多维体视方法论及其在地球科学研究中的意义

本文阐述”多维体视方法论”,主张立体透视与动态、多维地看问题;它起源于医学CT(计算机层析学)透视成像、核磁共振(MRI)等体视学方法研究疾病的生理解剖结构、病理特征、监测人体有关器官的各种变化,是行之有效的方法;已成功地应用于检测工业器械、航天器及地下结构等物体的内部结构,从而发展和演绎出来的认识论方法。在医学领域将CT、MRI所得二维信息和断面图像、对病灶区引入“体显示”和“面显示”等可视化技术,将能充分反映不同疾病的病理、药理特征;在航天、地学等领域同样应用着CT多维“可视化技术”。本文试图发扬综合预测的学术思想,将医学临床应用CT、核磁共振、体视学方法结合研究其他制约因素指标,从而区分出疾病的原发、继发分期,导致绝症的进程和前兆,概括为“多维体视预测方法”;也适用于地震孕育、强震发生与火山喷发预测的研究。     

Application of the Genetic Algorithm to the Problem of Reconstruction of Missing Data

We study the problem of reconstruction (interpolation and extrapolation) of the vertical profiles of hydrochemical and hydrobiological elements according to incomplete sets of data with simultaneous filtration of short-period components based on expansions in empirical orthogonal functions. The genetic algorithm is used to compute the coefficients of expansion of profiles with missing data. We present the results of processing the data arrays on oxygen, chlorophyll A, and biogenic elements collected in the Black Sea in 1982–1993. The mean error of reconstruction of the profiles enables us to conclude that the proposed method has considerable advantages over the conventional approaches.     

Effects of Hydrogel Amendment to Different Soils on Plant Available Water and Survival of Trees under Drought Conditions

The effect of super absorbent polyacrylate (SAP) hydrogel amendment to different soil types on plant available water (PAW), evapotranspiration and survival of Eucalyptus grandis, Eucalyptus citriodora, Pinus caribaea, Araucaria cunninghamii, Melia volkensii, Grevillea robusta, Azadirachta indica, Maesopsis eminii and Terminalia superba was investigated. The seedlings were potted in 3 kg size polythene bags filled with sand, loam, silt loam, sandy loam and clay soils, amended at 0 (control), 0.2 and 0.4% w/w hydrogel. The tree seedlings were allowed to grow normally with routine uniform watering in a glass house set up for a period of eight weeks, after which they were subjected to drought conditions by not watering any further. The 0.4% hydrogel amendment significantly (p < 0.05) increased the PAW by a factor of about three in sand, two fold in silt loam and one fold in sandy loam, loam and clay soils compared to the control. Similarly, the addition of either 0.2 or 0.4% hydrogel to the five soil types resulted in prolonged tree survival compared to the controls. Araucaria cunninghammi survived longest at 153 days, while Maesopsis eminii survived least (95 days) in sand amended at 0.4% after subjection to desiccation. Evapotranspiration was reduced in eight of the nine tree species grown in sandy loam, loam, silt loam and clay soils amended at 0.4% hydrogel. It is probable that soil amendment with SAP decreased the hydraulic soil conductivity that might reduce plant transpiration and soil evaporation.     

An ephemeral turbidity maximum generated by resuspension of organic-rich matter in a macrotidal estuary, S.W. Wales

An ephemeral estuarine turbidity maximum (ETM) occurs at high water in the macrotidal Taf estuary (SW Wales, United Kingdom). A new mechanism of ETM formation, due to resuspension and advection of material by flood tidal currents, is observed that differs from classical mechanisms of gravitational circulation and tidal pumping. The flood tide advances across intertidal sand flats in the main body of the estuary, progressively entraining material from the rippled sands. Resuspension creates, a turbid front that has suspended sediment concentrations (SSC) of about 4,000 mg I⁻¹ by the time it reaches its landward limit which is also the landward limit of salt penetration. This turbid body constitutes the ETM. Deposition occurs at high slack water but the ETM retains SSC values up to 800 mg I⁻¹, 1–2 orders of magnitude greater than ambient SSC values in the river and estuarine waters on either side. The ETM retreats down the estuary during the ebb; some material is deposited thinly across emergent intertidal flats and some is flushed out of the estuary. A new ETM is generated by the next flood tide. Both location and SSC of the ETM scale on Q/R³ where Q is tidal range and R is river discharge. The greatest expression of the ETM occurs when a spring tide coincides with low river discharge. It does not form during high river discharge conditions and is poorly developed on neap tides. Particles in the ETM have effective densities (120–160 kg m⁻³) that are 3–4 times less than those in the main part of the estuary at high water. High chlorophyll concentrations in the ETM suggest that flocs probably originate from biological production in the estuary, including production on the intertidal sand flats.     

A new technique to determine geoid and orthometric heights from satellite positioning and geopotential numbers

This paper takes advantage of space-technique-derived positions on the Earth’s surface and the known normal gravity field to determine the height anomaly from geopotential numbers. A new method is also presented to downward-continue the height anomaly to the geoid height. The orthometric height is determined as the difference between the geodetic (ellipsoidal) height derived by space-geodetic techniques and the geoid height. It is shown that, due to the very high correlation between the geodetic height and the computed geoid height, the error of the orthometric height determined by this method is usually much smaller than that provided by standard GPS/levelling. Also included is a practical formula to correct the Helmert orthometric height by adding two correction terms: a topographic roughness term and a correction term for lateral topographic mass–density variations.     

Maternal transfer of bioactive polychlorinated aromatic hydrocarbons in spawning chinook salmon (Oncorhynchus tschawytscha)

The biological potency (relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin. TCDD) of planar polychlorinated aromatic hydrocarbons (PCHs) in extracts of eggs and flesh from spawning female chinook salmon (Oncorhynchus tschawytscha) from Lake Michigan was determined by measuring the induction of 7-ethoxyresorufin O-deethylase activity in H-4-II-E rat hepatoma cells. TCDD-equivalents in flesh and egg samples ranged from 0 to 115·8 pg/g, and were approximately 5-fold greater in eggs than in flesh. These results suggest that the maternal transfer of PCHs may play a role in determining the reproductive success of Lake Michigan chinook salmon.     

Low‐accommodation and backwater effects on sequence stratigraphic surfaces and depositional architecture of fluvio‐deltaic settings (Cretaceous Mesa Rica Sandstone,Dakota Group,USA)

The adequate documentation and interpretation of regional‐scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. However, this is often challenged by the amalgamated nature of low‐accommodation settings and control of backwater hydraulics on fluvio‐deltaic stratigraphy. Exhumed examples of full‐transect depositional profiles across river‐to‐delta systems are key to improve our understanding about interacting controlling factors and resultant stratigraphy. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which allows mapping of down‐dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio‐deltaic deposition in the Tucumcari sub‐basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down‐dip into single‐story channel sandstones and eventually into contemporaneous distributary channels and delta‐front strata. Down‐dip changes reflect accommodation decrease towards the paleoshoreline at the Tucumcari basin rim, and subsequent expansion into the basin. Additionally, multi‐storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised‐valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta‐front geometries. This opposes criteria offered to differentiate incised valleys from flood‐induced backwater scours. As the incised valleys evidence relative sea‐level fall and flood‐induced backwater scours do not, the interpretation of incised valleys impacts sequence stratigraphic interpretations. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS). The RCS’ diachronous nature demonstrates that its down‐dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea‐level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low‐accommodation settings to dominantly promote bypass, especially during forced regressions. Source‐to‐sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea‐level cycle.