Evolution of the freeze-thaw cycles in the source region of the Yellow River under the influence of climate change and its hydrological effects

As an important water source and ecological barrier in the Yellow River Basin, the source region of the Yellow River (above the Huangheyan Hydrologic Station) presents a remarkable permafrost degradation trend due to climate change. Therefore, scientific understanding the effects of permafrost degradation on runoff variations is of great significance for the water resource and ecological protection in the Yellow River Basin. In this paper, we studied the mechanism and extent of the effect of degrading permafrost on surface flow in the source region of the Yellow River based on the monitoring data of temperature and moisture content of permafrost in 2013–2019 and the runoff data in 1960–2019. The following results have been found. From 2013 to 2019, the geotemperature of the monitoring sections at depths of 0–2.4 m increased by 0.16°C/a on average. With an increase in the thawing depth of the permafrost, the underground water storage space also increased, and the depth of water level above the frozen layer at the monitoring points decreased from above 1.2 m to 1.2–2 m. 64.7% of the average multiyear groundwater was recharged by runoff, in which meltwater from the permafrost accounted for 10.3%. Compared to 1960-1965, the runoff depth in the surface thawing period (from May to October) and the freezing period (from November to April) decreased by 1.5 mm and 1.2 mm, respectively during 1992–1997, accounting for 4.2% and 3.4% of the average annual runoff depth, respectively. Most specifically, the decrease in the runoff depth was primarily reflected in the decreased runoff from August to December. The permafrost degradation affects the runoff within a year by changing the runoff generation, concentration characteristics and the melt water quantity from permafrost, decreasing the runoff at the later stage of the permafrost thawing. However, the permafrost degradation has limited impacts on annual runoff and does not dominate the runoff changes in the source region of the Yellow River in the longterm.     

Tectonic evolution and geodynamics of the Neo-Tethys Ocean

The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south.The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from the northern margin of Gondwana.As the microblocks drifted northwards,the Neo-Tethys Ocean was expanded.Most of these microblocks collided with the Eurasia continent in the Late Triassic,leading to the final closure of the Paleo-Tethys Ocean,followed by oceanic subduction of the Neo-Tethys oceanic slab beneath the newly formed southern margin of the Eurasia continent.As the splitting of Gondwana continued,African-Arabian,Indian and Australian continents were separated from Gondwana and moved northwards at different rates.Collision of these blocks with the Eurasia continent occurred at different time during the Cenozoic,resulting in the closure of the Neo-Tethys Ocean and building of the most significant Alps-Zagros-Himalaya orogenic belt on Earth.The tectonic evolution of the Neo-Tethys Ocean shows different characteristics from west to east:Multi-oceanic basins expansion,bidirectional subduction and microblocks collision dominate in the Mediterranean region;northward oceanic subduction and diachronous continental collision along the Zagros suture occur in the Middle East;the Tibet and Southeast Asia are characterized by multi-block riftings from Gondwana and multi-stage collisions with the Eurasia continent.The negative buoyancy of subducting oceanic slabs can be considered as the main engine for northward drifting of Gondwana-derived blocks and subduction of the Neo-Tethys Ocean.Meanwhile,mantle convection and counterclockwise rotation of Gondwana-derived blocks and the Gondwana continent around an Euler pole in West Africa in non-free boundary conditions also controlled the evolution of the Neo-Tethys Ocean.     

Mechanisms and climatic-ecological effects of the Great Oxidation Event in the early Proterozoic

Science China Earth Sciences - This paper briefly introduces the conception and research history of the Great Oxidation Event (GOE) in the early Paleoproterozoic and summarizes the primary...     

The first extra-large helium-rich gas field identified in a tight sandstone of the Dongsheng Gas Field,Ordos Basin,China

Science China Earth Sciences - Helium gas is a scarce but important strategic resource, which is usually associated with natural gas. Presently, only one extra-large helium-rich gas field has been...     

Does exploring the characteristics of emergency supplies really matter for disaster response operations?

Natural Hazards - This article aims to provide a quantitative study of immediate food supplies based on a three-stage analysis. Firstly, a numerical autoregressive integrative moving average...     

Dynamic selection of emergency plans of geological disaster based on case-based reasoning and prospect theory

Natural Hazards - The Three Gorges reservoir area in the Yangtze River economic belt has frequent geological disasters. To assist decision-makers make effective emergency decisions based on their...     

Design of optimal sand fences around a desert solar park—a case study from Phase IV of the Mohammed bin Rashid Al Maktoum Solar Park

Natural Hazards - Solar energy parks in desert areas must resist the encroachment of moving sand and burial by migrating dunes. It is therefore important to design economical, effective sand fences...     

The Research on Stability of Surrounding Rock in Gob-Side Entry Driving in Deep and Thick Seam

Geotechnical and Geological Engineering - The gob-side entry driving is driving in low pressure area, which bears less support pressure and is easy to maintain, so it is widely used. Taking the...     

珠江口盆地惠州凹陷迁移型层序特征及其意义

迁移型层序是陆相湖盆中一种特殊的层序构型,但是其特征以及主控因素尚不清楚.通过对珠江口盆地惠州凹陷文昌组层序地层学研究,发现下文昌组三级层序PSQ1~PSQ4主要发育在凹陷南部,上文昌组三级层序PSQ5~PSQ7主要发育在凹陷北部;三级层序PSQ1~PSQ7逐渐由南东向北西发生跨洼陷迁移.这种迁移型层序是由幕式构造活动差异性造成的,在裂陷IA幕,惠州凹陷南部控凹断裂活动强度大,发育以下文昌组为主的T型层序构型;在裂陷IB幕,北部断裂活动加强,南部的断裂活动减弱,造成沉积、沉降中心迁移到惠州凹陷北部,发育以上文昌组为主的H型层序构型.迁移型层序及其控制下的砂体和烃源岩在侧向迁移、叠加过程中,更利于生、储、盖等油气成藏要素的有效配置,形成多区块、多层段油气藏组合.