Large-scale hydraulic conductivity distribution in an unconfined carbonate aquifer using the ocean tidal propagation

The hydraulic conductivity of an unconfined carbonate aquifer at the uplifted atoll of Minami-Daito, Japan, was evaluated by a combination of cross-spectral analysis, analytical solution, and density-dependent groundwater modeling based on observed groundwater levels in 15 wells and at sea level. The island area was divided into 10 subregions based on island morphology and on inland propagation of ocean tides. The hydraulic conductivity was obtained for each subregion using analytical solutions based on phase lags of M₂ constituents of ocean tides at each well by assuming two aquifer thicknesses (300 and 1,800 m) and two effective porosities (0.1 and 0.3). The density-dependent groundwater model evaluated the hydraulic conductivity of the subregions by reproducing observed groundwater levels. The hydraulic conductivity in the subregions was estimated as 3.46?×?10^?3 to 6.35?×?10^?2 m/s for aquifer thickness of 300 m and effective porosity of 0.1, and as 1.73?×?10^?3 to 3.17?×?10^?2 m/s for aquifer thickness of 1,800 m and the effective porosity of 0.3. It was higher in southern and northern areas, and higher in interior lowland than in the western and eastern areas. Fissures and dolomite distributions on the island control differences of the omnidirectional ocean tidal propagation and cause these differences in hydraulic conductivity. The method used for this study may also be applicable to other small islands that have few or no data for hydraulic conductivity.

     

Conceptual model of the evolution of groundwater quality at the wet zone in Sri Lanka

 The evolution of groundwater quality at a wet zone in Sri Lanka was made clear using field investigation, chemical and isotopic analyses methods. In the wet zone, the concentrations of major ions and electrical conductivity (EC) in the groundwater are low with small seasonal change. Except for sodium, silica and chloride, the EC and other major ion concentrations increase along the groundwater flow direction. The contributions of bicarbonate and calcium ions to the increase in EC are the largest among the major ions. The groundwater quality shows calcium-bicarbonate type, the initial stage of the Chebotarev series. There is a seasonal change in isotopic composition. The isotopically lighter groundwater was found at the valley bottom in the rainy season. Under the very heavy precipitation conditions, the slope of the regression line between δD and δ¹⁸O and deuterium excess for groundwater are close to 8 and 10, respectively. In other cases, the slopes of the regression lines and deuterium excess are, less than 8 and 10, respectively. Received: 5 August 1998 · Accepted: 19 October 1998     

Research and development of the New Generation Sea Surface Temperature for Open Ccean (NGSST-O) product and its demonstration operation

Real-time generation and distribution of the New Generation Sea Surface Temperature for Open Ocean (NGSST-O) product began in September 2003 as a demonstration operation of the Global Ocean Data Assimilation Experiment (GODAE) High-Resolution Sea Surface Temperature Pilot Project. Satellite sea surface temperature (SST) observations from infrared radiometers (AVHRR, MODIS) and a microwave radiometer (AMSR-E) are objectively merged to generate the NGSST-O product, which is a quality-controlled, cloud-free, high-spatial-resolution (0.05° gridded), wide-coverage (13–63° N, 116–166° E), daily SST digital map. The NGSST-O demonstration operation system has been developed in cooperation with the Japanese Space Agency (JAXA) and has produced six years of continuous data without gaps. Comparison to in situ SSTs measured by drifting buoys indicates that the root mean-square error of NGSST-O has been kept at approximately 0.9°C.     

Modeling seasonal variations of ocean and sea ice circulation in the Beaufort and Chukchi Seas： A model-data fusion study

A 3.8-kin Coupled Ice-Ocean Model （C1OM） was implemented to successfully reproduce many observed phenomena in the Beaufort and Chukchi seas, including the Bering-inflow-originated coastal current that splits into three branches： Alaska Coastal Water （ACW） , Central Channel, and Herald Valley branches. Other modeled phenomena include the Beaufort Slope Current （BSC） , the Beaufort Gyre, the East Siberian Current （ ESC）, mesoscale eddies, seasonal landfast ice, sea ice ridging, shear, and deformation. Many of these downscaling processes can only be captured by using a high-resolution CIOM, nested in a global climate model. The seasonal cycles for sea ice concentration, thickness, velocity, and other variables are well reproduced with Solid validation by satellite measurements. The seasonal cycles for upper ocean dynamics and thermodynamics are also well reproduced, which include the formation of the cold saline layer due to the injection of salt during sea ice formation, the BSC, and the subsurface upwelling in winter that brings up warm, even more saline Atlantic Water along the shelfbreak and shelf along the Beaufort coast.     

Crustal deformations associated with volcanic activities

Two models of pressure source to interpret the crustal deformations associated with volcanic activities are discussed by example. It is pointed that the magma pressure causing the crust to be deformed may sometimes trigger remarkable tectonic earthquakes around volcanoes.     

