Characterization and seasonal variations of surface active substances in the natural sea surface micro-layers of the coastal Middle Adriatic stations

Surface micro-layer (ML) samples were collected in different seasons over a long time period in the coastal area of the Middle Adriatic Sea including the seawater Rogoznica lake location and the semi-enclosed estuarine Martinska station. Natural surface micro-layers were studied as original samples and as ex-situ reconstructed films after previous extraction by organic solvents of different polarities (n-hexane and dichloromethane). Using alternating current (AC) voltammetry (out-of-phase mode) the concentration of surface active substances (SAS) in original ML of both locations was determined, and the enrichment factor (EF) in the ML was related to the underlayer water (ULW) samples collected at 0.5 m depth. Seasonal variability of SAS concentrations of the ML was observed at both locations. The ex-situ films were studied using a modified AC voltammetry method (out-of-phase mode) transferring an organic extract of natural micro-layers spread onto electrolyte from the air-water interface to the mercury electrode surface. The comparison of adsorption characteristics for model lipids of different polarities and those of transferred ex-situ reconstructed films has revealed that different types of lipid material were present in each ex-situ film of the same micro-layer. Additional characterization of the surface active material of natural MLs was carried out by AC voltammetry (in-phase mode) using cathodic reduction of cadmium ions as an indicator of permeability of different films adsorbed at the mercury electrode. The SAS of ML of both investigated locations induced an inhibition effect to the reduction of cadmium ions. Seasonal variations of inhibition have also been noticed. The electrochemical study contributed to the physicochemical characterization of the surface active matter of the surface micro-layer with the emphasis to the role of lipids which, although they represent a minor fraction of the total micro-layer organic material, contribute considerably to the micro-layer formation and stabilization at the air–water interface.     

中国海域有效波高、海表风速长期变化趋势的季节特征

Long-term variations in a sea surface wind speed(WS) and a significant wave height(SWH) are associated with the global climate change, the prevention and mitigation of natural disasters, and an ocean resource exploitation,and other activities. The seasonal characteristics of the long-term trends in China's seas WS and SWH are determined based on 24 a(1988–2011) cross-calibrated, multi-platform(CCMP) wind data and 24 a hindcast wave data obtained with the WAVEWATCH-III(WW3) wave model forced by CCMP wind data. The results show the following.(1) For the past 24 a, the China's WS and SWH exhibit a significant increasing trend as a whole, of3.38 cm/(s·a) in the WS, 1.3 cm/a in the SWH.(2) As a whole, the increasing trend of the China's seas WS and SWH is strongest in March-April-May(MAM) and December-January-February(DJF), followed by June-July-August(JJA), and smallest in September-October-November(SON).(3) The areal extent of significant increases in the WS was largest in MAM, while the area decreased in JJA and DJF; the smallest area was apparent in SON. In contrast to the WS, almost all of China's seas exhibited a significant increase in SWH in MAM and DJF; the range was slightly smaller in JJA and SON. The WS and SWH in the Bohai Sea, the Yellow Sea, East China Sea, the Tsushima Strait, the Taiwan Strait, the northern South China Sea, the Beibu Gulf, and the Gulf of Thailand exhibited a significant increase in all seasons.(4) The variations in China's seas SWH and WS depended on the season. The areas with a strong increase usually appeared in DJF.     

卫星遥感南海海表面日增温的时空变化特征

利用搭载在Aqua和Terra卫星上的MODIS(moderate resolution imaging spectroradiometer)、AMSR-E(advanced microwave scanning radiometer for the earth observing system)传感器测量反演的昼夜海表温度(SST),计算海表面日增温(sea surface diurnal warming),分析南海海表面日增温的短期和年变动特征。受观测平台过境时间、传感器测量SST方式、反演算法等影响,MODIS/Aqua计算的日增温幅度略大于AMSR-E/Aqua和MODIS/Terra,但在表征南海海表面日增温的时空分布特征以及变化趋势上三者并未见显著性差异。南海海表面日增温在时间分布上以冬季为最小,春季为最大;在空间分布上则是南部海域大于中部和北部海域,东部海域大于西部海域。春夏之交的吕宋海峡西北部尤其容易发生日增温事件。海表面日增温与太阳辐射、风速、云量等影响有关,其中风速与海表面日增温显著负相关。     

