Nutrient regeneration at bottom after a massive spring bloom in a subarctic coastal environment,Funka Bay,Japan

Nutrient regeneration and oxygen consumption after a spring bloom in Funka Bay were studied on monthly survey cruises from February to November 1998 and from March to December 1999. A high concentration of ammonium (more than 4 μmol l⁻¹) was observed near the bottom (80–90 m) after April. Phosphate and silicate gradually accumulated and dissolved oxygen decreased in the same layer. Salinity near the bottom did not change until summer, leading to the presumption that the system in this layer is semi-closed, so regenerated nutrients were preserved until September. Nitrification due to the oxidation of ammonium to nitrate was observed after June. Nitrite, an intermediate product, was detected at 4–7 μmol L⁻¹ in June and July 1999. Assuming that decomposition is a first order reaction, the rate constant for decomposition of organic nitrogen was determined to be 0.014 and 0.008 d⁻¹ in 1998 and 1999, respectively. The ammonium oxidation rate increased rapidly when the ambient ammonium concentration exceeded 5 μmol L⁻¹. We also performed a budget calculation for the regeneration process. The total amount of N regenerated in the whole water column was 287.4 mmol N m⁻² in 4 months, which is equal to 22.8 gC m⁻², assuming the Redfield C to N ratio. This is 34% of the primary production during the spring bloom and is comparable to the export production of 25 gC m⁻² measured by a sediment trap at 60 m (Miyake et al., 1998).     

Fluctuation in proteinaceous labile organic matter verified with degradation rate constants of terrestrial biochemical indicators

Biogenic amino acids, taken as representative of organic matter, were analyzed to determine the apparent degradation rate constant in boreal terrestrial sediment. Age determination using ¹⁴C dating gave two rate constants: the initial degradation rate constant for glycine (k_{GLY 1}), the simplest amino acid, was 1.5 × 10⁻³ yr⁻¹ (r = 0.97) until about 2200 yr BP. After the inflection point, the rate constant k_{GLY 2} was 9.1 × 10⁻⁵ yr⁻¹ (r = 0.73). The degradation of amino acids in the labile organic matter in the sediment was markedly affected by rapid processes. After the inflection point, the rate constant profiles for sub-surface amino acids were shown to have discontinuous relationships with sediment age. One pattern which emerged in the vertical distribution is that the biogenic amino acid degradation rate constant k was far greater in the labile organic matter phase than that in the refractory organic matter over the past 10,000 years.     

Assessing flood disaster impacts in agriculture under climate change in the river basins of Southeast Asia

Natural Hazards - This study focused on flood damage assessment for future floods under the impact of climate change. Four river basins of Southeast Asia were selected for the study. They included...     

Behavior of Cu, Ni and Cd during nutrient depletion in a spring bloom in Funka Bay

The concentrations of Cu, Ni and Cd were determined in Funka Bay during a spring phytoplankton bloom, consisting of diatoms. Just after the bloom, both dissolved Cd and nutrients were removed in the euphotic zone. However, the removal ratio of Cd to phosphate was very different from that in seawater. The removal of Cd took place at a Cd/phosphate ratio of 0.07×10⁻³, which was lower than in seawater before the bloom (0.25×10⁻³), leading to an increase in this ratio in seawater exceeding 0.7×10⁻³ at the end of the bloom. Elevated concentrations of Cd and phosphate were observed in the deeper layer after the bloom due to the decomposition of detrital materials produced in the bloom. The ratio of Cd/phosphate in the regeneration step was 0.24×10⁻³ which was different from the removal ratio of 0.07×10⁻³. These observations suggest that the high Cd/phosphate ratio in the regeneration would reflect a relatively high regeneration rate of Cd than that of phosphate. No significant decrease in Cu and Ni concentrations was observed during the development of the bloom, suggesting that biological removal of these metals was not so significant during the spring bloom. The concentrations of Cd, Cu and silicate in surface waters increased after the bloom with decreasing salinity due to the influence of a spring thaw.     

