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The extensive sea grass meadows in Torres Strait enable it to be a globally important habitat for the dugong, Dugong dugon, a marine mammal of cultural and dietary significance to Torres Strait Islanders and the basis for the substantial island-based fishery in the Torres Strait Protected Zone. Torres Strait sea grass communities are subjected to episodic diebacks which are now believed to be largely natural events. Information on dugong life history was obtained from specimens obtained from female dugongs as they were butchered for food by Indigenous hunters at two major dugong hunting communities in Torres Strait: Daru (9.04°S, 143.21°E) in 1978–1982 (a time of sea grass dieback and recovery) and Mabuiag Island (9.95°S, 142.15°E) in 1997–1999 (when sea grasses were abundant). Dugongs sampled in 1997–1999 had their first calf at younger ages (minimum of 6 cf. 10 years), and more frequently (interbirth interval based on all possible pregnancies 2.6±0.4 (S.E.) yr cf. 5.8±1.0 yr) than the dugongs sampled in 1978–1982. Pregnancy rates increased monotonically during 1978–1982, coincident with sea grass recovery. The age distribution of the female dugongs collected in 1997–1999 also suggested a low birth rate between 1973 and 1983 and/or or a high level of mortality for animals born during this period. These results add to the evidence from other regions that the life history and reproductive rate of female dugongs are adversely affected by sea grass loss, the effect of which cannot be separated from a possible density-dependent response to changes in dugong population size. Many green turtles in Torres Strait were also in poor body condition coincident with the 1970s sea grass dieback. The impacts of future sea grass diebacks need to be anticipated when management options for the traditional Torres Strait fisheries for dugongs and green turtles are evaluated. 相似文献
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Campaigns were conducted to measure Organic Carbon (OC) and Elemental Carbon (EC) in PM2.5 during winter and summer 2003 in Beijing. Modest differences of PM2.5 and PM10 mean concentrations were observed between the winter and summer campaigns. The mean PM2.5/PM10 ratio in both seasons was around 60%, indicating PM2.5 contributed significantly to PM10. The mean concentrations of OC and EC in PM2.5 were 11.2±7.5 and 6.0±5.0μg m-3 for the winter campaign, and 9.4±2.1 and 4.3±3.0 μg m-3 for the summer campaign, respectively. Diurnal concentrations of OC and EC in PM2.5 were found high at night and low during the daytime in winter, and characterized by an obvious minimum in the summer afternoon. The mean OC/EC ratio was 1.87±0.09 for winter and Z39±0.49 for summer. The higher OC/EC ratio in summer indicates some formation of Secondary Organic Carbon (SOC). The estimated SOC was 2.8 μg m-3 for winter and 4.2μg m-3 for summer. 相似文献
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Hong-Lin Yuan Shan Gao Meng-Ning Dai Chun-Lei Zong Detlef Günther Gisela Helene Fontaine Xiao-Ming Liu ChunRong Diwu 《Chemical Geology》2008,247(1-2):100-118
We describe an in situ method for simultaneous measurement of U–Pb–Hf isotopes and trace element compositions of zircons using a quadrupole and multiple-collector inductively-coupled-plasma mass spectrometer (Q-ICP-MS and MC-ICP-MS, respectively) connected to a single excimer laser-ablation system. A laser-generated zircon aerosol was split behind the ablation cell into two transport tubes via a Y-shaped connector and simultaneously introduced into the two mass spectrometers. Hafnium isotopes were measured on the MC-ICP-MS instrument, while U–Pb ages and trace element compositions were determined using the Q-ICP-MS. The precision and accuracy of this method was evaluated using six well-known and widely used zircon standards (91500, Temora-2, GJ-1, Mud Tank, BR266 and Monastery). Analyses were carried out using spot sizes of 32, 44 and 60 μm. For the 44 and 60 μm spot, the resulting U–Pb ages, Hf isotopic and rare earth element (REE) compositions of these six zircons agree with recommended/reported values within 2σ error. The difference in relative standard deviations (RSD) of 206Pb/238U ages between split-flow measurements and those obtained separately on the Q-ICP-MS is within ～ 20% for 91500, Temora-2 and GJ-1, and ～ 60% for Mud Tank (due to its lower U and Pb concentrations). Our method provides a precise approach for determining the U–Pb age and the Hf isotopic and trace element compositions of zircon within a single ablation event. This is in particular important for analysis of zircons that are small or contain complicated zoning patterns. Finally, the REE composition of zircon BR266 is more homogeneous than other zircons and could be a suitable standard by which to benchmark new standards for microprobe analyses of zircons. 相似文献
