Sources of Salinity Variation in a Coastal Lagoon in a Karst Landscape

Bahia de la Ascension (BA) is a shallow, mangrove-fringed coastal bay connected to the Caribbean through two inlets, outlined by the Mesoamerican Barrier Reef System. This work represents an initial investigation of the relative contribution of hydrometeorological and hydrodynamic forcing on salinity variation in this lagoon. Our objective is to assess the sensitivity of the salinity in BA to fluctuations in freshwater inflow and coastal oceanography. Two field trips were undertaken during rainy and dry seasons in 2007. Surface salinity was mapped across the system and CTD deployments carried out within BA and in the sea end-member to characterize temperature, conductivity, and water level. Also, cross-sectional CTD profiles were implemented to examine vertical stratification. The water balance indicated that 16 % of rainfall over the drainage basin (DB) becomes groundwater discharge plus surface runoff into BA during dry season, while 68 % of the precipitation input to the DB is supplied through groundwater–surface runoff to the bay during rainfalls. This combined inflow showed larger fluctuations than direct rainfall and, thus, has a greater potential to alter the seasonal salinity variations within BA. The tidal signal is selectively attenuated within BA, as diurnal frequencies are more readily filtered out than semidiurnal frequencies. Mesohaline conditions in the southwest bay are associated with freshwater sources, while saline water masses in the inlet are influenced by prevalent SE winds in the region and tidal phase, establishing a strong horizontal SW-NE estuarine salinity gradient.     

A closer look at the X-ray transient XTE J1908+094: identification of two new near-infrared candidate counterparts

We have reported, in our previous paper, on the near-infrared (NIR) identification of a possible counterpart to the black hole candidate XTE J1908+094 obtained with the European Southern Observatory/New Technology Telescope. Here, we present new, follow-up, Canada–France–Hawaii Telescope adaptive optics observations of the XTE J1908+094 field, which resolved the previously proposed counterpart in two objects separated by about 0.8 arcsec. Assuming that both objects are potential candidate counterparts, we derive that the binary system is a low-mass system with a companion star which could be either an intermediate/late type (A–K) main-sequence star at a distance of 3–10 kpc or a late-type (>K) main-sequence star at a distance of 1–3 kpc. However, we show that the brighter of the two objects ( J ∼ 20.1,  H ∼ 18.7,  K '∼ 17.8) is more likely to be the real counterpart of the X-ray source. Its position is more compatible with our astrometric solution, and colours and magnitudes of the other object are not consistent with the lower limit of 3 kpc derived independently from the peak bolometric flux of XTE J1908+094. Further multiwavelength observations of both candidate counterparts are crucial in order to solve the pending identification.     

Abundance of cosmic-ray elements from sulfur to nickel as a function of atmospheric depth

The measured elemental composition of cosmic rays with charge 16≤Z≤28 as a function of atmospheric depth was compared with a propagation calculation including energy loss. The resulting composition at the top of the atmosphere has better precision than previously possible on balloon borne experiments, and agrees well with the only satellite data available in this charge range. The extrapolation method also provides checks on assumed cross-sections for interactions of cosmic rays in air.     

Interaction mean-free-path of cosmic-ray Fe in air

The interaction mean-free-path of cosmic-ray iron in air has been determined by observing the change in flux as a function of atmospheric depth. A large detector and a large variation in altitude during the balloon flight result in a high precision measurement. The result is in agreement, though slightly larger than the mean-free-path deduced from the measurements of interactions of iron on different targets at the Bevalac accelerator.     

