Mechanisms controlling the temporal variation of the sea ice edge in the Southern Ocean

This paper examines the mechanism controlling the short time-scale variation of sea ice cover over the Southern Ocean. Sea ice concentration and ice velocity datasets derived from images of the Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) are employed to reveal this mechanism. The contribution of both dynamic and thermodynamic processes to the change in ice edge location is examined by comparing the meridional velocity of ice edge displacement and sea ice drift. In the winter expansion phase, the thermodynamic process of new ice production off the ice edge plays an important role in daily advances of ice cover, whereas daily retreats are mostly due to southward ice drift. On the other hand, both advance and retreat of ice edges in the spring contraction phase are mostly caused by the dynamic process of the ice drift. Based on the above mechanism and the linear relation between the degree of ice production at the ice edge and northward wind speed, the seasonal advance of ice cover can be roughly reproduced using the meridional velocity of ice drift at the ice edge.     

Correction method for full-depth current velocity with lowered acoustic Doppler current profiler (LADCP)

A new method is presented to process and correct full-depth current velocity data obtained from a lowered acoustic Doppler current profiler (LADCP). The analysis shows that, except near the surface, the echo intensity of a reflected sound pulse is closely correlated with the magnitude of the difference in vertical shear of velocity between downcast and upcast, indicating an error in velocity shear. The present method features the use of echo intensity for the correction of velocity shear. The correction values are determined as to fit LADCP velocity to shipboard ADCP (SADCP) and LADCP bottom-tracked velocities. The method is as follows. Initially, a profile of velocity relative to the sea surface is obtained by integrating vertical shears of velocity after low-quality data are rejected. Second, the relative velocity is fitted to the velocity at 100–800 dbar measured by SADCP to obtain an “absolute” velocity profile. Third, the velocity shear is corrected using the relationship between the errors in velocity shears and echo intensity, in order to adjust the velocity at sea bottom to the bottom-tracked velocity measured by LADCP. Finally, the velocity profile is obtained from the SADCP-fitted velocity at depths less than 800 dbar and the corrected velocity shear at depths greater than 800 dbar. This method is valid for a full-depth LADCP cast throughout which the echo intensity is relatively high (greater than 75 dB in the present analysis). Although the processed velocity may include errors of 1–2 cm s⁻¹, this method produced qualitatively good current structures in the Northeast Pacific Basin that were consistent with the deep current structures inferred from silicate distribution, and the averaged velocities were significantly different from those calculated by the Visbeck (2002) method.     

Effects of cold eddy on phytoplankton production and assemblages in Luzon strait bordering the South China Sea

The biochemical effects of a cold-core eddy that was shed from the Kuroshio Current at the Luzon Strait bordering the South China Sea (SCS) were studied in late spring, a relatively unproductive season in the SCS. The extent of the eddy was determined by time-series images of SeaWiFS ocean color, AVHRR sea surface temperature, and TOPEX/Jason-1 sea surface height anomaly. Nutrient budgets, nitrate-based new production, primary production, and phytoplankton assemblages were compared between the eddy and its surrounding Kuroshio and SCS waters. The enhanced productivity in the eddy was comparable to wintertime productivity in the SCS basin, which is supported by upwelled subsurface nitrate under the prevailing Northeastern Monsoon. There were more Synechococcus, pico-eucaryotes, and diatoms, but less Trichodesmium in the surface water inside the eddy than outside. Prochlorococcus and Richelia intracellularis showed no spatial differences. Water column-integrated primary production (IPP) inside the eddy was 2–3 times that outside the eddy in the SCS (1.09 vs. 0.59 g C m⁻²d⁻¹), as was nitrate-based new production (INP) (0.67 vs. 0.25 g C m⁻²d⁻¹). INP in the eddy was 6 times that in the Kuroshio (0.12 g C m⁻²d⁻¹). IPP and INP in the eddy were higher than the maximum production values ever measured in the SCS basin. Surface chlorophyll a concentration (0.40 mg m⁻³) in the eddy equaled the maximum concentration registered for the SCS basin and was higher than the wintertime average (0.29 ± 0.04 mg m⁻³). INP was 3.5 times as great and IPP was doubled in the eddy compared to the wintertime SCS basin. As cold core eddies form intermittently all year round as the Kuroshio invades the SCS, their effects on phytoplankton productivity and assemblages are likely to have important influences on the biogeochemical cycle of the region.     

凡纳滨对虾(Litopenaeus vannamei)体重、存活性状的遗传参数和基因型与环境互作效应

利用7个凡纳滨对虾(Litopenaeus vannamei)引进群体,通过双列杂交和巢式交配设计构建家系,建立育种基础群体,估计体重、存活性状的遗传参数和基因型与环境互作效应(genotype by environment interactions,G×E)。结果表明,凡纳滨对虾基础群体体重和存活性状的遗传力估计值范围分别在(0.19±0.09)—(0.43±0.09),(0.27±0.04)—(0.45±0.06),均属于中高遗传力水平,并且统计检验显著(P<0.05)。Z-score检验表明,体重和存活性状遗传力估计值在河北黄骅(HBHH)和青岛鳌山(QBAS)两个测试场间差异均不显著。体重和存活性状的表型和遗传相关系数分别为0.007和0.008,表现为低度线性负相关。对于体重和存活性状,HBHH和QBAS场间的遗传相关分别为0.83±0.04和0.40±0.11。体重性状的G×E效应不显著(K<0.5),但存活性状存在显著的G×E效应(K>0.5)。上述结果显示,凡纳滨对虾基础群体体重和存活性状的遗传变异丰富,多代选择可获得较大的遗传进展。     

