Origin and decomposition of sinking particulate organic matter in the deep water column inferred from the vertical distributions of its δN, δ and δ

Sinking particles were analyzed for their nitrogen isotopic ratio δ¹⁵N) of total particulate nitrogen (PN), stable carbon isotopic ratio (δ¹³C) and radioactive isotopic ratio (δ¹⁴C) of total particulate organic carbon (POC), at three different latitudinal (temperate, subpolar and equatorial) and geomorphological (trench, proximal abyssal plain and distal abyssal plain) sites in the western North Pacific Ocean using year-long time series sediment trap systems, to clarify the common vertical trends of the isotopic signals in deep water columns. Although the δ¹⁵N and δ¹³C values of sinking particulate organic matter (POM) were partly affected by the resuspension of sedimentary POM from the sea floor, especially in the trench, the changes in δ¹⁵N and δ¹³C values owing to the resuspension could be corrected by calculation of the isotopic mass balance from δ¹⁴C of sinking POC. After this correction, common downward decreasing trends in δ¹⁵N and δ¹³C values were obtained in the deep water columns, irrespective of the latitudes and depths. These coincidental isotopic signals between δ¹⁵N and δ¹³C values provide new constraints for the decomposition process of sinking POM, such as the preferential degradation of ¹⁵N- and ¹³C-rich compounds and the successive re-formation of the sinking particles by higher trophic level organisms in the deep water column.     

Seiches in bays forming a coupled system

The seiches occurring in two adjacent bays, Koaziro Bay and Moroiso Bay, situated in Miura Peninsula at the mouth of Tokyo Bay, are very regular, and the phenomenon of beat appears in their amplitudes of oscillation. Nakano once presented a theoretical explanation of this phenomenon, considering two rectangular bays of the same size and form as well as of uniform depth, by assuming that a kind of coupling takes place between the two bays through a portion of water flowing across the mouth of each bay. In the present paper, the validity of the theory has been proved in a series of hydraulic model experiments. The experiments have shown that, in the case of the two adjacent rectangular bays mentioned above, there are two distinct modes of oscillation viz. (i) the co-phasic oscillation and (ii) the contra-phasic oscillation, and since the frequencies of these oscillations are close to each other, when they come to interfere, the beat phenomenon occurs.It has also been found that, when a tsunami wave enters the two bays, the mode of oscillation of the seiches occurring in them changes in the following manner: the co-phasic oscillation the oscillation accompanied with the beat phenomenon the contra-phasic oscillation. As regards this phenomenon, the authors have presented a possible explanation by considering the dissipation of energy due to wave scattering.     

Vertical transport of organic materials in the northern North Pacific as determined by sediment trap experiment

Sediment traps were deployed at 5 depths of 100 through 5,250 m to collect suspended sediments in the northern North Pacific (47°51.1'N; 176°20.6'E, 5,300 m deep) in the summer of 1978. Fatty acid composition was determined in the samples of phytoplankton, particulate matter, trap sediment and bottom sediment.Fatty acid composition of the trap sediments revealed no significant vertical trend throughout the water column from depths of 100 to 5,250 m, and were also similar to those of the phytoplankton and the particulate matter from the euphotic layer. However, a marked difference in the fatty acid composition was observed between the trap sediments and the particulate matter from deep waters. Therefore, it can be concluded that the source of fatty acids in the trap sediments is the particulate matter from the euphotic layer but not from deep waters.Unsaturated fatty acids highly susceptible to biological agents were rather abundant in the trap sediments as well as in the phytoplankton and particulate matter from the euphotic layer, however no unsaturated fatty acid was found in the particulate matter from deep waters. From these findings, it is clear that the particulate matter of the euphotic layer is transported to deep waters very rapidly. As the sinking rate of fecal pellets produced by zooplankton is in the range of ten to hundreds of meters a day, fecal pellets are assumed to be the most likely carrier of rapid-transport of organic matter including fatty acids from the euphotic layer to deep waters.     

Spatiotemporal Decreases of Nutrients and Chlorophyll-a in the Surface Mixed Layer of the Western North Pacific from 1971 to 2000

Using time series of hydrographic data in the wintertime and summertime obtained along 137°E from 1971 to 2000, we found that the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001∼0.004 μmol-PO₄ l⁻¹ yr⁻¹ and 0.01∼0.04 μmol-NO₃ l⁻¹ yr⁻¹ with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27∼0.48 mg-Chl m⁻² yr⁻¹ and 0.08∼0.47 g-C-NCP m⁻² yr⁻¹ with a clear oscillation of 20.8±0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation Index (PDO) with a time lag of 2 years (R = 0.89 ± 0.02). Considering the recent significant decrease of O₂ over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over the western North Pacific.     

