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Using reanalysis data and snow cover data derived from satellite observations, respective influences of Indian Ocean Dipole (IOD) and El Niño/Southern Oscillation (ENSO) on the Tibetan snow cover in early winter are investigated. It is found that the snow cover shows a significant positive partial correlation with IOD. In the pure positive IOD years with no co-occurrences of El Niño, negative geopotential height anomalies north of India are associated with warm and humid southwesterlies to enter the plateau from the Bay of Bengal after rounding cyclonically and supply more moisture. This leads to more precipitation, more snow cover, and resultant lower surface temperature over the plateau. These negative geopotential height anomalies north of India are related to the equivalent barotropic stationary Rossby waves in the South Asian wave guide. The waves can be generated by the IOD-related convection anomalies over the western/central Indian Ocean. In contrast, in the pure El Niño years with no co-occurrences of the positive IOD, the anomalies of moisture supply and surface temperature over the plateau are insignificant, suggesting negligible influences of ENSO on the early winter Tibetan snow cover. Further analyses show that ENSO is irrelevant to the spring/early summer Tibetan snow cover either, whereas the IOD-induced snow cover anomalies can persist long from the early winter to the subsequent early summer. 相似文献
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Minoru Fujii Shinichiro Murashige Yuka Ohnishi Atushi Yuzawa Hitoshi Miyasaka Yoshimi Suzuki Hiroshi Komiyama 《Journal of Oceanography》2002,58(3):438-443
Decomposition experiments were conducted on cultured phytoplankton (Skeletonema costatum) in seawater containing decomposer and consumer of size less than 500 μm. We determined the decomposition rates of bulk particulate
organic matter (POM), the ratio of labile to semi-refractory fractions in the POM, and the POM carbon/ nitrogen (C/N) ratio
during decomposition. To identify the kinetic mechanisms involved in the reactions of different order (e.g., first- and second-order),
we studied the sensitivity of reaction rates to the initial concentration of POM, ranging from 2.4 to 71 mg-C L−1. The results showed that decomposition consists of two first-order reactions: decomposition of labile and of semi-refractory
particulate organic carbon (POC). The decomposition rate constants found for labile (0.13 day−1 at 20°C), and semi-refractory POC (0.008 day−1 at 20°C), and the carbon weight ratio of semi-refractory POC (13% at 20°C), were insensitive to the initial organic matter
concentration. The time-dependence of the C/N ratio was also independent of this initial concentration. The decomposition
rate constants and the content of semi-refractory POC did not change, regardless of the absence or presence of 25–500 μm organisms
in natural seawater.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Xiaoan Zuo Halin Zhao Xueyong Zhao Yirui Guo Jianying Yun Shaokun Wang Takafumi Miyasaka 《Environmental Geology》2009,58(6):1227-1237
The Horqin Sandy Land is one of the most severely desertified regions in northern China. Plant communities and soil conditions
at five stages of grassland desertification (potential, light, moderate, severe and very severe) were selected for the study
of vegetation pattern variation relating to soil degradation. The results showed that vegetation cover, species richness and
diversity, aboveground biomass (AGB), underground biomass, litter, soil organic carbon (C), total nitrogen (N), total phosphorus
(P), electrical conductivity, very fine sand (0.1–0.05 mm) content and silt (0.05–0.002 mm) content decreased with the desertification
development. Plant community succession presented that the palatable herbaceous plants gave place to the shrub species with
asexual reproduction and sand pioneer plants. The decline of vegetation cover and AGB was positively related to the loss of
soil organic C and total N with progressive desertification (P < 0.01). The multivariate statistical analysis showed that plant community distribution, species diversity and ecological
dominance had the close relationship with the gradient of soil nutrients in the processes of grassland desertification. These
results suggest that grassland desertification results in the variation of vegetation pattern which presents the different
composition and structure of plant community highly influenced by the soil properties. 相似文献
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Occurrence of water ponding on soil surfaces depending on infiltration rates on Mongolian rangeland 
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下载免费PDF全文 Katori Miyasaka Sho Shiozawa Kazuhiro Nishida Siilegmaa Batsukh Shuichiro Yoshida Undarmaa Jamsran 《水文研究》2017,31(22):3996-4005
The occurrence of water ponding on soil surfaces during and after heavy rainfall produces surface run‐off or surface water accumulation in low‐lying areas, which might reduce the water supply to soils and result in a reduction of the soil water that plants can use, especially in arid climates. On Mongolian rangeland, we observed ponded water on the surface of a specific soil condition subjected to a heavy rainfall of 30 mm/hr. By contrast, ponded water was not observed for the same type of soil where livestock grazing had been removed for 6–8 years via a fence or for nearby soil containing less clay. We measured the infiltration rate (the saturated hydraulic conductivity of the surface soil, Ks) of the three sites by applying ponded water on the soil surface (an intake rate test). The results showed that Ks in the rangeland was lower than the rainfall intensity in the site where water ponded on the soil surface; however, Ks of the soil inside of the fence has recovered to 3 times that of the soil outside of the fence to exceed the rainfall intensity. Heavy rainfall that exceeds the infiltration rate occurs several times a year at the livestock grazing site where we observed ponded water. Slight water repellency of the soil reduces rain infiltration to increase the possibility of surface ponding for the soil. 相似文献