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Bernhard?SchulzEmail author Klaus?Bombach Sabine?Pawlig Helene?Br?tz 《International Journal of Earth Sciences》2004,93(5):824-843
In the Austroalpine Basement to the south of the Tauern Window, distinct suites of metabasites occur with orthogneisses in pre-Early-Ordovician units. Tholeiitic and alkaline within-plate basalt-type metabasites are associated with acid meta-porphyroids in the post-Early-Ordovician Thurntaler Phyllite Group. According to their correlated trace element abundances, metabasite zircons crystallized with their host rocks. Protolith Pb–Pb zircon ages, whole-rock Ta/Yb–Th/Yb and oxygen, Sr, Nd isotope data define two principal evolution lines. An older evolution at elevated Th/Yb typical of subduction-related magmatism, started by 590-Ma N-MORB-type and 550–530 Ma volcanic arc basalt type basic suites, which mainly involved depleted mantle sources. It finished with mainly crustal-source 470–450-Ma acid magmatites. An other evolution line by tholeiitic and 430-Ma alkaline within-plate basalt-type suites in both pre- and post-Early-Ordovician units is characterized by an intraplate mantle metasomatism and enrichment trend along multicomponent sources. These magmatic evolution lines can be related to a plate tectonic scenario that involved terranes in a progressively mature Neoproterozoic to Ordovician active margin, and a subsequent Palaeo-Tethys passive margin along the north Gondwanan periphery. 相似文献
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Armin?ZehEmail author Ian?S.?Williams Helene?Br?tz Ian?L.?Millar 《Contributions to Mineralogy and Petrology》2003,145(6):691-706
Results of TIMS, SIMS and SEM analyses show that zircon and monazite in a high-grade paragneiss of the Ruhla Crystalline Complex, central Germany, were formed and/or altered during different stages of a tectono-metamorphic history between Early Devonian and Permian times. Detrital zircon cores of >460 Ma place an older limit on the age of anatexis, and show that the paragneiss sequence contains rocks at least as young as early Cambrian. Metamorphic zircon growth commenced at ~365 Ma, peaking at ~360–355 Ma at the same time that granite dykes were emplaced. In contrast, monazite in the paragneiss preserves little record of the metamorphic peak. Most monazite grains grew or were recrystallised in the Lower Carboniferous at ~339 Ma, contemporaneous with the emplacement of voluminous diorite and granite bodies. These intrusions and related tectonics caused some of the high-U zircon overgrowths to undergo moderate to severe Pb loss. A second Pb loss event, between 300 and 280 Ma, can be related to Late Carboniferous/Early Permian large-scale block faulting.Editorial responsibility: J. Hoefs 相似文献
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Environmental migration is a topic which has given rise to widespread debate and gloomy predictions about the state of the world in 2050, but where rigorous research and empirical evidence are unfortunately in short supply. In this paper, we review the existing research on and empirical evidence of how climate change and climate variability in Less Developed Countries (LDCs) affects two main drivers of migration identified by migration models in the economic literature, namely income level differentials between origin and destination areas and income variability in origin areas, and how they in turn affect migration. We find that there are serious gaps in both the economic and the environmental literature that render it impossible to make sound and robust predictions of how climate change and increased climate variability will affect the economic migration drivers, and of how these in turn may change existing migration patterns. There are some empirical indications that income differentials may increase due to lower income levels in the origin areas of LDCs, but virtually no evidence exists of the effects of climate change or increased climate variability on income variability. Furthermore, although a negative relationship between migration and rainfall has been established by many researchers, there is only very limited evidence as to what drives it. A clearer picture of the driving force behind the link between rainfall and migration would greatly benefit policymaking in this area. 相似文献