Science China Earth Sciences最新文献

Carbon emission accounting is an important basis for global climate governance. Based on the consumption-based accounting (CBA) method, the characteristics of carbon flow between national, regional, and product processes could be more clearly reflected. Therefore, CBA is more conducive to clarifying the attribution of responsibilities between producers and consumers, with the principles of fairness and justice. By accounting for carbon emissions in typical countries from 1990 to 2019, we found that the CBA emissions are higher than the production-based accounting (PBA) emissions in major developed countries, while the results are reversed for developing countries. In the past 30 years, the CBA emissions in targeted developed countries generally have shown a downward trend, while in developing countries, they have shown an upward trend. CBA emissions in China have shown a continuous growth trend from 1990 to 2019, but the pace has slowed down significantly over the last decade. Meanwhile, the embodied carbon intensity of China’s exports continues to decline, indicating that China is providing more green and low-carbon products to the world. Taking the PV industry as an example, this study further reveals the contribution of specific product industries to the country’s carbon transfer through product carbon footprint analysis. In order to provide a scientific basis for global mitigation and climate governance, it is urgent to innovate a scientific, practical, and standardized CBA technology system.

Oceanic submesoscales can significantly influence phytoplankton production and export owing to their similar timescales of days. Based on two-year Biogeochemical Argo (BGC-Argo) observations, this study investigated the development of submesoscale instabilities, particularly symmetric and mixed-layer baroclinic instabilities, and their impacts on biological production and export in the oligotrophic South China Sea basin. In the northern basin, near-surface winter blooms consistently cooccurred with seasonally deepened mixed layers. However, significantly stronger and weaker winter blooms were observed over two consecutive winters within the BGC-Argo observation period. During the first winter, symmetric-instability-induced upward nutrient entrainment played a crucial role in initiating the strong winter bloom in early December, when the mixed layer was approximately 20–30 m shallower than the nutricline. This bloom occurred approximately 20–30 days earlier than that anticipated owing to the contact between the seasonally deepened mixed layer and mesoscale-cyclone-induced uplifted nutricline. The symmetric instability also facilitated the export of fixed phytoplankton carbon from the surface to deeper layers. Conversely, during the second winter, remarkably intense mixed-layer baroclinic instability associated with an intense mesoscale anticyclone led to more significant shoaling of the mixed layer compared to the nutricline, thus increasing the vertical distance between the two layers. Under this condition, upward nutrient injection, phytoplankton bloom, and carbon export were suppressed. In contrast, the BGC-Argo float in the central basin revealed significantly inhibited seasonality of phytoplankton biomass and submesoscale instabilities compared to those in the northern basin, primarily owing to the significantly shallower winter mixed layer.

The strategy of carbon neutrality is reshaping the global landscape of resource flow and recycling. As the final sink of geological minerals, the proliferated anthropogenic minerals, also called secondary resources, play an increasingly important role in resource supply enrichment. Niobium is a critical metal that lacks full concern for its sustainability. The fundamental principle of niobium circularity is to recycle and maintain the material as close to the manufacturing process as possible. Here we estimate the niobium-containing applications lost at their end-of-life, underscoring the imperative to minimize such disposal. Additionally, we elucidate the extraction processes for scrap and alloy quantities throughout the industry’s lifecycle. Drawing from anticipated waste generated by the majority of niobium applications, a forecast indicates a potential loss of approximately 168 kt by 2090 in the absence of recycling. Contrastingly, with a recycling efficiency of 90% for niobium, the projected loss diminishes to approximately 16 kt. We delve into the significance of niobium’s circular economy and explore various aspects that demand further investigation for a seamless transition from linear to circular practices.

