Box model analysis on phytoplankton production and grazing pressure in a eutrophic estuary

To determine the quantitative relationship between phytoplankton production and zooplankton grazing pressure in Atsumi Bay, a eutrophic and partially-mixed estuary, a series of investigations, including measurements of hydrographic conditions, dissolved oxygen, dissolved total nitrogen, particulate organic nitrogen, and phyto- and zooplankton biomass were conducted 13 times at intervals of 2–7 days in June and July 1984. Continuous measurements of water flow and salinity were also carried out to examine transverse flow and horizontal diffusivity. The supply of freshwater and nitrogen was estimated from given data. The changes of hydrographic condition, net photosynthetic rate and community primary production were calculated by a two-layered box model analysis. The grazing rate on phytoplankton obtained as the difference between net photosynthetic rate and community primary production was compared to the one estimated from zooplankton biomass and sardine,Sardinops melanosticta, biomass. The agreement between the data was remarkable in the upper layer, showing the grazing pressure on phytoplankton followed phytoplankton production, suggesting that a large part of produced phytoplankton was immediately grazed by zooplankton. Consequently, the community primary production was depressed to a fairly lower level. An important role of nutrient supply and water circulation, to limit phytoplankton production, was also confirmed. Dynamic response observed between the calculated grazing pressure and the biomass of phytoplankton and protozoa was also analyzed.     

Growth characteristics ofChattonella antiqua (Raphidophyceae)

Chattonella antiqua (Raphidophyceae), which causes heavy red tides in the Seto Inland Sea, Japan, was placed in axenic clonal culture by micropipette washing. The effects of temperature, salinity, light intensity and pH on growth were monitored. Maximum growth occurred at 25°C, at salinities between 25 and 41‰, under light intensities above 0.04 ly min^?1. The pH effect was not significant in the pH range from 7.6 to 8.3. Comparisons of our results with those from field observations suggest that the development of theC. antiqua red tide is strongly temperature dependent.     

The uranium content and the activity ratio234U/238U in marine organisms and sea water in the western North Pacific

The uranium content and activity ratio A²³⁴U/A²³⁸U were determined in open ocean water, marine plankton, marine algae and sea water in the environment in which plankton and algae live. The average uranium content of 3.34±0.28×10⁻⁶ g/l and the average activity ratio of 1.13±0.04 were obtained in open ocean water. The uranium contents in plankton and algae were respectively from 1.7 to 7.8×10⁻⁷ g/g and 0.4 to 23.5×10⁻⁷ g/g on dry basis with the respective concentration factors of 48 to 260 and 10 to 733. The activity ratio in plankton and algae ranged from 1.07 to 1.18 which coincided well with those in the environmental sea water.     

High-temperature compression experiments of CaSiO3 perovskite to lowermost mantle conditions and its thermal equation of state

In order to examine pressure–volume–temperature (P–V–T) relations for CaSiO₃ perovskite (Ca-perovskite), high-temperature compression experiments with in situ X-ray diffraction were performed in a laser-heated diamond anvil cell (DAC) to 127 GPa and 2,300 K. We also employed an external heating system in the DAC in order to obtain P–V data at a moderate temperature of 700 K up to 113 GPa, which is the reference temperature for constructing an equation of state. The P–V data at 700 K were fitted to the second-order Birch–Murnaghan equation of state, yielding K _700,1bar = 207 ± 4 GPa and V _700,1bar = 46.5 ± 0.1 Å³. Thermal pressure terms were evaluated in the framework of the Mie–Grüneisen–Debye model, yielding γ _700,1bar = 2.7 ± 0.3, q _700,1bar = 1.2 ± 0.8, and θ _700,1bar = 1,300 ± 500 K. A thermodynamic thermal pressure model was also employed, yielding α_700,1bar = 5.7 ± 0.5 × 10^?5/K and (?K/?T) _V  = ?0.010 ± 0.004 GPa/K. Computed densities along a lower mantle geotherm demonstrate that Ca-perovskite is denser than the surrounding lower mantle, suggesting that Ca-perovskite-rich rocks do not rise up through the lower mantle. One of such rocks might be a residue of partial melting of subducted mid-oceanic ridge basalt (MORB) at the base of the mantle. Since the partial melt is FeO-rich and therefore denser than the mantle, all the components of subducted MORB may not return to shallow levels.     

