Under strong surface wind forcing during winter, direct current observations in the northern Sea of Japan show the existence of strong near-inertial currents in the deep water that is characterized by the extremely homogeneous vertical structures of temperature and salinity. However, the mechanism generating internal waves in the deep water of the northern Sea of Japan has not been well understood. In this study, to clarify the dynamical link between the surface wind forcing and near-inertial currents in the deep water of the northern Sea of Japan, we drive a general circulation model taking into account realistic wind stress, ocean bottom and land topography. In the northern Sea of Japan, the numerical results show that vertically coherent horizontal currents with a speed of ~ 0.05 m s?1 are excited throughout the homogeneous deep water. A two-layer model successfully reproduces the pattern of the horizontal current velocities shown by the general circulation model, indicating that internal waves emanate westward from the northwestern coast of Japan through coastal adjustment to the strong wind forcing event and, while propagating into the ocean interior, they excite evanescent near-inertial response throughout the lower layer below the interface. 相似文献
A model based on that of Kishi et al. (2001) has been extended to 15 compartments including silicon and carbon cycles. This model was applied to Station A7 off
Hokkaido, Japan, in the Northwestern Pacific. The model successfully simulated the observations of: 1. a spring bloom of diatoms;
2. large seasonal variations of nitrate and silicate concentrations in the surface water; and 3. large inter-annual variations
in chlorophyll-a. It also reproduced the observed features of the seasonal variations of carbon dioxide partial pressure (pCO2)—a peak in pCO2 in winter resulting from deep winter convection, a rapid decrease in pCO2 as a result of the spring bloom, and an almost constant pCO2 from summer through fall (when the effect of increasing temperature cancels the effect of biological production). A comparison
of cases with and without silicate limitation shows that including silicate limitation in the model results in: 1. decreased
production by diatoms during summer; and 2. a transition in the dominant phytoplankton species, from diatoms to other species
that do not take up silicate. Both of these phenomena are observed at Station A7, and our results support the hypothesis that
they are caused by silicate limitation of diatom growth.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
JGOFS has revealed the importance of marine biological activity to the global carbon cycle. Ecological models are valuable tools for improving our understanding of biogeochemical cycles. Through a series of workshops, the North Pacific Marine Science Organization (PICES) developed NEMURO (North Pacific Ecosystem Model Understanding Regional Oceanography) a model, specifically designed to simulate the lower trophic ecosystem in the North Pacific Ocean. Its ability to simulate vertical fluxes generated by biological activities has not yet been validated. Here compare NEMURO with several other lower trophic level models of the northern North Pacific. The different ecosystem models are each embedded in a common three-dimensional physical model, and the simulated vertical flux of POM and the biomass of phytoplankton are compared. The models compared are: (1) NEMURO, (2) the Kishi and Nakata Model (Kishi et al., 1981), (3) KKYS (Kawamiya et al., 1995, 2000a, 2000b), and (4) the Denman model (Denman and Peña, 2002). With simple NPZD models, it is difficult to describe the production of POM (Particulate Organic Matter) and hence the simulations of vertical flux are poor. However, if the parameters are properly defined, the primary production can be well reproduced, even though none of models we used here includes iron limitation effects. On the whole, NEMURO gave a satisfactory simulation of the vertical flux of POM in the northern North Pacific. 相似文献
To study geochemical processes for migration and fixation of fissiogenic rare earth elements (REE) in association with uranium dissolution, in situ isotopic analyses using an ion microprobe were performed on U- and REE-bearing secondary minerals, such as coffinite, françoisite, uraniferous goethite, and uraninite found in a sandstone layer 30 to 110 cm beneath a natural fission reactor at Bangombé, Gabon. Phosphate minerals such as phosphatian coffinite and françoisite with depleted 235U (235U/238U = 0.00609 to 0.00638) contained large amount of fissiogenic light REE, while micro-sized uraninite grains in a solid bitumen aggregate have normal U isotopic values (235U/238U = 0.00725) and small amount of fissiogenic REE components. The proportions of fissiogenic and non-fissiogenic REE components in four samples from the core of BAX03 vary in depth ranging from 30 cm to 130 cm beneath the reactor, which suggests mixing between fissiogenic isotopes from the reactor and non-fissiogenic isotopes from original minerals in the sandstone. Significant chemical fractionation was observed between Ce and the other REE in the secondary minerals, which shows evidence of an oxidizing atmosphere during their formation. Pb-isotopic analyses of individual minerals do not directly provide chronological information because of the disturbance of U-Pb decay system due to recent geologic alteration. However, systematic Pb-isotopic results from all of the minerals reveal the mobilization of fissiogenic isotopes, Pb and U from the reactor in association with dolerite dyke intrusion ∼0.798 Ga ago and the formation of the secondary minerals by mixing event between 2.05 Ga-old original minerals and reactor materials due to recent alteration. 相似文献