Sound velocities of Na0.4Mg0.6Al1.6Si0.4O4 NAL and CF phases to 73 GPa determined by Brillouin scattering method

The sound velocities of two aluminum-rich phases in the lower mantle, hexagonal new Al-rich phase (NAL) and its corresponding high-pressure polymorph orthorhombic Ca-ferrite-type phase (CF), were determined with the Brillouin scattering method in a pressure range from 9 to 73 GPa at room temperature. Both NAL and CF samples have identical chemical composition of Na_0.4Mg_0.6Al_1.6Si_0.4O₄ (40 % NaAlSiO₄–60 % MgAl₂O₄). Infrared laser annealing in the diamond anvil cell was performed to minimize the stress state of the sample and obtain the high-quality Brillouin spectra. The results show shear modulus at zero pressure G ₀ = 121.960 ± 0.087 GPa and its pressure derivative G’ = 1.961 ± 0.009 for the NAL phase, and G ₀ = 129.653 ± 0.059 GPa and G’ = 2.340 ± 0.004 for the CF phase. The zero-pressure shear velocities of the NAL and CF phases are obtained to be 5.601 ± 0.005 km/sec and 5.741 ± 0.001 km/sec, respectively. We also found that shear velocity increases by 2.5 % upon phase transition from NAL to CF at around 40 GPa.     

Geochemical modelling of basalts from DSDP Leg 65, East Pacific Rise,Gulf of California

Major and rare earth element (REE) data for basalts from Holes 483, 483B, and 485A of DSDP Leg 65, East Pacific Rise, mouth of the Gulf of California, support a simple fractional crystallization model for the genesis of rocks from this suite. The petrography and mineral chemistry (presented in detail elsewhere) provide no evidence for magma mixing, but rather a simple multistage cooling process. Based on its lowest TiO₂ content (0.88%), $\text{FeO}{}^1\text{MgO}$ ratio (0.95 with total Fe as FeO), and Mg# (100 $\text{Mg}\text{Mg + Fe}\text{″ = 70}$), sample 483-17-2-(78–83) has been selected as the most primitive primary magma of the samples analyzed. This is supported by the REE data which show this sample has the lowest total REE content, a $\text{La}\text{Sm}{}_{\mathrm{cn}}$ (chondrite-normalized) = 0.36, and $\text{Eu}\text{Sm}{}_{\mathrm{cn}}$ = 1.05. Because other samples analyzed have higher SiO₂, lower Mg#, and a negative Eu anomaly ($\text{Eu}\text{Sm}{}_{\mathrm{cn}}$ as low as 0.89), they are most likely derivative magmas. Wright-Doherty and trace element modelling support fractional crystallization of 14.1% plagioclase (An₈₈), 6.7% olivine (Fo₈₆), and 4.7% clinopyroxene (Wo₄₁En₄₉Fs₁₀) from 483-17-2-(78–83) to form the least differentiated sample with Mg# = 63. The $\text{La}\text{Sm}{}_{\mathrm{cn}}$ of this derivative magma is almost identical to the parent magma (0.35 to 0.36), but the other samples have higher $\text{La}\text{Sm}{}_{\mathrm{cn}}$ (0.45 to 0.51), more total REE, and lower Mg# (60 to 56). Both Wright-Doherty and trace element modelling indicate that the primary magma chosen cannot produce these more evolved samples. For the major elements, the TiO₂ and P₂O₅ are too low in the calculated versus the observed (1.38 to 1.90; 0.11 to 0.17, respectively, for example). Rayleigh fractionation calculates a lower $\text{La}\text{Sm}{}_{\mathrm{cn}}$ and requires about 60% crystal removal versus 40% for the Wright-Doherty. These more evolved samples must be derived from a parent magma different from the one selected here and, unfortunately, not sampled in this study. A magma formed by a smaller degree of partial melting with slightly more residual clinopyroxene left in the mantle than for sample 483-17-2-(78–83) is required.     