Phase transition in CaSiO3 perovskite

A phase transition in pure CaSiO₃ perovskite was investigated at 27 to 72 GPa and 300 to 819 K by in-situ X-ray diffraction experiments in an externally-heated diamond-anvil cell. The results show that CaSiO₃ perovskite takes a tetragonal form at 300 K and undergoes phase transition to a cubic structure above 490–580 K in a pressure range studied here. The transition boundary is strongly temperature-dependent with a slightly positive dT / dP slope of 1.1 (± 1.3) K/GPa. It is known that the transition temperature depends on Al₂O₃ content dissolved in CaSiO₃ perovskite [Kurashina et al., Phys. Earth Planet. Inter. 145 (2004) 67–74]. The phase transition in CaSiO₃(+ 3 wt.% Al₂O₃) perovskite therefore could occur in a cold subducted mid-oceanic ridge basalt (MORB) crust at about 1200 K in the upper- to mid-lower mantle. This phase transition is possibly ferroelastic-type and may cause large seismic anomalies in a wide depth range.     

Stabilities of NAL and Ca-ferrite-type phases on the join NaAlSiO<Subscript>4</Subscript>-MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> at high pressure

Stabilities of hexagonal new aluminous (NAL) phase and Ca-ferrite-type (CF) phase were investigated on the join NaAlSiO₄-MgAl₂O₄ in a pressure range from 23 to 58 GPa at approximately constant temperature of 1,850 K, on the basis of in situ synchrotron X-ray diffraction measurements in a laser-heated diamond-anvil cell. The results show that NAL is formed as a single phase up to 34 GPa, NAL + CF between 34 and 43 GPa, and only CF at higher pressures in 40%NaAlSiO₄-60%MgAl₂O₄ bulk composition. On the other hand, both NAL and CF coexist below 38 and 36 GPa, and only CF was obtained at higher pressures in 60%NaAlSiO₄-40%MgAl₂O₄ and 20%NaAlSiO₄-80%MgAl₂O₄ composition, respectively. These results indicate that NAL appears only up to 46 GPa at 1,850 K, and CF forms continuous solid solution at higher pressures on the join NaAlSiO₄-MgAl₂O₄. NAL has limited stability in subducted mid-oceanic ridge basalt crust in the Earth’s lower mantle and undergoes a phase transition to CF in deeper levels.     

Encystment ofChattonella antiqua in laboratory cultures

Cysts ofChattonella antiqua (Raphidophyceae) were obtained in laboratory cultures for the first time. They were formed on the surface of glass coverslips added to both P- and N- depleted mediums. The yield was 50–250 cysts cm^–2. Crossing experiments showed the highest cyst production in mixed cultures, although cysts were observed in clonal cultures as well. Cysts had approximately double the DNA content of synchronously growing vegetative cells (G₁ phase). The encystment process was also monitored: Under P-depleted conditions, small cells were formed that fused to become a triangle-shaped cell which in turn changed into a cyst.These results strongly suggest that cysts are the products of fusion and are diploid. Small cells, triangle-shaped cells, and cysts are considered to be gametes, planozygotes, and hypnozygotes, respectively. Significant mortality was observed in laboratory cysts stored in the cold and dark for five months, although those remaining were capable of germination to reestablish a motile, vegetative population.     

Thorium concentration and the activity ratios230Th/232Th and228Th/232Th in sea water in the western North Pacific

The concentration of thorium isotopes and the activity ratios of²³⁰Th/²³²Th and²²⁸Th/²³²Th in sea water collected in the Kuroshio region, the mixing area of Oyashio and Kuroshio, the Japan Sea and the East China Sea in the western North Pacific were determined. Thorium isotopes were analyzed by α-ray spectrometry after separating them with an anion exchange resin. The average content of thorium (²³²Th) of 2.2×10⁻⁹ g/l was obtained in the open Pacific waters. The ratio of²³⁰Th/²³²Th is in accord with that of the top layer of the sediment in the same area. The high values of²²⁸Th/²³²Th ratio up to 36 were observed in sea water. The excess²²⁸Th in sea water may be due to the migration of²²⁸Ra through the water-sediment interface. Thorium content in suspended matter was 10 to 20% of the total thorium content in the Pacific water.     

