Ozonation of seawater from different locations: formation and decay of total residual oxidant--implications for ballast water treatment

Ballast water is a likely cause for worldwide transfer of non-indigenous aquatic species because of the large volumes and frequency of possible inoculations. Ozone is one treatment option being considered for eliminating non-indigenous species in ballast water. When ozone is applied to seawater, secondary disinfectants are formed, commonly measured and expressed as total residual oxidant (TRO). The goal of this study was to determine those variables most likely to affect the rate of TRO increase during ozonation and the subsequent TRO decline that occurs over time. These parameters strongly influence the efficacy of ozone treatments aimed to eliminate organisms present in ballast water. Seawater was obtained from Puget Sound, Washington; Cape Fear, North Carolina; and San Francisco Bay. Results indicated that seawater characteristics, including the organic content and ammonia, affect the amount of ozone required to achieve a desired TRO level and rate of TRO decay, and therefore need to be considered in determining ozone requirements for ballast water treatment.     

Determining the depth and location of potential field sources without specifying the structural index

There are many semiautomatic interpretation methods for potential field data. Some only work for a specific model, such as a contact or dyke, while others can be applied to any structure which has a known structural index (S.I.) (which gives the rate of decrease with distance of the amplitude of the anomaly). Various strategies exist for the automatic determination of the S.I., some of which involve inversion, or the use of data from different altitudes. A simple new method of determining the depth, location, and S.I. of potential field sources is introduced here and demonstrated on potential field data from South Africa.     

利用北冰洋多光谱数据计算光合有效辐射的研究

光合有效辐射（PAR）是重要的生物光学量,与海洋浮游植物的初级生产过程有密切联系。PAR通常由单波段的PAR传感器直接测量,也可以由多光谱数据计算。在极区用多光谱数据计算PAR不仅面对不同谱宽度的问题,而且还有海冰的影响。本文研究了4种可能导致PAR计算误差的主要因素。多光谱仪器避开了大气对太阳辐射的主要吸收带,用多光谱数据计算会对PAR高估。实测数据分析表明多光谱计算的PAR与高光谱数据的计算结果非常接近,误差在1%以内。用本文建立的拟合函数进行校正,校正后的结果与高光谱数据计算的结果达到同样的精度。计算PAR的衰减率要用到进入海水表面的PAR（PAR0）,本文提出先确定表层衰减系数,再通过最小二乘拟合确定PAR0值,与水下观测数据有很好的衔接。海上同一站位不同时间的观测数据计算的PAR衰减系数相差很小,表明PAR的衰减系数是海水的光学性质,与辐射强度无关。在海冰覆盖的条件下,PAR的观测结果与无冰海水的PAR有明显差别。由于海冰选择性的吸收,穿透海冰进入海洋的PAR组分已经不同,海水对PAR的衰减系数也会相应变化。由此可以推断,不同海冰中成分的差别将导致进入海水中PAR的差别,影响PAR的衰减特性。通过本文的研究,解决了在极区用多光谱计算PAR的各种问题,使多光谱数据成为PAR的重要数据源。     

Three-dimensional numerical modeling of cohesive sediment transport and wind wave impact in a shallow oxbow lake

It was observed that in some closed inland lakes sediment transport was dominated by wind-induced currents, and the sediment resuspension was primarily driven by wind-induced waves. This paper presents the development and application of a three-dimensional numerical model for simulating cohesive sediment transport in water bodies where wind-induced currents and waves are important. In the model, the bottom shear stresses induced by currents and waves were calculated, and the processes of resuspension (erosion), deposition, settling, etc. were considered. This model was first verified by a simple test case consisting of the movement of a non-conservative tracer in a prismatic channel with uniform flow, and the model output agreed well with the analytical solution. Then it was applied to Deep Hollow Lake, a small oxbow lake in Mississippi. Simulated sediment concentrations were compared with available field observations, with generally good agreement. The transport and resuspension processes of cohesive sediment due to wind-induced current and wave in Deep Hollow Lake were also discussed.     

