Kinetics of nitrate and ammonium uptake by the natural populations of marine phytoplankton in the surface water of the Oyashio region during spring and summer     

Shiomoto  Akihiro  Sasaki  Katsuyuki  Shimoda  Toru  Matsumura  Satsuki 《Journal of Oceanography》1994,50(6):725-725

Journal of Oceanography -  相似文献   

Local high relief at the southern margin of the Andean plateau by 9 Ma: evidence from ignimbritic valley fills and river incision     

Carolina Montero‐López  Manfred R. Strecker  Taylor F. Schildgen  Fernando Hongn  Silvina Guzmán  Bodo Bookhagen  Masafumi Sudo 《地学学报》2014,26(6):454-460

A valley‐filling ignimbrite re‐exposed through subsequent river incision at the southern margin of the Andean (Puna) plateau preserves pristine geological evidence of pre‐late Miocene palaeotopography in the north western Argentine Andes. Our new ⁴⁰Ar/³⁹Ar dating of the Las Papas Ignimbrites yields a plateau age of 9.24 ± 0.03 Ma, indicating valley‐relief and orographic‐barrier conditions comparable to the present‐day. A later infill of Plio–Pleistocene coarse conglomerates has been linked to wetter conditions, but resulted in no additional net incision of the Las Papas valley, considering that the base of the ignimbrite remains unexposed in the valley bottom. Our observations indicate that at least 550 m of local plateau margin relief (and likely >2 km) existed by 9 Ma at the southern Puna margin, which likely aided the efficiency of the orographic barrier to rainfall along the eastern and south eastern flanks of the Puna and causes aridity in the plateau interior.  相似文献   

Recognition of a Locked State in Plate Subduction from Microearthquake Seismicity     

S. Matsumura  N. Kato 《Pure and Applied Geophysics》1999,155(2-4):669-687

—A tectonic state of a locked subduction is considered to be a possible source of a future interplate earthquake. Discriminating an actually locked state to verify its extent is therefore essential in constructing an accurate prospect against the forthcoming earthquake. Micorearthquake seismicity is an effective tool for such an analysis because it is considered to be a faithful indicator of the stress state, and is expected to exhibit a characteristic pattern in the area where the locked state in the subduction appears with a certain stress concentration. Focusing on the microearthquake seismicity around the Tokai district in central Japan, where a large interplate earthquake is feared to occur, we tried to identify such an area of locked subduction on the Philippine Sea plate, possibly related to the future earthquake. We investigated the microearthquake seismicity from various perspectives. First, the hypocenter distribution was analyzed to identify the extent of the locked area. The characteristic profile of the distribution was presumed to represent a stress concentrated area induced from the mechanical contact between both plates. The second approach is to interpret stress patterns reflected in focal mechanisms. The locked state was recognized and verified by a comparison of the P-axis distribution pattern with that expected from a model imaging a partially locked subduction. The third approach is to monitor the temporal change of the seismic wave spectrum. Analyzing predominant frequencies of P and S waves and monitoring their changes for a period of 10 years, we found a trend of gradual increase common to both waves. This means an increase of stress drop in microfracturings, and in its turn implies accumulation of stress around the focus area. The rate of the stress change converted from the frequency change was compared with the result derived from a numerical simulation. The simulation, performed on the basis of a constitutive friction law for a stick sliding on the plate interface, computed a changing rate of the maximum shear stress around the locked zone and showed its spatial variation along the subduction axis. Thus the simulated result indicated a certain compatibility with the observed one. Although ambiguities and uncertainties still exist in the study, all the results derived here seem to indicate an identical conclusion that the plate subduction is actually locked in this region at present.  相似文献   

Seasonality of the Kuroshio Transport Revealed in a Kuroshio Assimilation System   总被引：2，自引：2，他引：2  

Atsuhiko Isobe  Masafumi Kamachi  Yukio Masumoto  Hiroshi Uchida  Tsurane Kuragano 《Journal of Oceanography》2004,60(2):321-328

