Calculation of Interannual Variations of Sea Level in the Subtropical North Pacific

The interannual variations of sea level at Chichi-jima and five other islands in the subtropical North Pacific are calculated for 1961–95 with a model of Rossby waves excited by wind. The Rossby-wave forcing is significant east of 140°E. Strong forcing of upwelling (downwelling) Rossby wave occurs during El Niño (La Niña) and warm (cold) water anomaly in the eastern equatorial Pacific. The first and second baroclinic modes of Rossby wave are more strongly generated than the barotropic mode in the study area. A higher vertical mode of Rossby wave propagates more slowly and is more decayed by eddy dissipation. The best coefficient of vertical eddy dissipation is determined by comparing the calculated sea level with observation. The variation in sea level at Chichi-jima is successfully calculated, in particular for the long-term change of the mean level between before and after 1986 with a rise in 1986 as well as the variations with periods of two to four years after 1980. It is concluded that variations of sea level at Chichi-jima are produced by wind-forced Rossby waves, the first baroclinic wave primarily and the barotropic wave secondly. The calculation for other islands is less successful. Degree of the success in calculation almost corresponds to a spatial difference in quantity of wind data, and seems to be determined by quality of wind data.     

Water masses and currents of deep circulation southwest of the Shatsky Rise in the western North Pacific

We conducted full-depth hydrographic observations in the southwestern region of the Northwest Pacific Basin in September 2004 and November 2005. Deep-circulation currents crossed the observation line between the East Mariana Ridge and the Shatsky Rise, carrying Lower Circumpolar Deep Water westward in the lower deep layer (θ<1.2 °C) and Upper Circumpolar Deep Water (UCDW) and North Pacific Deep Water (NPDW) eastward in the upper deep layer (1.3–2.2 °C). In the lower deep layer at depths greater than approximately 3500 m, the eastern branch current of the deep circulation was located south of the Shatsky Rise at 30°24′–30°59′N with volume transport of 3.9 Sv (1 Sv=10⁶ m³ s⁻¹) in 2004 and at 30°06′–31°15′N with 1.6 Sv in 2005. The western branch current of the deep circulation was located north of the Ogasawara Plateau at 26°27′–27°03′N with almost 2.1 Sv in 2004 and at 26°27′–26°45′N with 2.7 Sv in 2005. Integrating past and present results, volume transport southwest of the Shatsky Rise is concluded to be a little less than 4 Sv for the eastern branch current and a little more than 2 Sv for the western branch current. In the upper deep layer at depths of approximately 2000–3500 m, UCDW and NPDW, characterized by high and low dissolved oxygen, respectively, were carried eastward at the observation line by the return flow of the deep circulation composing meridional overturning circulation. UCDW was confined between the East Mariana Ridge and the Ogasawara Plateau (22°03′–25°33′N) in 2004, whereas it extended to 26°45′N north of the Ogasawara Plateau in 2005. NPDW existed over the foot and slope of the Shatsky Rise from 29°48′N in 2004 and 30°06′N in 2005 to at least 32°30′N at the top of the Shatsky Rise. Volume transport of UCDW was estimated to be 4.6 Sv in 2004, whereas that of NPDW was 1.4 Sv in 2004 and 2.6 Sv in 2005, although the values for NPDW may be slightly underestimated, because they do not include the component north of the top of the Shatsky Rise. Volume transport of UCDW and NPDW southwest of the Shatsky Rise is concluded to be approximately 5 and 3 Sv, respectively. The pathways of UCDW and NPDW are new findings and suggest a correction for the past view of the deep circulation in the Pacific Ocean.     

Petrogenetic implications and geochronology of middle Miocene Tannayama igneous rocks,Goto Islands,Japan Sea southern margin,northwestern Kyushu,Japan

