Seasonal variation of volatile organic iodine compounds in the water column of Funka Bay,Hokkaido, Japan

Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH₂I₂, CH₂ClI, CH₃I, and C₂H₅I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C₂H₅I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO₄ ^3? variation profile. Correlation between C₂H₅I and PO₄ ^3? concentrations (r = 0.93) suggests that C₂H₅I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH₂I₂ and CH₂ClI concentrations increased substantially in the surface and subsurface layers (0–60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring).     

Importance of intracellular Fe pools on growth of marine diatoms by using unialgal cultures and on the Oyashio region phytoplankton community during spring

We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4–4.2 cell divisions with 1.2–2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions could often occur in surface waters of the Oyashio region from spring to summer.     

Utility of the 2-D Multi-Electrode Resistivity Imaging Technique in Groundwater Exploration in the Voltaian Sedimentary Basin, Northern Ghana

Guinea worm and other water borne diseases associated with untreated surface water use have necessitated that communities are supplied with groundwater in the Northern Region of Ghana. The Electrical Resistivity Survey (ERS) method is one of the common geophysical survey techniques used for borehole siting in Ghana. Various groundwater exploration programs have utilized it by employing the four electrode system. However, the ERS has not been able to locate potential borehole sites successfully in the Voltaian Sedimentary Basin (VSB) in the Northern Region of Ghana although it has been successful in other geological formations. Unsatisfactory results obtained from the employment of the ERS system in the VSB therefore necessitated an experiment with the 2-D Multi-Electrode Resistivity Imaging (2-D MERI) technique. Field results show that the 2-D MERI is a robust and efficient technique: an improvement on the four electrode ERS system in terms of amount and quality of data obtained. The 2-D MERI interpretations were confirmed with a much improved borehole drilling success rate of 60% compared to 38% obtained using the ERS within the mudstone and shale formations. The 2-D MERI also indicated that very low resistivity layers in the VSB may not necessarily be good targets for borehole drilling and the generally held notion that groundwater cannot be found at depths more than 25 m is no longer tenable.     

Diabatic heating and the low frequency dynamics in the tropics

Summary Using a General Circulation Model developed at FSU (FSUGCM), the role of the diabatic heating on the 30–60-day oscillation is investigated. To concentrate on the radiation and the moist convection processes, an aqua planet model is employed in this paper. We have obtained a 40-day oscillation with relatively lower frequency than other GCMs without strong heating in the lower troposphere. Unlike some GCMs and simple models, the convective area does not move eastward along with the oscillation. Adiabatic cooling due to the upward motion is mostly compensated by diabatic heating. This implies that Kelvin CISK theory might not explain our 40-day oscillation. We have also examined the impact of radiative heating on the low frequency oscillation. When we reduce the radiative cooling rate, our 40-day mode does not appear and a Kelvin CISK mode appears with a faster phase speed. The impact of the different convection schemes is also investigated. With an enhanced convection scheme, zonal wave number two with a 40-day period is generated.With 12 FiguresOn leave from Japan Meteorological Agency.     

Benthic Front and the Yamato Basin Bottom Water in the Japan Sea

Hydrographic observations have revealed detailed structure of the Bottom Water in the Japan Sea. The Yamato Basin Bottom Water (YBBW) exhibits higher temperatures and lower dissolved oxygen concentrations than those found in the Japan Basin Bottom Water (JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, forming a clear benthic front. The structure of the benthic front suggests an estuary-like water exchange between both Basins, with the inflow from the Japan Basin passing under the outflow from the Yamato Basin. It is inferred from the property distributions that the JBBW flowing into the Yamato Basin is entrained by the cyclonic circulation in the basin, and modified to become the YBBW. Vertical diffusion and thermal balance in the YBBW are examined using a box model. The results show that the effect of geothermal heating has about 70% of the magnitude of the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW from the Japan Basin. The box model also estimates the turnover time and vertical diffusivity for the YBBW as 9.1 years and 3.4 × 10⁻³ m²s^{− 1}, respectively.     

The use of low-grade and unsound crushed rock aggregates in Ghana for construction

Summary Ghana and many developing countries have relied heavily, in the past, on hard granites and granitic gneisses for the production of rock aggregates and rock products for civil engineering works including the construction of roads and buildings. Experience in Ghana has shown however, that the quantity of crushed rock aggregates produced from hard rocks have proved insufficient for the needs of the country. This situation has called for engineering geological studies into the use of rock types and rock formations previously designated as low grade and unsound for the production of aggregates. The major objective of this study was to review the occurrences of non-conventional hard rocks and gravels such as quartzites, silicified sandstones, metagreywackes, dolomitic limestones and quartz gravels. This was followed by the application of appropriate standard specification tests to establish criteria for the selection and recommendation for the use of low grade and unsound rocks and gravels for various civil engineering projects in Ghana and other developing countries, especially those of the subregion with similar geological formations.     