The diverse climates, distribution of snow and glaciers, and geographic locations directly affect the runoff response to climate change in the upper basins of the Third Pole. At present, a comprehensive analysis of runoff variations and their distinct responses to climate change in the westerlies- and monsoon-dominated upper basins is still lacking. This study comprehensively analyzed annual runoff variations in westerlies-dominated basins (the upper basins of the Aksu (UAKS), Syr Darya (USRD), Yarkant (UYK), Hotan (UHT), Amu Darya (UAMD), and Indus (UI)) and monsoon-dominated basins (the upper basins of the Yangtze (UYA), Yellow (UYE), Lancang (ULC), Nujiang (UNJ), and Yarlung Zangbo (UYZ)) of the Third Pole from 1961 to 2015. Using multi-source meteorological data and large-scale circulation factors, this study investigated the divergent responses of runoff in the upper basins to climate change, and explored the large-scale circulation mechanisms underlying runoff variations in these upper basins. The results showed that: (1) The annual runoff in the majority of upper basins (except for the UYE and UYZ) exhibited an increasing trend, and the annual runoff in the UAKS, UYK, and UI showed a significant increasing trend from 1961 to 2015. The annual runoff in the upper basins of the Third Pole changed abruptly from decreasing to increasing between the 1980s and 2000s, with the exception of the UYE. (2) The runoff in the monsoon-dominated upper basins has been controlled primarily by changes in precipitation over the past 55 years. In contrast, the runoff in the westerlies-dominated upper basins exhibited three distinct long-term responses to climate change: temperature-dominated (UYK and UHT), precipitation-dominated (USRD and UAMD), and the combined influence of precipitation and temperature (UAKS and UI). Since the 1960s, the sensitivity of runoff to warm season temperature changes in the most westerlies-dominated upper basins has decreased, while the response of runoff to precipitation changes has intensified. (3) The study revealed the connection between large-scale circulation, climate, and runoff in the upper basins of the Third Pole. The Atlantic Multidecadal Oscillation, the Westerly Index, and the El Niño-Southern Oscillation predominantly impact the precipitation or temperature in the upper basins of the Third Pole, which in turn affect the runoff variations in the upper basins dominated by either the westerlies or the monsoon. This study will be a valuable scientific reference for water resource management and climate change adaptation for both the westerlies- and monsoon-dominated upper basins in the Third Pole.

The effect of plant type on n-alkane biomarker has been widely studied, but the influence of plant type on n-alkanoic acids (n-FAs) has received less attention. Understanding the effect of the distribution of n-FAs and their hydrogen isotope composition (δ²H_FA) is critical for interpreting sedimentary δ²H_FA values as proxies of hydroclimate and/or vegetation changes. In this study, we systematically investigated the distribution of n-FAs and δ²H_FA values across seasons on the Chinese Loess Plateau (CLP). Our results showed that there were no significant seasonal differences in n-FAs distribution and δ²H_FA values, but there were significant differences in δ²H_FA values across plant types. The δ²H_FA values ranged from −185‰ to −125‰ in dicots (−161‰±28‰), and from −215‰ to −170‰ in monocots (−196‰±22‰) on the CLP. Isotope fractionation between δ²H_FA values and precipitation δ²H (ε_FA-P) was also ²H-enriched in dicots relative to monocots. At the regional scale of the CLP, δ²H_FA values were not correlated with δ²H values of precipitation. However, δ²H_FA values from the CLP were similar to expectations from a global comparison, both in terms of their mean values and high variability among plants growing in sites with similar δ²H values of precipitation. As some of this variability in ε_FA-P is due to the effect of plant type, a careful assessment of the likely sources of waxes in terrestrial sediments is critical when using δ²H_FA values for paleohydroclimate reconstruction.