The subduction of “hot” Shikoku Basin and the mantle upwelling related to the Japan Sea opening have induced extensive magmatism during the middle Miocene on both the back-arc and island-arc sides of southwest Japan. The Goto Islands are located on the back-arc side of northwestern Kyushu, and middle Miocene granitic rocks and associated volcanic, hypabyssal, and gabbroic rocks are exposed. The igneous rocks at Tannayama on Nakadori-jima in the Goto Islands consist of gabbronorite, granite, granite porphyry, diorite porphyry, andesite, and rhyolite. We performed detailed geological mapping at a 1:10 000 scale, as well as petrographical and geochemical analyses. We also determined the zircon U–Pb age dating of the igneous rocks from Tannayama together with a granitic rock in Yagatamesaki. The zircon U–Pb ages of the Tannayama igneous rocks show the crystallization ages of 14.7 Ma ± 0.3 Ma (gabbronorite), 15.9 Ma ± 0.5 Ma (granite), 15.4 Ma ± 0.9 Ma (granite porphyry), and 15.1 Ma ± 2.1 Ma (rhyolite). Zircons from the Yagatamesaki granitic rock yield 14.5 Ma ± 0.7 Ma. Considering field relationships, new zircon data indicate that the Tannayama granite formed at ~16–15 Ma, and the gabbronorite, granite porphyry, diorite porphyry, andesite, and subsequently rhyolite formed at 15–14 Ma, which overlaps a plutonic activity of the Yagatamesaki. The geochemical characteristics of the Tannayama igneous rocks are similar to those of the tholeiitic basalts and dacites of Hirado, and the granitic rocks of Tsushima in northwestern Kyushu. This suggests that the Tannayama igneous rocks can be correlated petrogenetically with the igneous rocks in those areas, with all of them generated by the upwelling of hot mantle diapirs during crustal thinning in an extensional environment during the middle Miocene.     

Some aspects of the biology of the micronektonic fishCyclothone pallida andC. acclinidens (Pisces: Gonostomatidae) in Sagami Bay,Central Japan

Some aspects of the biology of the micronektonic fishesCyclothone pallida andC. acclinidens are described on the basis of samples taken during a series of 20 cruises from December 1982 to November 1985 at a fixed station near the center of Sagami Bay, Central Japan.C. pallida is a regular component of theCyclothone population in Sagami Bay, being found in more than 90% of the samples. On the other hand,C. acclinidens was encountered sporadically, being found in less than 25% of the samples. The depth range ofC. pallida is estimated to be about 400–1,000 m. It spawns mainly during the spring and summer in Sagami Bay.C. pallida releases about 1,000–3,000 eggs and may spawn several times during its life span. On the average, it reaches 18.5 mm standard length (SL) in one year, 24 mm SL in two years and 29.5 mm SL in three years during its subadult stage. Extrapolation of the growth curve suggests that males and females attain first sexual maturity in three to four years at 30–35 mm and five to six years at 40–45 mm SL, respectively.Cyclothone pallida is concluded to have a regular life cycle in Sagami Bay. It remains uncertain whether or notC. acclinidens reproduces in this area.     

Monitoring of position of the Kuroshio axis in the Tokara Strait using sea level data

Properties of the index of position of the Kuroshio axis in the Tokara Strait, named the Kuroshio position index (KPI), were examined using sea-level data during 1984–92. The index is KPI=(X+M _x )/(Y+M _y whereX(Y) is the anomaly of sea-level difference of Nakanoshima (Naze) minus Nishinoomote from the 1984–92 meanM _x (M _y ). The correlation with the latitude of the Kuroshio axis in the Tokara Strait concluded that the KPI withM _x /M _y =0.83 and realisticM _y (100±40 cm) best indicates the position of the Kuroshio axis in the strait. The KPI withM _x =83 cm andM _y =100 cm was newly called the KPI as the best index. Using daily values of this KPI, the relation between the position of the Kuroshio in the strait and the large meander of the Kuroshio shown by Kawabe (1995) was confirmed and studied in detail. A large meander forms (ends) 3.3 (5.1) months after a northward (southward) shift of the Kuroshio in the Tokara Strait. Yet, a temporary southward shift with a duration of ten to twenty days does not finish the large-meander (LM) path. At the LM formation, a small meander southeast of Kyushu begins to move eastward associated with the northward shift. The processes of LM formation and decay are started by the meridional move of the Kuroshio axis in the Tokara Strait. The Kuroshio axis at the FES line during the LM path is located farther north by 7 latitude than that during the non-large-meander (NLM) path. The latitude during the LM formation (decay) stage is a little higher (lower) than that during the LM (NLM) period, though the Kuroshio still takes an NLM (LM) path.     

