Possibility of recent changes in vertical distribution and size composition of chlorophyll-a in the western North Pacific region     

Hiroshi Ishida  Yutaka W. Watanabe  Joji Ishizaka  Toshiya Nakano  Naoki Nagai  Yuji Watanabe  Akifumi Shimamoto  Nobuhiro Maeda  Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186

Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a (Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season, as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4 and 2.3% year⁻¹ in the subtropical area along 137°E (STA₁₃₇) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA₁₇₅) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year⁻¹ in STA₁₃₇ and KEA₁₇₅; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. Water density (σ _θ ) at 75 m depth had also decreased by 0.006 and 0.05 year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. The ratio of biogenic opal to biogenic CaCO₃ in the sinking flux decreased by 0.015 year⁻¹ in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density of surface water caused by warming in the western North Pacific, especially in the summer.  相似文献   

The mass of the star formed in a cloud core     

Takenori Nakano  Tetsuo Hasegawa  Colin Norman 《Astrophysics and Space Science》1995,224(1-2):523-524

The forming star grows by mass inflow from the parent cloud core, mainly through the accretion disk. However, the core matter which has not yet contracted much is seriously disturbed by the activities of the forming star. We consider mass outflow and emission of ultraviolet radiation as such activities and determine the stellar mass as a function of the physical quantities of the parent cloud core.  相似文献   

Role of basement in epithermal deposits: The Kushikino and Hishikari gold deposits, southwestern Japan     

Yuichi Morishita  Takanori Nakano 《Ore Geology Reviews》2008,34(4):597-609

The magma–ore deposit relationship of most low-sulfidation epithermal ore deposits is still unclear, partly because many stable isotopic studies of such deposits have indicated the predominance of meteoric waters within hydrothermal fluids. However, it is certainly true that hydrothermal systems are ultimately driven by magmatic intrusions, and epithermal gold deposits might therefore be produced by magmatic activity even in deposits having has no obvious links to a magma. We re-examine the genesis of two typical low-sulfidation epithermal gold deposits, the Kushikino and Hishikari deposits, using structural simulations and isotope data.Many epithermal gold deposits including the Kushikino and Hishikari deposits have been discovered in Kyushu, southwestern Japan. The Kushikino deposit comprises fissure-filling veins within Neogene andesitic volcanics that overlie unconformably Cretaceous sedimentary basement. The veins consist of gold- and silver-bearing quartz and calcite with minor amounts of adularia, sericite and sulfides. Although carbon and oxygen isotopic data for the veins indicate a meteoric origin of the ore fluid, finite element simulations suggest that the vein system might have formed in direct response to magma intrusion. In particular, geophysical data suggest that intruding magma has uplifted the basement rocks, thereby producing fractures and veins and a positive Bouguer anomaly, and providing the heat necessary to drive an ore-forming hydrothermal system.The second component of this study has been to investigate the nature and evolution of the Kushikino and Hishikari epithermal systems. Isotope data document the geochemical evolution of the hydrothermal fluids. We conclude that the existence of sedimentary basement rocks at depth might have affected the strontium and carbon isotopic ratios of the Kushikino and Hishikari ore fluids. The ⁸⁷Sr/⁸⁶Sr ratios and δ¹³C–δ¹⁸O trend reveal that major ore veins in the Hishikari deposit can be distinguished from shallow barren veins. It was suggested isotopically that fluids responsible for the barren veins in nearby shallow and barren circulation systems were only controlled by the shallow host rocks. Such multi-isotope systematics provide a powerful tool with which to determine the center of hydrothermal activity and thereby document the evolution of hydrothermal fluids.  相似文献   

Phylogeographical patterns of the gastropod Siphonaria pectinata (Linnaeus, 1758)          下载免费PDF全文

Free Espinosa  Clara Morey‐Rubio  Tomoyuki Nakano 《Marine Ecology》2016,37(1):227-233

Siphonaria pectinata is a marine gastropod distributed across the shores of the Western and Eastern Atlantic. Although previous studies have indicated that the species could be a recent introduction to Central and North America from Western Africa and Europe, other authors have questioned this statement. In fact, a recent study has shown that individuals from both sides of the Atlantic are genetically disconnected, rejecting the idea of a recent invasion. However, genetic information on this species is very scarce and based only on a single study using a limited number of specimens and sites. The data reported in the present study represent one step forward, collecting information from 119 specimens from 22 sites that cover the entire distributional range of the species. Populations from the Western Atlantic separated from eastern ones around 1.4?1.9 Mya, whereas the centre of dispersion is located on the eastern side of the Atlantic. Siphonaria pectinata should be considered native to the Western Atlantic and cannot be considered as a species with an amphi‐atlantic distribution owing to the lack of genetic connection between both sides of the Atlantic, as previous authors have pointed out. The presence of a star‐shaped phylogeny is discussed in the context of Plio‐Pleistocene glaciations.  相似文献   

