Seasonal variations and trophic ecology of microzooplankton in the southeastern Arabian Sea

The seasonal ecological response of microzooplankton in the southeastern Arabian Sea is presented. During the spring intermonsoon period, stratification and depletion of nitrate in the surface waters (nitracline was at 60 m depth) cause low integrated chlorophyll a (av. 19±11.3 mg m⁻²) and primary production (av. 164±91 mgC m⁻² d⁻¹). On the other hand, nutrient enrichment associated with coastal upwelling and river influx during the onset and peak summer monsoon resulted in high integrated chlorophyll a (av. 21±6 mg m⁻² and av. 29±21 mg m⁻², respectively) and primary production (av. 255±94 mgC m⁻² d⁻¹ and av. 335±278 mgC m⁻² d⁻¹, respectively). During all three periods, diazotropic cyanobacterium Trichodesmium erythraeum dominated in the nutrient depleted surface waters. A general increase in abundance of larger diatoms was evident in the surface waters of the inshore region during monsoon periods. The microzooplankton abundance was found to be significantly higher during the spring intermonsoon (av.241±113×10³ ind m⁻²) as compared to onset of summer monsoon (av. 105±89×10³ ind m⁻²) and peak summer monsoon (av.185±175×10³ ind m⁻²). Microzooplankton community during the spring intermonsoon was numerically dominated by ciliates while heterotrophic dinoflagellate was the dominant ones during the monsoon periods. The high abundance of ciliates during the spring intermonsoon could be attributed to the stratified environmental condition prevailed in the study area which favors high abundance of smaller phytoplankton and cyanobacteria, the most preferred food of ciliates. On the other hand, the dominance of heterotrophic dinoflagellates during the monsoon periods could be linked to their ability to graze larger diatoms which were abundant during the monsoon periods. The overall results show low abundance of microzooplankton in the eastern Arabian Sea during the monsoon periods mainly due to a decline in ciliates abundance. This decline during the monsoon periods could be the result of (a) low abundance of smaller phytoplankton and (b) high stock of mesozooplankton predators (av. 245 ml 100 m⁻³).     

Dynamics of westward propagation and intensification of Lakshadweep low in the southern Arabian Sea

Ocean Dynamics - Westward propagation and the dynamics of intensification of Lakshadweep low (LL) have been investigated in detail. In this study, it is observed that LL is not propagated westwards...     

中国南海海域北部地区现今地应力实测及综合分析研究

南海北部区域现今地应力场的状态和分布特征是进行海洋资源开发、地质环境和工程安全评价的主要参考依据,也是地球动力学研究的主要内容之一. 由于受到测量技术水平和自然条件等因素的影响,整个南海海域的地应力研究程度还比较低,有待于对该区域的地应力场的状态和控制因素进行较深入和细致的研究. 原地地应力测量是直接获取地壳浅表层现今主应力大小和方向特征的有效途径,同时利用海上油气田测井FMI资料能够有效地提取地应力信息. 结合区域构造环境,在实测地应力约束条件下,数值模拟方法能够有效地推测区域地应力的状态和分布特征. 在海南省乐东县开展了水压致裂原地地应力测量,测量获得的最大主应力方向区间为NW-NWW向. 根据Byerlee准则判别,钻孔附近的地应力远远小于引起断层活动地应力值的下限,钻孔邻近区域的断层活动性较弱. 对南海北部边缘海盆地有限的FMI测井资料进行地应力解译,获得莺歌海的最大主应力优势方位为NW-NNW向,琼东南的最大主应力优势方位为NWW向. 在对南海海域北部区域的板块构造环境和地球动力学背景分析的基础上,以上述地应力观测数据以及震源机制解资料为约束,对该区域现今地应力场进行了数值模拟分析,模拟结果表明,由于受印度板块、菲律宾板块和欧亚板块不同程度的影响,南海北部区域的地应力分布特征呈现了不同区域分化的趋势. 在靠近台湾岛区域,主要受到菲律宾板块与欧亚板块发生碰撞的影响,最大主应力方向为近E-W向;沿着滨海海岸带向西,由于受到欧亚板块在马尼拉海沟向下俯冲形成的拉伸作用,最大主应力的方向逐渐转换为S-N向、NW向.     

