Boron isotope fractionation during brucite deposition from artificial seawater

Experiments involving boron incorporation into brucite (Mg(OH)(2)) from magnesium-free artificial seawater with pH values ranging from 9.5 to 13.0 were carried out to better understand the incorporation behavior of boron into brucite and the influence of it on Mg/Ca-SST proxy and delta(11)B-pH proxy. The results show that both the concentration of boron in deposited brucite ([B](d)) and its boron partition coefficient (K(d)) between deposited brucite and final seawater are controlled by the pH of the solution. The incorporation capacity of boron into brucite is almost the same as that into corals, but much stronger than that into oxides and clay minerals. The isotopic compositions of boron in deposited brucite (delta(11)B(d)) are higher than those in the associated artificial seawater (delta(11)B(isw)) with fractionation factors ranging between 1.0177 and 1.0569, resulting from the preferential incorporation of B(OH)(3) into brucite. Both boron adsorptions onto brucite and the precipitation reaction of H(3)BO(3) with brucite exist during deposition of brucite from artificial seawater. The simultaneous occurrence of both processes determines the boron concentration and isotopic fractionation of brucite. The isotopic fractionation behaviors and mechanisms of boron incorporated into brucite are different from those into corals. The existence of brucite in corals can affect the delta(11)B and Mg/Ca in corals and influences the Mg/Ca-SST proxy and delta(11)B-pH proxy negatively. The relationship between delta(11)B and Mg/Ca in corals can be used to judge the existence of brucite in corals, which should provide a reliable method for better use of delta(11)B and Mg/Ca in corals to reconstruct paleo-marine environment.</p

Boron isotope variations and its geochemical application in nature

The high geochemical reactivity of boron and the large relative mass difference between B-10 and B-11 lead to significant boron isotope fractionation in nature. So far the measured range of boron isotope composition (B-11) varies between -70 and +75 parts per thousand. The negative B-11 values are found in non-marine evaporite borate minerals and tourmalines, whereas positive B-11 values are common in salt lake brines and evaporated seawater. Since the 1980s, with improved measurement methods, applications of boron isotope analysis have increased rapidly. At present, boron isotopes are successfully applied to reconstruct ancient marine environments, to determine depositional environments and ore genesis, to trace groundwater pollution and seawater intrusion, and to study continental erosion. This paper summarises the methods for boron isotope analysis, the mechanisms of boron isotope fractionation and the distribution of boron isotopes in nature, reviews the achievements and the problems of boron isotopes in geochemical applications, and proposes research directions of boron isotopes in geochemical fields.</p

Comparison of Elemental Carbon in Lake Sediments Measured by Three Different Methods and 150-Year Pollution History in Eastern China

Concentrations of elemental carbon (EC) were measured in a 150 yr sediment record collected from Lake Chaohu in Anhui Province, eastern China, using three different thermal analytical methods: IMPROVE_A thermal optical reflectance (TOR), STN_thermal optical transmittance (TOT), and chemothermal oxidation (CTO). Distribution patterns for EC concentrations are different among the three methods, most likely due to the operational definition of EC and different temperature treatments prescribed for each method. However, similar profiles were found for high-temperature EC fractions among different methods. Historical soot(ToR) (high-temperature EC fractions measured by the IMPROVE_A TOR method) from Lake Chaohu exhibited stable low concentrations prior to the late 1970s and a sharp increase thereafter, corresponding well with the rapid industrialization of China in the last three decades. This may suggest that high-temperature thermal protocols are suitable for differentiating between soot and other carbon fractions. A similar soot(ToR) record was also obtained from Lake Taihu (similar to 200 km away), suggesting a regional source of soot. The ratio of char(ToR) (low-temperature EC fraction measured by the IMPROVE_A TOR method, after correction for pyrolysis) to sootToR in Lake Chaohu shows an overall decreasing trend, consistent with gradual changes in fuel use from wood burning to increasing fossil fuel combustions. Average higher char(ToR)/soot(ToR) was observed in Lake Taihu than in Lake Chaohu in the past 150 years, consistent with the longer and more extensive industrialization around the Taihu region.</p

A telescopic divergent chimney for power generation based on forced air movement: Principle and theoretical formulation

We present a new renewable energy technology concept for electricity generation based on an upward Momentum created by a balanced forced air movement, which is initiated by an air blower, inside a telescopic divergent chimney constructed with adiabatic materials and equipped with a gas turbine. A theoretical model based on the principles of mass and energy conservation, and continuity was developed to investigate the forced air flow inside the system using a criterion defined as the difference between ambient pressure and static pressure at the outlet aloft of the chimney. The model results indicated that, as the air flow increasing to reach a threshold, there exists a steady state when the pressure difference equals to zero. At this state, a constant air flow velocity is attended such that the system becomes stable and the action of the blower is no longer required. In this condition, there is a non-linear relationship between the threshold velocity and the pressure difference with the geometry of the chimney, the installed load and ambient conditions are important dependent variables. With the estimated threshold velocity for chimneys from 15 to 150 m, the steady-state distributions of velocity and energies (internal, potential, kinetic, enthalpy and extractable mechanical energy) at five cross-sections of the chimney were evaluated. The maximum velocity is found at the section with the minimum area, where maximum mechanical energy can be extracted. The maximum velocity can reach similar to 45 m/s in a 100-m high chimney. The extractable energy is found to have an exponential relationship with the chimney heights. The novelty of the concept is that when the air is forced to reach a threshold velocity in the system, the air can maintain a steady state without further supply of driving power.</p

Electroweak measurements in electron–positron collisions at w-boson-pair energies at lep

Contains fulltext : 121524.pdf (preprint version ) (Open Access