4种海洋贝类对水体中Pb的富集规律

为了研究泥蚶、菲律宾蛤、缢蛏和单齿螺等海洋贝类对海水中Pb的富集规律,本文在设置Pb质量浓度分别为0.001 0,0.003 5,0.006 0,0.011 0,0.026 0和0.051 0 mg/L 6个试验组中,采用半静水法进行泥蚶、菲律宾蛤、缢蛏和单齿螺对海水中Pb的富集试验,分别在0,1,3,5,10,15,20,25和30 d时取出部分贝类用微波消解原子吸收光谱法测定Pb含量,并探讨了贝类对Pb的富集机制,比较了不同贝类对Pb的富集能力。实验结果表明:4种贝类均表现出了对Pb有一定的富集效应。水体中Pb质量浓度达到0.003 5 mg/L时,泥蚶对Pb富集明显;水体中Pb质量浓度达到0.006 0 mg/L时,菲律宾蛤对Pb富集明显。水体中Pb质量浓度达到0.011 0 mg/L时,缢蛏和单齿螺对Pb富集明显。总体上,贝类体内重金属含量随着水体中Pb质量浓度和富集时间的增加而增加。在Pb质量浓度低于0.051 mg/L的所有试验组中,时间越长,贝类体内富集的Pb含量越高,但在3 d左右时,贝类体内富集的Pb含量却出现低值。     

Nino2、3区的大洋科考船测气象海浪特征分析

通过分析中国大洋科考22航次第七航段海洋环境资料,重点研究了热带东太平洋洋中脊海域的气象与海浪特征,并分析了同期热带大洋气候背景.船测资料与卫星资料的分析结果一致显示,洋中脊海区受到了东南太平洋副热带高压偏强的影响.本文的分析结果将为更精确地研究Nin02、3区的海洋环境特征提供了数据支持.     

潮流对老虎石海滩养护工程响应的数值预测

为研究老虎石海滩养护工程对老虎石浴场及周围岬湾的水动力环境的影响,利用MIKE 21建立工程区海域二维潮流数学模型,通过实测流速、流向对模型进行验证,将验证后模型参数运用到工程设计方案下潮流场的模拟,比较分析工程前后水动力环境的变化。潮流场比较结果表明,修建潜坝会使得工程及其附近的潮流场发生小幅变化,但对该海域整体的潮流动力环境影响甚微。工程后老虎石海域的潮流动力仍然很弱,对保存海滩上人工养护的泥沙是非常有利的。     

三维弹性侧壁液舱内液体晃动波面的实验研究

通过物理模型实验,对弹性侧壁液舱和刚性液舱内液体晃荡问题进行了研究。由于流固耦合的影响,弹性侧壁液舱内液体晃荡的最低阶固有频率稍小于同尺寸的刚性液舱内液体晃荡的最低阶固有频率。液舱模型处于纵向简谐激励作用下,其中激励频率在最低阶固有频率附近。实验分析两种相对液深比h/L=0.167和h/L=0.333,在二阶模态的次共振和一阶模态的共振状况下,对弹性侧壁液舱与刚性液舱内不同测点的波面、振幅谱和晃动波高进行对比分析。结果表明:在浅液深(h/L=0.167)一阶共振下,流固耦合对波面形态的影响比较明显,弹性侧壁液舱内测点晃动波高明显大于刚性液舱内对应测点波高;而在一般液深(h/L=0.333)一阶共振下,水弹性效应减弱,弹性侧壁液舱与刚性液舱内对应测点处波高差异较小。     

青岛城市规划区不同岩性氡浓度差异及其控制因素

青岛是典型的花岗岩地区,通过分析青岛不同岩性的氡浓度探讨其差异和控制因素。结果表明：青岛不同岩芯的氡浓度变化范围为0.05～19.51 KBq/m3,平均值为2.56 KBq/m3（n=210）,花岗岩氡浓度均值为1.54 KBq/m3,同其他岩性相比氡浓度较低。不同岩性样品氡浓度释放量平均值表现为粉质黏土＞泥岩＞砂质泥岩＞泥质砂岩＞闪长岩＞粉土/填土＞砂岩＞正长花岗岩＞粗砂＞花岗岩＞二长花岗质片麻岩。综合来看,土壤层中氡浓度最高,其次是沉积岩和岩浆岩,变质岩中氡浓度最低。不同岩性氡浓度与其铀含量和孔隙率有关,除花岗岩外,沉积岩和变质岩中铀含量越高所含氡浓度越高,沉积岩、岩浆岩以及变质岩的氡浓度和孔隙率大小呈正相关,沉积岩中氡浓度高于岩浆岩,推测与其所含的富水砂层有关;土壤的土质均匀疏松,孔隙度最高,氡在土壤中有大量的存储空间,故在所有岩性中所含的氡浓度最大。     

Extended Finite Element Method for the Analysis of Discontinuities in Rock Masses

The strength and deformability of rock mass primarily depend on the condition of joints and their spacing and partially on the engineering properties of rock matrix. Till today, numerical analysis of discontinuities e.g. joint, fault, shear plane and others is conducted placing an interface element in between two adjacent rock matrix elements. However, the applicability of interface elements is limited in rock mechanics problems having multiple discontinuities due to its inherent numerical difficulties often leading to non-convergent solution. Recent developments in extended finite element method (XFEM) having strong discontinuity imbedded within a regular element provide an opportunity to analyze discrete discontinuities in rock masses without any numerical difficulties. This concept is based on partition of unity principle and can be used for cohesive rock joints. This paper summarizes the mathematical frameworks for the implementation of strong discontinuities in 3 and 6 nodded triangular elements and also provides numerical examples of the application of XFEM in one and two dimensional problems with single and multiple discontinuities.