Effects of the copepod community structure on fecal pellet flux in Kagoshima bay,a deep,semi-enclosed embayment

Seasonal changes in the shape and size composition of fecal pellets were investigated with sediment trap samples from 50 and 150 m in Kagoshima Bay to evaluate how the mesozooplankton community affects fecal pellet flux. Deep vertical mixing was evident in March, and thermal stratification was developed above 50 m in June, August and November. Chlorophyll a, suspended particulate organic carbon (POC) and copepod abundance were uniform throughout the water column during the seasonal mixing and concentrated above 50 m in the stratified seasons. Calanoids were the most predominant copepods in March and poecilostomatoids composed more than 45% of the copepod community in June, August and November. Fecal pellet fluxes at 50 and 150 m were the highest in March, nearly half of POC flux. The relative contribution declined considerably in the other months, especially for less than 4% of POC flux in August. The decline was corresponded to the predominance of cyclopoids and poecilostomatoids. Cylindrical pellets dominated the fecal matters at both depths throughout the study period, while larger cylindrical pellets nearly disappeared at 150 m in June, August and November. Copepod incubation revealed that cylindrical and oval pellets were egested by calanoids and the other copepods, respectively. We suggest that cylindrical fecal pellets produced by calanoid copepods contribute to feces flux but the predominance of poecilostomatoids and/or cyclopoids decreases feces flux via the increase of oval pellets and fragmentation of larger cylindrical pellets.     

A simple and robust procedure for coring unconsolidated sediment in shallow water

This article describes a simple, quick, and inexpensive procedure for coring unconsolidated sediment in shallow water (<30 m from water surface). A ∼1 m core is retrieved by a PVC pipe that penetrates sediment in response to the percussive force of a hand-operated hammering tool or air hammer. After retrieving the first core segment, a casing is inserted to allow access to deeper sediment layers. Pulverized sediment produced during coring is removed by a water-lubrication system that is powered by an electric pump attached to a generator. Using this system and procedure, five 2-m-long cores with excellent quality were retrieved.     

Vertical profiles of nitrous oxide and dissolved oxygen in marine sediments

The whole core squeezing method was used to simultaneously obtain profiles of nitrous oxide (N₂O), nitrogenous nutrients, and dissolved oxygen in sediments of Koaziro Bay, Japan (coastal water), the East China Sea (marginal sea), and the central Pacific Ocean (open ocean). In the spring of Koaziro Bay, subsurface peaks of interstitial N₂O (0.5–3.5 cm depth) were observed, at which concentrations were higher than in the overlying water. This was also true for nitrate (NO₃⁻) and nitrite (NO₂⁻) profiles, suggesting that the transport of oxic overlying water to the depth through faunal burrows induced in situ N₂O production depending on nitrification. In the summer of Koaziro Bay, sediment concentrations of N₂O, NO₃⁻ and NO₂⁻ were lower than in the overlying water. In most East China Sea sediments, both N₂O and NO₃⁻ decreased sharply in the top 0.5–2 cm oxic layer (oxygen: 15–130 μM), which may have indicated N₂O and NO₃⁻ consumption by denitrification at anoxic microsites. N₂O peaks at subsurface depth (0.5–6.5 cm) implied in situ production of N₂O and/or its supply from the overlying water through faunal burrows. However, the occurrence of the latter process was not confirmed by the profiles of other constituents. In the central Pacific Ocean, the accumulation of N₂O and NO₃⁻ in the sediments likely resulted from nitrification. Nitrous oxide fluxes from the sediments, calculated using its gradient at the sediment–water interface and the molecular diffusion coefficient, were −45 to 6.9 nmolN m⁻² h⁻¹ in Koaziro Bay in the spring, −29 to −21 nmolN m⁻² h⁻¹ in the summer, −46 to 37 nmolN m⁻² h⁻¹ in the East China Sea, 0.17 to 0.23 nmolN m⁻² h⁻¹ in the equatorial Pacific, and <±0.2 nmolN m⁻² h⁻¹ in the subtropical North Pacific, respectively.     

An interpretation of the decay characteristics of solar hard X-ray bursts

A simple trap model of solar hard X-ray bursts is discussed in which nonthermal electrons trapped in a magnetic bottle precipitate into the lower chromosphere through the resonant scattering by whistlers. In such a model, the X-ray spectra produced from trapped and precipitating electrons have different spectral shape, and both of the spectra will initially soften with time, provided the precipitation dominates over collisional degradation.     