Chemical environment for red tides due toChattonella antiqua

Environmental parameters that affect the growth ofChattonella antiqua were monitored throughout the outbreak period of this species around the Ie-shima Islands, the Seto Inland Sea, in the summer of 1987 (20 July–13 August). Averaged cell concentration ofC. antiqua over the water column (21 m) was below 10 cells· ml^–1 on 20 July, gradually increased to reach the maximum of 250 cells·ml^–1 on 7 August, and then rapidly decreased to the value of 30 cells·ml^–1 on 13 August.Thermal stratifications were prominent from 20 July to 3 August and were destroyed after 4 August. Temperature and salinity were optimum for the growth ofC. antiqua throughout the survey period.At the bloom initiation period (20–21 July), concentrations of N- and P-nutrients (S _N andS _P ) were high throughout the water column. From 22 July to 3 August, whenC. antiqua increased its populations,S _N andS _P at the depth of 0–5m were low but those at the depth of 10–20m kept a high value. After 4 August,S _n andS _P at the depth of 10–20m decreased rapidly due to wind mixing coupled with the nutrient uptake byC. antiqua. When the populations ofC. antiqua reached the maximum (7–9 August), N-nutrients were depleted throughout the water column but P-nutrients were not. Concentrations of vitamin B₁₂ were almost in the same range as those of the previous years and were optimum for the growth ofC. antiqua.GP- value (growth potential of the seawater with respect to nitrogen and phos-phorus) was higher than 0.6 even at the surface layer (0–5 m) at the bloom-initiation period. During the bloom development period (22 July–3 August), GP at the surface layer (0–5m) was low (<0.2), but GP at the depth of 10–20m kept a rather high value (>0.4).In situ growth rates ofC. antiqua at the depth of 0 and 5m estimated from bottle experiments coincided well with the values expected from GP. A high value of GP at the surface layer in the initiation period and a shallow GP-cline in the development period, combined with the ability of diurnal vertical migration seemed to be at least one reason that natural populations ofC. antiqua grew at a rather high rate and formed red tides in the summer of 1987.     

Contributions of slab fluid and sediment melt components to magmatism in the Mariana Arc–Trough system: Evidence from geochemical compositions and Sr,Nd, and noble gas isotope systematics

This study presents new major and trace element, mineral, and Sr, Nd, and noble gas isotope geochemical analyses of basalts, gabbro, and clinopyroxenite from the Mariana Arc (Central Islands and Southern Seamount provinces) including the forearc, and the Mariana Trough (Central Graben and Spreading Ridge). Mantle source compositions beneath the Mariana Arc and the Mariana Trough indicate a mantle source that is depleted in high field strength elements relative to MORB (mid‐oceanic ridge basalt). Samples from the Mariana Arc, characterized by high ratios of Ba/Th, U/Th, ⁸⁴Kr/⁴He and ¹³²Xe/⁴He, are explained by addition of fluid from the subducted slab to the mantle wedge. Correlations of noble gas data, as well as large ion lithophile elements, indicate that heavy noble gases (Ar, Kr, and Xe) provide evidence for fluid fluxing into the mantle wedge. On the other hand, major elements and Sr, Nd, He, and Ne isotopic data of basalts from the Mariana Trough are geochemically indistinguishable from MORB. Correlations of ³He/⁴He and ⁴⁰Ar/³⁶Ar in the Mariana Trough samples are explained by mixing between MORB and atmosphere. One sample from the Central Graben indicates extreme enrichment in ²⁰Ne/²²Ne and ²¹Ne/²²Ne, suggesting incorporation of solar‐type Ne in the magma source. Excess ¹²⁹Xe is also observed in this sample suggesting primordial noble gases in the mantle source. The Mariana Trough basalts indicate that both fluid and sediment components contributed to the basalts, with slab‐derived fluids dominating beneath the Spreading Ridge, and that sediment melts, characterized by high La/Sm and relatively low U/Th and Zr/Nb, dominate in the source region of basalts from the Central Graben.