Evolution of the Juan Fernandez microplate during the last three million years

During the spring of 1983, the R/V “Thomas Washington” surveyed an area located north of the Antarctic-Nazca-Pacific triple junction at 35°S.Magnetic and SEABEAM bathymetric data collected during the survey confirmed the existence of the Juan Fernandez microplate. This paper presents an analysis of the magnetic anomaly data.The western boundary of the microplate is a fast spreading center which has existed since 2 Ma and where the accretion rate has been about 14.5 cm/yr for the last 0.7 Ma.The eastern boundary of the microplate is characterized by a slow spreading center which separates the Juan Fernandez and Nazca plates. The accretion rate has been about 7.0 cm/yr between 0.7 and 0.4 Ma and about 1.6 cm/yr for the last 0.4 Ma.The two spreading centers are connected in the north and south by transform faults.Between the Juan Fernandez and Rapanui microplates, the East Pacific Rise is well defined between 30 and 32°S. In this region the axis displays a record accretion of about 17.2 cm/yr.South of the Juan Fernandez microplate, one magnetic profile (Oceano 7008) indicates that the opening rate is about 12.0 cm/yr on the Antarctic-Pacific ridge.The birth of the microplate is dated at about 2 Ma when the western boundary started to accrete. The evolution of the microplate corresponds to a transfer of accretion from the eastern boundary to the western axis. This is revealed by the net decrease of the opening rate from 7.0 cm/yr to 1.6 cm/yr observed at the eastern ridge where a small jump occurred at 0.4 Ma.     

Temporal and spatial variations of the atmospheric dust loading throughout West Africa over the last thirty years

The dust haze conditions, typical of the African atmosphere south of the Sahara, are a result of wind-generated dust from arid lands. The magnitude of the dust haze is evaluated for the 30-year period beginning in 1957 by calculating the number of occurrences where the observed visibility was reduced below threshold values of 10 km and 5 km. The frequency of low visibility was several times greater for the 1977–1986 period than for the 1957–1966 period. Large decreases in visibility are observed after the severe droughts of 1972–1973 and 1982-1984. Contrasting regional differences of the dustiness evolution are noticed. These differences are closely related to the differences in the regional rainfall evolution. The increase in dustiness is believed to arise from dust produced in new desertic areas which result from rainfall shortages along the southern border of the Sahara.     

Results of twenty years of atmospheric electricity research at Ibadan

The results of atmospheric electric measurements over a twenty year period (1961–1980) are reviewed for Ibadan situated in the tropical rain forest of Nigeria. The aim is to present the data in an easily accessible form.     

Review of Chinese atmospheric science research over the past 70 years: Atmospheric physics and atmospheric environment

Since the founding of the People's Republic of China 70 years ago,the subject of atmospheric physics and atmospheric environment has developed rapidly in China,providing important support for the development of atmospheric science and guarantee for the development of national economy.In this paper,the general advancement of atmospheric physics and atmospheric environment in last 70 years was described.The main research progress of atmospheric physics and atmospheric environment in the past 40 years of reform and opening-up was reviewed,the outstanding research achievements since the 21 st century were summarized,the major problems and challenges are pointed out,and the key directions and suggestions for future development are put forward.     

Geospatial-temporal analysis of land-use changes in the Yellow River Delta during the last 40 years

Research on land use/land cover changes (LUCC)has been the core project of the Global EnvironmentalChanges since the 1990s[1—6]. Scientists at home andabroad have been laying emphasis on integrationstudies on land-use change by “space and process”features[7—10] as researches on LUCC are in a greatdeal. It is of paramount important for us to studyLUCC at various spatial-temporal scales and build aquantitative assessment of land-use conversion by in-tegrated spatial-temporal features. …     

Vicissitude of Sogo Nur and environmental-climatic change during last 1500 years

Lakes in arid zone are sensitive to climatic changes. The lacustrine sediment sequence in Sogo Nur has well and truly recorded climatic events such as the Sui-Tang Dynasty Warm Period, the Song-Liao Dynasty Cold Period, the Medieval Warm Period, the Little Ice Age and the 20th Century Warm Period. Commonly, the climate in warm Periods was relatively humid,accordingly the lake area extended and water level rose, and vice versa. Apart from climatic change, human activity is also an important factor of influencing lake vicissitude, and they played the dominant role alternatively during different periods; the factor of climatic change predominated in historical period, while since the beginning of the 20th century the utilization of water resources by human has became decisive.     