The system iron-enstatite-water at high pressures and temperatures—formation of iron hydride and some geophysical implications

The system iron-enstatite-water was investigated at pressures around 5 GPa and at temperatures ranging from 1000 to 1200°C, using several different kinds of starting materials. Quenched samples showed the coexistence of iron, olivine and pyroxene. Synthesis of the Fe-containing olivine in the run products proves that a series of reactions, Fe + H₂O → FeH_x + FeO and FeO + MgSiO₃ → (Mg, Fe)₂SiO₄, have taken place. Spherical “balls of iron” were observed in the 1200°C run. This strongly indicates that the melting temperature of iron decreased by ～ 500 K by the possible dissolution of hydrogen. Following geophysical implications are derived from these experimental results. If water was retained in the hydrous minerals in the primordial material, the iron-water reaction is expected to occur throughout the core-formation process. The reaction product FeH_x will melt and then sink to form a proto-core and iron oxide will be dissolved in the Earth's mantle. The dissolution of hydrogen in the Earth's core is a natural consequence of the core-formation process.     

Altitude variation of ultraviolet oxygen night airglow

Night airglow of oxygen 130.4 and 135.6 nm emissions was measured by a spectrophotometer aborad an S520 sounding rocket, launched at 19:50 JST (10:50 UT) on 14 February, 1982 from Kagoshima, Japan. The altitude variation of the emissions was obtained from 110 to 266 km at zenith angles of 35.5°±4°. The emission intensity around 260 km was about 160R and is roughly compatible with model calculations taking account of O⁺+e ^– radiative recombination as well as O⁺–O^– mutual neutralization. Some excess of about 50R, compared to the model calculation, was observed around 200 km. Possible explanations of the excess are: (i) remnant oxygen ions during the transition period from day to night and (ii) diffuse radiation from the background sky. Model calculations taking account of remnant oxygen ions were also performed by adding an excess electron density to the original density profile. However, it was found that an unreasonably large electron density is required around 200 km (5×10⁵ cm^–3) to produce the observed intensity. It is also probable that some contribution from the background sky is present in the observed intensity.     

Formation of intermediate-mass black holes as primordial black holes in the inflationary cosmology with running spectral index

Formation of primordial black holes (PBHs) on astrophysical mass scales is a natural consequence of inflationary cosmology, if the primordial perturbation spectrum has a large and negative running of the spectral index as observationally suggested today because double inflation is required to explain it and fluctuations on some astrophysical scales are enhanced in the field-oscillation regime in between. It is argued that PBHs thus produced can serve as intermediate-mass black holes (IMBHs), which act as the observed ultraluminous X-ray sources (ULXs) by choosing appropriate values of the model parameters in their natural ranges. Our scenario can be observationally tested in near future because the mass of PBHs is uniquely determined once we specify the values of the amplitude of the curvature perturbation, spectral index and its running on large scales.     

Variations in sediment thickness and type along the northern Philippine Sea Plate at the Nankai Trough

Abstract   We documented regional and local variations in basement relief, sediment thickness, and sediment type in the Shikoku Basin, northern Philippine Sea Plate, which is subducting at the Nankai Trough. Seismic reflection data, tied with ocean drilling program drill cores, reveal that variations in the incoming sediment sequences are correlated with basement topography. We mapped the three-dimensional seismic facies distribution and measured representative seismic sequences and units. Trench-parallel seismic profiles show three regional provinces in the Shikoku Basin that are distinguished by the magnitude of basement relief and sediment thickness: Western (<200–400 m basement relief, >600 m sediment thickness), Central (>1500 m relief, ∼2000 m sediments), and Eastern (<600 m relief, ∼1200 m sediments) provinces. The total thickness of sediment in basement lows is as much as six times greater than that over basement highs. Turbidite sedimentation in the Shikoku Basin reflects basement control on deposition, leading to the local presence or absence of turbidite units deposited during the middle Oligocene to the middle Miocene. During the first phase of sedimentation, most basement lows were filled with turbidites, resulting in smooth seafloor morphology that does not reflect basement relief. A second phase of turbidite deposition in the Eastern Province was accompanied by significant amounts of hemipelagic sediments interbedded with turbidite layers compared to the other provinces because of its close proximity to the Izu–Bonin Island Arc. Both regional and local variations in basement topography and sediment thickness/type have caused lateral heterogeneities on the underthrusting plate that will, in turn, influence lateral fluid flow along the Nankai accretionary prism.