Wetland ecosystems have become one of the long-term solutions for mitigating global climate change due to their strong carbon sequestration potential. However, the key carbon cycle processes in wetland ecosystems still lack a systematic summary. In the context of wetland protection and restoration, there is still a lack of consensus on the technical pathways to realize carbon sink multiplication in wetland ecosystems. In this paper, the key processes of carbon cycle, such as photosynthetic carbon uptake, microbial carbon decomposition and carbon deposition and burial, are sorted out and summarized in four major wetland types, namely, swamp and peat wetlands, river and riparian wetlands, lake and lakeshore wetlands, and estuarine and coastal wetlands. Based on the key processes of carbon cycle, three technological pathways for carbon sink multiplication are proposed, including, vegetation carbon sequestration and sink enhancement technology, soil carbon emission reduction technology and carbon deposition and burial technology. The key technologies under each pathway are further refined. And the carbon sink effects of the carbon sink technologies in different wetland types are qualitatively described. Also, wetland protection and restoration methods in corresponding regions are given in the light of the regional characteristics of wetlands in China. This will provide a scientific basis for the strategy of doubling the carbon sinks of China’s wetland ecosystems.

The origin of agriculture in the farming-pastoral zone of northern China remains in dispute. The central region of the Inner Mongolia Plateau is located in the core area of the farming-pastoral zone; thus, it is a critical region for exploring the origin of the dryland farming system in northern China. This study selected the Yumin Site and Banan Site, which belong to the Yumin Culture-the beginning of Neolithic culture in Inner Mongolia-as the research objects. Based on the quartz optically stimulated luminescence (OSL) dating on the sedimentary sections from the Yumin site (YM) and Banan site (BN1 and BN2), the Holocene chronology framework of each section was established. After that, by identifying carbonized grains in the Yumin site and the multi-proxy analysis of each section, we investigated the relationship between the origin of agriculture and climate change in this region. The results revealed that the timing of the origin of agriculture recorded in the Yumin site lagged behind the timing of a significant increase of precipitation during the early Holocene but coincided with the timing of a significant increase of vegetation around 8.4 ka. This phenomenon was further confirmed by the published high-resolution paleoenvironmental records from the surrounding area of the Yumin Culture. We propose that with the gradual amelioration of hydrothermal conditions since the beginning of the Holocene, the regional ecosystem had been improved, resulting in the gradual conversion of the land surface from infertile sand to organic-rich soil, providing an appropriate environmental foundation for the origin of dryland farming in northern China around 8.4 ka. This study highlighted that the “accumulative environmental effects” during the early Holocene played a vital role in the origin of agriculture in northern China and provided a reference for agricultural management in the context of future climate change.

The 2022 Yangtze mega-flash drought is characterized by strong intensity and rapid development both in time and space, accompanied by a persistent anticyclonic circulation anomaly. However, the causes of the extreme event remain elusive given the multiscale nature of drought. Here we presented a brief overview for the oceanic and terrestrial causes of the mega-flash drought during the summer of 2022, and estimated the risk in a changing climate. Using the soil moisture percentile as the drought index, it was found that the drought expanded to the entire Yangtze River basin within two months, with 80% of basin under severe drought conditions at the end of August. Both the intensity and onset speed of the 2022 mega-flash drought were ranked as the first during the past 62 years, with return periods of 86 and 259 years, respectively. The results of composite analysis showed that the spring La Niña can facilitate the abrupt change from a wet/normal condition in May–June to drought in July–August over the Yangtze River basin, which was beneficial for the increase of flash drought intensity and onset speed in 2022. The analysis through the linear regression also indicated that the unprecedented intensity was associated with the negative phase of the Pacific Decadal Oscillation. Quantified by a coupling strength index for soil moisture and vapor pressure deficit, it was found that there was a strong land-atmosphere coupling over the Yangtze River basin during July–August 2022. The attribution by using CMIP6 climate models suggested that land-atmosphere coupling increased the risks of flash drought intensity and onset speed like 2022 by 61%±6% and 64%±7% under natural climate forcings, and the synergy of coupling and anthropogenic climate change would increase the risks by 75%±22% and 85%±12%. Our findings emphasized the role of land-atmosphere coupling combined with anthropogenic climate change in intensifying flash droughts.