. Flood level indicators were used to measure the maximum water level along the river in the aftermath of the flood. Using the Manning's equation, peak discharge is calculated for eight locations along the Ahr River, as well as for nine tributaries. For this purpose, field measurements of topography and slope were made, and the characteristics of the inundated areas were recorded. We estimate the peak discharge of the July 2021 flood in the range between 1000 and 1250 m³/s near the town of Dernau, which exceeds the largest measured flood up to the 2021 flood by a factor of five.

The exceptional standing is put into perspective when historical floods are also considered in the comparison. 53 historical floods of River Ahr are documented, mostly in written sources. Five historical floods are documented by flood marks, which allows the quantification of the peak discharge. In calculating the peak discharges of these five floods, the same approach is used as in the calculation of the flood of 2021. It is shown that in July 1804 a flood occurred in the Ahr valley which was surprisingly similar to the flood of 2021 in its destructive power and peak discharge.

The evaluation of the flood of 2021 varies depending on the period under consideration. While it has a unique position in the period since the beginning of the gauge measurements in 1947, it is one of several catastrophic floods of the Ahr in the historical context. Thus, the assessment of the flood as a unique new event is not valid.

Terrestrial vegetation carbon use efficiency (CUE) is a key measure for assessing carbon transfer from the atmosphere to terrestrial biomass, crucial for understanding carbon cycling and allocation in ecosystems. CUE provides valuable insights into how terrestrial ecosystems respond to environmental changes. In this study, we utilized satellite datasets (MODIS and GLASS), MsTMIP models, and TRENDY models to analyze the spatiotemporal distribution characteristics of global vegetation CUE. We found that the average CUE for global land vegetation is 0.44 ± 0.06, with a slight annual increase and significant spatial heterogeneity, characterized by latitude gradients and vegetation types. High-latitude regions demonstrated higher CUE values compared to low-latitude regions. Further employing an integrated attribution approach, we identified the response mechanisms of vegetation CUE to global changes. The comprehensive response of vegetation CUE to climate change, land use change, atmospheric CO₂, and nitrogen deposition was found to fluctuate and increase, with a model-averaged CUE increase of approximately 0.01. Land use change was identified as the largest contributor to the annual trend of overall global CUE (48.8%), while climate change was the main factor influencing the interannual variability (IAV) of global CUE (91.7%). Regarding global distribution, the IAV of vegetation CUE is mainly influenced by climate change. CUE annual trends in more regions were influenced by climate change, with 65% and 73% of the ensemble mean of the MsTMIP and TRENDY models, respectively. The results of the MsTMIP and TRENDY models consistently show that, globally, land use change affects about a quarter of the total annual trend of CUE. Land use change affected CUE annual trends to a greater extent than climate change. In addition, the vegetation type most affected by climate change is the deciduous needleleaf forests, and the CUE annual trend of cropland is most affected by land use change. Our findings reveal global patterns and drivers of CUE variability, highlighting the significant impact of climate change and land use change.

Drought is a regional phenomenon and progressive in specific dimensions of time and space, with significant continuity and dynamic characteristics on a spatiotemporal scale. The meteorological drought acts as a driving factor for vegetation drought, and studying the response characteristics of vegetation drought to meteorological drought is crucial for comprehending the mechanisms of drought evolution. In this study, based on a three-dimensional spatiotemporal clustering algorithm, meteorological and vegetation drought events in the Yellow River Basin (YRB) from 1982 to 2020 were identified, and the dynamic characteristics of typical drought events were depicted, elucidating the inherent correlations and propagation features between meteorological and vegetation drought events. Additionally, according to the spatiotemporal matching criteria of drought events, the meteorological-vegetation drought event pairs were successfully matched, which can reveal the lag time between meteorological drought and vegetation drought. From a three-dimensional perspective, we revealed the dynamic propagation characteristics of meteorological and vegetation drought events, which could provide an effective way for monitoring and mitigating regional vegetation drought, restoring ecosystem functionality, and promoting sustainable development of the ecological environment.

