Numerical study of the meridional overturning circulation with “mixing hotspots” in the Pacific Ocean

Using an idealized ocean general circulation model, we examine the effect of “mixing hotspots” (localized regions of intense diapycnal mixing) predicted based on internal wave-wave interaction theory (Hibiya et al., 2006) on the meridional overturning circulation of the Pacific Ocean. Although the assumed diapycnal diffusivity in the mixing hotspots is a little larger than the predicted value, the upwelling in the mixing hotspots is not sufficient to balance the deep-water production; out of 17 Sv of the downwelled water along the southern boundary, only 9.2 Sv is found to upwell in the mixing hotspots. The imbalance as much as 7.8 Sv is compensated by entrainment into the surface mixed layer in the vicinity of the downwelling region. As a result, the northward transport of the deep water crossing the equator is limited to 5.5 Sv, much less than estimated from previous current meter moorings and hydrographic surveys. One plausible explanation for this is that the magnitude of the meridional overturning circulation of the Pacific Ocean has been overestimated by these observations. We raise doubts about the validity of the previous ocean general circulation models where diapycnal diffusivity is assigned ad hoc to attain the current magnitude suggested from current meter moorings and hydrographic surveys.     

The Structure of A Turbulent Jet in A Crossflow-Effect of Jet-Crossflow Velocity

A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentr     

Meiobenthic Organisms as Indicators of Mixing Processes in the Baltic Surface Sediments*

Abstract. Two sediment cores were collected in the southern Baltic Sea and sliced into 1.0cm-thick layers. Sediments of each layer were analysed for activities of ²¹⁰Pb, ¹³⁷Cs, ¹³⁴Cs and for the density of meiobenthic organisms (meiofauna). Zones with the rapid mixing occur in the uppermost layers (0–3 cm) of the cores based on ^I34Cs profiles. The extent and density of meiofauna confirmed the rapid mixing and revealed layers with slow mixing (4–8 cm). Sedimentation rates were derived from ²¹⁰Pb profiles below the mixing zones (1.21 and 1.72 mm a-^I) and were confumed by ¹³⁷Cs distribution. Of twenty-one major meiofauna taxa commonly found in the Baltic sediments, three were present in the cores.     

深层搅拌法在超软弱港口地基上的工程应用

某港口堆场地基上部5．0m系吹填而成，地表下18m范围均属软土，经真空预压初级加固后地基承载力仅在80—90kPa，局部区域上部淤泥土层土性指标较差，含水量大于50％，地基承载力不足60kPa。为了使地基达到230kPa的承载要求，设计采用深层搅拌法加固超软弱地基。通过现场成桩工艺试验和检测表明，桩身水泥土强度在90d龄期时大于1．80MPa，单桩承载力标准值大于150kN，以φ600桩径、桩长13．5m、置换率为0．308和φ500桩径、桩长13．5m、置换率为0．267两种方案布置的复合地基承载力标准值均超过了230kPa的设计要求。试验结果表明，深层搅拌法在港口超软弱地基土应用只要施工工艺适当，完全可以使地基承载力提高2—3．5倍以土，从而节省大量的工程投资。     

思林水电站通航建筑物高边坡稳定分析和评价

应用ANSYS结构分析软件,模拟了思林水电站通航建筑物高边坡的地形、地质条件以及开挖的过程,建立边坡开挖的有限元计算分析模型,分析边坡在自然状态、分级开挖以及锚杆支护加固等工况下的应力、变形及其整体稳定性.定义单元的局部安全系数,得到了边坡开挖加固后稳定安全系数的分布.根据计算成果,指出现设计加固措施可以保证边坡稳定,无需增加其他工程措施.     

新疆北部石炭纪地层、岩相古地理与烃源岩

依据近几年新疆区域地质调查结果,结合新疆油田与吐哈油田最新勘探成果,通过区域构造背景和沉积充填演化特征推断石炭系沉积建造样式,理顺了新疆北疆地区石炭纪地层层序,目的是推断石炭纪烃源岩发育层段与主力生烃区范围。下石炭统有效烃源岩分布较广,主要发育于北疆西准噶尔达尔布特山前、博格达山前、准噶尔东部陆东—五彩湾地区早石炭世被动陆缘海相和海陆过渡相沉积盆地;上石炭统有效烃源岩分布相对局限,主要发育于东准噶尔克拉美丽山前石钱滩区、布尔津—吉木乃区及库普—三塘湖区海陆过渡相沉积盆地内。石炭系油气成藏严格遵循"源控论",有效生烃区决定其有效成藏范围,所伴随发育的火山岩体决定其富集程度。优选西准噶尔、东准噶尔、库普—三塘湖区、博格达山前区、布尔津—吉木乃区石炭系烃源岩发育区及其相邻构造带,作为今后石炭系油气勘探战略选区的重要领域和区带。     

火山沉积岩及其矿床研究中伽马测井曲线解释的误区

根据酸性凝灰岩和酸性火山事件粘土岩的自然伽马测井曲线,对当前流传的"沉积岩层的放射性强度(或放射性核素的含量)随泥质含量的增加而增高"的概念和用自然伽马值及经验公式求泥质含量提出质凝。酸性凝灰岩的自然伽马曲线有高异常响应,若解释为泥岩显然是误解,故将沉积岩伽马曲线高异常一律解释为泥岩是片面的。各类火山事件粘土岩的伽马值相差悬殊,但其泥质含量几乎相等,用它们的伽马值计算泥质含量误差甚大。最后对铝土矿层的伽马曲线稍加解释,指出核测井应用的远景。     

贵州中东部剩余重力异常与区域矿产分布关系

重点研究1:20万剩余重力异常,结合航磁、物性、地质等资料,初步圈定区内隐伏、半隐伏岩浆岩体,对研究与重力异常、岩体分布关系密切的矿产的时间、空间分布及其成因,有一定参考价值和指示意义。     

化学地层学研究中的若干注意事项

化学地层学因其交叉学科特点和研究对象的复杂性使得研究过程中任何一个环节的不足都将造成测试出现偏差,成果的可信度也将出现问题。高昂的成本也要求研究者把有限的资源集中到正确的目标上。近20年研究历程却恰恰将此类性质的问题陆续暴露了出来。如采样阶段获取原生性状考虑不充分或依据不足、测试阶段缺乏校验、数据分析阶段挖潜和综合利用有待完善以及化学岩、碎屑岩和生物岩各自的基础性和针对性研究有待提高等。有些问题带有相当程度的普遍性,有些甚至是严重的核心技术问题。笔者结合最新相关研究成果对上述问题进行了逐一分析和系统修正。     

上宫构造蚀变岩型金矿床地质特征及化探找金经验

上宫金矿位于河南省西部熊耳山北麓,在该区1 020 km²范围内进行了1:5万的地球化学水系沉积物测量,按水系划分取样单元,取样本着"小沟多取,支流放稀,大河不管"的原则进行。本次水系沉积物测量的特点是:取样少,控制面积大,速度快,省钱、省人、省物,找矿效果好、经济效益好。本区水系沉积物测量中所发现的金异常,后经异常检查、地质普查评价及钻探验证,确定为一大型构造蚀变岩型金矿床。