Groundwater Assessment for Current and Future Water Demand in the Daka Catchment,Northern Region,Ghana

The use of untreated surface water for domestic purposes has resulted in the infection of some people by guinea worm and other water borne diseases in the Northern Region of Ghana. The aim of this study is to assess the current groundwater quantity and quality conditions in the 7,820 km² Daka catchment and project the water demand in 2025. Results of groundwater analyses generally show good water quality for domestic use. Borehole analyses indicate that the catchment’s groundwater system can be characterized by a regolith aquifer underlain by a deeper fractured rock aquifer in some areas. The current per capita water demand is estimated at 40 l/day although 60 l/day is the desired amount, indicating that with the current population of 363,350, the projected water demand for the communities is 21,800 m³/day. With a projected population of 555,500 in 2025, an expected 33,300 m³/day of water is required. The estimated optimum potential groundwater available for use in the catchment is 154 × 10⁶ m³/year (4.24 × 10⁵ m³/day). However, the current total groundwater abstraction is only 8,876 m³/day or 2% of the optimum. In comparison, the projected total current and 2025 water demands are only 5 and 8%, respectively, of the optimum potential groundwater available for use in the catchment. In addition, only 1,780 m³/day (0.65 × 10⁶ m³/year) or 0.06% of the average annual flow of 1,016 × 10⁶ m³/year of the Daka River is treated for domestic use. These figures reveal that a significantly very large water resource potential exists for both surface and groundwater development in the Daka catchment. It is suggested that their development should proceed conjunctively.     

Calibration of Shallow Borehole Drilling Sites Using the Electrical Resistivity Imaging Technique in the Granitoids of Central Region,Ghana

The electrical resistivity imaging (ERI) technique has been used to calibrate existing successful and dry borehole drilling locations in the Cape Coast Granitoid Complex of the Central Region of Ghana. The area has a low groundwater potential and most of the communities do not have access to potable water. Surface water is generally expensive to treat and is therefore not considered as a good water supply option in such rural and dispersed communities where incomes are low. Supply of water to communities from existing boreholes is inadequate. Therefore, there was the need to construct more boreholes to increase access to potable water to meet coverage targets. Results show that the ERI technique is capable of detecting shallow bowl-shaped conductive zones up to 75 m represented by low resistivity values mainly due to weathered granitoids and/or fractures within the granitoids. Resistivity values typically less than 500 Ω-m obtained between depths of 10–50 m on model resistivity sections accounted for about 80% of successful productive boreholes. Resistivity values in the range 500–1,500 Ω-m represented marginally successful borehole locations which could be suitable for hand-pump installation and values greater than 1,500 Ω-m were confirmation for dry borehole locations.     

Impacts of elevated CO2 on particulate and dissolved organic matter production: microcosm experiments using iron-deficient plankton communities in open subarctic waters

Response of phytoplankton to increasing CO₂ in seawater in terms of physiology and ecology is key to predicting changes in marine ecosystems. However, responses of natural plankton communities especially in the open ocean to higher CO₂ levels have not been fully examined. We conducted CO₂ manipulation experiments in the Bering Sea and the central subarctic Pacific, known as high nutrient and low chlorophyll regions, in summer 2007 to investigate the response of organic matter production in iron-deficient plankton communities to CO₂ increases. During the 14-day incubations of surface waters with natural plankton assemblages in microcosms under multiple pCO₂ levels, the dynamics of particulate organic carbon (POC) and nitrogen (PN), and dissolved organic carbon (DOC) and phosphorus (DOP) were examined with the plankton community compositions. In the Bering site, net production of POC, PN, and DOP relative to net chlorophyll-a production decreased with increasing pCO₂. While net produced POC:PN did not show any CO₂-related variations, net produced DOC:DOP increased with increasing pCO₂. On the other hand, no apparent trends for these parameters were observed in the Pacific site. The contrasting results observed were probably due to the different plankton community compositions between the two sites, with plankton biomass dominated by large-sized diatoms in the Bering Sea versus ultra-eukaryotes in the Pacific Ocean. We conclude that the quantity and quality of the production of particulate and dissolved organic matter may be altered under future elevated CO₂ environments in some iron-deficient ecosystems, while the impacts may be negligible in some systems.     

Constrained gravity models and structural evolution of the Ashanti Belt, southwest Ghana

The Palaeoproterozoic terrane of southwest Ghana comprises a sequence of folded sedimentary/volcaniclastic rocks which separate a series of northeast trending volcanic belts. While the stratigraphy and structure of the belts are similar, the Ashanti Belt is characterised by a more tectonised northwest margin along which most of the major epigenetic Au deposits in Ghana are located. Early models of the tectonic evolution of this belt, which generally invoked two phases of deformation, are inconsistent with more recent structural and isotopic evidence (Eisenlohr and Hirdes, 1992). Modelling of regional gravity data by Hastings (1982) acknowledged the tectonic significance of the belt margins but lacked the benefit of constraints provided by more detailed mapping. This paper re-examines existing gravity data over the Ashanti Belt and presents constrained cross-sectional models which honour the mapped geology along the length of the belt and are consistent with the concept of a single, continuous deformational event. A synoptic scenario for the large-scale structural evolution of the belt is proposed which has implications for the location and timing of Au mineralisation.