The response of sedimentation in three varved lacustrine sequences to air temperature,precipitation and human impact

Human activity and climatic forcing have influenced sedimentation in three of Finland's deepest lakes during the last centuries. High-resolution sediment sequences of Lake Päijänne, Lake Pääjärvi and Lake Pyhäjärvi represent records of the last 440 years, 839 years and 633 years, respectively. The accumulation rates of dry matter, organic carbon and biogenic silica refer to changes in human activity in the catchments. However, they also reveal the importance of climatic forcing on lake sediment deposition. A significant correlation was found between instrumentally measured records of temperature (163 years) and precipitation (148 years), and varve thickness. Warm winter months indicating a short ice-cover period have the strongest control on varve thickness. This shows that wind-driven resuspension of littoral material is the forcing mechanism of climate on lake sediments. The long-term human-induced erosion pulses observed may even have magnified the climatic signals in some cases. Nevertheless, increased anthropogenic field erosion in the catchment, and the associated leaching of bioavailable nutrients, hampers the observation of climate signals, especially during the last 50 years, in the lakes studied.This is the second paper a series of papers published in this issue on high-resolution paleolimnology. These papers were presented at the Sixth International Palaeolimnology Symposium held 19-April, 1993 at the Australian National University, Canberra, Australia. Dr A. F. Lotter and Dr. M. Sturm served as guest editors for these papers.     

Changing predictability of Indian monsoon rainfall anomalies?

The predictability of Indian summer monsoon rainfall from pre-season circulation indices is explored from observations during 1939–91. The predictand is the all-India average of June–September precipitation NIR, and the precursors examined are the latitude position of the 500 mb ridge along 75°E in April (L), the pressure tendency April minus January at Darwin (DPT), March-April-May temperature at six stations in west central India (T6), the sea surface temperature (SST) anomaly in the northeastern Arabian Sea in May (ASM), SST anomaly in the Arabian Sea in January (ANJ), northern hemisphere temperature anomaly in January–February (NHT), and Eurasian snow cover in January (SNOW). Monsoon rainfall tends to be enhanced with a more northerly ridge position, small Darwin pressure tendency, warmer pre-season conditions, and reduced winter snow cover. However, relationships have varied considerably over the past half-century, with the strongest associations during 1950–80, and a drastic weakening in the 1980s. Four prediction models were constructed based on stepwise multiple regression, using as predictors combinations of L, DPT, T6, ASM, and NHT, with 1939–68 as “dependent” dataset, or training period, and 1969–91 as “independent” dataset or verification period. For the 1969–80 portion of the verification period calculated and observed NIR values agreed closely, with the models explaining 74–79% of the variance. By contrast, after 1980 predictions deteriorated drastically, with the explained variance for the 1969–89 time span dropping to 25–31%. The monsoon rainfall of 1990 and 1991 turned out to be again highly predictable from models based on stepwise multiple regression and linear discriminant analysis and using as input L + DPT or L + DPT + NHT, and with this encouragement an experimental real-time forecast was issued of the 1992 monsoon rainfall. These results underline the need for investigations into decadal-scale changes in the general circulation setting and raise concern for the continued success of seasonal forecasting.     

福建山地气候生态特征及其宜茶气候带的划分

福建山地分布近海面至海拔2158米,立体气候特征极其明显。本文根据福建山地气候生态特征和茶树的生物学特性,将山地划分为:1.大叶种茶树最适宜、适宜、不适宜种植三个气候带;2.中、小叶种茶树最适宜、适宜、次适宜、不适宜四个气候带。并依此提出科学开发福建山地茶叶生产的五项关键技术措施。     

Analyse isotopique de l'air piégé dans la glace pour quantifier les variations de température

Isotopic measurements in polar ice core have shown a succession of rapid warming periods during the last glacial period over Greenland. However, this method underestimates the surface temperature variations. A new method based on gas thermal diffusion in the firn manages to quantify surface temperature variations through associated isotopic fractionations. We developed a method to extract air from the ice and to perform isotopic measurements to reduce analytical uncertainties to 0.006 and 0.020$\text{‰}$ for δ¹⁵N and δ⁴⁰Ar. It led to a 16±1.5 °C surface temperature variation during a rapid warming ($\text{?70}\text{000}$ yr). To cite this article: A. Landais et al., C. R. Geoscience 336 (2004).     