Chemical studies on organic matter and carbon cycle in the ocean

Chemistry of organic materials of the suspended and sinking particles, and the evaluation of the particulate materials for the carbon cycle of the ocean are described in this paper. Organic carbon (POC) and nitrogen (PON) of the suspended particles collected from various areas of the North through South Pacific were determined with considerably high variabilities in their concentration. Higher values of the POC and PON were obtained in the surface water of the higher latitudinal areas of both northern and southern hemispheres and the equatorial Pacific, while the lower values of these organic elements were measured in the middle latitudinal areas of the Pacific. These facts clearly indicate that inorganic nutrients supply to the surface water layers from the underlying water is primarily determinative factor to govern the concentration of the POC and PON in the surface water layer. POC and PON concentrations in the intermediate through deep waters, however, are much less variable in time and space. Carbohydrates, free and combined amino acids and lipid materials were major organic constituents of the suspended particles. The organic composition of the particles was extensively variable in region, time and depth. Such change in the organic composition was mainly caused by the production and decay of the free and combined amino acids, lipid materials and water extractable carbohydrate. Sinking particle which has high sinking rate over 100 m day⁻¹ and can be collected only by sediment trap, also consists of carbohydrates, free and combined amino acids and lipid materials. A detailed analysis of the particle indicate that the sinking particle was much different from the suspended particle from the intermediate through deep waters in terms of the abundance of the biologically susceptible organic materials such as unsaturated hydrocarbon, fatty acid and water extractable carbohydrate often found in phytoplankton. These facts clearly indicate that the sinking particle plays an important role on the vertical transport of the biologically susceptible organic materials from the surface water to the deep water. Vertical flux of organic materials in various water depths was extensively measured in the North Pacific and Antarctic Ocean using the depth-series sediment trap system to collect the sinking particles from various depths of the waters. Regional and seasonal variabilities of the organic carbon flux at the various depths were obviously observed, however the attenuation rate of the organic carbon flux in the intermediate through deep water was not changed so much irrespective of the sampling time and region. The time-series sediment trap system was also using to determine the seasonal variation of the organic carbon flux. An average organic carbon flux at 1 km depth from this trap system was almost comparable to the amount of organic carbon degraded in the water deeper than 1 km depth, which was calculated from oxygen consumption rate of the deep water. Thus, it is clear that the sinking particle must play an important role in the carbon cycle of the deep water.     

The dust distribution in some smallHII regions

Based on the calibrated maps in the Hα andV bands, simple shell models for the distributions of ionized gas and dust are calculated for the smallHii regions S237 and S254–S257. In deriving the dust distribution from theV-band maps, it is assumed that scattering particles are made of dirty ice. The results of calculation show that a dust depletion zone should be placed in the central region of each of the observedHii regions. The formation of this dust depletion zone and the evolutionary state of theseHii regions are briefly discussed.     

Source mechanism of long-period events at Kusatsu–Shirane Volcano, Japan, inferred from waveform inversion of the effective excitation functions

We investigate the source mechanism of long-period (LP) events observed at Kusatsu–Shirane Volcano, Japan, based on waveform inversions of their effective excitation functions. The effective excitation function, which represents the apparent excitation observed at individual receivers, is estimated by applying an autoregressive filter to the LP waveform. Assuming a point source, we apply this method to seven LP events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1–3 Hz. The results of the waveform inversions show dominant volumetric change components accompanied by single force components, common to all the events analyzed, and suggesting a repeated activation of a sub-horizontal crack located 300 m beneath the summit crater lakes. Based on these results, we propose a model of the source process of LP seismicity, in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack. The rapid discharge of fluid causes the collapse of the fluid-filled crack and excites acoustic oscillations of the crack, which produce the characteristic waveforms observed in the LP events. The presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid-filled conduit linking the crack and the base of the crater lake.     

Geochemical Characteristics of the Akiyoshi Limestones, Japan and Their Bearing on Exploration for Blind Skarn Deposits

Abstract. Carboniferous-Permian limestones of the Akiyoshi Plateau, in the Inner Zone of southwestern Japan, are composed of essentially pure calcium carbonate containing only small amounts of other elements, and they are accompanied by marble and copper skarn deposits near the contact with late Cretaceous granitoids. The δ¹⁸O values of the Akiyoshi limestones range widely from 7.6 to 28.3% and are mostly lower than those of other areas of the same age (23–29%), whereas the differences among the δ¹³C values are small. The δ¹⁸O values are negatively correlated with Mn and Fe contents. Samples with high δ¹⁸O (>25%) and δ¹³C (>2%) values do not contain Fe, Zn, or Pb, but those with low δ¹⁸O values tend to be rich in these elements, indicating that these elements were introduced by interaction with H₂O dominant fluids, possibly of magmatic origin. Potential scores for evaluating the degree of interaction with hydro thermal fluids were calculated for δ¹⁸O, δ¹³C, Fe, Mn, Zn, Pb, and Sr. Higher scores implying much hydrothermal interaction were evident in the Mt. Hananoyama area, where there are many skarn deposits, and along faults oriented mainly NNW-SSE. Therefore, these are promising areas for exploring for blind deposits. It is likely that the hydrothermal fluid traveled through the limestones along fractures at the time of the granitic intrusions. However, the potential scores here are much smaller than those in the Pb-Zn mineralized area of the Kamioka mine, so more detailed petrological and mineralogical investigations are necessary.     

A dataset of continental river discharge based on JRA-55 for use in a global ocean circulation model

A dataset of historical river discharge into oceans was created using the CaMa-Flood global river routing model and adjusted runoff from the land component of JRA-55. The major rivers were well resolved with a 0.25° horizontal resolution. The total runoff on each drainage basin exhibits a distinctive bias on decadal time scales. The input runoff data were modified using 5-year low-pass-filtered multiplicative factors to fit the annual mean climatology and decadal variations in the reference dataset. The model incorporated data from 1958 to 2016. The yearly and seasonal variations of the major rivers are well represented by the model.