Seasonal variations in the nitrogen isotopic composition of settling particles at station K2 in the western subarctic North Pacific

Intensive observations using hydrographical cruises and moored sediment trap deployments during 2010 and 2012 at station K2 in the North Pacific Western Subarctic Gyre (WSG) revealed seasonal changes in δ ¹⁵N of both suspended and settling particles. Suspended particles (SUS) were collected from depths between the surface and 200 m; settling particles by drifting sediment traps (DST; 100–200 m) and moored sediment traps (MST; 200 and 500 m). All particles showed higher δ ¹⁵N values in winter and lower in summer, contrary to the expected by isotopic fractionation during phytoplankton nitrate consumption. We suggest that these observed isotopic patterns are due to ammonium consumption via light-controlled nitrification, which could induce variations in δ ¹⁵N(SUS) of 0.4–3.1 ‰ in the euphotic zone (EZ). The δ ¹⁵N(SUS) signature was reflected by δ ¹⁵N(DST) despite modifications during biogenic transformation from suspended particles in the EZ. δ ¹⁵N enrichment (average: 3.6 ‰) and the increase in C:N ratio (by 1.6) in settling particles suggests year-round contributions of metabolites from herbivorous zooplankton as well as TEPs produced by diatoms. Accordingly, seasonal δ ¹⁵N(DST) variations of 2.4–7.0 ‰ showed a significant correlation with primary productivity (PP) at K2. By applying the observed δ ¹⁵N(DST) vs. PP regression to δ ¹⁵N(MST) of 1.9–8.0 ‰, we constructed the first annual time-series of PP changes in the WSG. This new approach to estimate productivity can be a powerful tool for further understanding of the biological pump in the WSG, even though its validity needs to be examined carefully.     

Paleomagnetic Constraints on Mineralization Age of the Nansatsu-type Gold Deposits in Southern Kyushu, Japan

Abstract: Two mineralization stages, stage I and stage II, have been identified from textural, mineralogical and crosscutting relationships in gold ore from the Nansatsu-type gold deposits of Kasuga, Iwato and Akeshi. Mineralization age of each stage in each deposit was determined with paleomagnetic methods on 432 specimens from 312 oriented samples. As results, mineralization ages of stage I of each deposit fall in the same period, the reversed polarity subchron of 4.18–3.58 Ma, and those of stage II are limited in the normal and reversed polarity subchrons of 3.58–3.22 Ma. Contrasting with previous results based only on K-Ar ages, our conclusion shows that these Nansatsu-type gold deposits were formed contemporaneously.     

Phytoplankton productivity in the western subarctic gyre of the North Pacific in early summer 2006

We deployed a profiling buoy system incorporating a fast repetition rate fluorometer in the western subarctic Pacific and carried out time-series observations of phytoplankton productivity from 9 June to 15 July 2006. The chlorophyll a (Chl a) biomass integrated over the euphotic layer was as high as 45–50 mg Chl a m⁻² in the middle of June and remained in the 30–40 mg Chl a m⁻² range during the rest of observation period; day-to-day variation in Chl a biomass was relatively small. The daily net primary productivity integrated over the euphotic layer ranged from 144 to 919 mg C m⁻² day⁻¹ and varied greatly, depending more on insolation rather than Chl a biomass. In addition, we found that part of primary production was exported to a 150-m depth within 2 days, indicating that the variations in primary productivity quickly influenced the organic carbon flux from the upper ocean. Our results suggest that the short-term variability in primary productivity is one of the key factors controlling the carbon cycle in the surface ocean in the western subarctic Pacific.     

Geology and Hydrothermal Alteration of the Milyang Pyrophyllite Deposit, Southeast Korea