Sea level rise in the north-western part of the Arabian Gulf

Relative sea level variations in the north-western part of the Arabian Gulf have been estimated in the past using no more than 10 to 15 years of observations. In this study, we have almost doubled the period to 28.7 years by examining all available tide gauge data in the area and constructing a mean gauge time-series from seven coastal tide gauges. We found for the period 1979–2007 a relative sea level rise of 2.2 ± 0.5 mm/year. Using the subsidence observed at 6 GPS stations within a radius of 100 km of the tide gauges as an indication of the vertical land motion, the corresponding absolute sea level rise is 1.5 ± 0.8 mm/year that is in agreement with the global estimate of 1.9 ± 0.1 mm/year (Church and White, 2011) for the same studied period. By taking into account the temporal correlations we conclude that previous published results underestimate the true sea level rate uncertainty in this area by a factor of 5–10.     

Fluorophores in the Arabian Sea and their relationship to hydrographic conditions

 Water mass distributions, upwelling and filament formation are of complex significance for biological and chemical processes. Temperature and salinity are routinely used to characterize these hydrographic conditions. In situ profiles and sample analyses from the cruise So119 of RV Sonne in May 1997 into the Arabian Sea indicate that optical parameters such as the fluorescence of phytoplankton pigments, gelbstoff and proteins reflect hydrographic processes as well, and are useful to describe and explain biochemical processes. The dependence of bio-optical parameters to DOC and chlorophyll a concentrations is examined. While the relation between extracted chlorophyll and chlorophyll fluorescence is quite reasonable, DOC and gelbstoff fluorescence do not show a functional dependency. This is mainly due to sunlight-induced degradation of fluorophores in the surface layer. Enhanced gelbstoff signals in intermediate and deep waters are related to Persian Gulf Water. The optical data reveal a relation between the depth of the chlorophyll maximum, the depth of 1% surface light and the geographical latitude. In the context of remote sensing of phytoplankton biomass from ocean colour images, the depth of the chlorophyll maximum is a crucial parameter. Thus, the revealed dependency on latitude is useful for the evaluation of primary production with satellite remote sensing. Received: 22 May 2002 / Accepted: 18 February 2003 Responsible Editor: Andreas Oschlies Acknowledgements. This work was supported by a grant from the Federal Minister of Education and Technology, Bonn, within the framework of the JGOFS Arabian Sea program. We are grateful to the captain and the crew of RV Sonne for their support. Special thanks are given to the chief scientist of the cruise, Pr. V. Ittekkot, for helpful discussions. We are indebted to Mr. Rüdiger Heuermann and Mr. Nils Bürckel for their participation in the cruise and their support in the data analysis.     

Interpreting the sea surface temperature warming trend in the Yellow Sea and East China Sea

Previous studies have demonstrated that the low-frequency sea surface temperature (SST) variability in the Yellow Sea and East China Sea (YECS) is linked to large-scale climate variability, but explanations on the mechanisms vary. This study examines the low-frequency variability and trends of some atmospheric and oceanic variables to discuss their different effects on the YECS warming. The increasing temperature trend is also observed at a hydrographic section transecting the Kuroshio. The increasing rate of ocean temperature decreases with depth, which might result in an increase in vertical stratification and a decrease in vertical mixing, and thus plays a positive role on the YECS warming. The surface net heat flux (downward positive) displays a decreasing trend, which is possibly a result of the YECS warming, and, in turn, inhibits it. Wind speeds show different trends in different datasets, such that its role in the YECS warming is uncertain. The trends in wind stress divergence and curl have large uncertainties, so their effects on SST warming are still unclear. The Kuroshio heat transport calculated in this study, displays no significantly increasing trend, so is an unlikely explanation for the SST warming. Limited by sparse ocean observations, sophisticated assimilative climate models are still needed to unravel the mechanisms behind the YECS warming.     

