Subsurface Water Masses in the Central North Pacific Transition Region: The Repeat Section along the 18° Meridian     

Toshio Suga  Kazunori Motoki  Kimio Hanawa 《Journal of Oceanography》2003,59(4):435-444

A repeat hydrographic section has been maintained over two decades along the 180° meridian across the subarctic-subtropical transition region. The section is naturally divided into at least three distinct zones. In the Subarctic Zone north of 46°N, the permanent halocline dominates the density stratification, supporting a subsurface temperature minimum (STM). The Subarctic Frontal Zone (SFZ) between 42°–46°N is the region where the subarctic halocline outcrops. To the south is the Subtropical Zone, where the permanent thermocline dominates the density stratification, containing a pycnostad of North Pacific Central Mode Water (CMW). The STM water colder than 4°C in the Subarctic Zone is originated in the winter mixed layer of the Bering Sea. The temporal variation of its core temperature lags 12–16 months behind the variations of both the winter sea surface temperature (SST) and the summer STM temperature in the Bering Sea, suggesting that the thermal anomalies imposed on the STM water by wintertime air-sea interaction in the Bering Sea spread over the western subarctic gyre, reaching the 180° meridian within a year or so. The CMW in this section originates in the winter mixed layer near the northern edge of the Subtropical Zone between 160°E and 180°. The CMW properties changed abruptly from 1988 to 1989; its temperature and salinity increased and its potential density decreased. It is argued that these changes were caused by the climate regime shift in 1988/1989 characterized by weakening of the Aleutian Low and the westerlies and increase in the SST in the subarctic-subtropical transition region. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Hydrothermal Vent Geology and Biology at Earth’s Fastest Spreading Rates     

Richard N. Hey  Gary J. Massoth  Robert C. Vrijenhoek  Peter A. Rona  John Lupton  David A. Butterfield 《Marine Geophysical Researches》2006,27(2):137-153

Earth’s fastest present seafloor spreading occurs along the East Pacific Rise near 31°–32° S. Two of the major hydrothermal plume areas discovered during a 1998 multidisciplinary geophysical/hydrothermal investigation of these mid-ocean ridge axes were explored during a 1999 Alvin expedition. Both occur in recently eruptive areas where shallow collapse structures mark the neovolcanic axis. The 31° S vent area occurs in a broad linear zone of collapses and fractures coalescing into an axial summit trough. The 32° S vent area has been volcanically repaved by a more recent eruption, with non-linear collapses that have not yet coalesced. Both sites occur in highly inflated areas, near local inflation peaks, which is the best segment-scale predictor of hydrothermal activity at these superfast spreading rates (150 mm/yr).  相似文献   

A map series of the Southern East Pacific Rise and its flanks, 15° S to 19° S     

Daniel S. Scheirer  Ken C. Macdonald  Donald W. Forsyth  Stephen P. Miller  Dawn J. Wright  Marie-Hélène Cormier  Charles M. Weiland 《Marine Geophysical Researches》1996,18(1):1-12

Four large-scale bathymetric maps of the Southern East Pacific Rise and its flanks between 15° S and 19° S display many of the unique features of this superfast spreading environment including abundant seamounts (the Rano Rahi Field), axial discontinuities, discontinuity migration, and abyssal hill variation. Along with a summary of the regional geology, these maps will provide a valuable reference for other sea-going programs on-and off-axis in this area, including the Mantle ELectromagnetic and Tomography (MELT) experiment.  相似文献   

Processes Causing the Temporal Changes in Si/N Ratios of Nutrient Consumptions and Export Flux during the Spring Diatom Bloom     

Naoki?YoshieEmail author  Yasuhiro?Yamanaka 《Journal of Oceanography》2005,61(6):1059-1073

Two processes are generally explained as causes of temporal changes in the stoichiometric silicon/nitrogen (Si/N) ratios of sinking particles and of nutrient consumption in the surface water during the spring diatom bloom: (1) physiological changes of diatom under the stress of photosynthesis of diatom and (2) differences of regeneration between silicon and nitrogen. We investigated which process plays an important role in these changes using a one-dimensional ecosystem model that explicitly represents diatom and the other non-silicious phytoplankton. The model was applied to station A7 (41°30′ N, 145°30′ E) in the western North Pacific, where diatom regularly blooms in spring. Model simulations show that the Si/N ratios of the flux exported by the sinking particles at 100 m depth and of nutrient consumptions in the upper 100 m surface water have their maxima at the end of the spring diatom bloom, the values and timings of which are significantly different from each other. Analyses of the model results show that the differences of regeneration between silicon and nitrogen mainly cause the temporal changes of the Si/N ratios. On the other hand, the physiological changes of diatoms under stress can hardly cause these temporal changes, because the effect of the change in the diatom's uptake ratio of silicon to nitrogen is cancelled by that in its sinking rate.  相似文献   

North Pacific Synthesis of the Joint Global Ocean Flux Study: Overview     

Toshiro Saino  Alexander Bychkov  Chen-Tung Arthur Chen  Paul J. Harrison 《Journal of Oceanography》2004,60(1):1-4

This special issue is comprised of 13 papers, including this overview, and focuses on the synthesis of the Joint Global Ocean Flux Study (JGOFS) in the North Pacific which took place from 1997 through 2003. The effort was led by the JGOFS North Pacific Synthesis Group, with the aim of quantifying CO₂ drawdown by physical and biological pumps in the North Pacific by identifying and studying the regional, seasonal to inter-annual variations in the key processes, and understanding their regulating mechanisms. Emphasis was placed on the similarities and differences of the biogeochemical regimes in the eastern and western subarctic Pacific. Effort was also made to address the future research directions which arose from the scientific findings during the North Pacific JGOFS process study. A brief overview of the papers from view points of CO₂ drawdown by physical and biological pumps, spatial variability, and temporal variability from seasonal to decadal scales is made, followed by suggestions for the directions of future research. This revised version was published online in July 2006 with corrections to the Cover Date.  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   

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   

Swath mapping of the seafloor and its application to deep-bottom fisheries in New Caledonia     

Patrick Lehodey  René Grandperrin 《Marine Geophysical Researches》1996,18(2-4):449-458

A bottom longline fishery operated in the EEZ of New Caledonia from 1988 to 1991. Fishing focused on five seamounts with summits at depths ranging from 500 to 750 m. The target species was alfonsino, Beryx splendens. As the soundings available from marine charts were not detailed enough, the fishing masters had to make their own charts in order to set the gear in the right location. A series of 11 scientific cruises devoted to a research program on alfonsino was launched in late 1991. During the first scientific cruises, several days were spent mapping the seabed to improve the existing knowledge of the topography of three seamounts by coupling the EDO echosounder depth measurements to the GPS positions. As this procedure is slow, it is applicable to limited areas or, if a wider grid is used, to large zones to locate major structures such as ridges and seamounts. The emergence of the multibeam echosounder has greatly improved seabed mapping performance. This tool seems to fit the requirement of exploratory deep-bottom fishing particularly well, as it covers large areas while providing details of the bottom. The EM 12 was used to obtain bathymetry and imagery of the SE portion of the EEZ of New Caledonia, covering an approximate area of 70,000 km² in two weeks. For depths ranging from 500 to 4,500 m, the results were impressive. They confirmed the known major features and provided greater topographical detail, revealing fine unknown structures. They also provided information on the type of substratum, information which might influence the fishing strategy. Finally, they made it possible to obtain an accurate estimate of the exploitable area which in turn led to new stock estimates.  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