Several studies in the last 20 years have revealed that morphological asymmetry in fish can be characterized as ‘antisymmetry’. Antisymmetry is a lateral dimorphism in which each population consists of individuals with well‐developed left sides (lefties) and well‐developed right sides (righties). This dimorphism influences predator–prey interactions. In some piscivorous fishes, it has been found that predators can catch more prey of the opposite morphological type to themselves (cross‐predation) than of the same morphological type (parallel‐predation). Our previous work clarified that the predominance of cross‐predation is caused by lateralized behaviors of predators and prey that correspond to their morphological antisymmetry. Moreover, based on the results of our behavioral observations, we hypothesized that parallel‐predation can predominate when predators encounter the potential prey frontally. To test this hypothesis, in the present study we investigated the relationship between lateral morphological types of anglerfish (Lophiomus setigerus) and those of the prey fishes found in their stomachs. Anglerfish attract potential prey using their first dorsal fin (illicium) as a lure, and their frontal encounters with potential prey fishes were photographed in situ and observed in an aquarium. The results of a stomach contents analysis indicated that parallel‐predation predominated in five benthopelagic prey fish species (perches and eels). By contrast, five benthic prey fishes (gobies and weevers) exhibited the predominance of cross‐predation. These results not only demonstrate the predominance of parallel‐predation in a natural fish community, but also suggest that the relationship between morphological types of predator and prey species can be reversed depending on the lifestyle of prey. 相似文献
Isotopic ratios and abundances of all REE in two Oklo ore samples have been measured. We have succeeded in developing a new method to estimate the neutron fluence, the conversion factor of uranium and the average neutron energy (or temperature) based on Gd and U isotopic ratios. This new calculation is found to be useful in evaluating those parameters for the natural nuclear reactors at Oklo. Comparison is made between the neutron fluence values evaluated by our new method employing Gd isotopes and a previous one [11] employing Sm and Nd isotopes. The relative agreement becomes better with the increase of fluence. A relationship between the abundances of fissiongenic nuclides of La, Ce, Nd, Sm, and Gd and their mass numbers is also presented. 相似文献
Lateritic Ni ore mined in the Rio Tuba Mine, Philippines, derived from ultramafic rock by tropical intense weathering, is generally composed of two accumulated zones, an upper laterite zone and a lower saprolite zone. These two zones are very different in appearance, mineral assemblage, chemical composition, and in other ways. A transitional zone may be seen between the upper and lower zones, but it does not develop to any appreciable thickness. Although serpentine and goethite are still predominant in the constituent minerals, other clay minerals are increasing.
The transitional zone may be subdivided into three groups based on chemical composition. The behaviour of the chemical composition in this horizon indicates a complicated process of component transportation under the weathering process.
In the ore, chemical components are closely related in particle size of constituent minerals. In the laterite - transitional - saprolite sequence, a common variation range and tendency in chemical composition for each particle size can be seen. However, taking samples with the same particle size the chemical composition obviously differed, representing the characteristics of the components for each zone.
Concerning the correlation coefficient of the chemical components of each zone, a somewhat different inter-component relationship can be seen in these zones. These differences of correlation suggest the different complicated lateritized conditions under which they are formed. 相似文献
The Eoarchaean (>3,600 Ma) Itsaq Gneiss Complex of southern West Greenland is dominated by polyphase orthogneisses with a
complex Archaean tectonothermal history. Some of the orthogneisses have c. 3,850 Ma zircons, and they vary from rare single
phase metatonalites to more common complexly banded migmatites. This is due to heterogeneous strain, in situ anatexis and
granitic veining superimposed during younger tectonothermal events. In the single-phase tonalites with c. 3,850 Ma zircon,
oscillatory-zoned prismatic zircon is all 3,850 Ma old, but shows patchy ancient loss of radiogenic Pb. SHRIMP spot analyses
and laser ablation ICP-MS depth profiling show that thin (usually < 10 μm) younger (3,660–3,590 Ma and Neoarchaean) shells
of lower Th/U metamorphic zircon are present on these 3,850 Ma zircons. Several samples with this simple zircon population
occur on islands near Akilia. In contrast, migmatites usually contain more complex zircon populations, with often more than
one generation of igneous zircon present. Additional zircon dating of banded gneisses across the Complex shows that samples
with c. 3,850 Ma igneous zircon are not just a phenomenon restricted to Akilia and adjacent islands. For example, migmatites
from Itilleq (c. 65 km from Akilia) contain variable amounts of oscillatory-zoned 3,850 Ma and 3,650 Ma zircon, interpreted,
respectively, as the rock age and the time of crustal melting under Eoarchaean metamorphism. With only 110–140 ppm Zr in the
tonalites and likely magmatic temperatures of >850°C, zircon solubility–melt composition relationships show that they were
only one-third saturated in zircon. Any zircon entrained in the precursor magmas would thus have been highly soluble. Combined
with the cathodoluminesence imaging, this demonstrates that the c. 3,850 Ma oscillatory zoned zircon crystallised out of the
melt and hence gives a magmatic age. Thus the rare well-preserved tonalites and palaeosome in migmatites testify that c. 3,850 Ma
quartzo–feldspathic rocks are a widespread (but probably minor) component in the Itsaq Gneiss Complex. C. 3,850 Ma zircon
with negative Eu anomalies (showing growth in felsic systems) also occurs as detrital grains in rare c. 3,800 Ma metaquartzites
and as inherited grains in some 3,660 Ma granites (sensu stricto). These demonstrate that still more c. 3,850 Ma rocks were present, but were recycled into Eoarchaean sediments and crustally
derived granites. The major and trace element characteristics (e.g. LREE enrichment, HREE depletion, low MgO) of the best-preserved
c. 3,850 Ma rocks are typical of Archaean TTG suites, and thus argue for crust formation processes involving important contributions
from melting of hydrated mafic crust to the earliest Archaean. Five c. 3,850 Ma tonalites were selected as the best preserved
on the basis of field criteria and zircon petrology. Four of these samples have overlapping initial ɛNd (3,850 Ma) values from +2.9 to +3.6± 0.5, with the fourth having a slightly lower value of +0.6. These data provide additional
evidence for a markedly LREE-depleted early terrestrial mantle reservoir. The role of c. 3,850 Ma crust should be considered
in interpreting isotope signatures of the younger (3,800–3,600 Ma) rocks of the Itsaq Gneiss Complex.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献