Verification of the wind-driven transport in the North Pacific subtropical gyre using gridded wind-stress products

Wind-stress products supplied by satellite scatterometers carried the European Remote-sensing Satellite (ERS) and QuikSCAT (QSCAT), together with numerical weather predictions from the European Centre for Medium Range Weather Forecasting (ECMWF) and the National Centre for Environmental Prediction (NCEP) were used to estimate wind-driven transports of the North Pacific subtropical gyre. At 30°N, we compared the wind-driven transports with geostrophic transports calculated from World Ocean Database 2005. The wind-driven transports for QSCAT and NCEP are in good agreement with the geostrophic transport within reasonable error, except for a regional difference in the eastern part of the section. The difference in the eastern part suggests an anti-cyclonic deviation of the geostrophic transport, resulting from an anti-cyclonic anomalous flow in the surface layer. It is suggested that this anomalous flow is the Eastern Gyral, produced by the thermohaline process associated with the formation of the Eastern Subtropical Mode Water. To investigate the validity of QSCAT and NCEP data, we examined whether or not the Sverdrup transports for these products are consistent with the transport of the western boundary current estimated by past studies. The net southward transport, given by the sum of the Sverdrup transport for QSCAT and NCEP and the thermohaline transport, agrees well with the net northward transport of the western boundary current. From this result, together with the fact that the wind-driven transports for these products are in good agreement with the geostrophic transport, we conclude that the Sverdrup balance can hold in the North Pacific subtropical gyre.     

Empirical formula to relate the auroral electrojet intensity with interplanetary parameters

An empirical formula has been constructed using the results of correlative analyses to determine in what form the AL index, as a measure of the intensity of the westward auroral electrojet, depends on interplanetary parameters. The formula thus obtained shows that AL is mainly determined by B_sV² where B_s is the southward component of the IMF and V is the solar wind velocity, and is modulated in a characteristic way by the combined effect of the east-west component of the IMF and the tilt angle of the Earth's dipole axis toward the Sun-Earth line. In contrast, effects of the solar wind density and the IMF variability were found to be insignificant.Implications of the empirical formula are discussed mainly in relation to the problem of the location in the dayside magnetosphere of the region where the reconnection process to initiate the substorm takes place.     

Petrography and petrochemistry of latest Pliocene olivine-tholeiites of Taos area,northern New Mexico,U.S.A.

In north-central New Mexico, U.S.A., enormous volumes of basaltic rocks erupted in latest Pliocene time, forming large flat plateaus along the western foot of the Rocky Mountain Range.Petrographically, and also geologically, the volcanic rocks are divided into three series. Of these, the lava flows of the middle series accounted for more than ninety-five per cent of both area and volume. The first two series are composed of olivine-tholeiite while the last one is composed of calc-alkaline andesite.Twenty volcanic rocks, five groundmass plagioclases and five groundmass clinopyroxenes have been chemically analysed.The basalts are intermediate between tholeiitic and alkaline types and are rather similar to the high-alumina basalt from Oregon and the Cascade Range. However, the crystallization trends of groundmass plagioclase and clinopyroxene closely resemble those found in Japanese and Kilauean tholeiitic series.     

Evaluation of Seasonal Sea Level Variation at Syowa Station, Antarctica, Using GPS Observations

Global Positioning System (GPS) measurements of the vertical displacement of fast ice near Syowa Station, Antarctica, were conducted between April and December 1998 to evaluate measurements of sea level variation derived with a conventional bottom pressure gauge (BPG). The BPG-derived sea level revealed a seasonal variation of about 0.13 m, with a high in April–June and a low in November–December. The GPS-derived sea level, combined with observed sea ice thickness, supported the BPG result, with an RMS error of 0.007 m. Our result also demonstrates that GPS is a powerful technique for monitoring sea level variations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Middle Miocene to Pleistocene magneto-biostratigraphy of ODP Sites 1150 and 1151, northwest Pacific: Sedimentation rate and updated regional geological timescale

