• Energy Research

Discussing the development and shrinkage process of glaciers is of great significance for the in–depth comprehension of regional environmental evolution and predicting global changes. However, there is little understanding of the developmental and retreat processes of mountain glaciers during the Late Quaternary (150 ka) in the East Asian Monsoon region. Using the latest chronological glacial data from eastern China, Taiwan, the Russian Far East, and the Japanese islands of Hokkaido and Honshu, which are all regions impacted by the East Asian Monsoon, we screened reliable glacial age data. This study compiled and compared the age sequences of the different mountain glaciations (dating techniques included optically–stimulated luminescence (OSL), thermoluminescence (TL), electron spin resonance (ESR), U–series (U), cosmogenic nuclides (10Be/CRN), carbon–14 (14C) and potassium–argon (K–Ar), etc.). Based on the evolutionary features of the glaciations in these mountains, by comparison with the marine isotope stage (MIS) environment, the influence of monsoonal circulation patterns on the regional development of glaciers was analyzed. This study determined that Japanese mountain glacial stages since 150 ka are the most complete in the East Asian Monsoon region, having developed during MIS 6–1. Taiwanese mountain glaciers developed during MIS 4–1, but glacial stages in continental East Asia were relatively short, with glaciers first developing only during MIS 3b–1. The reason for this this phenomenon is that the tectonic uplift in different subregions was significantly different; on the other hand, it is also related to the difference of precipitation between land and sea in monsoon climate. By comparing the glacial glaciations in the East Asian Monsoon region with western China, we found that there were significant differences between the extent, onset time, and length of glacial periods. Since the Last Glacial Period, precipitation levels have become transitional and concentrated during the summer months, and temperatures have been continuously changing as a result of the many periodic changes in the East Asian Monsoon. From the Early Last Glacial Period (MIS 4) to the Middle Last Glacial Period (MIS 3b) to the Last Glacial Period (MIS 2/LGM–YD), climatic conditions increasingly restricted the development of glaciers; the regional environment continued to warm until glaciers completely disappeared during the Late Holocene.

The Qinghai-Tibetan plateau (QTP) stores a large amount of soil organic carbon and is the headwater region for several large rivers in Asia. Therefore, it is important to understand the influence of environmental factors on river water quality and the dissolved organic carbon (DOC) export in this region. We examined the water physico-chemical characteristics, DOC concentrations and export rates of 7 rivers under typical land cover types in the Three Rivers Headwater Region during August 2016. The results showed that the highest DOC concentrations were recorded in the rivers within the catchment of alpine wet meadow and meadow. These same rivers had the lowest total suspended solids (TSS) concentrations. The rivers within steppe and desert had the lowest DOC concentrations and highest TSS concentrations. The discharge rates and catchment areas were negatively correlated with DOC concentrations. The SUVA254 values were significantly negatively correlated with DOC concentrations. The results suggest that the vegetation degradation, which may represent permafrost degradation, can lead to a decrease in DOC concentration, but increasing DOC export and soil erosion. In addition, some of the exported DOC will rapidly decompose in the river, and therefore affect the regional carbon cycle, as well as the water quality in the source water of many large Asian rivers.

AbstractThe Arctic has experienced rapid change associated with warming since the 1970s. The rapid retreat of the terrestrial cryosphere can release a large amount greenhouse gas from the permafrost regions into the air, and the sea ice decline will affect the CO2 and CH4 balance in the ocean. Changes in the Arctic provide feedback mechanisms that can also impinge on the global ocean’s thermohaline circulation. During the past years, the overall natural processes in the Arctic have been studied although the magnitude and timing of carbon release from the cryosphere changes require further investigation. However, few studies have been conducted to link the natural and social systems in the Arctic. Scientists and policymakers must consider the coupled Arctic land, ocean, and social systems in their decisions for coping with climate change.

The Qinghai–Tibet Plateau is an area known to be sensitive to global climate change, and the problems caused by permafrost degradation in the context of climate warming potentially have far-reaching effects on regional hydrogeological processes, ecosystem functions, and engineering safety. Soil thermal conductivity (STC) is a key input parameter for temperature and surface energy simulations of the permafrost active layer. Therefore, understanding the spatial distribution patterns and variation characteristics of STC is important for accurate simulation and future predictions of permafrost on the Qinghai–Tibet Plateau. However, no systematic research has been conducted on this topic. In this study, based on a dataset of 2972 STC measurements, we simulated the spatial distribution patterns and spatiotemporal variation of STC in the shallow layer (5 cm) of the Qinghai–Tibet Plateau and the permafrost area using a machine learning model. The monthly analysis results showed that the STC was high from May to August and low from January to April and from September to December. In addition, the mean STC in the permafrost region of the Qinghai–Tibet Plateau was higher during the thawing period than during the freezing period, while the STC in the eastern and southeastern regions is generally higher than that in the western and northwestern regions. From 2005 to 2018, the difference between the STC in the permafrost region during the thawing and freezing periods gradually decreased, with a slight difference in the western hinterland region and a large difference in the eastern region. In areas with specific landforms such as basins and mountainous areas, the changes in the STC during the thawing and freezing periods were different or even opposite. The STC of alpine meadow was found to be most sensitive to the changes during the thawing and freezing periods within the permafrost zone, while the STC for bare land, alpine desert, and alpine swamp meadow decreased overall between 2005 and 2018. The results of this study provide important baseline data for the subsequent analysis and simulation of the permafrost on the Qinghai–Tibet Plateau.

