Temperature and precipitation responses to El Niño-Southern Oscillation in a hierarchy of datasets with different levels of observational constraints

Climate Dynamics - El Niño-Southern Oscillation (ENSO) is the dominant mode of climate variability, affecting climate conditions over large areas of the globe. There are, however, substantial...     

PAH transport by sinking particles in the open Mediterranean Sea: a 1 year sediment trap study

One year time series of sinking particles were collected at two depths in the open Mediterranean Sea and analysed for polycyclic aromatic hydrocarbons (PAH). Average total PAH concentrations were 593+/-284 ng g(-1) at 250 m and 551 +/- 198 ng g(-1) at 2850 m. Total PAH fluxes averaged 73 +/- 58 ng m(-2) d(-1) at 250 m and 53 +/- 39 ng m(-2) d(-1) at 2850 m. Contamination levels and, thus, exposure of marine organisms to PAH are comparable in surface and deep waters. Deep waters appear as a significant, yet overlooked, PAH sink. PAH temporal patterns show noticeable seasonality. This is partly due to varying levels of specific components such as the winter increase of pyrolytic PAH. Downward transport processes and the nature of sinking particles also impact on PAH fluxes, as inferred during periods of increasing productivity. Different phase-associations and interactions with particulate organic carbon for low-MW fossil PAH and high-MW pyrolytic PAH influence their downward transport efficiency.     

洞穴碳酸盐230Th-234U-238U测年初始钍校正的等时线研究

初始钍的校正是不纯沉积碳酸盐230Th 234U 238U测年的一个重要方面，洞穴石笋初始Th校正通常采用230Th/232Th的原子比值为（4.4±2.2）×10-6。多年来4种不同的等时线方法应用到不纯碳酸盐测年初始Th的校正中，其中全样品的等时线方法是目前公认的较为完善的一种方法。通过测定云南同一石笋2个不同层位的9个样品的U、Th同位素组成,并进行等时线分析，结果表明2层样品初始钍230Th/232Th原子比值分别为（3.5±2.8）×10-6和（10.6±2.2）×10-6，这说明即使在同一地区，由于其混入Th来源的复杂性，230Th/232Th初始比值在同一样品不同层位仍可能有较大的差异，因此不能够完全采用单一层位等时线获得的初始值对整个样品进行校正。考虑到在实验测量过程中，232Th含量的过高对于230Th的准确测定也有很大的影响，应尽量选择纯净石笋样品进行测年研究，在样品的选择和前处理过程中就减少初始钍的影响，这对获得高精度的测年结果有着重要的意义。     

Comparison of stress-dependent geophysical,hydraulic and mechanical properties of synthetic and natural sandstones for reservoir characterization and monitoring studies

Synthetic rock samples can offer advantages over natural rock samples when used for laboratory rock physical properties studies, provided their success as natural analogues is well understood. The ability of synthetic rocks to mimic the natural stress dependency of elastic wave, electrical and fluid transport properties is of primary interest. Hence, we compare a consistent set of laboratory multi-physics measurements obtained on four quartz sandstone samples (porosity range 20–25%) comprising two synthetic and two natural (Berea and Corvio) samples, the latter used extensively as standards in rock physics research. We measured simultaneously ultrasonic (P- and S-wave) velocity and attenuation, electrical resistivity, permeability and axial and radial strains over a wide range of differential pressure (confining stress 15–50 MPa; pore pressure 5–10 MPa) on the four brine saturated samples. Despite some obvious physical discrepancies caused by the synthetic manufacturing process, such as silica cementation and anisotropy, the results show only small differences in stress dependency between the synthetic and natural sandstones for all measured parameters. Stress dependency analysis of the dry samples using an isotropic effective medium model of spheroidal pores and penny-shaped cracks, together with a granular cohesion model, provide evidence of crack closure mechanisms in the natural sandstones, seen to a much lesser extent in the synthetic sandstones. The smaller grain size, greater cement content, and cementation under oedometric conditions particularly affect the fluid transport properties of the synthetic sandstones, resulting in lower permeability and higher electrical resistivity for a similar porosity. The effective stress coefficients, determined for each parameter, are in agreement with data reported in the literature. Our results for the particular synthetic materials that were tested suggest that synthetic sandstones can serve as good proxies for natural sandstones for studies of elastic and mechanical properties, but should be used with care for transport properties studies.     

‘Paleoenvironmental study of modern charcoal making activity on forest soils in the Northern Vosges Mountains (Bitche,France): A multidisciplinary study of two remaining charcoal platforms and associated soils sequences’

This multidisciplinary study aims to decipher the impact of ancient charcoal production on past and present-day soils in the northern Vosges Mountains. Soil observations in the field and laboratory were complemented by charcoal and phytolith studies on large thin sections, molecular analyses of organic pollutants, and phytolith analysis on bulk samples. The complex technosol platform records an ancient natural soil sequence buried by a human-made platform on which charcoal accumulated. The current upslope soil is an entic Podzol. Palaeoecological data collected in the buried soil are reliable owing to low bioactivity due to soil acidity. Podzolisation predated the platform construction. The presence of ashes induced low soil alkalisation developed in the charcoal hearth remains and appears to have generated the migration of subsequent iron/clay/organic bands throughout the platform sediment and the buried soil. Charcoal studied in thin sections revealed mainly Quercus and Fagus taxa. Phytolith studies suggest that a less dense or degraded forest preceded platform construction, probably due to former woodland coppicing or earlier disorganised wood gathering. The specific distribution of polycyclic aromatic hydrocarbons sorbed on charcoal has persisted in soils throughout centuries, but we have no evidence that charcoal-making activities contributed to diffuse global pollution.