Impact of in-consistency between the climate model and its initial conditions on climate prediction     

Liu  Xueyuan  Köhl  Armin  Stammer  Detlef  Masuda  Shuhei  Ishikawa  Yoichi  Mochizuki  Takashi 《Climate Dynamics》2017,49(3):1061-1075

We investigated the influence of dynamical in-consistency of initial conditions on the predictive skill of decadal climate predictions. The investigation builds on the fully coupled global model “Coupled GCM for Earth Simulator” (CFES). In two separate experiments, the ocean component of the coupled model is full-field initialized with two different initial fields from either the same coupled model CFES or the GECCO2 Ocean Synthesis while the atmosphere is initialized from CFES in both cases. Differences between both experiments show that higher SST forecast skill is obtained when initializing with coupled data assimilation initial conditions (CIH) instead of those from GECCO2 (GIH), with the most significant difference in skill obtained over the tropical Pacific at lead year one. High predictive skill of SST over the tropical Pacific seen in CIH reflects the good reproduction of El Niño events at lead year one. In contrast, GIH produces additional erroneous El Niño events. The tropical Pacific skill differences between both runs can be rationalized in terms of the zonal momentum balance between the wind stress and pressure gradient force, which characterizes the upper equatorial Pacific. In GIH, the differences between the oceanic and atmospheric state at initial time leads to imbalance between the zonal wind stress and pressure gradient force over the equatorial Pacific, which leads to the additional pseudo El Niño events and explains reduced predictive skill. The balance can be reestablished if anomaly initialization strategy is applied with GECCO2 initial conditions and improved predictive skill in the tropical Pacific is observed at lead year one. However, initializing the coupled model with self-consistent initial conditions leads to the highest skill of climate prediction in the tropical Pacific by preserving the momentum balance between zonal wind stress and pressure gradient force along the equatorial Pacific.

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Simultaneous vertical measurements of in situ pH and CO2 in the sea using spectrophotometric profilers     

Yoshiyuki Nakano  Hideshi Kimoto  Shuichi Watanabe  Koh Harada  Yutaka W. Watanabe 《Journal of Oceanography》2006,62(1):71-81

We have developed new systems capable of profiling to >1000 m for measuring in situ pH and fugacity of CO₂ (fCO₂) in the ocean using spectrophotometric analysis (pH and CO₂ profilers). The in situ pH is determined by detecting the color change of the pH indicator (m-cresol purple). It can withstand ambient pressure to 1000 m depth. The CO₂ profiler analyzed in situ fCO₂ by detecting the change of pH in an inner solution, equilibrated with the seawater through a gas permeable membrane. It can be operated to 2500 m depth. We used an amorphous fluoropolymer tubing form of AF-2400 for the gas permeable membrane due to its high gas permeability coefficients. The inner solution was a mixture of 2 μM bromocresol purple (BCP) and 5 μM sodium hydroxide. This system gave us a response time of 1 minute, which is twice as fast as previous systems. The precisions of pH and CO₂ profilers were within 0.002 and 2.5% respectively. We have used these profilers to study the North Pacific, obtaining good agreement with the difference between the data from profilers and a discrete bottle of 0.002 ± 0.005 pH (SE, n = 25) and −0.4 ± 3 μatm (SE, n = 31).  相似文献   

Tidal Mixing in the Kuril Straits and Its Impact on Ventilation in the North Pacific Ocean     

Tomohiro Nakamura  Takahiro Toyoda  Yoichi Ishikawa  Toshiyuki Awaji 《Journal of Oceanography》2004,60(2):411-423

