Thorium isotopes as tracers of particles dynamics and deep water circulation in the Indian sector of the Southern Ocean (ANTARES IV)     

L. Coppola  M. Roy-Barman  S. Mulsow  P. Povinec  C. Jeandel 《Marine Chemistry》2006,100(3-4):299

Dissolved and particulate samples were collected to study the distribution of thorium isotopes (²³⁴Th, ²³²Th and ²³⁰Th) in the water column of the Indian sector of the Southern Ocean (from 42°S to 47°S and from 60°E to 66°E, north of the Polar Front) during Austral summer 1999. Vertical profiles of excess ²³⁰Th (²³⁰Th_xs) increases linearly with depth in surface water (0–100 m) and a model was applied to estimate a residence time relative to the thorium scavenging (τ_scav). Low τ_scav in the Polar Front Zone (PFZ) are found, compared to those estimated in the Subtropical Front Zone (STZ). Changes in particle composition between the PFZ and STZ could influence the ²³⁰Th_xs scavenging efficiency and explain this difference. An innovative coupling between ²³⁴Th and ²³⁰Th_xs was then used to simultaneously constrain the settling velocities of small (0.6–60 μm) and large (above 60 μm) particles. Although the different hydrological and biogeochemical regimes visited during the ANTARES IV cruise did not explain the spatial variation of sinking velocity estimates, our results indicate that less particles may reach the seafloor north (60 ± 2 m d^− 1, station 8) than south of the Agulhas Return Current (119 ± 23 and 130 ± 5 m d^− 1 at stations 3 and 7, respectively). This information is essential for understanding particle transport and by extension, carbon export. In the deep water column, the ²³⁰Th_xs concentrations did not increase linearly with depth, probably due to lateral transport of North Atlantic Deep Water (NADW) from the Atlantic to the Indian sector, which renews the deep waters and decreases the ²³⁰Th_xs concentrations. A specific ²³⁰Th_xs transport model is applied in the deep water column and allows us to assess a “travel time” of NADW ranging from 2 to 15 years.  相似文献   

海底剖面声阻抗分布声遥测模拟实验研究     

杨振华  林俊轩  马恒仁 《中国海洋大学学报(自然科学版)》1989,(4)

本文介绍一种声遥测海底平面层系声阻抗分布的模拟实验结果。实验在油漆厂冷却水池中进行,采用取样平均迭代的反演方法,对三介质层系的遥测结果与实测值较好地接近。  相似文献   

Accumulation of organic and inorganic carbon in Pliocene–Pleistocene sediments along the SW African margin     

Jacques Giraudeau  Philip A. Meyers  Beth A. Christensen   《Marine Geology》2002,180(1-4):49-69

The Ocean Drilling Program Leg 175 recovered a unique series of stratigraphically continuous sedimentary sections along the SW African margin, an area which is presently affected by active coastal upwelling. The accumulation rates of organic and inorganic carbon are a major component of this record. Four Leg 175 sites (1082, 1084, 1085, 1087) are chosen as part of a latitudinal transect from the present northern to southern boundaries of the Benguela Current upwelling system, to decipher the Pliocene–Pleistocene history of biogenic production and its relationship with global and local changes in oceanic circulation and climate. The pattern of CaCO₃ and C_org mass accumulation rates (MARs) over 0.25-Myr intervals indicates that the evolution of carbon burial is highly variable between the northern and the southern Benguela regions, as well as between sites that have similar hydrological conditions. This, as well as the presence over most locations of high-amplitude, rapid changes of carbon burial, reflect the partitioning of biogenic production and patterns of sedimentation into local compartments over the Benguela margin. The combined mapping of CaCO₃ and C_org MARs at the study locations suggests four distinct evolutionary periods, which are essentially linked with major steps in global climate change: the early Pliocene, the mid-Pliocene warm event, a late Pliocene intensification of northern hemisphere glaciation and the Pleistocene. The early Pliocene spatially heterogeneous patterns of carbon burial are thought to reflect the occurrence of mass-gravitational movements over the Benguela slope which resulted in disruption of the recorded biogenic production. This was followed (3.5–3 Ma) by an episode of peak carbonate accumulation over the whole margin and, subsequently, by the onset of Benguela provincialism into a northern and a southern sedimentary regime near 2 Ma. This mid and late Pliocene evolution is interpreted as a direct response to changes in the ventilation of bottom and intermediate waters, as well as to dynamics of the subtropical gyral circulation and associated wind stress.  相似文献   