Holocene yardangs in volcanic terrains in the southern Andes,Argentina

Yardangs of different sizes were developed in the Payun Matru Volcanic Field, a semiarid area east of the southern Andes mountains. Yardangs from volcanic terrains have not been described previously from Earth, although studies from Mars interpreted linear ridges found by Mariner and Viking images as yardangs. The Payun Matru Volcanic Field is an extensive plateau at 2000 m a.s.l. covered by basaltic lava and ignimbrite flows. Strong westerly winds affect the extensive plateau. Micro‐ and mesoyardangs are formed on the ignimbrite rock blanket, and macroforms or megayardangs, several kilometres in length, are developed in the basaltic lava flows as long parallel troughs. They all have a distinctive 320° azimuth, which is the prevailing wind direction. No yardang features are noted in the more recent lava flows, younger than 1000 years, indicating that their formation needed a longer time or they developed in earlier periods with stronger winds. The yardang development is explained by the strong unidirectional winds, the poor vegetational cover due to the aridity of the region, the available quartz sand and volcanic ash particles as abrasive agents, and the volcanic lithology texture and flow structure. Copyright © 2001 John Wiley & Sons, Ltd.     

川滇菱形块体顺时针转动的构造学与古地磁学证据

川滇菱形块体内部受NE向丽江 -小金河断裂的切割 ,可进一步划分为川西北次级块体和滇中次级块体等南北 2个部分 ;各次级块体东边界断裂有规律地左旋滑动、西边界断裂的右旋滑动及其滑动速率值的差异 ,反映出新生代时期各次级块体作向SE的水平滑移叠加绕垂直轴顺时针转动的复合运动。其中 ,川西北次级块体SE向的水平滑移速率 5mm/a ,顺时针转动角速度 1 4°/Ma ;滇中次级块体SE向的水平滑移速率 3 5mm/a ,顺时针转动角速度约 1 5°/Ma。在滇中次级块体内部姚安、大姚、永仁、昆明北马街等地采集到约 90个古新世地层的定向样品 ,通过交变退磁和热退磁获得了它们各自的剩磁矢量 (实验磁偏角和磁倾角 ) ,由实测磁偏角与期望磁偏角相比可知川滇地区滇中次级块体中新世早期以来的顺时针转动累积量可达 30°～ 4 8°。次级块体的整体转动与块边活动断裂的左旋滑动符合左旋走滑断裂作用区块体作顺时针转动的运动学模式     

Detection of the water level in fractured phreatic aquifers using nuclear magnetic resonance (NMR) geophysical measurements

Correlation of geophysical data collected using the NMR method in the Negev Desert, Israel, with hydrogeological data from nearby observation wells is presented. The experiment was conducted near Kibbutz Revivim in the Besor drainage system (Fig. 1). The objective of the survey was to detect groundwater layers in the Quaternary cover filling and Eocene fractured aquifers down to a depth of 100 m. The experiment was performed using a combination of two different geophysical techniques, namely the NMR and time domain electromagnetic (TDEM) methods. The geophysical results were verified by measuring the water level in three observation wells, two of which were drilled several months after the geophysical survey was carried out.The water level measured in these follow-up observation wells shortly after drilling did not coincide with the geophysical data. However, it settled over a period of time and finally stabilized at a depth very similar to that obtained from the NMR measurements. This phenomenon is caused by the fractured nature of the phreatic aquifer. Since the flow of water in such aquifers is confined by the fractures, the appearance of water in the well during or shortly after drilling is determined solely by the intersection of the well and the fracture. Our experiments showed that geophysical measurements in fractured phreatic aquifers may have a distinct advantage over direct borehole measurements, since the former average the depth to the water table over large areas (several thousand square meters) while the latter are limited by the area of the borehole cross-section (several tens of square centimeters).     

Shear Strength Development with Burial in Eel River Margin Slope Sediments

As part of the STRATAFORM project, a series of cores were obtained from the Eel River Margin area of Eureka, California. The geotechnical analysis of intact specimens and of reconstituted samples provides some insight on the development of shear strength with burial. The results show the effect of bioturbation in the early part of the lifetime of a sediment. SEDCON tests were used to proposed various relationships which help predict the changes in density, liquidity index, and strength as a function of depth. These relationships are found useful from near the water sediment-interface down to a depth of at least 400 m in the sediment column.