Vicissitude of Sogo Nur and environmental-climatic change during last 1500 years

Lakes in arid zone are sensitive to climatic changes. The lacustrine sediment sequence in Sogo Nur has well and truly recorded climatic events such as the Sui-Tang Dynasty Warm Period, the Song-Liao Dynasty Cold Period, the Medieval Warm Period, the Little Ice Age and the 20th Century Warm Period. Commonly, the climate in warm Periods was relatively humid, accordingly the lake area extended and water level rose, and vice versa. Apart from climatic change, human activity is also an important factor of influencing lake vicissitude, and they played the dominant role alternatively during different periods; the factor of climatic change predominated in historical period, while since the beginning of the 20th century the utilization of water resources by human has became decisive.     

Molecular biomarker record of paleooceanographic environment in the East China Sea during the last 35000 years

By reference of the δ¹⁸O and δ¹³C isotopic compositions of G.sacculifer and accelerator mass spectrometry (AMS)¹⁴C dates, the U _K ³⁷ , ∑C _– ²¹ /∑C _+- ²² and Pr/Pn in core DGKS9603 have been used to characterize the changes of paleooceanographic environment occurring in the East China Sea (ECS) during the last 35000 years. The stratigraphic records of these proxies have shown that during the last 35 ka the Okinawa Trough has gone through 7 stronger cold-climate events (C₁–C₇) and 9 terrigenous matter-decreasing events (e₂–e₉), of which, the C₁ corresponds to the cold episode occurring in the middle late Holocene, C₂–C₄ and C₇ correspond to the H₁–H₄ events, respectively. e₁ and e₃–e₈ correspond to the decrease of sea surface temperature (SST), respectively. The terrigenous inputs increased when Heinrich events occurred. Climate colding resulted in the decrease of terrigenous matter transported by rivers, and the increase of that transported by winter monsoon. Heinrich events are closely related to East Asia monsoon. During the Last Glacial Maximum (LGM, 15.5–25.8 Cal ka BP), reduction environment fluctuated strongly, bringing forth three stronger reduction events (R₁–R₃) and one weaker reduction event (O), of which, R₁–R₃ correspond to the decrease of SST and increase of terrigenous nutrient and O corresponds to the decrease of terrigenous nutrient. The fluctuation of reduction condition must be related to the change of sea surface productivity.     

近60年全球大气环流经向模态的气候变化

本文根据1948～2004年NCEP/NCAR 1000 hPa、500 hPa、100 hPa高度场逐月再分析资料,分析了近60年全球大气环流经向模态的气候变化. 结果表明：近60年来第一模态从低层到高层都表现出高纬与低纬地区之间明显的反向变化关系,且随时间有明显的增强趋势. 第一模态位相发生了相反的改变,低纬地区由负距平演变为正距平,高纬地区由正距平演变为负距平. 1000 hPa和500 hPa高度场上的南半球比北半球变化激烈,而100 hPa高度场上的北半球比南半球变化激烈. 第二模态在1000 hPa高度场上,主要表现为南极涛动（AAO）和北极涛动(AO),且两涛动在年际、年代际尺度上表现出明显的负相关关系;在100 hPa高度场上,主要表现为南北半球高纬度地区之间的反向变化;500 hPa高度场是1000 hPa和100 hPa的一个过渡层次,主要表现出明显的南极涛动(AAO). 第二模态可能是南北半球中高纬环流相互作用的桥梁.     

Review of Chinese atmospheric science research over the past 70 years: Synoptic meteorology

Synoptic meteorology is a branch of meteorology that uses synoptic weather observations and charts for the diagnosis,study,and forecasting of weather.Weather refers to the specific state of the atmosphere near the Earth's surface during a short period of time.The spatial distribution of meteorological elements in the atmosphere can be represented by a variety of transient weather phenomena,which are caused by weather systems of different spatial and temporal scales.Weather is closely related to people's life,and its development and evolution have always been the focus of atmospheric scientific research and operation.The development of synoptic meteorology is closely related to the development of observation systems,dynamical theories and numerical models.In China,observation networks have been built since the early 1950 s.Up to now,a comprehensive meteorological observation systembased on ground,air and space has been established.In particular,the development of a new generation of dense radar networks,the development of the Fengyun satellite series and the implementation of a series of large field experiments have brought our understanding of weather from large-scale environment to thermal dynamics,cloud microphysical structure and evolution characteristics of meso and micro-scale weather systems.The development of observation has also promoted the development of theory,numerical model and simulation.In the early days,China mainly used foreign numerical models.Lately,China has developed numerical model systems with independent intellectual property rights.Based on the results of high-resolution numerical simulations,in-depth understanding of the initiation and evolution mechanism and predictability of weather at different scales has been obtained.Synoptic meteorology has gradually changed from an initially independent development to a multidisciplinary approach,and the interaction between weather and the change of climate and environment has become a hot and frontier topic in atmospheric science.This paper reviews the important scientific and technological achievements made in China over the past 70 years in the fields of synoptic meteorology based on the literatures in China and abroad,from six aspects respectively including atmospheric dynamics,synoptic-scale weather,typhoon and tropical weather,severe convective weather,numerical weather prediction and data assimilation,weather and climate,atmospheric physics and atmospheric environment.     