The interpretation of the generalised derivative operator

The Generalised Derivative Operator is an image‐processing tool for the enhancement of potential field data. It produces an amplitude‐balanced image of the derivative of a potential field in any direction in three‐dimensional space. This paper shows how, by using the correct inclination angle ?, the Generalised Derivative Operator can be used to produce images where its maxima/minima lie directly over dipping contacts and thin dykes with arbitrary magnetisation vectors. The dip of contacts and dykes can be found by varying ? until a symmetrical result is obtained (in the absence of unknown remanent magnetisation). Furthermore, the width of the peak of the Generalised Derivative Operator can then be used to determine the depth of the contact or dyke.     

Applying the tilt‐depth and contact‐depth methods to the magnetic anomalies of thin dykes

A new method for the calculation of the depth, location, and dip of thin dykes from pole‐reduced magnetic data is introduced. The depth can be obtained by measuring the distance between chosen values of a tilt angle that is based upon the ratio of the magnetic field and its Hilbert transform over the dyke. Alternatively, it can be obtained from the horizontal derivative of the ratio of the Hilbert transform of the field to the field itself, over the dyke. The latter method also allows the dip of the dyke to be estimated from the gradient of the depth estimates.     

Improved structural interpretation of legacy 3D seismic data from Karee platinum mine (South Africa) through the application of novel seismic attributes

Seismic detection of faults, dykes, potholes and iron-rich ultramafic pegmatitic bodies is of great importance to the platinum mining industry, as these structures affect safety and efficiency. The application of conventional seismic attributes (such as instantaneous amplitude, phase and frequency) in the hard-rock environment is more challenging than in soft-rock settings because the geology is often complex, reflections disrupted and the seismic energy strongly scattered. We have developed new seismic attributes that sharpen seismic reflections, enabling additional structural information to be extracted from hard-rock seismic data. The symmetry attribute is based on the invariance of an object with respect to transformations such as rotation and reflection; it is independent of the trace reflection amplitude, and hence a better indicator of the lateral continuity of thin and weak reflections. The reflection-continuity detector attribute is based on the Hilbert transform; it enhances the visibility of the peaks and troughs of the seismic traces, and hence the continuity of weak reflections. We demonstrate the effectiveness of these new seismic attributes by applying them to a legacy 3D seismic data set from the Bushveld Complex in South Africa. These seismic attributes show good detection of deep-seated thin (∼1.5 m thick) platinum ore bodies and their associated complex geological structures (faults, dykes, potholes and iron-rich ultramafic pegmatites). They provide a fast, cost-effective and efficient interpretation tool that, when coupled with horizon-based seismic attributes, can reveal structures not seen in conventional interpretations.     

Modeling cave cross-section evolution including sediment transport and paragenesis

Deposits within caves are often used to interpret past landscape evolution and climate conditions. However, cave passage shapes also preserve information about past conditions. Despite the usefulness of passage shape, no previous models simulate cave cross-section evolution in a realistic manner. Here we develop a model for evolving cave passage cross-sections using a shear stress estimation algorithm and a shear stress erosion rule. Our model qualitatively duplicates observed cave passage shapes so long as erosion rates vary with shear stress, as in the case of transport limited dissolution or mechanical erosion. This result provides further evidence that erosion rates within caves are not typically limited by surface reaction rates, even though current speleogenesis models predict surface-rate limitation under most turbulent flow conditions. By adding sediment transport and alluviation to the model we successfully simulate paragenetic channels. Simulations duplicate the hypothesized dynamics of paragenesis, whereby: 1) the cross-section of a phreatic passage grows until shear stress is sufficiently reduced that alluviation occurs, 2) the floor of the passage becomes armored and erosion continues on the ceiling and walls, 3) negative feedback produces an equilibrium cross-sectional area such that shear stress is sufficient to transport incoming sediment. We derive an approximate scaling relationship that indicates that equilibrium paragenetic channel width scales with the square root of discharge, and weakly with the inverse of sediment supply. Simulations confirm this relationship and show that erosion mechanism, sediment size, and roughness are secondary controls. The inverse scaling of width with sediment supply in paragenetic channels contrasts with surface bedrock channels, which respond to larger sediment supplies by widening. Our model provides a first step in simulating cave cross-section evolution and points to the need for a better understanding of the dominant erosion mechanisms in soluble bedrock channels. © 2020 John Wiley & Sons, Ltd.