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It has been pointed out that climatological-mean precipitation-evaporation difference (P–E) should increase under global warming mainly through the increasing saturation level of moisture. This study focuses on evaporation changes under global warming and their dependency on the direct warming effect, on the basis of future projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Over most of the tropical, subtropical and midlatitude regions, the direct contribution from surface temperature increase is found to dominate the projected increase in evaporation. This contribution is nevertheless offset partially, especially over the oceans, by contributions from weakening surface winds and increasing near-surface relative humidity. Greater warming of surface air than of the sea surface also acts to reduce surface evaporation, by reducing both the exchange coefficient and humidity contrast at the surface. Though generally of secondary importance, this contribution is the dominant factor over the subpolar oceans. Over the polar oceans, the effect of sea-ice retreat dominantly contributes to the evaporation increase in winter, whereas the reduced exchange coefficient and surface humidity contrast coupled with the sea-ice retreat account for most of the response during summertime. Over the continents, changes in the surface exchange coefficient, reflecting changes in soil moisture and vegetation among other factors, are important to modulate the direct effects of the warming and the generally reduced surface air relative humidity. 相似文献
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T. Miyasaka T. OkuroH. Zhao X. ZhaoX. Zuo K. Takeuchi 《Journal of Arid Environments》2011,75(11):1155-1163
We examined changes in soil properties, crop biomass, and weed communities in the Horqin Sandy Land of China to elucidate cropland degradation. We studied three local cropland types having periods of cultivation of up to 20 years: maize cropland on lowlands without irrigation (nonirrigated lowland), maize cropland on flat sandy lands with irrigation (irrigated flatland), and bean-centered cropland on sand dunes without irrigation (nonirrigated dunes). Soil properties and crop biomass were more degraded in nonirrigated lowland and nonirrigated dunes than in irrigated flatland. Weed communities in the nonirrigated croplands were the type that become established in drier conditions, whereas wetland weeds were more abundant on irrigated flatland. Trends of change in each indicator did not always occur in parallel and differed statistically among the cropland types. Monitoring these indicators within the context of local land-use systems can provide scientific evidence on which to base local management practices or recommendations for change. 相似文献
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Food sources of the pearl oyster in coastal ecosystems of Japan: Evidence from diet and stable isotope analysis 总被引：1，自引：0，他引：1
Kayoko Fukumori Misa Oi Hideyuki Doi Noboru Okuda Hitomi Yamaguchi Michinobu Kuwae Hitoshi Miyasaka Kenji Yoshino Yoshitsugu Koizumi Koji Omori Hidetaka Takeoka 《Estuarine, Coastal and Shelf Science》2008
We estimated the composition of two food sources for the cultured pearl oyster Pinctada fucata martensii using stable isotopes and stomach content analysis in the coastal areas of the Uwa Sea, Japan. The δ13C values of oysters (−17.5 to −16.8‰) were intermediate between that of particulate organic matter (POM, −20.2 to −19.1‰) and attached microalgae on pearl cages (−13.0‰). An isotope mixing model suggested that oysters were consuming 78% POM (mainly phytoplankton) and 22% attached microalgae. The attached microalgal composition of the stomach content showed a strong resemblance to the composition of that estimated through the isotope mixing model, suggesting preferential utilization of specific components is unlikely in this species. These results indicate that P. fucata martensii feed on a mixture of phytoplankton and attached microalgae, and that the attached microalgae on pearl cages can serve as an important additional food source. 相似文献
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We report here the occurrence of pink sapphires in association with a variety of gemstones from the Trivandrum Granulite Block south of the Achankovil Shear Zone in southern India. The mineralization is associated with pegmatites or veins emplaced within granulite facies aluminous supracrustals. The sapphires show near-pure A1,0, composition (98.43-99.48 wt.%) with traces of Cr, O, (0.02-0.12 wt.%) and FeO (0.01-0.12 wt.%). The available radiometric age of 513-2 Ma for gem quality zircon associated with pink sapphire in the Melankode locality confirms that the mineralization is of late Pan-African age. Pink sapphires have been widely reported from a number of localities in southern Madagascar including Betroka, Illakaka, Antranondambo and Ambossary. Sapphires of various hues also occur in the Ratnapura gem district in the southwestern part of Sri Lanka. The pink sapphire occurrences in southern Madagascar and southern Kerala provide strong evidence for India-Madagascar juxtaposition in the Gondwana assembly with the Ranotsara Shear Zone in southern Madagascar extending into the Achankovil Shear Zone in southern India. 相似文献
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