中国近50年来群发性高温事件的识别及统计特征

本文提出一种简化的识别群发性气候事件方法,对近50多年来全国群发性高温事件识别结果表明该方法物理意义明确,客观有效,符合实际.通过对近50年来群发性高温事件统计发现,不论是从发生频数、持续时间、影响站数还是综合强度来看,2000年以后的群发性高温事件都是5个年代中最显著的.与此同时,群发性高温事件具有明显的区域特征,长江以南地区发生频率最高,其次为黄河下游华北地区,以新疆为主的西北地区亦是多发区,各个区域群发性高温事件在不同月份的分布差异体现了我国季风雨带移动及下垫面的影响.     

安宁河—则木河断裂带1993～2012年重力动态变化

利用安宁河—则木河断裂带区域1993～2012年的流动重力观测数据,作出重力场动态图像和部分重力点值时序变化图,总结在这20年里安宁河—则木河断裂带的活动规律,分析研究安宁河—则木河断裂带区域及其临近区域较大震级的地震孕育过程中区域的重力变化情况,为安宁河—则木河断裂带区域地震预测预报提供经验和参考资料.     

鲜水河断裂带近20年磁场变化特征

通过对流动地磁重复测量数据的计算处理,得出鲜水河断裂带上各测点相邻两期的磁场总强度变化,使用surfer软件绘制出鲜水河断裂带上磁场变化的时空分布。由图分析鲜水河断裂带的磁场变化特征,并着重探究鲜水河断裂带2000年至2003年的活动情况以及从磁力资料方面来分析汶川地震对鲜水河断裂带的影响。     

Turbulent measurements in the stable atmospheric boundary layer during SHEBA: ten years after

This paper surveys results of the comprehensive turbulent measurements in the stable boundary layer (SBL) made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) in the Beaufort Gyre from October 1997 through September 1998. Turbulent fluxes and mean meteorological data were continuously measured and reported hourly at five levels on a 20-m main SHEBA tower. Eleven months of measurements during SHEBA cover a wide range of stability conditions, from the weakly unstable regime to very stable stratification, and allow studying the SBL in detail. A brief overview of the SBL regimes, the flux-profile relationships, the turbulent Prandtl number, and other parameters obtained during SHEBA is given. The traditional Monin—Obukhov approach, z-less scaling, and gradient-based scaling are evaluated and discussed based on the data from SHEBA.     

Annual temperatures during the last 2485 years in the mid-eastern Tibetan Plateau inferred from tree rings

By combining living trees and archaeological wood, the annual mean temperatures were reconstructed based on ring-width indices of the mid-eastern Tibetan Plateau for the past 2485 years. The climate variations revealed by the reconstruction indicate that there were four periods to have average temperatures similar to or even higher than that mean of 1970 to 2000 AD. A particularly notable rapid shift from cold to warm, we call it the “Eastern Jin Event”, occurred from 348 AD to 413 AD. Calculation results show that the temperature variations over the mid-eastern Tibetan Plateau are not only representative for large parts of north-central China, but also closely correspond to those of the entire Northern Hemisphere over long time scales. During the last 2485 years, the downfall of most major dynasties in China coincides with intervals of low temperature. Compared with the temperature records in other regions of China during the last 1000 years, this reconstruction from the Tibetan Plateau shows a significant warming trend after the 1950s. Supported by National Natural Science Foundation of China (Grant Nos. 40525004, 40599420, 40890051), National Basic Research Program of China (Grant Nos. 2007BAC30B00, 2004CB720200, 2006CB400503) and the Swedish International Development Cooperation Agency (SIDA, Grant to Hans W. Linderholm)     