Abstract Shipboard and shore‐based investigation on siliceous and calcareous microfossil biostratigraphy, magneto‐stratigraphy and tephrostratigraphy identified numerous datum events from the sedimentary sequences of Sites 1150 and 1151 drilled on the forearc basin of northern Japan by the Ocean Drilling Program Leg 186. Some 83 datum events were selected to construct new age–depth models for the sites. Based on the reliable magneto‐stratigraphy from the Pleistocene to the Upper Miocene, which were correlated to the standard geomagnetic polarity timescale, and on excellent records of diatom and radiolarian biostratigraphy throughout the sequences, the shipboard age model was revised. Major revisions referred to stratigraphic position of the Miocene–Pliocene boundary that has been shifted more than 200 m downward in each sequence. The age–depth relations of the forearc sites represent drastic changes in the sedimentation rate—extremely high (40 cm/k.y. on average) in the Early Pliocene and low (less than 2 cm/k.y. on average) in the Middle Miocene—and several hiatuses exist throughout the sequence. The drastic changes can be related mostly to changes in diatom sedimentation and the tectonics of the Japanese Island Arc. Local ages for some foraminiferal, calcareous nannofossil and radiolarian bioevents are estimated from the age–depth models at each site. These newly calibrated bioevents and biozones as well as established diatom biostratigraphy are incorporated into the updated magneto‐biochronologic timescale, which will contribute to an improvement in biochronologic accuracy of Neogene sediments in northern Japan and adjacent areas.     

Ar and Sr isotopes of mantle-derived rocks from the Japanese Islands

⁴⁰Ar-³⁰Ar and Sr isotope analyses have been made for ultramatic nodules in basaltic rocks from Itinome-gata and the Oki-Dōgo Island, northeast and southwest of Japan respectively, in order to examine the state of the upper mantle under the Japanese Islands. ⁴⁰Ar-³⁰Ar analyses have revealed that ultramafic nodules from Oki-Dōgo Island were involved in events which caused Ar redistribution in these rocks and probably were related to their formation not older than several tens of millions of years ago. These nodules are relatively depleted in both Rb and Sr contents together with some other incompatible elements compared to similar nodules from the other regions in the world. This may be typical for ultramafic nodules from the Japanese Islands. Ultramafic nodules show mostly a little higher⁸⁷Sr/⁸⁶Sr ratios (0.704–0.706) than those of host basaltic rocks (0.703–0.705) indicating the accidental origin for these nodules. Present results also suggest both horizontal and vertical inhomogeneities of the uppermost part of the mantle with respect to Sr isotopes on a regional scale. Hence, the ultramafic nodules in volcanic rocks may not always directly represent the upper mantle materials from which the magma is produced at present. Such ultramafic nodules might be relatively old material from the uppermost part of the mantle under the Japanese Islands.     

40Ar/39Ar analyses of phlogopite nodules and phlogopite-bearing peridotites in South African kimberlites

⁴⁰Ar/³⁹Ar analyses have been made on phlogopite-bearing peridotite nodules from Bultfontein and phlogopite nodules from Du Toitspan, Kimberley area, South Africa. Neither definite plateau nor isochron age could be obtained due to the occurrence of an excess⁴⁰Ar in phlogopite. However, the extrusion age of a phlogopite nodule from Du Toitspan has been estimated to be about 86 m.y. from the combination of the youngest⁴⁰Ar/³⁹Ar age in the intermediate temperature fraction with Rb/Sr age data reported for this area.Excess⁴⁰Ar correlates with K-derived³⁹Ar in some phlogopites suggesting that it is trapped in K- or K-similar sites and has been incorporated during phlogopite formation.The occurrence of large amounts of excess⁴⁰Ar in phlogopite suggests that it was not formed at a shallow depth.     

The major element composition of the upper mantle estimated from the composition of lherzolites

The compilation of analyses of continental and oceanic spinel Iherzolites show that these two types of Iherzolites have very similar compositions. Their composition range differ from that of African garnet Iherzolites, and the data suggest that the mantle beneath Africa has an anomalous composition. If the composition of the upper mantle may be estimated from that of Iherzolites, the compositions of spinel Iherzolite should form the basis for this estimate. It is suggested that the compositions of spinel Iherzolite represent both undepleted and depleted compositions, and a representative composition for the primitive mantle is proposed on this basis.