The seasonal variation of the Kuroshio transport south of Japan has been investigated using the results of an assimilation model. Annual and semiannual variations of the transport and dynamic depth anomaly are reconstructed by CEOF (complex orthogonal empirical function) analysis. In the basin west of the Izu-Ogasawara Ridge, the annual component of the variation propagates westward with the phase speed of the long Rossby wave associated with the first baroclinic mode. The variation also shows a similar tendency to that reproduced in a wind-driven, two-layer model with a ridge. This suggests that the annual variation revealed in the assimilation model is associated with the baroclinic first mode of motion excited above the Izu-Ogasawara Ridge. Furthermore, it is found that both the semiannual component and the annual component are important members determining the seasonal variation of the Kuroshio transport south of Japan. The semiannual component is revealed as a double gyre pattern in the basin west of the Izu-Ogasawara Ridge. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Kinetics of nitrate and ammonium uptake by the natural populations of marine phytoplankton in the surface water of the Oyashio region during spring and summer     

Akihiro Shiomoto  Katsuyuki Sasaki  Toru Shimoda  Satsuki Matsumura 《Journal of Oceanography》1994,50(5):515-529

The maximum uptake rate (_max) and affinity constant (K _s) for nitrate and ammonium were estimated in the surface water of offshore Oyashio in May (spring) and September (summer), 1990. The average _max/Chl.a for ammonium was 2.1 times larger than that of nitrate in both seasons. The average _max/Chl.a for both nitrogens were 3.5 times larger in summer than in spring. Water temperature and size composition of phytoplankton population were related to the seasonal difference in the _max/Chl.a. Phytoplankton population showed high affinity for both nitrogens in the spring and summer. In addition, the contribution of new production to total production was estimated by _max[_max–No₃/(_max–NO₃+_max–NH₄)]. The spring value was in the range of 0.26 to 0.45 (mean±SD=0.35±0.092), and the values in spring bloom were especially a little over 0.4. The summer value was in the range of 0.30 to 0.37 (0.34±0.04).  相似文献   

Interannual and Decadal Variabilities of NPIW Salinity Minimum Core Observed along JMA’s Hydrographic Repeat Sections     

Toshiya?NakanoEmail author  Ikuo?Kaneko  Masahiro?Endoh  Masafumi?Kamachi 《Journal of Oceanography》2005,61(4):681-697

We investigated the variation of the North Pacific Intermediate Water (NPIW) distribution in the western North Pacific, focusing on the intermediate salinity minimum (S < 34.2) core observed along the meridional hydrographic sections including the 137°E repeat section by the Japan Meteorological Agency. This core is a cross-section of a low salinity tongue extending westward along the recirculation in the subtropical gyre. The core size shows remarkable variabilities in interannual and decadal time scales. The salinity change in the density layer during the period of core expansion (shrinking) represents the spatial salinity change in the tongue toward the west (east). Thus, we conclude that the core size variation is associated with the zonal wobble of the tongue having thicker distribution to the east, rather than temporal changes of the water mass itself. The core size at 137°E is well correlated with the meridional gradient of the depth in the isopycnal surface at the salinity minimum representing the recirculation intensity, suggesting a relation with the intensity of the subtropical gyre. A significant lag-correlation between the gradient and the wind forcing over the North Pacific suggests that the first mode baroclinic Rossby waves excited in the central North Pacific propagated westward to change the intensity of the recirculation in interannual time scales. In decadal time scales, it is found that the wind stress curl and heat flux fields in the North Pacific precede the recirculation by about 11 years.  相似文献   

Application of Nonlinear Constraints in a Three-Dimensional Variational Ocean Analysis     

Yosuke?FujiiEmail author  Shiro?Ishizaki  Masafumi?Kamachi 《Journal of Oceanography》2005,61(4):655-662