Seismic ambient noise around the South China Sea: seasonal and spatial variations, and implications for its climate and surface circulation

With its strong seasonal variation in wave climate and various bathymetric features due to the complex tectonics, the South China Sea (SCS) provides a natural laboratory to study the microseism. We collected data from seismic stations around the SCS and calculated their noise spectra, through which seasonal and spatial variations of microseism, as well as the general feature of seismic ambient noise in this marginal sea were revealed. Microseism seasonal variations in general reflect influences of the East Asian monsoon in winter and the Indian monsoon in summer, respectively. The two microseism components, the single frequency microseism (SFM) and the double frequency microseism (DFM), show striking alternating variation patterns both seasonally and spatially. These variation patterns, along with the bathymetric feature near the stations, indicate SFM and DFM are generated through different physical mechanisms. More interestingly, seasonal and spatial variations of DFM appear to be consistent with the basin-scale surface circulation model of the SCS, in which the upper SCS experiences cyclonic in winter and anti-cyclonic in summer. These consistencies provide observational evidence for the hypothesis that the cyclonic depression is a favorable condition to generate DFM.     

Spectral properties of sea level and time scales of Kuroshio path variations

Spectral properties of sea levels at Naze, Nishinoomote, Kushimoto, Uragami, Miyake-jima and HachijÔ-jima are examined for the non-large-meander (February 1964 – May 1975) and large-meander (October 1975 – December 1979) periods, and the periodicity of variation of the Kuroshio path is clarified.The large meander of the Kuroshio occurs with a primary period of about 20 years and secondary period of 7 to 8. 5 years. During the non-large-meander period, the Kuroshio alternately takes the nearshore and offshore non-large-meander paths with a primary period of 1. 6–1. 8 years. This variation is moreover composed of 110-day, around 195-day and annual periods. The 110-day variation of the Kuroshio path appears to have influence on the coastal sea levels between the Kii Peninsula and the Izu Ridge;i. e., the coastal sea levels rise and fall with one-month time lag after the Kuroshio has begun to approach and leave the Japanese coast. During the large-meander period, the 70 and 110-day variations are remarkable in sea levels south of Japan except Miyake-jima and HachijÔ-jima. The 70-day variation is highly coherent throughout the south coast of Japan; the coherent area of the 110-day variation seems to be smaller.The sea-level variations at Naze and Nishinoomote are not significantly coherent for any of the periods except for annual and semiannual cycles during both the non-large-meander and large-meander periods. That is, the sea-level variations are incoherent between the onshore and offshore sides of the Kuroshio, except for seasonal variation.     

In-situ diurnal sea surface temperature variations and near-surface thermal structure in the tropical hot event of the Indo-Pacific warm pool

Diurnal Sea Surface Temperature (SST) variations and the near-surface thermal structure of the tropical hot event (HE) have been investigated using advanced in-situ equatorial observations with hourly temporal resolution. The information on the HE area defined by the satellite cloud-free SSTs is used to sample the in-situ observations. The in-situ SSTs sampled for the HE conditions show that a maximum (minimum) SST has a histogram mode at 30.8°C (29.0°C), and frequently appears at 15:00 (07:00) local time. The amplitude of the diurnal SST variation (DSST) is defined by the difference between the maximum and minimum SSTs. The mean DSST during HEs is greater than 0.5°C, and has a maximum of about 0.75°C at the HE peak. The time series of mean DSST gradually increases (rapidly decreases) before (after) the peak. The satellite SST has a systematic positive bias against the corresponding daytime SST measured by the Triangle Trans-Ocean buoy Network. This bias is enhanced under conditions of large in-situ DSST. One-dimensional numerical model simulation suggests that the systematic bias is caused by the sharp vertical temperature gradient in the surface layer of HE. The near-surface thermal structure is generated by conditions of high insolation and low wind speed, which is the typical HE condition.     

