超疏水表面水下减阻研究进展

超疏水表面在水下可以束缚气膜层，把部分固液接触界面转变为气液接触界面，并在气液界面上产生速度滑移以减小流动阻力，是一种新型高效减阻方法。从超疏水表面润湿特性出发，重点总结了超疏水表面水下减阻研究现状，分析了超疏水表面气液界面稳定维持的主要技术途径。最后，给出了提升气液界面稳定性的潜在突破方法，可为超疏水表面水下减阻技术的发展提供借鉴。     

海表扩散层中气体行为的分子动力学模拟*

尽管影响气体在海气界面间交换的因素很多,但迄今却仅仅用风速来估算气体在海气界面的传输速度。另一方面,直接实验测量气体在海气界面的传输也十分困难。因此,气体穿过海气界面的传输速度仍然存在很大的不确定性。文章采用分子动力学方法模拟了二氧化碳、氧气、氮气以及惰性气体氩、氪在海表扩散层内部的扩散过程,求得不同温度下这些气体的扩散系数,与现有的实验值平均相差约19.4%,并重点讨论了二氧化碳在扩散层内部的行为,为进一步研究气体在海气界面的传输速度提供了新的理论手段。     

雨滴对水-气界面溶解氧与pH扩散影响的平面光极观测方法

水-气界面是一个重要的物质交换过程界面，对生态系统及生物地球化学循环过程有着重要影响。自然界的降雨可以改变水体表面平衡状态，提高气体在界面的通量交换速率，使得水体界面溶解氧和pH的水平、垂直方向浓度分布发生变化。本文利用平面传感膜具有高时空分辨率、可提供两维浓度分布信息的特点，开展了雨滴对水-气微界面层中的氧气扩散和pH值分布变化模拟实验，采用双参数平面光极同步测量获取低溶解气体在水-气界面的两维分布浓度变化。实验结果证明在受风速、温度影响较小区域，降雨过程对调节表层水体的溶解氧含量和pH值变化具有重要作用，雨滴可以打破水-气界面的微表层平衡机制，促进大气中氧气在表层水体的溶解，使得水面垂直方向23 mm内的溶解氧平均升高2.3 mg/L；降雨对水面12 mm之内表层水体pH值产生的影响较为明显，pH值平均降低了0.2~0.4个单位，表明降雨雨滴促进大气在水-气界面的迁移进程，溶解的CO₂使得表层水体向酸性方向转化。本文提出的基于平面光极两维观测方法为评估低风速、高降雨或低降雨区域的海岸带溶解氧和pH值的变化提供高空间分辨率的水-气界面实时观测新的技术支撑。     

南黄海溶解氧在海——空之间的交换

海空界面之间的气体交换，是研究气体在海洋中循环的一个重要内容。而大气中的一些可能影响气候的痕量气体，以及由海洋产生，并向大气释放的气体，在海空界面之间的交换通量及交换速度，近年来更引起人们的注意。了解气体在海空界面上的交换速度对解决这些问题是非常重要的。     

天然气水合物沉积的地震定量分析方法

反射地震剖面能提供天然气水合物区域性存在的间接证据。尽管这一技术经过三十多年不断深入的发展，但将此相关技术应用于天然气水合物研究方面仍然存在一些未决问题和需求。举例来说，在似海底反射（BSR）处观测到负的波阻抗差，气体水合物在负阻抗差形成中所起作用一直存在争论。此外，振幅随角度变化（AVA）分析是应用于储层存在游离气时获取信息的一种勘探方法，由此获得的定量信息的确定性尚有争议。本文研究采用有效介质理论（EMT），将AVA分析应用于长偏移距高分辨率的叠前地震数据。以海洋浅部沉积物的原位物理性质为约束条件合成AVA响应并建立模型，作为BSR处气体水合物浓度和游离气饱和度的函数。经过仔细处理后，结果表明这一方法检测游离气是可能的，并且游离气的低饱和度可以量化。气体水合物对观测到的阻抗差的贡献非常小，特别是在气体水合物浓度小于10％时。这一分析已经应用于哥斯达黎加和沙巴大陆边缘的海洋地震数据。     

