Sensitivity of CFCs and Anthropogenic CO2 Uptake in a North Pacific GCM to Mixing Parameterization and Surface Forcing

Distributions and characteristics of water mass and chlorofluorocarbons (CFCs) in the North Pacific are investigated by using a General Circulation Model (GCM). The anthropogenic CO₂ uptake by the ocean is estimated with velocity fields derived from the GCM experiments. The sensitivity of the uptake to different diffusion parameterizations and different surface forcing used in the GCM is investigated by conducting the three GCM experiments; the diffusive processes are parameterized by horizontal and vertical eddy diffusion which is used in many previous models (RUN1), parameterized by isopycnal diffusion (RUN2), and isopycnal diffusion and perpetual winter forcing for surface temperature and salinity (RUN3). Realistic features for water masses and CFCs can be simulated by the isopycnal diffusion models. The horizontal and vertical diffusion model fails to simulate the salinity minimum and realistic penetration of CFCs into the ocean. The depth of the salinity minimum layer is better simulated under the winter forcing. The results suggest that both isopycnal parameterization and winter forcing are crucial for the model water masses and CFCs simulations. The oceanic uptake of anthropogenic CO₂ in RUN3 is about 19.8 GtC in 1990, which is larger by about 10% than that in RUN1 with horizontal and vertical diffusive parameterization. RUN3 well simulates the realistic water mass structure of the intermediate layer considered as a candidate of oceanic sink for anthropogenic CO₂. The results suggest that the previous models with horizontal and vertical diffusive parameterization may give the oceanic uptake of anthropogenic CO₂ underestimated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Discovery of an ancient tsunami deposit in coastal sequences of southwest Japan: Verification of a large historic tsunami

Abstract A tsunamigenic sand layer is present in coastal sequences of the Masuda Plain, southwest Japan. The radiometric age of the layer has been estimated at 930 ± 80 years BP. It is proposed that the deposit is the product of a large historic tsunami believed to have occurred in the Japan Sea on 16 June 1026 AD.     

Hydrothermal carbonates in altered wall rocks at the Uwamuki Kuroko deposits, Japan

Magnesite, siderite and dolomite are characteristic alteration minerals occurring in Miocene hanging wall rocks of dacitic composition which host the Kuroko orebodies. These carbonates generally occur in a more stratigraphically upper horizon than chlorite alteration zone surrounding the orebodies. The Mg/(Mg+Fe) ratios of the carbonates decrease from the central alteration zone to marginal zone. The Mg/(Mg+Fe) ratios of carbonates and chlorite positively correlate. The δ¹⁸O and δ¹³C values of magnesite, siderite and dolomite positively correlate with each other and lie between the igneous and marine carbonate values. The petrographic, isotopic and fluid inclusion characteristics and thermochemical modelling calculations indicate that magnesite and dolomite formed in the central zone close to the orebodies due to the interaction of hydrothermal solutions with the biogenic marine carbonates. Calcite formed further from the orebodies from hydrothermal fluids which did not contain a biogenic marine carbon component. The compositional and textural relationships indicate that superimposed alterations (chlorite alteration and carbonate alteration) occurred in hanging wall rocks. The mode of occurrences and the Mg/(Mg+Fe) ratios of magnesite and dolomite occurring in hanging wallrocks are useful in the exploration for concealed volcanogenic massive sulfide-sulfate deposits. Received: 9 September 1997 / Accepted: 23 September 1997     

The detectability of shallow slow earthquakes by the Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET) in Tonankai district,Japan

In order to understand the characteristics of shallow very low-frequency (VLF) events as revealed by recent ocean-floor observation studies, we perform a trial simulation of earthquake cycles in the Tonankai district by taking the characteristics of the 1944 Tonankai earthquake and assuming that slow earthquakes occur on numerous small asperities. Our simulation results show that the increase of moment release rate of shallower VLF events in the pre-seismic stage of a megathrust earthquake is higher than that of deeper VLF events. This increase may make leveling change due to VLF swarms detectable at Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET). We also introduce the time series of hydraulic pressure data at DONET, comparing with the leveling change expected from our numerical simulation. Since leveling change due to shallower VLF swarms is so local as to be incoherent, removal of the moving-averaged data from the data stacked by four nearby observation points in the same node may be useful to detect the short-term local leveling change.     

Strength Anisotropy of Compacted Decomposed Granite Soils

In order to investigate the strength and deformation anisotropy of compacted decomposed granite soils, a series of drained triaxial compression tests was performed on unsaturated and saturated decomposed granite soils. The specimens were subjected to compression tests such that the angle δ of the direction of the major principal stress, σ ₁, during triaxial compression relative to the compaction plane (bedding plane) varies, with δ = 0°, 45° and 90°. Test results indicated that the compressive strain of the specimens subjected to isotropic consolidation was influenced strongly by the angle δ. In addition, the effect of the angle δ on the triaxial compressive strength and deformation was more evident in unsaturated specimens than in saturated specimens. Based on the test results, a procedure which can be used to estimate the shear strength of unsaturated soils taking into account various angles δ was proposed.