Recognition of conjugate solid-type and liquid-type relationship among the oceanic basalts,with respect to REE

The REE abundances and their chondrite-normalized pattern lead one to consider that the basalt from the Caroline ridge area southeast of the Marianas Arc and the one from the Puerto Rico Trench happen to be equivalent to conjugate liquid-type and solid-type materials, respectively, reflecting an equilibrium of a 20% partial melting. This line of interpretation enables us not only to assess the REE abundances in the original solid-type material (M), but also to estimate the corresponding values in the product (¯L) of a very small (say, less than 1 %) extent of a partial melting. It is also found that the relative REE abundances in a basalt from directly east of the Marianas Trench are quite the same as those thus estimated. Alternatively, it is possible to interpret this basalt as representing the residual liquid left after the primary fractional differentiation of the mantle.It is suggested that the straight-type bulk partition coefficients, the absence of the apparent europium anomaly, and the higher pressure are closely associated.     

Properties of sea ice and overlying snow in the Southern Sea of Okhotsk

The general properties of sea ice and overlying snow in the southern Sea of Okhotsk were examined during early February of 2003 to 2005 with the P/V “Soya”. Thin section analysis of crystal structure revealed that frazil ice (48% of total core length) was more prevalent than columnar ice (39%) and that stratigraphic layering was prominent with a mean layer thickness of 12 cm, indicating that dynamic processes are essential to ice growth. The mean thickness of ice blocks and visual observations suggest that ridging dominates the deformation process above thicknesses of 30 to 40 cm. As for snow, it was found that faceted crystals and depth hoar are dominant (78%), as which is also common in the Antarctic sea ice, and is indicative of the strong vertical temperature gradients within the snow. Stable isotope measurements (δ¹⁸O) indicate that snow ice occupies 9% of total core length and that the mass fraction of meteoric ice accounts for 1 to 2% of total ice volume, which is lower than the Antarctic sea ice. Associated with this, the effective fractionation coefficient during the freezing of seawater was also derived. Snow ice was characterized by lower density, higher salinity, and nearly twice the gas content of ice of seawater origin. In addition, it is shown that the surface brine volume fraction and freeboard are well correlated with ice thickness, indicating some promise for remote sensing approaches to the estimation of ice thickness.     

POM and Two-Way Nesting POM Study of Kuroshio Damping Phenomenon Caused by a Strong Wind

A Kuroshio damping phenomenon of a few days scale caused by a strong wind was studied using the Princeton Ocean Model (POM) and a two-way nesting model for the POM. We simulated an idealized eastward Kuroshio in a zonal channel in terms of the inflow/outflow condition at the western/eastern boundaries and examined responses of the idealized Kuroshio to a strong easterly wind. This study was motivated by observations of JMA research vessel Shumpu Maru which reported deformation of isopycnals and damping of the Kuroshio before and after the attack of Typhoon 6804. Deformation of isopycnals and damping of the Kuroshio are found to depend on magnitude of wind stress, intensity of stratification, distance of the Kuroshio from coast, and grid resolution. The deformation of isopycnals is related to the vertical circulation pattern caused by the divergence/convergence of the onshore Ekman transport. A simple stratification model composed of Niiler (1969)'s modification of the Ekman transport and the coastal boundary is proposed to explain the damping phenomenon. An idealized cape was added in other experiments in order to study whether the Kuroshio damping mechanism discussed here works in three dimensions. The newly developed two-way nesting model for the POM was applied for this experiment and made it possible to clarify more detailed features of response in the nested area than did the coarse grid model.     

Surface-temperature history during the last 1000 years near Prudhoe Bay, Alaska: applying control theory to the inversion of borehole temperature profiles

The temperature-depth profile data by Lachenbruch et al. (1982) in ice-bearing permafrost near Prudhoe Bay, Alaska, are analyzed with control theory to retrodict the last 1000-yr history of the surface temperature. For this purpose, an inversion scheme for a nonlinear problem of heat diffusion in permafrost is developed. The following conclusions are made: (1) During the last 1000 years, the surface temperature near Prudhoe Bay, Alaska, oscillated with amplitude of 3 ± 1°C. (2) There was a minimum of the temperature in 1853 AD between two maxima at 1623 AD and 1937 AD. (3) A net warming by 4°C occurred from 1853 AD to 1973 AD.     