液气共存的耗散粒子动力学模拟

传统的耗散粒子动力学方法(DPD)由于采用了纯排斥的守恒力相互作用,从而不能适应液气共存或者带有自由面流体的模拟.这里研究了DPD方法中新近提出的一种短程排斥、长程吸引相互作用,探索了这种改进势能对于DPD方法模拟液气共存的能力.模拟了这种新势能所形成的液气过渡界面,计算了过渡界面区的应力分布,发现应力分布与多体DPD方法所得结果一致.进一步对表面张力进行了研究,验证了这种势能所形成的界面满足Laplace定律,而通过理论公式与Laplace定律分别所得到的表面张力也彼此相符.     

塔基海-气界面动量通量观测：向岸风和离岸风情形比较

本文使用塔基直接观测法研究海洋大气边界层中的海-气界面动量通量。首先，我们收集数据并和前人观测结果比对，其比对结果符合一致。其次，在低风速至中等风速条件下，我们发现海-气界面动量通量的交换系数（又称拖曳系数）对于向岸风和离岸风两种情形有所差异。为此，我们使用一个考虑表面波的参数化方案解释海-气界面动量通量对于表面波的依赖关系。这些结果一方面证实表面波对于海-气界面动量通量的影响，另一方面验证一个考虑表面波参数化方案的有效性。     

波弗特海大陆边缘之下与气体水合物相关的BSR地震研究

位于阿拉斯加北部波弗特海上陆坡海底之下300－700m处有一强的似海底反射层（BSR），与上覆的气体水合物和下覆的天然气及孔隙水之间的相界面对应。世界各地BSRs具有类似的成因，这里通常解释为含本水合物碎屑沉积物之底界，下覆沉积物内可能有或没有游离气。令人惊奇的是，对这些强反向起因知之甚少。在这篇论文里，通过对合成的BSR振幅和波形（随震源－检波器偏移距变化）与穿越波弗特海发育较好的BSR多道地震反射资料比较，分析产生BSRs的物性差异。为了区分BSR之下是否有游离气，需要补充近垂直入射资料和叠前偏移资料。对振幅随偏移距变化（AVO）的分析暗示出：BSR的产生主要是由于BSR之下碎屑沉积物内存在游离气。据垂直入射合成地震记录，估计游离气带厚度薄于11－16m。若气体浓度深度而减少，则游离气带厚度可能大于16m。据AVO模拟，初估BSR之上沉积物内气体水合物饱和度不足孔隙体积的10％。     

南黄海西部地区浅层气地震特征

通过近年来南黄海西部地区的浅层地震调查,发现该地区浅层气地震特征丰富而多变,特别是多处海底面、海水层中的浅层气地震记录,揭示本区存在较多浅层气,且部分浅层气由海底逸出,释放到海水层中。该区的浅层气地震特征按空间位置分为3大类:(1)地层中的特征:声学空白、声学幕、声学扰动、不规则强反射顶界面、两侧相位下拉;(2)海底面的特征:海底麻坑、大型塌陷坑;(3)海水层中的特征:声学羽流、云状扰动、点划线反射。选择相应特征的典型浅层气地震记录,进行了声学成因解释,讨论了大型塌陷坑的浅层气成因、海水层中声学反射与浅层气体的成因关系以及浅层气地震特征的气体浓度指示作用。根据南黄海西部地区浅层气地震特征,绘制了该区的浅层气分布图。     

微藻细胞的气浮法采收

实验以螺旋藻为模型藻种，较为系统地研究了气固比，气浮塔构造特征，溶气压力和溶气时间等操作条件对微藻气浮采收效率的影响。结果表明，调节藻液pH值为12.0可使藻液产生良好的絮凝性能；高径比较大的气浮塔具有更优越的采收效应；气浮采收率随气固化，溶气压力的增以及溶气时间的延长而上升，提出的气浮采收动力学模型与实验数据拟合良好。     

Estimation of the oxygen and CO2 mean exchange between the ocean and the atmosphere in key areas of the ocean