黄河断流对河口空间场后效反馈的遥感复合信息研究     

刘宝银  王岩峰  郝庆祥 《海洋学报》2001,23(3):35-47

就黄河断流对河口空间场后效所涉及的地理要素的演变,以所建河口演变概念-遥感信息系统,分析研究了黄河口近期演变的互关联信息基础,并依据研究目标的信息需求分析(IRA)与水下地貌趋势面分析的结果,阐述了河口空间场诸种反馈信息、变异中直观信息及隐伏信息.  相似文献   

Relationships Between Community Structure of the Intertidal Macroinfauna and Sandy Beach Characteristics Along the Chilean Coast   总被引：2，自引：0，他引：2  

Eduardo Jaramillo  Heraldo Contreras  Cristian Duarte  & Pedro Quijón 《Marine Ecology》2001,22(4):323-342

Abstract. Eight sandy beaches were seasonally sampled along the coast of Chile, from ca. 21 to 42° S (about 3000 km) to study the relationship between community structure of the intertidal macroinfauna and beach characteristics. Sediment samples (0.1 m², 30 cm deep) were collected (July – September 1998 and December 1998 – January 1999) with plastic cylinders at 15 equally spaced levels along three replicated transects extending from above the drift line to the swash zone. The sediment was sieved through a 1 mm mesh and the organisms collected stored in 5 % formalin. To define beach types, Dean's parameter (Ω) was calculated from wave heights and periods, and fall velocity of sand particles from the swash zone. Crustaceans (mainly peracarids) were the most diverse group with 14 species, followed by polychaetes with 5 species. The talitrid amphipod Orchestoidea tuberculata , the cirolanid isopods Excirolana braziliensis and E. hirsuticauda and the anomuran decapod Emerita analoga were the most widely distributed and common species. Regression analyses between species richness, abundance and biomass of the whole macroinfauna versus sediment characteristics, beach face slopes and morphodynamic beach states showed no significant relationships. Thus, macroinfaunal community characteristics did not increase linearly from lower intermediate to higher intermediate or dissipative beach states as had been found before in Chile or in other coasts. A comparative analysis with data from sandy beaches of other world regions showed that the number of species inhabiting Chilean sandy beaches was generally lower, whereas total population abundances were generally higher compared with values reported elsewhere.  相似文献   

Bathymetry of Molloy Deep: Fram Strait between Svalbard and Greenland     

Jörn Thiede  Stephanie Pfirman  Hans-Werner Schenke  Wolfgang Reil 《Marine Geophysical Researches》1990,12(3):197-214

The sea floor of Fram Strait, the over 2500 m deep passage between the Arctic Ocean and the Norwegian-Greenland Sea, is part of a complex transform zone between the Knipovich mid-oceanic ridge of the Norwegian-Greenland Sea and the Nansen-Gakkel Ridge of the Arctic Ocean. Because linear magnetic anomalies formed by sea-floor spreading have not been found, the precise location of the boundary between the Eurasian and the North American plate is unknown in this region. Systematic surveying of Fram Strait with SEABEAM and high resolution seismic profiling began in 1984 and continued in 1985 and 1987, providing detailed morphology of the Fram Strait sea floor and permitting better definition of its morphotectonics. The 1984 survey presented in this paper provided a complete set of bathymetric data from the southernmost section of the Svalbard Transform, including the Molloy Fracture Zone, connecting the Knipovich Ridge to the Molloy Ridge; and the Molloy Deep, a nodal basin formed at the intersection of the Molloy Transform Fault and the Molloy Ridge. This nodal basin has a revised maximum depth of 5607 m water depth at 79°8.5N and 2°47E.  相似文献   

National ocean policy—new opportunities for Malaysian ocean development     

Abdul Hamid Saharuddin   《Marine Policy》2001,25(6)