Abstract: The Milyang pyrophyllite deposit, which is embedded in the Late Cretaceous Yuchon Group of the Kyongsang Supergroup, is one of the largest hydrothermal clay deposits in the Kyongsang basin, southeast Korea. Host rocks of the deposit are porphyritic andesite lava and minor andesitic lapilli tuff. In the Milyang district, a hydrothermally altered zone is about 2 × 3 km in extent; we can recognize the concentric arrangement of advanced argillic, propylitic, and sericitic alteration zones from the central to peripheral parts of the zone. The Milyang pyrophyllite deposit forms a part of the advanced argillic alteration zone. The Milyang pyrophyllite deposit is subdivided into the following four zones based on mineral assemblages: the pyrophyllite zones 1, 2, 3, and the silicified zone. The pyrophyllite zone 1, which occupies the central part of the deposit, comprises mainly pyrophyllite, kaolinite, and diaspore without quartz. Diaspore nodules often concentrate in beds 40–50 cm thick. Andalusite, dumortierite, and tourmaline locally occur as network veins, crack‐filler, or small spherulitic spots. The Al₂O₃ content of the ore ranges from 27 to 36 wt%. The pyrophyllite zone 2, which constitutes a major part of the deposit, comprises mainly pyrophyllite, kaolinite, and quartz. The Al₂O₃ content of the ore ranges from 15 to 24 wt%. The pyro‐phyllite zone 3 is the hematite‐rich marginal facies of the deposit. The silicified zone, which occurs as beds and septa, is mostly composed of quartz with minor pyrophyllite and kaolinite; the SiO₂ contents range from 79 to 90 wt%. Comparing chemical compositions of the high‐Al ores with those of unaltered host andesite, the Fe, Ca, alkalis, HFSE, and HREE contents are significantly depleted, whereas S, B, As, Sr, and LREE are enriched. The hydrothermal alteration of the Milyang pyrophyllite deposit can be classified into the following four stages: 1) extensive sericitic and propylitic alteration, 2) medium‐temperature (200–250°C) advanced argillic alteration, 3) high‐temperature (250–350°C or more) advanced argillic alteration, and 4) retrograde low‐temperature alteration. The heat and some volatile components such as B and S would be derived from the Pulguksa Granite intruded underneath the deposit.     

Four lunar mare meteorites: Crystallization trends of pyroxenes and spinels

Abstract— We studied crystallization trends of pyroxene and spinel in four Antarctic meteorites known to be derived from mare regions of the Moon: Y-793169 and A-881757 (YA meteorites) are unbrecciated igneous basalts, EET 87521 is a fragmental breccia, and Y-793274 is a regolith breccia. All have relatively low bulkrock TiO₂ content, and the YA meteorites are uncommonly ancient. Our electron probe microanalysis (EPMA) data indicate that the YA meteorites and the dominant mare components of Y-793274 and EET 87521 conform to a general trend for Ti-poor (low-Ti and very low-Ti) mare basalts. Their pyroxenes show a strong correlation between Fe/(Fe + Mg) (Fe#) and Ti/(Ti + Cr) (Ti#), both ratios typically increasing from core to rim. These trends presumably reflect local crystallization differentiation of interstitial melt. Previous studies (M. J. Drake and coworkers) have suggested that the detailed configurations of such Fe# vs. Ti# trends may reflect the bulk TiO₂ contents of the parent magmas (basalts). As a more systematic approach to this problem, we plot bulk-rock TiO₂ as a function of the Fe# = 0.50 intercept of each rock's pyroxene Fe# vs. Ti# trend. We call this intercept the Fe#-normalized Ti#. Based on our data for EET 87521, the YA meteorites, and Apollo 12 basalts 12031 and 12064, plus literature data for several other Ti-poor mare basalts, we find a strong correlation between Fe#-normalized Ti# and the bulk TiO₂ content of the parent basalt. This correlation confirms that fragmental breccia EET 87521 is nearly pure very low-Ti (VLT) basalt and that the YA meteorites, for which bulk-rock TiO₂ results scatter due to unusually coarse grain size (A-881757) or scarcity of available sample (Y-793169), are pieces of an uncommonly Ti-poor, but not quite VLT, variety of low-Ti mare basalt. Extrapolating from this correlation, the dominant mare component of regolith breccia Y-793274 is probably of VLT affinity. Besides the normal mare pyroxene trend of strong correlation between Fe# and Ti#, Y-793274 includes two additional pyroxene compositional trends, both showing a wide range of Ti# despite relatively constant (and low, by mare standards) Fe#. The most magnesian of these trends consists of a single clast with a mode of orthopyroxene + MgO-rich ilmenite. These two trends are of uncertain origin. Possibly one or both represents the highland component of this regolith breccia, although, unlike most highland pyroxenes, these appear relatively unaltered by impact brecciation and metamorphism. Compositions of spinels in the coarse-grained A-881757 show an extraordinary distribution: chromite and ulvöspinel components vary among grains but are nearly constant within grains. Despite its old age and unusually coarse grain sizes, mineralogical evidence (i.e., heterogeneity within both pyroxene and spinel; typical pyroxene exsolution scale very coarse by mare standards but exceeded by the pyroxenes of EET 87521 and Y-793274) indicates that A-881757 was cooled only slightly more slowly than typical mare basalts and may have formed near the center of an uncommonly thick lava flow. Both of the VLT basaltic lunar meteorite breccias, EET 87521 and Y-793274, are composed dominantly of pyroxenes with exsolution coarser than normal for mare basalts. Possibly VLT basalt flows tend to be systematically thicker, and thus more slowly cooled, than more Ti-rich flows.     