Current estimations of gas exchange between the ocean and the atmosphere are based on the concepts about diffusive gas transfer across the interface and about a stationary character of the processes; however, under a strong wind, these concepts are invalid. Transfer equations for gas constitutents of the air are incorporated into a numerical model of a nonstationary upper layer of the ocean. These equations contain the source function—gas transfer by bubbles, which becomes noticeable even at a wind speed of 8–10 m/s. The fluxes of oxygen and CO₂ are calculated at a specified wind speed, dependences of these fluxes on the wind speed are constructed, and estimates for the average annual fluxes are obtained for several areas of the Gulf Stream and Kuroshio. A substantial change in the difference of the air-water gas contents under a strong wind, caused by the turbulent exchange growth and appreciably affecting the gas exchange, is noted. The influence of the carbonate system of seawater on the CO₂ transfer during a storm is estimated. The results obtained are compared to the estimates based on the traditional approach.     

Correcting underwater images distorted by surface waves

An experiment on the correction of underwater images distorted by waves at the air-water interface was conducted using a laboratory modeling installation intended for experimental examination of light and image transfer across a water surface covered with waves. A digital color camera was used for the simultaneous formation of the image of the underwater test object through the disturbed surface and of the superimposed glitter pattern. Both images are spectrally separated. Processing the glitter pattern makes it possible to obtain the values of the surface slopes at a limited number of points and to use these slopes for retrieval of image fragments. The total corrected image is formed by integration of about 300 partially corrected fragments. This image is close to that obtained through a wave-free water surface.     

Model estimates for the mean gas exchange between the ocean and the atmosphere under the conditions of the present-day climate and its changes expected in the 21st century

Annual mean fluxes of CO₂ and oxygen across the sea surface are estimated with the use of numerical modeling for several regions located in the Gulf Stream and Kuroshio zones. The present-day climatic conditions and the climatic conditions expected in the middle and at the end of the 21st century are considered. Specific features of gas exchange under a strong wind that are associated with gas exchange by bubbles and with changes in the air-water difference of the gas concentrations were taken into account in the calculations. The estimates obtained differ substantially from the results based on the traditional approach, which disregards the above features. A considerable increase in the absorption of CO₂ by the ocean, which is mainly caused by the continuing increase in the CO₂ concentration in the air during its small changes in the ocean, is expected in the 21st century. At the same time, no trends are revealed in the annual mean fluxes of oxygen across the ocean surface. The conclusion is made that, in calculations of CO₂ absorption by the world ocean, it is necessary to take into account both specific features of gas transfer under a strong wind and an increase in the atmospheric concentration of CO₂.     

Estimating of gas transfer velocity using triple isotopes of dissolved oxygen

The atmosphere-ocean exchange of climatically important gases is determined by the transfer velocity (k) and concentration gradient across the interface. Based on observations in the northwestern subarctic Pacific and Sagami Bay, we report here the results of the first ever application of the natural abundance of triple isotopes of dissolved oxygen (¹⁶O, ¹⁷O and ¹⁸O) for direct estimation of k and propose a new relationship with wind speed. The k values estimated from nighttime variations in oxygen isotopes are found to be higher than the direct estimations at low wind speed (<5 m s⁻¹) and lower at high wind speeds (>13 m s⁻¹) and showed significant spatial variability. The method presented here can be used to derive seasonal and spatial variations in k and the influence of surface conditions on the value, leading to improved estimates of biogenic/anthropogenic gas exchange at the air-sea interface.     

A correcting “prism” for underwater viewpoints

The angular field observable in water by an observer in air depends on the configuration of the air-water interface. When the interface is a plane, the absolute limit to observable field is about from the normal to the interface. A practical limit, because of lateral chromatic aberration is considerably less, approximately 30°. A conventionally used configuration in research submersibles, is a polymethyl methacrylate port with inner and outer surfaces parallel. This has the same optical limitations as the plane air-water interface. It is shown that if the inner and outer surfaces are not required to be parallel to each other, there are solutions which permit extending the observable field to nearly a full hemisphere with acceptably small distortion and lateral chromatic aberration.     