Long-term changes in vegetation cover of the Tibetan Plateau (TP) are essential for understanding vegetation change under future climate. Previous studies have mainly concentrated on the Holocene and the eastern region of the TP, but here, we establish a relationship between modern pollen data (including both pollen percentage and concentration) and vegetation cover using a random forest (RF) model based on 362 soil-surface samples from the TP, as well as using it to quantitatively reconstruct the vegetation cover history of the Dagze Co (central TP, covering the last 19.5 cal. ka BP) and Koucha Lake (eastern TP, covering the last 33.8 cal. ka BP) regions. The RF results indicate that both the models based on pollen percentages or concentrations perform similarly (former: R² = 0.538, RMSEP = 19.772%; latter: R² = 0.540, RMSEP = 19.723%). However, when considering the reconstructed vegetation cover of Dagze Co and Koucha Lake, the results based on pollen concentrations appear to be more reliable. Before 13.4 and 16.8 cal. ka BP, Dagze Co and Koucha Lake has low vegetation cover of 25% and 30%, respectively, dominated by alpine desert or desert steppe. After that, changes in vegetation cover show different trends. At Dagze Co, the vegetation cover reaches a high level (54%) between 13.4 and 5.3 cal. ka BP, followed by a decrease until it starts increasing again at 2 cal. ka BP, in response to the change in the Indian Summer Monsoon (ISM). At Koucha Lake, the vegetation cover fluctuates at around 60%, indicating less sensitivity to climate change. Our research highlights the importance of pollen concentrations in quantitatively reconstructing past vegetation cover and the sparse vegetation status during the LGM on the TP.

The Permian–Triassic (P-Tr) transition marks a vital period in Earth's history, characterized by major environmental perturbations and the largest mass extinction event of the Phanerozoic, with volcanic activities playing a key role. Previous investigations of mercury (Hg) anomalies in over 50 marine and terrestrial sections spanning the P-Tr boundary (PTB) have suggested a predominant volcanogenic influence. However, there remains ongoing debate regarding the exact timing and primary sources of these anomalies in different regions. In this study, we present stratigraphically high-resolution (∼7× higher compared to the previous work in the same section) Hg records from the shallow marine strata of the Qubu section, located at the Himalayan Tethys Zone of southern Tibet, Southwest China. Our analysis reveals peak Hg concentrations of approximately 80 to 100 ng/g and Hg/TOC ratios of 111 to 263 (ppb/wt%) at the uppermost Permian. Notably, new measurements of Hg isotopes, characterized by ∼0‰ of Δ¹⁹⁹Hg values, provide unambiguous evidence supporting the prevailing volcanic influence. Our results are consistent with similar observations of Hg anomalies in proximal shallow-marine sections around the Neo-Tethys Ocean, including those in northern India and western Australia. However, we found that relatively shallower marine settings (shelf, lagoon or inshore) tend to exhibit Hg spikes in the latest Permian, whereas deeper sections (outer-shelf or deep carbonate ramp) show peaks in the Early Triassic. Since Hg anomalies for all the sections have been verified to be volcanogenic based on their near-zero values of Δ¹⁹⁹Hg, the discrepancies among them concerning timing and water depth may be attributed to prolonged volcanic influences extending into the Triassic period. Our findings underscore the complexity of sedimentary Hg records and further raise questions about the spatiotemporal consistency of Hg anomalies during the P-Tr transition. Additionally, the most negative Δ¹⁹⁹Hg value (−0.20‰) in the uppermost black shale in the Qubu section likely resulted from photic zone euxinia consistent with globally developed P-Tr shallow-marine anoxic conditions, while other low values of Δ¹⁹⁹Hg with low Hg concentrations were derived from some moderate terrestrial influx.

The Mediterranean Sea is warming about 20 % more rapidly than global ocean and this phenomenon is impacting ecosystems and biodiversity. Planktonic foraminifera are an important component of surface and subsurface water ecosystems and food chains. Their species communities have been altering across the oceans since the Industrial Era, in response to the ongoing climate change, especially in the western Mediterranean Sea, where a significant productivity decrease has been recently reported.

Here we show planktonic foraminifera and multispecies stable isotopes from three short sediment cores, recovered on the eastern flank of the Sicily Channel, central Mediterranean Sea. Results fully confirm the planktonic foraminifera productivity decrease in the Industrial Era, which is especially relevant for the second half of the 20th century. The planktonic foraminifera productivity decrease matches with a higher number of Large Azores High events, i.e., the establishment of an exceptional and persistent winter atmospheric high-pressure ridge over the western-central Mediterranean Sea. This is an unprecedented atmospheric phenomenon for the last millennia Mediterranean Sea history, as a direct response of the global warming. Surface productivity and DCM species are especially declining since ∼1960 CE, at expenses of winter mixed layer taxa, suggesting that the Azores High activity prevents a sustained water column vertical mixing and surface water nutrient fuelling. Our results document and confirm that the climate change has already been affecting Mediterranean marine ecosystems and the basic level of the trophic chain, by extending the surface water stratification period.