Fluctuation of dissolved organic carbon in seawater of Sagami Bay during 1971–1972

Fluctuation of dissolved organic carbon (DOC) was studied during 1971–1972 at monthly intervals in surface layers of Sagami Bay. Concentration of DOC varied from 0.8 to 1.7 mgC/l in surface water (0 m). Maximum concentration of 1.7 mgC/l was observed in July 1971 and after then DOC decreased gradually to a minimum of 0.8 mgC/l in May 1972. The fluctuation of DOC during the observation periods seems to have close relations with those of water temperature and salinity. High DOC concentration found in summer months may be associated with bloom of phytoplankton or intrusion of seawater from Tokyo Bay and/or inland water containing high DOC.     

Barotropic instability of a viscous boundary jet

The barotropic instability of a boundary jet on a beta plane is considered with emphasis on the effect of internal viscosity. An eigenvalue problem for the disturbance equations and its inviscid version are solved by the aid of numerical methods, and instability characteristics are determined as functions of the Reynolds numberR for various values of the beta-parameter. Typical disturbance structures (eigenfunctions) are also computed. Numerical examples show that the minimum critical Reynolds numberR _cr for instability is smaller than 100. At a Reynolds number of the order of hundreds, there appears a second mode of instability in addition to the first unstable mode originating atR _cr ; a kind of ‘resonance’ between the first and second eigenvalues occurs at the particular value ofR. The neutral stability curves are accordingly multi-looped. Although each of the two unstable modes asymptotically approaches its inviscid counterpart asR→∞, the asymptotic approach to the inviscid limit is rather slow and the effect of varyingR is conspicuous even atR∼O (10⁴). It is thus demonstrated that the Reynolds number is an essential stability parameter for real boundary jets. The main part of the material contained in this paper was presented at 1981-Autumn Assembly of the Oceanographical Society of Japan.     

Elemental and isotopic abundances of lithium in chondrule constituents in the Allende meteorite

Elemental and isotopic abundances of lithium in chondrule constituents in the Allende CV3 meteorite were determined using secondary ion mass spectrometry. Olivines and mesostasis dominated by a feldspathic phase are depleted in Li ( and , respectively). In contrast, low-Ca pyroxenes and mesostasis dominated by a Na-rich phase are enriched in Li ( and , respectively) and the interchondrule matrix is generally enriched in Li ( on average). The Li isotopic abundance of olivine ranges from to 21. The spatial distributions of elemental and isotopic abundances of Li in olivines within individual chondrules exhibit no systematic pattern. This suggests that the distribution of Li in olivine was not disturbed during aqueous alteration or thermal metamorphism on the Allende meteorite parent body. Although mesostasis is the last crystallizing phase from a chondrule melt and is expected to be enriched in Li, in the Allende meteorite it is generally depleted in Li. We suggest that during aqueous alteration on the CV asteroid, Li in mesostasis was leached out by aqueous fluids. The Li-enriched Na-rich mesostasis was probably produced later by infiltration of Na-rich fluids. It seems likely that aqueous fluids sequestered alkali elements from the Allende-chondrite region in the CV parent asteroid, although significant amounts of Li are preserved in ferrous olivine in the interchondrule matrix.     

Simulating the diurnal cycle of rainfall in global climate models: resolution versus parameterization

The effects of horizontal resolution and the treatment of convection on simulation of the diurnal cycle of precipitation during boreal summer are analyzed in several innovative weather and climate model integrations. The simulations include: season-long integrations of the Non-hydrostatic Icosahedral Atmospheric Model (NICAM) with explicit clouds and convection; year-long integrations of the operational Integrated Forecast System (IFS) from the European Centre for Medium-range Weather Forecasts at three resolutions (125, 39 and 16 km); seasonal simulations of the same model at 10 km resolution; and seasonal simulations of the National Center for Atmospheric Research (NCAR) low-resolution climate model with and without an embedded two-dimensional cloud-resolving model in each grid box. NICAM with explicit convection simulates best the phase of the diurnal cycle, as well as many regional features such as rainfall triggered by advancing sea breezes or high topography. However, NICAM greatly overestimates mean rainfall and the magnitude of the diurnal cycle. Introduction of an embedded cloud model within the NCAR model significantly improves global statistics of the seasonal mean and diurnal cycle of rainfall, as well as many regional features. However, errors often remain larger than for the other higher-resolution models. Increasing resolution alone has little impact on the timing of daily rainfall in IFS with parameterized convection, yet the amplitude of the diurnal cycle does improve along with the representation of mean rainfall. Variations during the day in atmospheric prognostic fields appear quite similar among models, suggesting that the distinctive treatments of model physics account for the differences in representing the diurnal cycle of precipitation.