Fe and Al oxides distribution in some ultisols and inceptisols of southeastern Nigeria in relation to soil total phosphorus

Ten highly weathered soils in southeastern Nigeria were sampled from their typical A and B horizons for analyses. The objectives were to determine the different forms of Fe and Al oxides in the soils and relating their occurrence to phosphate availability and retention in the soils. The soils are deep and often physically degraded but are well drained and coarse in the particle size distribution. They are mostly dominated by kaolinite in their mineralogy with very high values of SiO₂. The soils are acidic with low soil organic carbon (SOC) contents. The elements in the exchange complex are also low thus reflecting in the low CEC of the soil. Available phosphorus (P) in the soils are generally low while total P ranged from 157 to 982 mg kg⁻¹ with an overall average of 422 mg kg⁻¹. Total Fe in the soil is highest and their order represented as follows: Fe_t > Fe_d > Fe_ox ≥ Fe_p. The pyrophosphate extractable Fe was always higher in the top soil than in the subsoil and was attributed to the fact that these forms of Fe are associated with organic matter which is more abundant in topsoil than in subsoil. Like in Fe forms, the order of Al occurrence could generally be presented as; Al_t > Al_d > Al_ox > Al_p. More Fe and Al oxides in the soils are strongly crystalline while a small quantity is poorly crystalline Fe forms. The amorphous forms of both Fe and Al are very low in the soils when compared with the crystalline forms. The oxides that show very strong affinity to total P are Fe_d–Fe_ox, Fe_d, Al_d, Fe_t, Fe_ox and Al_ox/Al_d. To overcome this problem of P retention in the soil, we recommend constant liming of these soils to neutralize them, application of organic matter and of high dosage of phosphate fertilizer to the soils.     

Sea surface wind stress and drag coefficients: The hexos results

Turbulent fluxes have been measured in the atmospheric surface layer from a boom extending upwind from the Dutch offshore research platform Meetpost Noordwijk (MPN) during HEXMAX (Humidity Exchange over the Sea Main Experiment) in October–November, 1986. We started out to study eddy flux of water vapour, but discrepancies among simultaneous measurements made with three different anemometers led us to develop methods to correct eddy correlation measurements of wind stress for flow distortion by nearby objects. We then found excellent agreement among the corrected wind stress data sets from the three anemometers on the MPN boom and with eddy correlation measurements from a mast on a tripod. Inertial-dissipation techniques gave reliable estimates of wind stress from turbulence spectra, both at MPN and at a nearby ship. The data cover a range of wave ages and the results yield new insights into the variation of sea surface wind stress with sea state; two alternative formulas are given for the nondimensional surface roughness as a function of wave age.     

南海南部巽他陆架氧同位素3期粘土矿物记录及其古环境意义

南海南部低海平面时期巽他陆架陆源碎屑的物源区变化,对于研究海陆变迁过程古环境演化具有重要意义.选择巽他陆架外缘对海平面变化影响非常敏感的氧同位素3期岩心记录(18282-2孔),开展高分辨率陆源碎屑粘土矿物分析,以期获得海平面变化影响下的物源区演化历史.研究结果显示,在氧同位素3期44.5～36.0 cal ka BP期间,巽他陆架外缘含有较高的蒙脱石(29%～44%)与中等含量的高岭石(21%～27%)、伊利石(19%～27%)和绿泥石(14%～20%).物源区分析表明,这个时期的蒙脱石主要由苏门答腊岛和泰国中部河流提供,高岭石主要由马来半岛、苏门答腊岛和婆罗洲西部河流提供,而伊利石和绿泥石主要由湄公河提供.在此期间,海平面长时间位于-80 m以下,巽他出露陆架上发育的大型古河流(北巽他河、古昭披耶河及古湄公河)可将来自周边物源区的陆源碎屑物质直接输送到陆架外缘.研究岩心的蒙脱石/(伊利石+绿泥石)比值与海平面变化具有良好的对应关系:当海平面下降时,蒙脱石/(伊利石+绿泥石)比值增大;反之亦然.这一现象表明海平面变化是影响巽他陆架外缘氧同位素3期沉积环境演化的最重要因素,即海平面升降...