Clay Minerals in an Active Hydrothermal Field at Iheya‐North‐Knoll,Okinawa Trough

Iheya‐North‐Knoll is one of the small knolls covered with thick sediments in the Okinawa Trough back‐arc basin. At the east slope of Iheya‐North‐Knoll, nine hydrothermal vents with sulfide mounds are present. The Integrated Ocean Drilling Program (IODP) Expedition 331 studied Iheya‐North‐Knoll in September 2010. The expedition provided us with the opportunity to study clay minerals in deep sediments in Iheya‐North‐Knoll. To reveal characteristics of clay minerals in the deep sediments, samples from the drilling cores at three sites close to the most active hydrothermal vent were analyzed by X‐ray diffraction, scanning electron microscope and transmission electron microscope. The sediments are classified into Layer 0 (shallow), Layer 1 (deep), Layer 2 (deeper) and Layer 3 (deepest) on the basis of the assemblage of clay minerals. Layer 0 contains no clay minerals. Layer 1 contains smectite, kaolinite and illite/smectite mixed‐layer mineral. Layer 2 contains chlorite, corrensite and chlorite/smectite mixed‐layer mineral. Layer 3 is grouped into three sub‐layers, 3A, 3B and 3C; Sub‐layer 3A contains chlorite and illite/smectite mixed‐layer mineral, sub‐layer 3B contains chlorite/smectite and illite/smectite mixed‐layer minerals, and sub‐layer 3C contains chlorite and illite. Large amounts of di‐octahedral clay minerals such as smectite, kaolinite, illite and illite/smectite mixed‐layer mineral are found in Iheya‐North‐Knoll, which is rarely observed in hydrothermal fields in mid‐ocean ridges. Tri‐octahedral clay minerals such as chlorite, corrensite and chlorite/smectite mixed‐layer mineral in Iheya‐North‐Knoll have low Fe/(Fe + Mg) ratios compared with those in mid‐ocean ridges. In conclusion, the characteristics of clay minerals in Iheya‐North‐Knoll differ from those in mid‐ocean ridges; di‐octahedral clay minerals and Fe‐poor tri‐octahedral clay minerals occur in Iheya‐North‐Knoll but not in mid‐ocean ridges.     

Stable isotopes in precipitation in the volcanic island of Cheju,Korea

Stable isotopes in precipitation sampled at different locations and altitudes over the volcanic island of Cheju, Korea, were analysed to elucidate the circulation patterns of water over the island where groundwater is a major water resource and the characteristics of stable isotopes in precipitation inputs to the hydrological cycle are a very important indicator of groundwater flow. Areal and altitudinal variation of stable isotopes in precipitation showed the contribution of different air masses to the precipitation on mountain slope areas and in the atmosphere above and below the boundary at around 1000 m a.s.l. Seasonal change of the isotopic composition of precipitation also gave a good illustration of the influence of the dominant regional air currents on precipitation inputs. Copyright © 1999 John Wiley & Sons, Ltd.     

Estimation of heat flux through the eastern Bering Strait

We estimated the northward heat flux through the eastern channel of the Bering Strait during the ice-free seasons between 1999 and 2008. This is likely about half of the total heat flux through the strait. The net volume transport and heat flux through the eastern channel of the strait were estimated from multiple linear regression models with in-situ/satellite remotely sensed datasets and NCEP reanalysis 10 m wind. The net volume transport was well explained by the west-east slope of sea level anomaly and NNW wind component at the strait. On the heat flux, the contributions of both barotropic and baroclinic components were taken into account. Estimated volume transport and vertical profile of temperature were used to calculate northward heat flux through the eastern channel of the strait. The magnitude of the estimated heat flux is comparable to estimates from in-situ measurements. Averaged heat flux in the eastern Bering Strait between 2004 and 2007 was about 1.9 times larger than that between 2000 and 2003. Maximum heat flux occurred in 2004, and same magnitude of heat flux was estimated from 2005 to 2007. This resulted not only from the increase in northward volume transport but also anomalous warm water intrusion from the Bering Sea. Our results suggest a candidate among the important parameters controlling heat budget, which contributes to the Arctic sea ice reduction, whereas more studies are required to confirm that this mechanism is actually responsible for the interannual and longer timescale variability.     

Nondestructive Sensor Using Microwaves From Laser Plasma by Subnanosecond Laser Pulses

Conventional ground-penetrating radar (GPR) requires large-aperture antennas or long-span measurements to survey a remote location precisely. We propose a laser-driven GPR (LGPR) as a new detection method. LGPR uses microwaves from laser-produced plasmas as remote transmitters and can survey a remote location using a compact instrument. We performed numerical simulations to investigate the radiation mechanism of microwaves from laser plasmas and confirmed the pulsewidth of the laser suitable for LGPR. Experiments with subnanosecond pulse lasers clarified the feasibility and detection performance of LGPR.