三疣梭子蟹4个野生群体肥满度的初步研究与比较分析

采用Le Cren相对状态指数Kn,比较4个野生群体(鸭绿江口、莱州湾、海州湾、舟山)三疣梭子蟹的肥满度情况,发现鸭绿江口>莱州湾>海州湾>舟山,其中10月中旬鸭绿江口群体与舟山群体肥满度存在极显著差异(P<0.01);4个野生群体雄性个体肥满度均大于雌性个体,但无显著差异(P>0.05)。三疣梭子蟹选育品系在养殖过程中肥满度为120日龄>100日龄>80日龄,但差异不显著(P>0.05)。     

Sr and Nd isotopes as tracers of clastic sources in Lake Le Bourget sediment (NW Alps, France) during the Little Ice Age: Palaeohydrology implications

Geochemical methods (major elements and Sr, Nd isotopes) have been used to (1) characterize Lake Le Bourget sediments in the French Alps, (2) identify the current sources of the clastic sediments and estimate the source variability over the last 600 years. Major element results indicate that Lake Le Bourget sediments consist of 45% clastic component and 55% endogenic calcite. In addition, several individual flood levels have been identified during the Little Ice Age (LIA) on the basis of their higher clastic content (> 70%).Potential sources of Lake Le Bourget clastic sediments have been investigated from Sr and Nd isotope compositions. The sediments from the Sierroz River and Leysse River which are mainly derived from the Mesozoic Calcareous Massifs are characterised by lower ⁸⁷Sr/⁸⁶Sr ratios and slightly lower ?_Nd(0) ratios than the Arve River sediments which are derived from the Palaeozoic Mont-Blanc External Crystalline Massifs. The Rhône River appears to have been the main source of clastic sediments into the lake for the last 600 years, as evidenced by a similar Sr and Nd isotopic compositions analyzed in core B16 sediments (⁸⁷Sr/⁸⁶Sr = 0.719, ?_Nd(0) = − 10) and in the sediments of the Rhône River (⁸⁷Sr/⁸⁶Sr = 0.719, ?_Nd(0) = − 9.6).The isotopic signatures of flood events and background samples from core B16 in Lake Le Bourget are also similar. This indicates that prior to ∼ 1800, the inputs into the lake have remained relatively homogeneous with the proportion of clastic component mainly being a function of the palaeohydrology of the Rhone River. Early human modification (deforestation and agriculture) of the lake catchment before the 1800s appears to have had little influence on the source of clastic sediments.     

In situ X-ray diffraction study of an aluminous phase in MORB under lower mantle conditions

In situ X-ray diffraction study was conducted to identify the crystal structure of the “Al-phase”, which was previously reported to form in basaltic compositions at pressures and temperatures of the uppermost part of the lower mantle. Le Bail whole-pattern fitting method was adopted to investigate the structure of the Al-phase under high pressure and temperature as well as ambient conditions. Observed patterns were satisfactorily fitted using the “hexagonal phase” with space group P6₃/m (plus minor amount of garnet) under both of these conditions. On the other hand, the calcium ferrite structure model proposed in some earlier studies based on quench experiments yielded profile-fitting results at significantly lower confidence levels, particularly at simultaneous high pressure and high temperature conditions, suggesting that this phase may not form in oceanic crust materials subducted in the uppermost lower mantle. The difference in densities of hexagonal and calcium ferrite phases, however, is only ~1% under pressures and temperatures of the uppermost part of the lower mantle conditions, which yields a negligible effect on the bulk density of the subducted oceanic crust.