Lake Ladoga ice phenology: Mean condition and extremes during the last 65 years

Winter conditions play an important role for the largest lake in Europe—Lake Ladoga. The ice cover lasts for 171 ± 3 days on average from the early November until the mid‐May. We investigated the ice regime of Lake Ladoga using a constructed ice database of aircraft surveys and satellite images. More than 1250 surveys of the lake's ice cover from 1943 to 2010 were collected and analysed to determine mean and extreme ice conditions for winters of different types of severity. The time series of ice cover percentage over the lake was plotted. On average, 18 observational ice charts were made every winter. Individual ice phenology records show considerable year‐to‐year variation. For this reason, records typically have been combined and analysed as groups (categories). Extremely cold winters were determined as winters with complete ice cover that lasts more than three months which is approximately 90% quartiles from all winters with complete ice cover. The lake surface was completely covered with ice for more than three months during 5 seasons. Extremely warm winters when the maximum ice cover was less than 70% of the lake area occurred during 5 seasons as well. A basic relationship between the winter severity as winter maximum of accumulated freezing degree‐days (AFDD) and the earlier derived Relative Ice Cover Index (RICI) was established. We have used teleconnection indices such as North Atlantic Oscillations (NAO) and Arctic Oscillation (AO) for the period from October to May for estimation of different types of Lake Ladoga's ice conditions. The AO index in winter months and local winter maximum of AFDD explained much of the interannual variation in ice cover. Copyright © 2011 John Wiley & Sons, Ltd.     

Complex disturbance-driven reactivation of near-surface sediments in the largest dunefield in North America during the last 200 years

Understanding the historical activity of desert dune systems is important for identifying both the palaeoenvironmental drivers of change and the likelihood of future reactivation. Dating dune sediments in the Nebraska Sandhills has identified regional-scale dune activity over centennial and millennial timescales during the Holocene, occurring at 9.6–6.5, 3.8 and 2.5 ka, and most recently spanning the Medieval Climatic Anomaly 1050–650 years BP. These periods have been interpreted as palaeoclimatic evidence of intense aridity lasting decadal and centennial timescales. A detailed record of dune activity in the historical period, since EuroAmerican arrival, is lacking however, yet important for interpreting the role of human agency amongst the factors influencing disturbance. Without a high-resolution record of short-term, historical, local sediment mobilization, it is not possible to distinguish the environmental factor(s) responsible for local reactivation. In this paper, the individual drivers of vegetation disturbance are reviewed and presented alongside a luminescence-dated reconstruction of dune sediment deposition ages. This allows an integrated assessment of the relationship between drivers and environmental response over a recorded period. We focused our investigation on the aeolian reactivations of surface dune sediments and blowout features around the Niobrara Valley Preserve in the northern limits of the Nebraska Sandhills. Results show a near-continuous (within uncertainties) timeline of local reactivation across the sites studied, with variation between the individual features indicating that both regional (i.e. climatic) and local (i.e. land use) forcings contribute to surface disturbance. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

近50年来环境变化对巢湖硅藻组合演替的影响

湖泊生态系统往往受营养、水文和气候等诸多环境因子的影响.区分不同环境因子的影响是揭示湖泊生态环境演化机制的关键.本文基于巢湖岩芯210Pb和137Cs测年、硅藻、地球化学指标和粒度分析结果以及流域水文、气候、人口和农业资料,利用冗余分析,定量区分1950年来营养、水文和气侯对硅藻组合演替的影响.1978年前硅藻组合中A...     

Variations in monsoon precipitation over southwest China during the last 1500 years and possible driving forces

Science China Earth Sciences - Understanding hydroclimatic patterns and their possible driving mechanisms during distinct climate periods over the last 1500 years—such as the Medieval Warm...     

Oxygen isotope stratigraphy and events in the northern South China Sea during the last 6 million years

Based on the stable isotopic analysis of more than 1000 samples of planktonic and benthic foraminifers from ODP Site 1148 in the northern South China Sea (SCS), the oxygen isotope stratigraphy has been applied to the last 3 million years for the first time in the SCS. Furthermore, the paleoceanographic changes in the northern SCS during the last 6 million years have been unraveled. The benthic foraminiferal δ¹⁸O record shows that before δ3.1 Ma the SCS was much more influenced by the warm intermediate water of the Pacific. The remarkable decrease in the deepwater temperature of the SCS during the period of 3.1-2.5 Ma demonstrates the formation of the Northern Hemisphere ice-sheet. However, the several sea surface temperature (SST) reductions during the early and middle Pliocene, reflected by the planktonic foraminiferal δ¹⁸O, might be related to the ice-sheet growth in the Antarctic region. Only those stepwise and irreversible SST reductions during the period of δ2.2-0.9 Ma could be related to the formation and growth of the Northern Hemisphere ice-sheet.