Mapping surface soil moisture with microwave radiometers

Summary Water stored in the soil serves as a reservoir for the evapotranspiration (ET) process on land surfaces, therefore knowledge of the soil moisture content is important for partitioning the incoming solar radiation into latent and sensible heat components. There is no remote sensing technique which directly observes the amount of water in this reservoir, however microwave remote sensing at long wavelengths (>10 cm) can give estimates of the moisture stored in the surface 5-cm layer of the soil. This approach is based on the large dielectric contrast between water and dry soil, resulting in emissivity changes from 0.96 for a dry smooth soil to less than 0.6.In this paper, basic relationships between soil moisture and emissivity are described using both theory and observations from various platforms. The ability of the approach to be extended to large regions has been demonstrated in several aircraft mapping experiments, e.g., FIFE, Monsoon 90, Washita 92 and HAPEX Sahel. Some results from Monsoon 90 are presented here. Applications of these soil moisture maps in runoff prediction, rainfall estimation, determining the direct evaporation from the soil surface and serving as a boundary condition for soil profile models are presented.With 10 Figures     

红海及亚丁湾间之海水交换

分析表观耗氧量、滴定碱度及总二氧化碳量等资料来研判红海及亚丁湾间之海水交换。结果显示,红海深层水的方解石及霰石饱和度均比亚丁湾和阿拉伯海深层水的饱和度高。红海全水柱之方解石和霰石都处於过饱和状态,亚丁湾和阿拉伯海中各深度之方解石亦呈过饱和状态,但霰石的饱和探度则大约在500m左右。分析深层水之生物体无机碳与有机碳的分解比值,可以发现此地区深层水中,大约有25％的总二氧化碳增加量是由无机碳酸钙溶解而来。     

Barium- and LREE-rich, olivine-mica-lamprophyres with affinities to lamproites, Mt. Bundey, Northern Territory, Australia

Primitive olivine-mica-K-feldspar lamprophyre dykes, dated at 1831 ± 6 Ma, intrude lower greenschist facies rocks of the Early Proterozoic Pine Creek Inlier, of northern Australia. They are spatially, temporally and probably genetically associated with a post-tectonic composite granite-syenite pluton (Mt. Bundey pluton). The dykes have unusually high contents of large-ion-lithophile (LILE) and LREE elements (e.g. Ba up to 10,000 ppm, Ce up to 550 ppm, K₂O up to 7.5 wt. %) that resemble the concentrations found in the West Kimberley olivine and leucite lamproites. However, mineralogically the Mt. Bundey lamprophyres resemble shoshonitic lamprophyres and lack any minerals diagnostic of lamproites; leucite or leucite-pseudomorphs are absent. Mineral compositions are also unlike those in lamproites: micas contain higher Al₂O₃ than lamproitic mica; amphiboles are secondary actinolites after diopside; and oxides consist of zincian-chromian magnetite and groundmass magnetite. Heavy mineral concentrates contain mantle-derived xenocrysts of magnesiochromite, pyrope, Cr-diopside and rutile indicating a depth of sampling > 70 km. The Mt. Bundey lamprophyres are non-peralkaline to borderline peralkaline (molar (K + Na)/Al = 0.8 − 1.0) and potassic rather than ultrapotassic (molar K/Na < 2.5). They have distinctive major element compositions (≈46−49 wt. % SiO₂, ≈1.5−2 wt. % MgO, ≈7 wt. % CaO), and element ratios (e.g. molar Al/Ti ≈10, K/Na ≈2) that indicate they are best classified amongst transitional lamproites, i.e. potassic rocks such as cocites, jumillites and Navajominettes, that have geochemical characteristics transitional between Groups I and III. (Foley et al., 1987). The Mt. Bundey lamprophyres have LILE enrichment patterns that resemble the W. Kimberley pamproites but have moderate negative Ta---Nb---Ti anomalies and HREE abundances that are closely similar to the jumillites of southeastern Spain and Mediterranean-type lamproites. Single-stage modelling of Rb---Sr data is consistent with enrichment of the source-region of the Mt. Bundey lamprophyres ≈ 120–170 Ma before partial melting; i.e. at 1.95–2.10 Ga. Source enrichment does not appear to be associated with subduction processes, but may instead relate to incipient rifting of the Archaean basement. Negative Ta---Nb---Ti anomalies in the Mt. Bundey dykes may, therefore, relate to stability of residual titanate minerals in an oxidized subcontinental mantle source. This view is supported by high Fe³⁺/ΣFe ratios of mantle-derived magnesiochromite xenocrysts which indicate oxidized mantle conditions (ƒ_o2 ≈ FMQ + 1 long units), and by the presence of xenocrystic Cr-bearing rutile. Although the Mt. Bundey dykes have sampled upper mantle material, the oxidized nature of the magma source-region, and of the magma itself, suggests that conditions may not be favourable for diamond survival at depth nor for diamond transport in transitional lamproite magmas of this kind.     