Le réchauffement rapide récent a eu des impacts inégaux sur la composition, la structure et le fonctionnement des écosystèmes nordiques. On ne sait toujours pas comment les facteurs climatiques contrôlent les tendances linéaires et non linéaires de la productivité des écosystèmes. Sur la base d'un produit d'indice de phénologie végétale (IPP) à une résolution spatiale de 0,05° sur 2000-2018, nous avons utilisé un schéma d'ajustement polynomial automatisé pour détecter et caractériser les types de tendances (c.-à-d. tendances polynomiales et non tendances) dans l'IPP annuel intégré (PPIINT) pour les écosystèmes nordiques (> 30°N) et leur dépendance aux facteurs climatiques et aux types d'écosystèmes. La pente moyenne pour les tendances linéaires (p < 0,05) de PPIINT était positive dans tous les écosystèmes, parmi lesquels les forêts de feuillus à feuilles larges et les forêts de feuillus à aiguilles (ENF) ont montré les pentes moyennes les plus élevées et les plus basses, respectivement. Plus de 50% des pixels dans les ENF, les arbustes arctiques et boréaux et les zones humides permanentes (PW) avaient des tendances linéaires. Une grande fraction de PW a également montré des tendances quadratiques et cubiques. Ces tendances concordent bien avec les estimations de la productivité globale de la végétation basées sur la fluorescence de la chlorophylle induite par le soleil. Dans tous les biomes, PPIINT dans les pixels avec des tendances linéaires a montré des valeurs moyennes plus faibles et des coefficients de corrélation partielle plus élevés avec la température ou les précipitations que dans les pixels sans tendances linéaires. Dans l'ensemble, notre étude a révélé l'émergence d'une convergence latitudinale et d'une divergence dans les contrôles climatiques sur les tendances linéaires et non linéaires de PPIINT, ce qui implique que les déplacements nordiques de la végétation et le changement climatique peuvent potentiellement augmenter la nature non linéaire des contrôles climatiques sur la productivité des écosystèmes. Ces résultats peuvent améliorer notre compréhension et notre prévision des changements induits par le climat dans la phénologie et la productivité des plantes et faciliter la gestion durable des écosystèmes en tenant compte de leur résilience et de leur vulnérabilité au changement climatique futur. El rápido calentamiento reciente ha causado impactos desiguales en la composición, estructura y funcionamiento de los ecosistemas del norte. Se desconoce cómo los impulsores climáticos controlan las tendencias lineales y no lineales en la productividad de los ecosistemas. Con base en un producto de índice de fenología vegetal (PPI) a una resolución espacial de 0.05° durante 2000-2018, utilizamos un esquema de ajuste polinómico automatizado para detectar y caracterizar los tipos de tendencias (es decir, tendencias polinómicas y no tendencias) en el PPI integrado anual (PPIINT) para los ecosistemas del norte (> 30°N) y su dependencia de los impulsores climáticos y los tipos de ecosistemas. La pendiente promedio para las tendencias lineales (p < 0.05) de PPIINT fue positiva en todos los ecosistemas, entre los cuales los bosques caducifolios de hoja ancha y los bosques perennifolios de hoja de aguja (ENF) mostraron las pendientes medias más altas y más bajas, respectivamente. Más del 50% de los píxeles en ENF, matorrales árticos y boreales y humedales permanentes (PW) tuvieron tendencias lineales. Una gran fracción de PW también mostró tendencias cuadráticas y cúbicas. Estos patrones de tendencia coincidieron bien con las estimaciones de la productividad global de la vegetación basadas en la fluorescencia de la clorofila inducida por el sol. En todos los biomas, PPIINT en píxeles con tendencias lineales mostró valores medios más bajos y coeficientes de correlación parcial más altos con la temperatura o la precipitación que en píxeles sin tendencias lineales. En general, nuestro estudio reveló la aparición de convergencia latitudinal y divergencia en los controles climáticos sobre las tendencias lineales y no lineales de PPIINT, lo que implica que los