Empirical method of diurnal correction for estimating sea surface temperature at dawn and noon

An empirical method has been developed for estimation of sea surface temperature (SST) at dawn and noon in local time from microwave observations at other times of the day. By using solar radiation, microwave sea surface wind, and SSTs, root-mean-square differences were reduced to approximately 0.75 and 0.8 °C for dawn and noon, respectively. The pseudo SST variation and spatial patterns found in daily mean SST values by simple averaging of samples were damped down by use of diurnal correction. The satellite SST with the diurnal correction shows highly significant coherent variation with in-situ measurements.     

Deep convection in the ocean general circulation model: Variability on the diurnal,seasonal, and interannual time scales

Features of geographical localization and of temporal variability of convective mixing were examined based on numerical experiments with the general ocean circulation model developed at the Hydrometeorological Research Center of the Russian Federation. The computations were performed using 6-h data on atmospheric forcing, which allows one to simulate the variability in a broad range of time scales—from diurnal to interannual. On the whole, the results of the numerical experiments are consistent with the available scarce observational data available on the deep convection in the North Atlantic. A pronounced regionalization of the deep convection in the open ocean is noted, as well as a significant spatial and temporal intermittence of convective events on time scales from a day to a few days. On the interannual time scale, a correlation is recognized with the variations of the atmospheric forcing and with the hydrophysical conditions in the ocean, in particular, with the cyclonic circulation within the baroclinic layer.     

Differences in seasonal variations in the patterns of diurnal earthquake periodicity in the southern and northern hemispheres

Seasonal variations in the form of diurnal periodicity are compared in three regions of the world, two of which (Alaska and Japan) are located in the Northern Hemisphere and one (New Zealand) is in the Southern Hemisphere. It is found that, in the Northern Hemisphere, the duration of the night interval of an increased number of earthquakes in December is greater than in June, while in the Southern Hemisphere it is smaller. The intra-annual character of variations in the form of diurnal earthquake periodicity agrees with the seasonal variations in the length of the day.     

High-frequency forward scattering from the sea surface: thecharacteristic scales of time and angle spreading

Forward scattering from the sea surface is discussed in the contest of a forward bounce path, or channel, through which high-frequency sound energy is transmitted. Such a channel might be used in an underwater communication or imaging task. Both time and angle spreading are inherent to the process of forward scattering by a roughened sea surface. Spreading in each domain relates, via Fourier transform, to a conjugate or coherence separation variable, e.g., angle spreading and spatial coherence. The measurement and modeling of time and angle spreading are discussed, with the modeling incorporating the bistatic cross section of the sea surface. A characteristic scale for each spread variable is defined: L for the time spread and σ_&thetas;h and σ_&thetas;v for the horizontal and vertical angular spread, respectively. Simplified expressions for these characteristic scales as a function of array acquisition geometry and sea surface conditions are also obtained. Data from two field experiments are discussed, one conducted in shallow waters of 30-m depth, and one conducted in deep, pelagic waters of 4000-m depth. Both experiments utilized frequencies ⩾20 kHz. The role of bubbles in forward scattering is illustrated using measurements from the deep-water experiment. It was demonstrated that bubbles can attenuate the forward-scattered signal, but otherwise have little effect on L and σ_&thetas;h,v until their concentrations approach those necessary to nearly extinguish the signal scattered from the air/sea interface     

Vertical distribution of heavy metals and its seasonal variations in Beppu Bay

From July to November, the thermocline which has strong temperature gradient (0.7C m^–1) is formed in the bottom water of Beppu Bay, and it prevents the downward mixing of surface water. This has caused the bottom water of the basin to become depleted in oxygen, and in November the bottom water below about 60 m depth becomes anoxic. Accordingly manganese and iron are reduced and more soluble under the anoxic condition, those concentrations are high relative to surface water, and the maximums are 1,240g l^–1 and 80g l^–1. Under the anoxic condition, the flux of dissolved manganese from the sediment is about 10g cm^–2 day^–1.     