The isotopic composition of strontium in Central American ignimbrites

Voluminous sheets of rhyolitic ignimbrites were crupted during Miocene time in a region of Central America that is underlain by a thick sequence of middle Paleozoic and older metamorphic and plutonic rocks. Strontium isotopic ratios of fifteen ignimbrites range from 0.7035 to as high as 0.7175. These values are markedly higher than those measured for cale-alkaline lavas of the same province, but overlap the range found in basement rocks that may have served as source rocks for anateetic magmas. This relationship is in contrast to that found in the western United States where siliceous ignimbrites are not significantly richer in radiogenic strontium than are the basalt erupted through the same basement series. Several possible models for the origin of the large volumes of siliceous magma are examined in terms of major-element and isotopic relations, experimental studies of phase relations, and the thermal requirements of melting or assimilating basement rocks. A mathematical model for the effects of assimilation in open and closed systems permits a comparison of predicted chemical and isotopic compositions with those observed and places limits on the plausibility of various schemes of contamination with or without concurrent crystal fractionation. None of the models is without its flaws. Recent suggestions that large volumes of siliceous magma may be derived from the mantle or lower crust explain certain aspects of the Central American ignimbrites very well if one postulates that the high strontium ratios resulted from contamination of the magma with radiogenic strontium released by the break-down of mieas in basement rocks through which the magmas rose. Such a model fails to explain the apparent restriction of large rhyolitic ignimbrite cruptions to areas underlain by thick continental crust.     

Xenoliths in recent basaltic andesite flows from Arenal Volcano,Costa Rica: inference on the composition of the lower crust

Basaltic andesite flows erupted between 1973 and 1980 from Arenal Volcano contain abundant inclusions of anorthosite, olivine gabbro, and pyroxenites, and megacrysts of olivine and anorthite. The anorthosites with large (20 mm) anorthite grains (An_96-92) exhibit deformation twinning and granulation between grain boundaries. Some olivine gabbros have angular clasts of anorthite with bent twins, pyroxene, and olivine in a finer-grained matrix which is distinctly foliated. These textural features suggest that these inclusions were deformed. An exotic (xenolithic) origin is supported in part by the mineral compositions and the estimated temperatures of equilibration: a temperature of about 975° C is obtained by two-pyroxene and Fe-Ti oxide geothermometers for the gabbros, but two-pyroxene temperatures are higher (1064 to 1120° C) for the basaltic andesite host. The olivine gabbro is thought to have crystallized at a pressure between 8.5 and 9.5 kb; whereas the lava phenocrysts crystallized at a much lower pressure of less than 5 kb. These xenoliths probably represent fragments of the lower crust below Arenal volcano. The lava flows show evidence for some contamination especially from fragments of anorthite broken apart from the larger megacrysts and xenoliths. A few phenocrysts of plagioclase in the lava samples have deformation twins. The unusually high Al₂O₃ content (19.4 to 23.2 wt%) of the lava samples can be attributed directly to the addition of anorthite; in fact the observed chemical variation in the lava flows (the increasing alumina and lime contents with decreasing silica) can be explained by this contamination.     

A Study Of The Atmospheric Boundary Layer Using Radon And Air Pollutants As Tracers

Concentrations of radon ²²²Rn andair pollutants, meteorological parametersnear the surface and vertical profiles of meteorological elements were measured atUchio (Okayama City, Okayama Prefecture, Japan) 12 km north from the coast ofthe Inland Sea of Japan. In the nighttime, the ²²²Rn concentration increased in the case of weak winds, but did not increase as much in the case of moderate or strong winds, as had been expected. In the daytime, the ²²²Rn concentrationheld at a slightly higher than average level for the period from sunrise to about 1100 JST. It is considered that this phenomenon is due to a period of morning calm, that is, a transition period from land breeze to sea breeze.NO, which is sensitive to traffic volume,brought information concerning advection.Oxidant concentrations,which reflect the availability of sunlight,acted in the reverse manner to ²²²Rnconcentrations. Thus, a set of ²²²Rn and air pollutants could provide useful information regarding the local conditions of the atmospheric boundary layer.