cambios septentrionales de la vegetación y el cambio climático pueden aumentar potencialmente la naturaleza no lineal de los controles climáticos sobre la productividad de los ecosistemas. Estos resultados pueden mejorar nuestra comprensión y predicción de los cambios inducidos por el clima en la fenología y la productividad de las plantas y facilitar la gestión sostenible de los ecosistemas al tener en cuenta su resiliencia y vulnerabilidad al cambio climático futuro. Recent rapid warming has caused uneven impacts on the composition, structure, and functioning of northern ecosystems. It remains unknown how climatic drivers control linear and non-linear trends in ecosystem productivity. Based on a plant phenology index (PPI) product at a spatial resolution of 0.05° over 2000-2018, we used an automated polynomial fitting scheme to detect and characterize trend types (i.e., polynomial trends and no-trends) in the yearly-integrated PPI (PPIINT) for northern (> 30°N) ecosystems and their dependence on climatic drivers and ecosystem types. The averaged slope for the linear trends (p < 0.05) of PPIINT was positive across all the ecosystems, among which deciduous broadleaved forests and evergreen needle-leaved forests (ENF) showed the highest and lowest mean slopes, respectively. More than 50% of the pixels in ENF, arctic and boreal shrublands, and permanent wetlands (PW) had linear trends. A large fraction of PW also showed quadratic and cubic trends. These trend patterns agreed well with estimates of global vegetation productivity based on solar-induced chlorophyll fluorescence. Across all the biomes, PPIINT in pixels with linear trends showed lower mean values and higher partial correlation coefficients with temperature or precipitation than in pixels without linear trends. Overall, our study revealed the emergence of latitudinal convergence and divergence in climatic controls on the linear and non-linear trends of PPIINT, implying that northern shifts of vegetation and climate change may potentially increase the non-linear nature of climatic controls on ecosystem productivity. These results can improve our understanding and prediction of climate-induced changes in plant phenology and productivity and facilitate sustainable management of ecosystems by accounting for their resilience and vulnerability to future climate change. تسبب الاحترار السريع الأخير في تأثيرات غير متكافئة على تكوين وبنية وأداء النظم الإيكولوجية الشمالية. لا يزال من غير المعروف كيف تتحكم المحركات المناخية في الاتجاهات الخطية وغير الخطية في إنتاجية النظام البيئي. استنادًا إلى منتج مؤشر الفينولوجيا النباتية (PPI) بدقة مكانية تبلغ 0.05درجة خلال الفترة 2000-2018، استخدمنا مخططًا آليًا للتركيب متعدد الحدود لاكتشاف وتمييز أنواع الاتجاهات (أي الاتجاهات متعددة الحدود وعدم وجود اتجاهات) في مؤشر أسعار المنتجين السنوي المتكامل (PPIINT) للنظم الإيكولوجية الشمالية (> 30درجةشمالًا) واعتمادها على الدوافع المناخية وأنواع النظم الإيكولوجية. كان المنحدر المتوسط للاتجاهات الخطية (p < 0.05) لـ PPIINT إيجابيًا في جميع النظم الإيكولوجية، من بينها الغابات المتساقطة ذات الأوراق العريضة والغابات دائمة الخضرة ذات الأوراق الإبرية (ENF) التي أظهرت أعلى وأدنى المنحدرات المتوسطة، على التوالي. كان لأكثر من 50 ٪ من وحدات البكسل في ENF، والشجيرات القطبية والشمالية، والأراضي الرطبة الدائمة (PW) اتجاهات خطية. أظهر جزء كبير من المياه الصالحة للشرب أيضًا اتجاهات تربيعية ومكعبة. اتفقت أنماط الاتجاه هذه بشكل جيد مع تقديرات إنتاجية الغطاء النباتي العالمي بناءً على فلورة الكلوروفيل المستحثة بالطاقة الشمسية. في جميع المناطق الحيوية، أظهر PPIINT بالبكسل مع الاتجاهات الخطية قيمًا متوسطة أقل ومعاملات ارتباط جزئية أعلى مع درجة الحرارة أو هطول الأمطار مقارنة بالبكسل بدون اتجاهات خطية. بشكل عام، كشفت دراستنا عن ظهور تقارب وتباعد خطوط العرض في الضوابط المناخية على الاتجاهات الخطية وغير الخطية لـ PPIINT، مما يعني أن التحولات الشمالية للغطاء النباتي وتغير المناخ قد تزيد من الطبيعة غير الخطية للضوابط المناخية على إنتاجية النظام الإيكولوجي. يمكن أن تحسن هذه النتائج فهمنا وتنبؤنا بالتغيرات الناجمة عن المناخ في علم الظواهر النباتية والإنتاجية وتسهيل الإدارة المستدامة للنظم الإيكولوجية من خلال مراعاة مرونتها وقابليتها للتأثر بتغير المناخ في المستقبل.