(The) geochemical cycle of platinum group and rare earth elements in the earth surface environment

학위논문 (박사)-- 서울대학교 대학원 : 지구환경과학부, 2011.8. 허영숙.Docto

Concentrations of rare earth elements in pore waters of IODP Holes 323-U1345A and 323-U1345B

We studied the diagenetic behavior of rare earth elements (REEs) in a highly productive passive margin setting of the Bering Sea Slope. Site U1345 was drilled during the Integrated Ocean Drilling Program Expedition 323 at a water depth of 1008 m currently in the center of an oxygen minimum zone. Pore water concentrations of fourteen REEs were determined down to ~ 140 meters below the seafloor (mbsf). The REE concentrations were higher in the pore water than the deep seawater, indicating that there was significant liberation from the sediments during diagenesis. There was a major peak at ~ 10 mbsf that was more pronounced for the heavy REE (HREE); this peak occurred below the sulfate-methane transition zone (6.3 mbsf) and coincided with high concentrations of dissolved iron and manganese. At ~ 2 mbsf, there was a minor peak in REE and Mn contents. Below ~ 40 mbsf, the REE concentration profiles remained constant. The Ce anomaly was insignificant and relatively constant (PAAS-normalized Ce/Ce = 1.1 ± 0.2) throughout the depth profile, showing that the Ce depleted in seawater was restored in the pore water. HREE-enrichment was observed over the entire 140 m except for the upper ~ 1 m, where a middle REE (MREE)-bulge was apparent. REE release in shallow depths (2-4 mbsf) is attributed to the release of light REEs (LREEs) and MREEs during the organoclastic reduction of Mn oxides in anoxic sediments. The high HREE concentrations observed at ~ 10 mbsf can be attributed to the reduction of Fe and Mn minerals tied to anaerobic oxidation of methane or, less significantly, to ferromagnesian silicate mineral weathering. The upward diffusion flux across the sediment-water interface was between 3 (for Tm) and 290 (for Ce) pmol/m**2/y

Combination of multiple stable isotope and elemental analyses in urban trees reveals air pollution and climate change effects in Central Mongolia

The Ulaanbaatar area in Mongolia has become one of the most polluted regions worldwide due to the rapid increase in urbanization, industrial activity and traffic. However, we critically lack knowledge on the impacts of air pollution on surrounding forest ecosystems that may be further amplified by the ongoing climate change. Here, we apply a novel combination of multiple stable isotope analyses (nitrogen: δ15N, carbon: δ13C, oxygen: δ18O, hydrogen: δ2H) in foliar and tree-ring samples from different tree species, including deciduous, broadleaf species (poplar and birch), a deciduous conifer (larch) and needle evergreen species (spruce and Scots pine). This was complemented by trace element analysis, to study the influence of air pollution and climate on urban, suburban and more remote forests in and around Ulaanbaatar. We found indications of pollution effects in urban and suburban sites in foliar material, particularly in δ15N, with unusually high values of > 10‰, that could be related to tree uptake of NOx. Results were similar for all species, but with a smaller effect for Scots pine. The tree-ring δ15N values were found to be clearly enriched in recent years compared to 50 years ago at the urban sites, consistent with a pollution signal. Leaves and needles at suburban and urban sites had accumulated higher concentrations of various trace elements including Al, B, Ba, Ca, Cr, Cu, Fe, Mg, Na, S and Zn compared to the more distant sites, confirmed by Principal Component Analysis. Our data on δ13C, δ18O and δ2H enabled us to infer possible physiological effects induced by air pollution. Consistently increasing tree-ring δ13C values over recent decades for all investigated species indicated increasing plant stress, like hampered stomatal conductance and photosynthesis, but this was found for all sites, suggesting climate change rather than air pollution effects. In summary, we show that our multi-isotope and -element approach provides new insights into the threats to forests in urban areas, where the occurrence of more frequent droughts acts together with air pollution