A numerical study using a 3-D nonhydrostatic model has been applied to baroclinic processes generated by the K ₁ tidal flow in and around the Kuril Straits. The result shows that large-amplitude unsteady lee waves are generated and cause intense diapycnal mixing all along the Kuril Island Chain to levels of a maximum diapycnal diffusivity exceeding 10³ cm²s⁻¹. Significant water transformation by the vigorous mixing in shallow regions produces the distinct density and potential vorticity (PV) fronts along the Island Chain. The pinched-off eddies that arise and move away from the fronts have the ability to transport a large amount of mixed water (∼14 Sv) to the offshore regions, roughly half being directed to the North Pacific. These features are consistent with recent satellite imagery and in-situ observations, suggesting that diapycnal mixing within the vicinity of the Kuril Islands has a greater impact than was previously supposed on the Okhotsk Sea and the North Pacific. To examine this influence of tidal processes at the Kurils on circulations in the neighboring two basins, another numerical experiment was conducted using an ocean general circulation model with inclusion of tidal mixing along the islands, which gives a better representation of the Okhotsk Sea Mode Water than in the case without the tidal mixing. This is mainly attributed to the added effect of a significant upward salt flux into the surface layer due to tidal mixing in the Kuril Straits, which is subsequently transported to the interior region of the Okhotsk Sea. With a saline flux into the surface layer, cooling in winter in the northern part of the Okhotsk Sea can produce heavier water and thus enhance subduction, which is capable of reproducing a realistic Okhotsk Sea Mode Water. The associated low PV flux from the Kuril Straits to the open North Pacific excites the 2nd baroclinic-mode Kelvin and Rossby waves in addition to the 1st mode. Interestingly, the meridional overturning in the North Pacific is strengthened as a result of the dynamical adjustment caused by these waves, leading to a more realistic reproduction of the North Pacific Intermediate Water (NPIW) than in the case without tidal mixing. Accordingly, the joint effect of tidally-induced transport and transformation dominating in the Kuril Straits and subsequent eddy-transport is considered to play an important role in the ventilation of both the Okhotsk Sea and the North Pacific Ocean. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Seiches in bays forming a coupled system     

Masito Nakano  Naohiro Fujimoto 《Journal of Oceanography》1987,43(2):124-134

The seiches occurring in two adjacent bays, Koaziro Bay and Moroiso Bay, situated in Miura Peninsula at the mouth of Tokyo Bay, are very regular, and the phenomenon of beat appears in their amplitudes of oscillation. Nakano once presented a theoretical explanation of this phenomenon, considering two rectangular bays of the same size and form as well as of uniform depth, by assuming that a kind of coupling takes place between the two bays through a portion of water flowing across the mouth of each bay. In the present paper, the validity of the theory has been proved in a series of hydraulic model experiments. The experiments have shown that, in the case of the two adjacent rectangular bays mentioned above, there are two distinct modes of oscillation viz. (i) the co-phasic oscillation and (ii) the contra-phasic oscillation, and since the frequencies of these oscillations are close to each other, when they come to interfere, the beat phenomenon occurs.It has also been found that, when a tsunami wave enters the two bays, the mode of oscillation of the seiches occurring in them changes in the following manner: the co-phasic oscillation the oscillation accompanied with the beat phenomenon the contra-phasic oscillation. As regards this phenomenon, the authors have presented a possible explanation by considering the dissipation of energy due to wave scattering.  相似文献   

Application of Sensitivity Analysis Using an Adjoint Model for Short-Range Forecasts of the Kuroshio Path South of Japan     

Yoichi Ishikawa  Toshiyuki Awaji  Nobumasa Komori  Takahiro Toyoda 《Journal of Oceanography》2004,60(2):293-301

A sensitivity experiment has been performed by assimilating altimetric data into a 1.5-layer primitive equation model as a first attempt to examine the impact of initialization on forecasts of the Kuroshio path variability south of Japan. By exploiting the advantage of an adjoint model, our approach clearly shows that a small meander off Shikoku Island has a large impact on the prediction of meander growth in the Kuroshio region. Further, the strengthening of the Kuroshio current and its recirculation clearly becomes an important factor in the development of the meander. These results demonstrate the effectiveness of our assimilation approach in identifying efficient initialization schemes on numerical forecasting of the Kuroshio south of Japan and should help in the construction of an effective observing system for improving the forecasting. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Spatiotemporal Decreases of Nutrients and Chlorophyll-a in the Surface Mixed Layer of the Western North Pacific from 1971 to 2000     

Yutaka?W.?WatanabeEmail author  Hiroshi?Ishida  Toshiya?Nakano  Naoki?Nagai 《Journal of Oceanography》2005,61(6):1011-1016

Using time series of hydrographic data in the wintertime and summertime obtained along 137°E from 1971 to 2000, we found that the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001∼0.004 μmol-PO₄ l⁻¹ yr⁻¹ and 0.01∼0.04 μmol-NO₃ l⁻¹ yr⁻¹ with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27∼0.48 mg-Chl m⁻² yr⁻¹ and 0.08∼0.47 g-C-NCP m⁻² yr⁻¹ with a clear oscillation of 20.8±0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation Index (PDO) with a time lag of 2 years (R = 0.89 ± 0.02). Considering the recent significant decrease of O₂ over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over the western North Pacific.  相似文献