The input of organic material to the oceans: air—sea interactions and the organic chemical composition of the sea surface

In order to understand and quantify the way in which organic matter is transported from the atmosphere to the oceans it is important to know not only the various mechanisms by which the material is transferred between the two phases, but also the role of natural organic material at the air—sea interface in modifying such transport. In order to predict the latter it is necessary to have some knowledge of the organic chemistry and physico-chemical properties of material at the sea surface. Its organic chemistry is presently the subject of considerable controversy, although surface pressure measurements and force-area data for sea surface material, together with its very mixed chemical nature, strongly suggest that over most of the oceans it cannot form a coherent film.Transfer of organic material across the air—sea interface can be by either wet (liquid) or dry (gas and solid) deposition. The flux carried by each path can be characterised by the product of the rate of transfer of the substance concerned and its concentration in the transporting phase. Any modifying effect of material at the sea surface will vary depending on the mode of transfer, as well as the properties of the interfacial material. Application of these ideas is illustrated by calculation of atmosphere—ocean fluxes for total organic carbon, CCI₄, CCI₃F, PCBs and DDT.     

Simulation of the indirect impact that the 11-year solar cycle has on the gas composition of the atmosphere

An interactive three-dimensional chemistry-climate model combining models of the gas composition and general circulation of the lower and middle atmosphere is used to study the impact of changes in extra-atmospheric solar radiative fluxes induced by solar activity on the stratospheric heating and subsequent temperature and ozone variations in the stratosphere and troposphere. The results have shown that a change in the atmospheric radiative heating resulting from variations in solar activity has a direct effect on the temperature and circulation of the atmosphere. Atmospheric temperature variations affect the rates of temperature-dependent chemical reactions, and this is considered the first type of indirect impact of solar activity on the atmospheric gas composition. On the other hand, as a result of the variation in atmospheric heating, its circulation changes, thus affecting the transport of minor gases into the atmosphere. This effect is considered the second type of indirect impact of solar activity on atmospheric gases. The results of our calculations have shown that both types of indirect impact of the variation in solar activity on the atmospheric gas composition are comparable in order of magnitude to the direct impact of solar activity on atmospheric gases.     

海浪对北太平洋海-气二氧化碳通量的影响

利用4种海-气界面气体传输速率公式对比研究了北太平洋气体传输速率及其CO₂通量的季节变化特征。与单纯依赖风速的算法相比, 考虑波浪影响的气体传输速率和CO₂通量在空间分布和季节变化上具有明显差异。在低纬度地区(0°～30°N), 波浪参数使气体传输速率下降, 海洋对大气CO₂的吸收减少, 而在30°N以北范围内则出现新的气体传输速率高值区, 海洋对大气的吸收增加。进一步研究了黑潮延伸体区域的气候态月平均气体传输速率和CO₂通量。结果表明, 该区域气体传输速率和CO₂通量最大值分别出现于冬季和春季, 引入波浪参数后, 虽然该区域气体传输速率和CO₂通量平均值没有明显差异, 但季节变化强度显著增强。     

Estimation of the transports through the Strait of Gibraltar

An acoustic doppler current profiler (ADCP) is used to measure the currents and estimate the transports over the Camarinal Sill at the Strait of Gibraltar. The deepest measurements of the ADCP compare well with an underlying conventional current meter. The exchange interface between the Atlantic and the Mediterranean water is defined as the depth of the maximum vertical shear. The mean depth of the shear interface is 147 m. The time series of the depth of the interface and the currents are used to estimate the transports across the Strait. The resulting values are 0.78 Sv for the Atlantic inflow and −0.67 Sv for the Mediterranean outflow. The time series of the shear interface include fortnightly oscillations of 19 m. The time series of the transports are compared with the pressure and sea level difference records across the Strait. Linear multiple regression is used to estimate the (statistical) contribution of each parameter on the variation of transports. The cross strait sea level difference is well correlated with the Atlantic inflow and accounts for 57% of the variability of the transport records which improves to 78% when the fortnightly and monthly cycles are included in the linear regression. The Mediterranean outflow is best correlated with the along strait sea level difference which accounts for only 10% of the variability of the transport record. Again the addition of the M_sf and the MM cycles improves the percentage of the variance accounted for to 37%. The local, along strait wind component is significantly correlated with, both the Atlantic inflow and the across strait sea level difference.