Cu(II) adsorption at the calcite-water interface in the presence of natural organic matter: Kinetic studies and molecular-scale characterization

We have characterized the adsorption of Suwannee River humic acid (SRHA) and Cu(II) on calcite from preequilibrated solutions at pH 8.25. Sorption isotherms of SRHA on calcite follow Langmuir-type behavior at SRHA concentrations less than 15 mg C L⁻¹, whereas non-Langmuirian uptake becomes evident at concentrations greater than 15 mg C L⁻¹. The adsorption of SRHA on calcite is rapid and mostly irreversible, with corresponding changes in electrostatic properties. At pH 8.25, Cu(II) uptake by calcite in the presence of dissolved SRHA decreases with increasing dissolved SRHA concentration, suggesting that formation of Cu-SRHA aqueous complexes is the primary factor controlling Cu(II) sorption at the calcite surface under the conditions of our experiments. We also observed that surface-bound SRHA has little influence on Cu(II) uptake by calcite, suggesting that Cu(II) coordinates to calcite surface sites rather than to surface-bound SRHA.Cu K-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectroscopic results show that the local coordination of Cu adsorbed at the calcite surface is very similar in the presence and absence of SRHA. Ca backscatterers at ∼3.90 Å indicate that Cu(II) forms tetragonally distorted inner-sphere adsorption complexes in both binary and ternary systems. Subtle differences in the XANES and EXAFS between binary sorption samples and ternary sorption samples, however, prevent us from ruling out the formation of ternary Cu-SRHA surface complexes. Our findings demonstrate that SRHA plays an important role in controlling the fate and transport of Cu(II) in calcite-bearing systems.     

Interplay between river discharge and topography of the basin floor in a hyperpycnal lacustrine delta

Basin‐floor topography influences the flow path of hyperpycnal plumes and delta morphology during progradation of the Red River delta in Lake Texoma, USA. The Red River discharge is typically a hyperpycnal plume due to elevated total dissolved solids. Because the river plume is a bottom‐hugging hyperpycnal flow, lake bathymetry and topography strongly influence deposition and subsequent delta morphology. In addition to elevated total dissolved solid concentrations compared with Lake Texoma water, the density contrast of the Red River outflow is increased by high suspended‐sediment concentrations during high‐discharge events. Steep lateral slopes in the Lake Texoma basin deflect hyperpycnal river plumes and, subsequently, change the delta progradation direction before the delta reaches the opposite bank of the lake. Analysis of multi‐temporal aerial and satellite images indicates that the hyperpycnal delta follows the steepest lake‐bottom gradients, corresponding to the pre‐impoundment river thalweg (i.e. bypassing shallow parts of the lake). An analytical model for the hyperpycnal‐plume trajectory indicates plume deflection during low‐discharge or high‐discharge events, towards the deepest part of the basin. The magnitude of plume deflection is a function of river discharge and basin‐margin gradients. Plume deflection can vary between 10° and 80° from the channel axis towards the old river thalweg. The high deflection appears in the case of maximum basin side gradients of 12·8° and in conditions of low river discharge. During low‐discharge periods, the Red River delta builds a lobate shape with multiple terminal distributary channels whereas, during high‐discharge periods the Red River delta builds an elongate shape with a single large distributary channel. The elongate morphology of the delta is formed through the development of a single distributary channel and abandonment of the other distributaries. Therefore, the lobate shaped delta is expected to be preserved in the rock record.