用非线性近似方法反演单多普勒雷达风场

回顾了近年来由单多普勒雷达观测反演风场的各种方法。这些方法大部分基于线性假设，因此风场的非线性交化经常影响反演结果，使得反演的风场误差增大。我们提出一种以非线性近似理论为基础的反演方法，该方法主要考虑了风场分片光滑的特点并充分利用了雷达的径向风场数据。我们把该方法应用到1998年淮河能量与水循环实验的两个个例中。通过同双多普勒雷达观测的结果比较，发现该方法能反演较高分辨率和淮确性的水平风场，反演的垂直风场也比较合理。     

Mineralogical records of early planetary processes on the howardite,eucrite, diogenite parent body with reference to Vesta

Abstract— Mineralogical information recovered from the howardite, eucrite, diogenite (HED) meteorites was employed to reconstruct the history of the parent body and relate it to 4 Vesta. These interpreted crustal evolution processes were then compared to the expected geological features on the surface of a likely proto-planet, 4 Vesta. The original crustal materials of the HED parent body were preserved as mineral grains and lithic clasts, but in many eucrites, Fe/Mg ratios in pyroxenes were homogenized by diffusion after crystallization. The crystallization trend of the protocrust has been deciphered by (1) examining monomict and crystalline samples and using their mineralogical and chemical information to formulate a sequence of crystallization and cooling trends; and by (2) reconstructing the original crust prior to cratering events from lithic clasts and mineral fragments in polymict breccias such as howardites and polymict eucrites. Mineral components are identical, both in the individual HED and in polymict breccias, and no remnants of primitive materials were preserved in the polymict breccias. A layered crust model reconstructed from such breccias consists of an upper crust with extrusive lava-like eucrites that have been brecciated and metamorphosed, diogenite mantle, and cumulate eucrites of varying thickness between them. This model can be used to explain the surface geological features of Vesta observed from the Hubble space telescope. A large crater with diogenitic orthopyroxene at the crater floor is consistent with the deepest diogenitic layer of the layered crust model; and an underlying olivine layer is expected from early crystallized olivine in the crystal fractionation model. The old terrain of eucritic surface materials of Vesta can be howardites, polymict eucrites, or regolith-like eucrites produced from eucrites extruded and impacted on the surface. Partial melting models of eucrites seem to be favored by the rare-earth element (REE) chemistry and experimental studies. Unfortunately, partial melting models have not demonstrated how the HED parent body is converted to a layered crust without producing any metamorphosed primitive material in the layered crust. The origin of cumulate eucrites with systematic variation of textures and chemistries of pyroxene can be explained by the layered crust model with excavation and mixing of trapped liquid. Discovery of basaltic materials with Na-rich plagioclase and augite in iron meteorites, which are the products of partial melting, suggests that eucrites may be unique to a body that underwent large-scale differentiation and metamorphism.     

Petrology of a mantle-derived rhyolite, Hokkaido, Japan

The Miocene Kitami rhyolite, consisting of orthopyroxene and plagioclase-phyric lavas and dikes, occurs on the back-arc side of the Kuril arc with coeval basalts and Fe-rich andesites. Temperatures estimated from orthopyroxene–ilmenite pairs exceed 900°C. Although the whole rock compositions of the Kitami rhyolite correspond to S-type granites (i.e., high K, Al, large ion lithophile elements, and low Ca and Sr), Sr–Nd isotope compositions are remarkably primitive, and similar to those of the coeval basalts and andesites. They are distinct from those of lower crustal metamorphic rocks exposed in the area. Comparison of chondrite-normalized rare earth element (REE) patterns between the rhyolite and the basalts and andesites show that the rhyolite is more light REE enriched, but has similar heavy REE contents than the basalts. All rhyolites show negative Eu anomalies. The geochemical data suggest that did not formed by simple dehydration melting of basaltic rocks or fractional crystallization of basaltic magmas. The features of slab-derived fluids expected from recent high pressure experimental studies indicates that mantle wedge is partly metasomatized with “rhyolitic” materials from subducted slabs; it is more likely that very low degree partial melting of the metasomatized mantle wedge formed the rhyolite magma.