Geostrophic balance over the Arabian Sea and Bay of Bengal regions

Geostrophic balance over the Arabian Sea and Bay of Bengal regions has been studied using the wind data obtained from the AVRO (HS-748) aircraft during the FGGE-MONEX-79.In the Arabian Sea and the Bay of Bengal regions, the observed wind south of 20°N was found to be sub-geostrophic. In the Arabian Sea region the departure at 1500 m was 75–95% and at 3050 m it was 60–65%. In the Bay of Bengal region the departure was 85–95%. In a few cases north of 20°N the observed winds at 3050 m were found to be super-geostrophic in the regions of enhanced monsoon activity, cyclonic circulation reaching up to 6000 m and in the region of monsoon trough.     

Radionuclide fluxes in the Arabian Sea: the role of particle composition

We investigated the influence of the composition of the vertical particle flux on the removal of particle reactive natural radionuclides (²³⁰Th and ²³¹Pa) from the water column to the sediments. Radionuclide concentrations determined in sediment traps moored in the western, central and eastern Arabian Sea were related to the major components (carbonate, particulate organic matter (POC), opal, lithogenic material) of the particle flux. These data were combined with sediment trap data previously published from the Southern Ocean, Equatorial Pacific and North Atlantic [Z. Chase, R.F. Anderson, M.Q. Fleisher, P.W. Kubik, The influence of particle composition and particle flux on scavenging of Th, Pa and Be in the ocean, Earth Planet. Sci. Lett. 204 (2002) 215–229; J.C. Scholten, F. Fietzke, S. Vogler, M. Rutgers van der Loeff, A. Mangini, W. Koeve, J. Waniek, P. Stoffers, A. Antia, J. Kuss, Trapping efficiencies of sediment traps from the deep eastern North Atlantic: The ²³⁰Th calibration, Deep Sea Research II 48 (2001) 2383–2408]. The correlations observed between the particle-dissolved distribution coefficients (K_d) of ²³⁰Th and ²³¹Pa and the concentrations of the particle types depend on the sediment trap data set used. This result suggests that scavenging affinities of the nuclides differ between oceanic regions. Several factors (K_d values, reactive surface areas of particles, inter-correlations in closed data set) can, however, influence the observed relationships and thus hamper the interpretation of these correlation coefficients as a measure of relative scavenging affinities of the nuclides to the particle types investigated. The mean fractionation factor (F(Pa/Th)=K_d(Pa)/K_d(Th)) from the Equatorial Pacific (F=0.11±0.03) is similar to that from the North Atlantic (F(Pa/Th)=0.077±0.026), and both are lower than the factors from the Arabian Sea (F(Pa/Th)=0.35±0.12) and from the Southern Ocean (F(Pa/Th)=0.87±0.4). For opal concentrations exceeding 60%, an increase in the fractionation factors is observed causing a higher mean fractionation factor for the Southern Ocean trap data set. For the other areas investigated, differences in the mean fractionation factors cannot be related to the particles types considered. In the Arabian Sea, seasonally variable ²³¹Pa_ex/²³⁰Th_ex ratios observed in the sediment traps as well as differences of the ratios between recently deposited phytodetritus (fluff) and normal surface sediments indicate seasonal changes in scavenging processes which the generally accepted reversible scavenging models do not envisage. We assume that variable sinking rates of particles, and/or particles not considered in this study (e.g. colloids, manganese oxides, transparent exopolymer particles) may play an important but as yet unexplored role in deep-water scavenging processes.     

Dimethylsulfide and Phaeocystis poucheti in the southeastern Bering Sea

Dimethylsulfide (DMS), a volatile excretion product of marine phytoplankton, was determined in the water column during the spring phytoplankton bloom on the southeastern Bering Sea shelf. In the same samples, a broad range of variables which characterize the biological processes in this region were measured. DMS was correlated with phytoplankton chlorophyll in the outer shelf and oceanic domains, but not in the middle shelf domain. A very strong correlation between the cell density of the haptophyte Phaeocystis poucheti and the DMS concentration in seawater was found, which suggests that this species accounts for most of the DMS present in the study region. We propose that in P. poucheti and certain other phytoplankton species the excretion of DMS is incidental to the release of acrylic acid which serves to inhibit bacterial attack upon the algae.     

