Science in China Series D: Earth Sciences

By using 2-D chemical model, the trend of total column ozone over the Tibetan Plateau is simulated. The results show that from 1980 to 1993, the total column ozone over the Tibetan Plateau decreases; after 1995, it starts to recover. But until 2050, it will not still reach the level of 1980 total column ozone. Under Tibetan special circulation, its total column ozone recovers more rapidly than zonal mean. Therefore, the Tibetan special meridional circulation is not a main reason why the total column ozone over the Tibetan Plateau decreases more strongly than zonal mean.

The abundance of radiolarian, diatom and sponge spicule and H4SiO4 in pore-waters increase abruptly at the boundary between Early and Late Oligocene (about 30-27.5 Ma) at Site 1148 of the northern South China Sea (SCS), indicating high biogenic silica accumulation during this time. At the same time (about 30-28 Ma), high biogenic silica deposition occurred in the central equatorial Pacific. Comparison of the biogenic silica accumulation at Site 1148 of the SCS with that at Site 929 of the Atlantic verifies that the biogenic silica accumulation between the low latitude Pacific and Atlantic oceans expresses the evident relationship of compensation during the Oligocene. Biogenic silica accumulation decreased in the Atlantic, whereas it increased in the Pacific at the boundary between the Early and Late Oligocene. It resulted from the formation and presence of North Atlantic deep water (NADW) in the Atlantic basin, indicating an intensive basin-basin fractionation. XRD analysis and SEM observation of the samples from Site 1148 demonstrate that most of radiolarian, diatom and sponge spicule have suffered from dissolution and reprecipitation, suggested by the opal-A→opal-CT transformation. As a result of the transformation, porosity increased, but dry and bulk densities decreased, reflecting the consequence of diagenesis on the physical property of sediment.

Soil moisture data of 45 years from European Center for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) and the in situ observational data are used to study the temporal and spatial characteristics of the soil moisture in boreal spring in the area to the east of 100°E in China. Results show that ERA-40 soil moisture well reproduces the temporal and spatial features of observations. ERA-40 data capture the spatial pattern that the soils in Northeast China and Southwest China are wetter than those in Inner Mongolia and North China and represent the inter-annual variability in observations. The dry trends of spring soil moisture are evident over the whole eastern China. It is especially prominent for the dry trend in southwest China where the spring soil from surface to deep-layer show drying and the trend became significant after the 1980s. The dry trend in Northeast China is weak after early 1970s in near-surface layer but aggravates after latel 1970s in deep layers. In the mid-latitude zone, the inter-annual variation of spring soil is robust and shows no dry trend except in deep-layer after 1988.

Four layers of cherts were found for the first time in the Yangla copper deposit, western Yunnan Province. The cherts possessed the following geochemical characteristics: 1 Low TiO2 and Al2O3 contents, but high ore-forming element (e.g. Cu, Au, Ag) contents; 2 low total REE contents and clear negative Eu anomalies when normalized to chondrite similar to the REE contents and distribution patterns of associated massive sulfide ores; 3 silicon isotopic compositions of cherts in the Yangla deposit being the same as cherts and geyserite of hot-water sedimentary origin; 4 lead and sulfur isotopic compositions of cherts in the Yangla deposit being similar to those of the massive sulfide ores in the Yangla deposit; 5 Rb-Sr isochron age of cherts from the Yangla deposit being identical with that of host strata. Hence, we conclude that the cherts in the Yangla deposit are of hot-water sedimentary origin, which have a close relationship with the massive sulfide ores. The discovery of hydrothermal cherts from the Yangla copper deposit provides further evidence for the hydrothermal exhalative origin of the massive sulfide deposits.

To examine the application potential of hyperspectral remote sensing techniques in classifying very low-grade metamorphic belts, the composition of clay minerals and the cyrstallinity of illite from mudstones were measured using XRD and VIS-SWIR (400–2500 nm) reflectance spectroscopy. Based on the illite cyrstallinity, Kübler Index (KI), the Early Triassic LuoLou Group and the Middle Triassic lower Baifeng Formation were classified as the lower Epizone with KIΔ2θ° ranging from 0.22 to 0.25, the upper Baifeng Formation as upper anchizone with KIΔ2θ° ranging from 0.26 to 0.33, and the Hekou Formation as lower anchizone with KIΔ2θ° ranging from 0.38 to 0.40. According to a KIΔ2θ° value of 0.43, it is possible that there may exist a local diagenetic zone in the upper strata. The illite cyrstallinity Kübler index and the metamorphic grade increase from the bottom to the top of the stratigraphic sequence. The metamorphic grade boundaries nearly match the stratigraphic boundaries, indicating a burial metamorphism nature for the stratigraphic sequence. From the bottom to the top of the sequence, the spectral absorption band center of clay minerals from fresh rocks is around 2200 nm. The absorption band centers change towards shorter wavelengths: the Luolou Group being at 2220 nm, the Baifeng Formation at 2217–2213 nm, the lower member of the Hekou Formation at 2214–2206 nm, and the upper member of the Hekou Formation at 2205–2197 nm. The spectral absorption band center of illite shows the same change pattern. These results indicate that very low-grade metamorphic belts can be subdivided using spectral indices of clay minerals, which are measured by using field portable spectroradiometers. However, it may not work well with satellite and airborne sensors.

The minimum variance and tangential discontinuity analyses are used to find the normal directions of the magnetopause using 550 crossings from ISEE 1 and 2, AMPTE/IRM, and IMP 8 satellites. Then, the average shape of the magnetopause is studied by using two-region fit procedure. These studies show: (i) most of the crossings are reasonably characterized as tangential discontinuity; (ii) there does appear to be east-west and north-south asymmetry in the shape of the magnetopause; (iii) the magnetopause in the equatorial region is swept back from the vacuum location for both northward and southward IMF, which means that the simple single conic section used in previous fits may not be appropriate to the entire shape of the magnetopause, especially at the nightside.