北冰洋浮游生物空间分布及其季节变化的模拟

低营养级浮游生物生态动力过程对环境变化的响应非常敏感。随着全球气候变化加剧,北冰洋正在经历快速的环境变化。厘清北冰洋低营养级浮游生物季节分布与变化特征是探究北冰洋生态系统对环境快速变化响应的前提,也是评估北极海区固碳能力的重要依据。基于此,本文构建了海洋–海冰–生物地球化学循环模型,并对北冰洋叶绿素浓度以及浮游生物结构的时空变化特征进行了模拟,结果表明:(1)北冰洋表层叶绿素浓度的峰值主要出现在5月,且太平洋一侧叶绿素浓度高于大西洋一侧;随着海水层化,表层受营养盐限制的海区呈现次表层叶绿素浓度最大值现象,且由陆架向海盆,次表层叶绿素浓度最大值层逐渐加深;9月,叶绿素浓度高值重回水体上层,太平洋一侧海区表层叶绿素浓度呈现较为明显的次峰值。(2)由于太平洋和大西洋入流营养盐浓度及结构的不同,北冰洋表层浮游生物群落结构存在明显空间差异。太平洋一侧,硅藻和中型浮游动物占优,硅藻在5月和9月出现生物量峰值,微型浮游植物在3月、5月和6月维持相对较高生物量;而大西洋一侧,在早春－春末夏初－夏秋经历了微型浮游植物－硅藻－微型浮游植物的演替,总体而言,微型浮游植物和微型浮游动物占优。此外,两侧海区浮游动物浓度峰值相较浮游植物滞后约半月。     

基于CORA资料的中国海海表面温度季节和年际变化特征分析

基于1986-2008年的中国近海及邻近海域再分析产品(CORA),采用经验正交函数分解方法(EOF)分析了海表面温度(SST)的季节及年际变化特征,并用相应的SODA、AVHRR以及Levitus资料对CORA做了对比评估。相比于AVHRR而言,CORA资料SST的偏差和均方根误差均小于SODA,相比Levitus资料而言CORA资料温度盐度的均方根误差随深度的变化皆小于SODA。 CORA与SODA资料相比,两者前3个模态的时空分布大体一致,区别在于CORA资料能更好地反映参量的一些细微特征。结果表明,CORA资料能很好的刻画中国近海SST的季节、年际变化特征,尤其是黑潮流经区域SST的局地变化特征。季节EOF第二模态显示的是SST对由风引起的潜热释放的响应特征。第三模态刻画了冬夏转换季的分布特征,主要揭示了东北-西南走向的锋面特征。SST年际变化与ENSO密切相关,区域平均的南海SSTA与Nino指数的吻合程度CORA优于SODA。     

Long-term comparison of satellite and in-situ sea surface temperatures around the Korean Peninsula

Ocean Science Journal - Satellite remotely sensed sea surface temperature (SST) was compared with in-situ SST in the seas around the Korean Peninsula from 1984 to 2013. A matchup dataset between...     

三阶非线性海浪波面斜率的联合概率统计分布

从Longuet-Higgins于1963年建立的非线性随机海浪模型出发,对各向同性波面斜率的联台概率统计分布进行了理论研究.结果表明,在三阶近似下,波面斜率联合概率统计分有为截断的Gram-Charlier级数,截断的项数取决于非线性近似的阶数,每一阶近似均对前一阶近似结果有所修正如果不考虑非线性耦合相互作用的影响,则分布蜕化为高斯分布.     

Fluctuations I: spatial and temporal scales of importance for low-frequency propagation

Over the past 5 to 10 years much of the work in fluctuations has been broadly exploratory, intended to characterize observable time and space scales of fluctuation and to identify the environmental phenomena responsible. Much of Project MIMI (Miami/Michigan), with both fixed-system and moving-source experiments, has been devoted to this task. Although the data base now established is useful in providing direction for future work that is more application-oriented, more survey data of this type are needed, particularly at very low acoustic frequencies. More information is required, for example, on the space and time scale of fluctuations which degrade performance in array reception and which influence phase coherence at multisite receivers. A better definition is needed also of the relative importance of temporal and spatial variability in the medium for fluctuations in signals from moving sources. This paper presents data and discussion pertinent to these needs.     

Fluctuations II: spatial and temporal scales of importance for low-frequency propagation

Acoustic fluctuation data of characteristic time scales from 1 hour to 2 hours at a frequency of 406 Hz are extrapolated to frequencies under 100 Hz. These results indicate that fluctuations on this scale may have little consequence in applications involving relative phase stability between widely separated hydrophones. Fluctuation model results are reported. The model uses a source moving in a vertically stratified ocean of relatively simple structure to generate fluctuations similar to experimental data.