基于地面实测光谱的太湖水体富营养化水平估算

富营养化指数是评价水体污染情况的一个重要的综合性指标．通过对高光谱遥感数据和水体富营养化指数的分析,确立了反演水体富营养化水平的高光谱敏感波段,进而用选择的敏感波段和波段组合来建立模型．通过对几个模型的比较,选出了较为理想的估算模型．最后对模型进行精度分析,认为该模型具有一定的可靠性和实用性．从而确定了直接由高光谱遥感数据监测水体富营养化水平的可能性,为实现由高光谱遥感数据开展大范围的水质调查奠定了一定的理论基础．     

Enhanced red fluorescence emission in the oxygen minimum zone of the Arabian Sea

 Depth profiles of fluorescence at several excitation and emission wavelengths were measured along with CTD data during the cruise So119 of RV Sonne in the Arabian Sea from 12 May to 10 June 1997. In addition to chlorophyll fluorescence from phytoplankton in the near-surface layer, the profiles in the oxygen minimum region well below the euphotic zone show enhanced red fluorescence. Red fluorescence intensity is inversely related to the oxygen concentration in intermediate and deep waters. A relationship to characteristic water masses of the region cannot be found in the data, and this holds also with chemical data such as DOC. Absorbance spectra of water samples taken in the oxygen minimum zone show an absorption band at 420 nm wavelength with about 50 nm bandwidth, much weaker than gelbstoff absorbance in the same wavelength range. The absorption band remains stable after sample filtration with 0.45 μm glass fibre filters. Hence, the size of the absorbing matter is in the range of dissolved molecules or particles much smaller than 1 μm. Fluorescence spectra of unfiltered samples with 420 nm excitation show a weak emission band at 600 nm and a more pronounced one at 660 nm wavelength. The trailing edge of the 660 nm band falls into the range of chlorophyll emission, thus giving rise to the observed depth profiles of red fluorescence in the oxygen minimum zone. Red fluorescence measured on samples remain stable during a few hours after sampling even in the presence of oxygen. It is not detectable after several weeks of sample storage in the dark and cannot be reproduced even after depletion of dissolved oxygen. Received: 22 May 2002 / Accepted: 18 February 2003 Responsible Editor: Andreas Oschlies Acknowledgements. This work was supported by a grant from the Federal Minister of Education and Technology, Bonn, within the frame work of the JGOFS Arabian Sea program. We are grateful to the captain and the crew of RV Sonne for their support. We are indebted to Mrs. Kirsten Neumann from the Institute of Marine Chemistry and Biogeochemistry of the University of Hamburg for providing the oxygen data, and to Mr. Nikolai Delling from the same institute for making the DOC and chlorophyll data available to us.     

Numerical modeling of the development of southeastern Red Sea continental margin

The Red Sea continental margin (RSCM) corresponds to a wide hinge zone between Red Sea and Arabian plate. This margin has been studied through geological and geophysical observations primarily in regard to the evolution of Red Sea rift. This margin is characterized by occurrence of thin sediments, significant onshore uplift, tectonic subsidence of the offshore sedimentary basin, active faulting and seismicity. Studies indicate that sedimentary sequences of the margin are deformed by faults and folds resulti...     

Residence time of pollutants discharged in the Gulf of Kachchh, northwestern Arabian Sea

A 2D Hydrodynamic-Particle Analysis model was applied to the Gulf of Kachchh (GoK) to estimate the residence time of pollutants. The tidal currents in the Gulf have a strong E-W component, which prevents the material in the north being transported towards south. In the regions situated very close to the open boundary, where the GoK waters exchange freely with the northern Arabian Sea, dilution takes place rapidly with the incoming waters and hence, the residence time is on the order of 1 day. Influence of eddies and a dynamic barrier across the Sikka-Mundra section on the residence time is apparent. Eastern GoK shows a relatively large residence time, on the order of 2-4 days, warranting caution while releasing industrial wastes in the northeastern Gulf. The region around location-5 behaves like a bay; the dissolved matter gets trapped in this bay and the residence time increases by 3-4 days.     