The layered structure of lunar maria: Identification of the HF-radar reflector in Mare Serenitatis using multiband optical images

Comparison of the Lunar Radar Sounder (LRS) data to the Multiband Imager (MI) data is performed to identify the subsurface reflectors in Mare Serenitatis. The LRS is FM-CW radar (4–6 MHz) and the 2 MHz bandwidth leads to the range resolution of 75 m in a vacuum, whereas the sampling interval in the flight direction is about 75 m when an altitude of the spacecraft with polar orbit is nominal (100 km). Horizontally continuous reflectors were clearly detected by LRS in limited areas that consist of about 9% of the whole maria. The typical depth of the reflectors is estimated to be a few hundred meters. Layered structures of mare basalts are also discernible on some crater walls in the MI data of the visible bands (VIS). The VIS range has nine wavelengths of 415, 750, 900, 950, and 1000 nm, and their spatial resolution is 20 m/pixel at a nominal altitude. The stratigraphies around Bessel and Bessel-H craters in Mare Serenitatis are examined in this paper. It was revealed that the subsurface reflectors lie on the boundaries between basalt units with different chemical compositions. In addition, model calculations using the simplified radar equation indicate that the subsurface reflectors are not compositional interfaces but layer boundaries with a high-porosity contrast. These results suggest that the detected reflectors in Mare Serenitatis are regolith accumulated during so long hiatus of mare volcanisms enough for chemical composition of magma to change, not instantaneously. Therefore combination of the LRS and MI data has a potential to reveal characteristics of a series of magmatism forming each lithostratigraphic unit in Mare Serenitatis and other maria.     

Low altitude remote-sensing method to monitor marine and beach litter of various colors using a balloon equipped with a digital camera

This study aims to establish a low-altitude remote sensing system for surveying litter on a beach or the ocean using a remote-controlled digital camera suspended from a balloon filled with helium gas. The resultant images are processed to identify the litter using projective transformation method and color difference in the CIELUV color space. Low-altitude remote sensing experimental observations were conducted on two locations in Japan. Although the sizes of the litter and the areas covered are distorted in the original photographs taken at various angles and heights, the proposed image process system is capable of identifying object positions with a high degree of accuracy (1-3 m). Furthermore, the color difference approach in the CIELUV color space used in this study is well capable of extracting pixels of litter objects of various colors allowing us to estimate the number of objects from the photographs.     

Sedimentary Steryl Chlorin Esters (SCEs) and Other Photosynthetic Pigments as Indicators of Paleolimnological Change Over the Last 28,000 Years from the Buguldeika Saddle of Lake Baikal

Detailed depth profiles of photosynthetic pigments in a sediment core (G-12) collected at the BDP93 site, the Buguldeika saddle, of south Lake Baikal, along with depth profiles of total organic carbon (TOC) and biogenic silica, were studied to elucidate the temporal changes of phytoplankton assemblages in the lake during the past 28 kyr. In addition to the quantification of carotenoids by high-performance liquid chromatography with photodiode-array detection (HPLC-PDA), steryl chlorin esters (SCEs) were analyzed by HPLC-PDA, HPLC-mass spectrometry (LC-MS) and sterols in SCEs by gas chromatography–mass spectrometry (GC–MS) to enrich the taxonomical information on the phytoplankton composition. Allochthonous input of organic matter from the Selenga River resulted in the higher TOC contents in core G-12 than in a previously reported core (G-6) collected at another site from the southern basin. The poorer correlation in core G-12 than in G-6 between TOC and chlorophyll-a-originating pigments, which are indicative of autochthonous production, also indicated a significant allochthonous input at the site. The abundance of lutein among the carotenoids detected, and the good correlation of total chlorophyll a and b shows that green algae represented a significant portion of the phytoplankton, accompanying the diatoms at the G-12 site, after the last glacial period. The presence of cryptomonads and cyanobacteria were confirmed from marker carotenoids in the sediment core. GC–MS analysis of sterols in SCEs detected marker sterols of diatoms, green algae, chrysophytes and dinoflagellates. The depth profiles of the measured indicators gave consistent features for temporal changes in phytoplankton assemblage at the G-12 site of Lake Baikal after the last glacial maximum. Notably, the profile of a chrysophyte-specific sterol in SCEs was consistent with the reported distribution of chrysophyte cysts during the Holocene. The presence of phytoplankton, such as green algae, diatoms and chrysophytes, in Lake Baikal during the late last glacial period was indicated by the analysis of sterols in SCEs. Sedimentary carotenoids and sterols in SCEs were found to give complementary information about phytoplankton composition. These molecular indicators allow us to reconstruct past lake phytoplankton assemblages responding to environmental changes with a time resolution as high as age–depth relationship in sediments attainable at present.