Numerical analysis of the source-sink alternation of composite global warming potential of the paddy ecosystem in the Yangtze Delta

The three important greenhouse gases, namely CO2, CH4 and N2O[1,2], participate in the process of carbon and nitrogen cycling in the paddy field simultaneously. CO2 is assimilated by rice through photosynthesis, which means the paddy field is the sink of …     

内蒙古赤峰地区沙尘暴发生特点及成因

用 1 2个观测站的 1 96 1～ 2 0 0 0年 4 0年的沙尘暴、大风日数和降水量等观测资料 ,分析了内蒙古赤峰地区沙尘暴发生的地理分布、年际和年代际变化特征等。结果表明 :赤峰地区近 4 0年来沙尘暴呈减少趋势 ,其特殊的地形特征和多风的气候特点是沙尘暴多发的主要原因。     

Climatic fluctuation and disasters during recent 100 years in China’s tropics

China's tropics belongs to the humid tropical zone of Asian monsoon. The north boundary of China's tropics lies about 24oN but the eastern part of the boundary tends northwards and the western part tends southwards. The land area of China's tropics is 51.85×104 km2, accounting for 5.4% of the total land area of China and 28% of the total area of China's territory if the South China Sea is taken into account. During recent 100 years, based on the background of global changes, the climatic …     

塔克拉玛干沙漠东南部气象参数及沙丘横断面风速特征研究

以塔克拉玛干沙漠东南部国道G315线若羌-且末沙漠公路沿线为研究区域，分析研究了塔克拉玛干东南部近43a气候特征和气候变化趋势。在上述基础上，选取复合沙丘顶部、半坡、底部和平沙地四种典型风沙地貌为床面，采用YNZX—多功能全自动集沙仪，进行野外风沙监测，获取一批有关沙丘横断面不同高度脉动风速、输沙量的珍贵资料，分析了塔克拉玛干沙漠东南部沙丘横断面风速特征，为沙漠地区修筑公路以及选线参数研究提供科学依据。     

Warming in Arctic intermediate and deep waters around Chukchi Plateau and its adjacent regions in 1999

Warming in the Arctic Intermediate Water (AIW) has been reported in a series of articles in recent years. Prior to 1992, the water temperature of AIW off the Chukchi Continental Slope had never exceeded 0.5℃. Aagaard et al.[1] and Carmack[2] were the first to report that the temperature in AIW in the area in 1993 was close to 1℃, based on the data observed in a Canadian expedition. In 1994, the temperature of AIW around the Chukchi Sea and Mendeleyev Ridge again rose by at least an…     

Ground Surface Warming History in Northern Canada Inferred from Inversions of Temperature Logs and Comparison with Other Proxy Climate Reconstructions

— Well temperature logs from 61 sites located in discontinuous and continuous permafrost regions of northern Canada are analyzed. The method of functional space inversion (FSI) is applied to the set of precise temperature logs from wells located between 60 ° and 82 °N. There is strong evidence of extensive ground surface temperature (GST) warming beginning in the late 18^th century and lasting until the 20^th century. This was preceded by a lengthy period of cooling. The approximate average increase of the surface temperature of Canadian Arctic, based on all individual GST histories, is > 1.3 °C for the last 200 years. Simultaneous inversion of all well temperature data suggests an even higher warming (approximately 2 °C). There has been no strong south-to-north gradient in the ground warming magnitude when northern Canadian data are compared with eastern and central Canadian data south of 60 °N which also shows warming close to 2 °C. In Alaska, warming of some 2 °C has been restricted mainly to the 20^th century. In general, however, a high warming magnitude is common for most of Canada and Alaska for the previous century. The averaged GST history (GSTH) for the Canadian Arctic is calibrated with and compares visually with a variety of recently published regional and hemispheric proxy climate reconstructions. These show that GST warming derived from well temperature logs is generally higher than one shown by other proxy (mainly tree-ring reconstructions).Received April, 2003