Phase velocities of Rayleigh waves in southeastern Europe and Eastern Mediterranean Sea

Summary Measurements of phase velocities along several paths in southeastern Europe and along one path in the Eastern Mediterranean have been made in the period range 15 to 60 sec for the fundamental mode of Rayleigh waves. The data are fitted by layered models of the crust and upper mantle. The crust in the Balkan peninsula is thicker than the normal continental crust by about 10 km while the crust in the northern Aegean Sea has the normal continental thickness. The existence of a low shear velocity layer of thickness equal to 140 km with its top in a depth of 90 km interpretes the data well for the longer periods. The data for the eastern Mediterranean show that this region has an oceanic character. The mean crustal thickness in this area is of the order of 20 km.     

Role of fronts in the formation of Arabian Sea barrier layers during summer monsoon

The barrier layer (BL) — a salinity stratification embedded in the upper warm layer — is a common feature of the tropical oceans. In the northern Indian Ocean, it has the potential to significantly alter the air–sea interactions. In the present paper, we investigate the spatio-temporal structure of BL in the Arabian Sea during summer monsoon. This season is indeed a key component of the Asian climate. Based on a comprehensive dataset of Conductivity–Temperature–Depth (CTD) and Argo in situ hydrographic profiles, we find that a BL exists in the central Arabian Sea during summer. However, it is highly heterogeneous in space, and intermittent, with scales of about ～100 km or less and a couple of weeks. The BL patterns appear to be closely associated to the salinity front separating two water masses (Arabian Sea High Salinity Water in the Northern and Eastern part of the basin, fresher Bay of Bengal Water to the south and to the west). An ocean general circulation model is used to infer the formation mechanism of the BL. It appears that thick (more than 40 m) BL patterns are formed at the salinity front by subduction of the saltier water mass under the fresher one in an area of relatively uniform temperature. Those thick BL events, with variable position and timing, result in a broader envelope of thinner BL in climatological conditions. However, the individual patterns of BL are probably too much short-lived to significantly affect the monsoonal air–sea interactions.     

Signature of ENSO Signals in the Coral Growth Rate Record of Arabian Sea and Indian Monsoons

We examine here three sets of recently published data: (1) Updated Indian Rainfall (IRF) time series of the entire country covering the time span of 1826–1994, (2) coral growth rate time series for a period of 42 years spanning 1948–1990 from the Arabian Sea, and (iii) NINO3 temperature records to investigate the signature of ENSO response of the Indian monsoon. Multiple spectral techniques (e.g., multi-taper method (MTM), maximum entropy method (MEM), wavelet and cross spectra) are used to identify the coherent cyclic and nonstationary modes in these records. MTM analysis of IRF time series resolves statistically significant variability (>90% C.I) (i) at multi-decadal (66–70 years) scales related to the well-known global temperature variability of internal atmospheric-ocean origin, (ii) relatively weak signals at 13 and 22 years (solar cycles) and (iii) the 2.5 to 7.5-year cycles associated with the ENSO frequency band. The MTM spectra of the coral growth rate record also reveal statistically significant periodicities (>90% C.I.) within 1.8–4.2 ENSO frequency band, and a relatively weak signal at 12.8 years. MEM analysis confirms the stability of above spectral peaks. Wavelet spectral analyses of the above time series reveal nonstationary localized modes of ENSO evolution corresponding to 2–7 years and higher order terms. Although matching periodicities are present in these records, cross-spectral analysis of IRF and NINO3 temperature records exhibits significant coherency (>80% CI) only at periods 5.4 years and 2.7 years, suggesting the significant role of ENSO dynamics in organizing the subtle Indian monsoon at these frequencies. These results may provide significant implication for the modeling of Indian monsoon.     

钻孔千斤顶压裂测量技术的发展和原地测量

为了测量距地表1 000 m以下位置的地壳应力状态,我们研究并开发了钻孔千斤顶压裂技术.技术的原理是:当钻孔千斤顶对钻孔壁加载时,与钻孔轴向平行的方向将会产生两个相对的新裂隙;卸载之后,如果千斤顶对钻孔壁的同一个地方进行施压,这对裂隙将会再次张开.与钻孔轴向垂直的平面上的两个主应力的大小和方向分别是由重张压力和裂隙的方...