Trend and seasonal variations of atmospheric CH_4 in Beijing

The atmospheric CH\-4 in Beijing is still increasing, even though its increasing rate has significantly decreased from 1.76%/a during 1985—1989 to 0.50%/a during 1990—1997. The seasonal variation of CH\-4 concentration showed a double\|peak pattern, one peak appearing in winter and the other in summer. It is evident that the annually seasonal variations of atmospheric CH\-4 in Beijing are different. From 1986 to 1997, the atmospheric CH\-4 increased by 185 ppbv, 37% and 21% of which were due to the increase in winter and in summer, respectively. After 1993, the annually seasonal increasing rate of CH\-4 concentration in summer (due to emission from biogenic sources) is negative while the increasing rate in winter (due to emission from non\|biogenic sources) is positive about 25 ppbv/a. As a result, the increase of CH\-4 emission from non\|biogenic sources in winter is the major reason that caused the annually seasonal increasing rate from 1993 to 1997. The biogenic sources in Beijing are shrinking while the non\|biogenic ones (such as fossil fuel combustion) are enlarging.

Seasonal and inter-annual variations of the primary types of the Arctic sea-ice drifting patterns

Abstract Monthly mean sea ice motion vectors and monthly mean sea level pressure （SLP） for the period of 1979-2006 are investigated to understand the spatial and temporal changes of Arctic sea-ice drift. According to the distinct differences in monthly mean ice velocity field as well as in the distribution of SLP, there are four primary types in the Arctic Ocean： Beaufort Gyre＋Transpolar Drift, Anticyclonic Drift, Cyclonic Drift and Double Gyre Drift. These four types account for 81% of the total, and reveal distinct seasonal variations. The Cyclonic Drift with a large-scale anticlockwise ice motion pattern trends to prevail in summer while the Anticyclonic Drift with an opposite pattern trends to prevail in winter and spring. The prevailing seasons for the Beaufort Gyre＋Transpolar Drift are spring and autumn, while the Double Gyre Drift trends to prevail in winter, especially in Feb- ruary. The annual occurring times of the Anticyclonic Drift and the Cyclonic Drift are closely correlated with the yearly mean Arc- tic Oscillation （AO） index, with a correlation coefficient of -0.54 and 0.54 （both significant with the confident level of 99%）, re- spectively. When the AO index stays in a high positive （negative） condition, the sea-ice motion in the Arctic Ocean demonstrates a more anticlockwise （clockwise） drifting pattern as a whole. When the AO index stays in a neutral condition, the sea-ice motion becomes much more complicated and more transitional types trend to take place.

Seasonal and annual variations of marine sinking particulate flux during 1993 ~ 1996 in the central South China Sea

A total of 67 samples from the upper and lower sediment traps in the central South China Sea were analyzed, which were collected during 1993 ~ 1996. It is indicated that the distribution of stable isotope values, surface primary productivity, fluxes of total particulate matter, carbonate, biogenic opal, organic carbon, planktonic foraminiferal species and their total amount exhibit obviously seasonal and annual fluctuations. High values of the fluxes occurred in the prevailing periods of the northeastern and southwestern monsoons, and the low values occurred during the periods between the two monsoons. The fluxes of some planktonic foraminiferal species （ Globigerinoides sacculifer , G. ruber , Globigerinita glutinata, Neogloboquadrina dutertrei ） and their percentages also exhibit two prominent peaks during the prevailing periods of the northeastern and southwestern monsoons respectively, while those of Globigerina bulloides, Globorotalia menardii and Pulleniatina obliquiloculata only exhibit one peak in the prevailing periods of the northeastern monsoon. In addition, fluxes and percentages of Globigerinoides sacculifer and Globorotalia menardii as well as the fluxes of carbonate and total amount of planktonic foraminifera decrease gradually from 1993 to 1996, and those of Globigerina bulloides, Globigerinita glutinata and biogenic opal increase gradually from 1993 to 1996. The fluxes of carbonate and organic carbon in the upper trap are higher than those in the lower one. The study indicates that the seasonal and annual variations of the sediment fluxes and planktonic foraminiferal species are mainly controlled by the changes of surface primary productivity and hydrological conditions related to the East Asian monsoon. The lower carbonate and organic carbon fluxes in the lower trap are related to the dissolution.

Three-year Variations of Water, Energy and CO_2 Fluxes of Cropland and Degraded Grassland Surfaces in a Semi-arid Area of Northeastern China

Based on 3 years （2003-05） of the eddy covariance （EC） observations on degraded grassland and cropland surfaces in a semi-arid area of Tongyu （44°25′N, 122°52′E, 184 m a.s.1.）, Northeast China, seasonal and annual variations of water, energy and CO2 fluxes have been investigated. The soil moisture in the thin soil layer （at 0.05, 0.10 and 0.20 m） clearly indicates the pronounced annual wet-dry cycle; the annual cycle is divided into the wet （growing season） and dry seasons （non-growing season）. During the growing season （from May to September）, the sensible and latent heat fluxes showed a linear dependence on the global solar radiation. However, in the non-growing season, the latent heat flux was always less than 50 W m^-2, while the available energy was dissipated as sensible, rather than latent heat flux. During the growing season in 2003-05, the daily average sensible and latent heat fluxes were larger on the cropland surface than on the degraded grassland surface. The cropland ecosystem absorbed more CO2 than the degraded grassland ecosystem in the growing season in 2003-05. The total evapotranspiration on the cropland was more than the total precipitation, while the total evapotranspiration on the degraded grassland was almost the same as the total annual precipitation in the growing season. The soil moisture had a good correlation with the rainfall in the growing season. Precipitation in the growing season is an important factor on the water and carbon budget in the semi-arid area.

SEASONAL AND ANNUAL TEMPERATURE VARIATIONS SINCE 1470 AD IN EAST CHINA

The ten-year mean anomalies of seasonal and annual temperatures were reconstructed on the basis of historical documents of cold events such as severe snowing and freezing of lakes and rivers.The assorted events were calibrated with instrumental observations of temperature and transformed into ten-year mean anomalies. The reconstructed temperature series show predominance of cold climate in the first four hundred years of the period examined.The centenary seasonal temperature anomalies for the 16th to the 19th century vary between -0.1 and -0.7K.The coldest decades concentrated in the middle of 17th and 19th centuries.It provided the irrefutable evidence of the occurrence of the Little Ice Age in China.The minima of ten-year mean temperature anomalies ranged about -1.5 to 2.0K in spring and winter.Meanwhile,the variance of ten-year mean tempera- ture was increased by more than 20％ in comparison to the 20th century.