Two kinds of nonlinear constraints, not previously studied in oceanography, have been adopted with the Preconditioned Optimizing Utility for Large-dimensional analyses (POpULar) in a three-dimensional oceanic variational analysis in the equatorial Pacific. One is the constraint for the variational Quality Control (QC) procedure and the other is used to avoid density and temperature inversions. Estimation of the large heat content anomaly in the upper ocean related to El Nino and La Nina phenomena is improved with the variational QC. For example, it prevents unusual but correct observation data on the thermocline deepening in the 1997/98 El Nino from being ignored. As a result, it improves the temperature field estimation in the eastern equatorial Pacific. The constraint for avoiding inversions prevents the low salinity layer at the surface and the barrier layer in the eastern equatorial Pacific in the El Nino period from being destroyed by the convective adjustment procedure performed after minimizing the cost function. Incorporating nonlinear constraints in variational analyses is thus a strong candidate for increasing the accuracy of analysis.  相似文献   

Short-Range Prediction Experiments with Operational Data Assimilation System for the Kuroshio South of Japan   总被引：3，自引：3，他引：3  

Masafumi Kamachi  Tsurane Kuragano  Satoshi Sugimoto  Kumi Yoshita  Toshiyuki Sakurai  Toshiya Nakano  Norihisa Usui  Francesco Uboldi 《Journal of Oceanography》2004,60(2):269-282

The short-range (one month) variability of the Kuroshio path was predicted in 84 experiments (90-day predictions) using a model in an operational data assimilation system based on data from 1993 to 1999. The predictions started from an initial condition or members of a set of initial conditions, obtained in a reanalysis experiment. The predictions represent the transition from straight to meander of the Kuroshio path, and the results have been analyzed according to previously proposed mechanisms of the transition with eddy propagation and interaction acting as a trigger of the meander and self-sustained oscillation. The reanalysis shows that the meander evolves due to eddy activity. Simulation (no assimilation) shows no meander state, even with the same atmospheric forcing as the prediction. It is suggested therefore that the initial condition contains information on the meander and the system can represent the evolution. Mean (standard deviation) values of the axis error for all 84 cases are 13, 17, and 20 (10, 10, and 12) km, in 138.5°E, in the 30-, 60-, and 90-day predictions respectively. The observed mean deviation from seasonal variation is 30 km. The predictive limit of the system is thus about 80 days. The time scale of the limit depends on which stage in the transition is adopted as the initial condition. The gradual decrease of the amplitude in a stage from meander to straight paths is also predicted. The predictive limit is about 20 days, which is shorter than the prediction of the opposite transition. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Balance of Volume Transports between Horizontal Circulation and Meridional Overturn in the North Pacific Subarctic Region     

Tsurane Kuragano  Masafumi Kamachi 《Journal of Oceanography》2004,60(2):439-451

Horizontal and meridional volume transports on timescales from intra-seasonal to interannual in the North Pacific subarctic region were investigated using a reanalysis dataset for 1993–2001 that was constructed from an assimilation of the TOPEX altimeter and in situ data into an eddy-permitting North Pacific ocean general circulation model. The barotropic flow is excited along east of the Emperor Seamounts by the western intensification dynamics. The volume transport of this flow compensates for that across the interior region east of the Seamounts below the summit depth of the Seamounts. The Oyashio, which is also considered as a compensation flow for the transport in the whole interior region, includes baroclinic as well as barotropic components. Baroclinic transports in the whole interior region exceed those in the western boundary region in the upper (200–1000 m) and lower (2000–5000 m) layers, and the total transport is northward (southward) in the upper (lower) layer. These excesses of the baroclinic transport are balanced by a vertical transport of the meridional overturn. The meridional overturn has a complementary relation to the basin-scale baroclinic circulation in the North Pacific subactic region. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Ocean Data Assimilation in the Tropical Pacific: A Short Survey     

Masafumi Kamachi  Yosuke Fujii  Xiaobing Zhou 《Journal of Oceanography》2002,58(1):45-55

This short survey presents several research and operational developments of ocean data assimilation in the tropical Pacific, primarily for climate-scale phenomena. Aspects of theoretical error estimations, diagnostics and practical reduced space techniques are also briefly reported. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献