Being a littoral state, Malaysian maritime sectors provide the basis for the growth and development of marine-related activities. As the country enters the new millennium along with the ‘2020 Vision’ which serves as the basic template against which the economic performance of these sectors should be judged, it poses a new challenge for Malaysia in developing these sectors. This paper attempts to address three basic issues: Firstly, is there any national ocean policy in place? Secondly, are the maritime sectors adequately organized to play an important role in achieving the objectives? Thirdly, what are the opportunities available in developing the ocean?It can be seen that existing policies to develop comprehensive ocean governance have not received the full attention they deserve. Organizational structures governing the ocean for implementing national policies are well in place but in a fragmented and uncoordinated fashion. As a result, sectoral and intersectoral management problems were created such as multiple-use conflicts, overlapping of jurisdiction and duplication of efforts. Environmental problems have also not been properly addressed. A few sectors have been identified as offering opportunities to further develop the Malaysian maritime areas. Among these are marine education and human resources development, marine tourism and the seafood industry.  相似文献   

Remote estimation of surficial seafloor properties through the application Angular Range Analysis to multibeam sonar data   总被引：2，自引：2，他引：2  

Luciano Fonseca  Larry Mayer 《Marine Geophysical Researches》2007,28(2):119-126

The variation of the backscatter strength with the angle of incidence is an intrinsic property of the seafloor, which can be used in methods for acoustic seafloor characterization. Although multibeam sonars acquire backscatter over a wide range of incidence angles, the angular information is normally neglected during standard backscatter processing and mosaicking. An approach called Angular Range Analysis has been developed to preserve the backscatter angular information, and use it for remote estimation of seafloor properties. Angular Range Analysis starts with the beam-by-beam time-series of acoustic backscatter provided by the multibeam sonar and then corrects the backscatter for seafloor slope, beam pattern, time varying and angle varying gains, and area of insonification. Subsequently a series of parameters are calculated from the stacking of consecutive time series over a spatial scale that approximates half of the swath width. Based on these calculated parameters and the inversion of an acoustic backscatter model, we estimate the acoustic impedance and the roughness of the insonified area on the seafloor. In the process of this inversion, the behavior of the model parameters is constrained by established inter-property relationships. The approach has been tested using a 300 kHz Simrad EM3000 multibeam sonar in Little Bay, NH. Impedance estimates are compared to in situ measurements of sound speed. The comparison shows a very good correlation, indicating the potential of this approach for robust seafloor characterization.  相似文献   

Phytoplankton biomass and size fractions in surface waters of the Australian sector of the southern ocean     

Wendy Ehnert  C. Peter McRoy 《Journal of Oceanography》2007,63(2):179-187

We collected surface water along the 142nd E meridian from Tasmania to Antarctica in December 1999. We measured temperature, salinity and total chlorophyll a; additionally, we collected suspended particle size fractions and used fluorometric analysis to determine the quantity of chlorophyll a in each of four cell size classes: picoplankton (<3 μm), two nanoplankton fractions (3–10 μm and 10–20 μm) and microplankton (> 20 μm). Changes in temperature and salinity show that we crossed 6 water masses separated by 5 fronts. We found low abundance (<0.2 mg m⁻³) of chlorophyll in all size classes, with the exception of higher values near the continent (0.2 to 0.4 mg m⁻³). Lowest chlorophyll values (<0.1 mg m⁻³) were found in the Polar Frontal Zone (51° to 54°S). Microplankton made up the largest portion of total chlorophyll throughout most of the region. We conclude that biomass of all phytoplankton fractions, especially pico-and nanoplankton, was constrained by limiting factors, most probably iron, throughout the region and that ecosystem dynamics within a zone are not circumpolar but are regionalized within sectors.  相似文献   

基于二次散射的水污染遥感模型及其在珠江口水域的应用   总被引：10，自引：1，他引：10  

邓孺孺  何执兼  陈晓翔 《海洋学报》2003,25(6):69-78

根据水中悬浮物、污染物和水分子等的散射和吸收物理机制建模是实现水污染定量遥感的有效途径.基于一次散射的水污染遥感模型简单易行,但在浑浊度较大时其精度不高.在基于一次散射模型的基础上分析了多次散射的能量组成特点,提出再考虑二次散射可使模型的精度显著提高且不至于使模型过于复杂;导出了二次散射的补偿因子,同时给出了考虑二次散射因子的简单计算方法.将该模型应用于珠江口水域的水污染遥感的结果表明,较之基于一次散射的模型,考虑二次散射的水污染遥感模型在精度上有明显改进.遥感提取结果显示,珠江口水域重污染区主要分布在伶仃洋东北部,香港维多利亚港和深圳湾.  相似文献