Geochemistry and Origin of Ananai Stratiform Manganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. Major and trace element contents are reported for Permian manganese ore and associated greenstone from the Ananai manganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The manganese deposit occurs between greenstone and red chert, or among red chert beds. Chemical compositions of manganese ore are characterized by enrichments in Mn, Ca, P, Co, Ni, Zn, Sr and Ba, and negative Ce and positive Eu anomalies relative to post-Archean average Australian Shale (PAAS). Geochemical features of the manganese ore are similar to those of modern submarine hydrother-mal manganese deposits from volcanic arc or hotspot setting. In addition, geochemical characteristics of the greenstone closely associated with the Ananai manganese deposit are analogous to those of with-in plate alkaline basalt (WPA). Consequently, the Ananai manganese deposit was most likely formed by hydrothermal activity related to hotspot volcanism in the Panthalassa Ocean during the Middle Permian. This is the first report documenting the terrestrially-exposed manganese deposit that was a submarine precipitate at hotspot.     

Timing of the late-glacial climate reversal in the Southern Hemisphere using high-resolution radiocarbon chronology for Kaipo bog, New Zealand

The pattern of climate change in the Southern Hemisphere during the Younger Dryas (YD) chronozone provides essential constraint on mechanisms of abrupt climate change only if accurate, high-precision chronologies are obtained. A climate reversal reported previously at Kaipo bog, New Zealand, had been dated between 13,600 and 12,600 cal yr B.P. and appeared to asynchronously overlap the YD chron, but the chronology, based on conventionally radiocarbon-dated bulk sediment samples, left the precise timing questionable. We report a new high-resolution AMS ¹⁴C chronology for the Kaipo record that confirms the original chronology and provides further evidence for a mid-latitude Southern Ocean cooling event dated between 13,800 and 12,400 cal yr B.P. (2σ range), roughly equivalent to the Antarctic Cold Reversal.     

A high resolution relative paleointensity record from the Gerlache-Boyd paleo-ice stream region, northern Antarctic Peninsula

Herein we document and interpret an absolute chronological dating attempt using geomagnetic paleointensity data from a post-glacial sediment drape on the western Antarctic Peninsula continental shelf. Our results demonstrate that absolute dating can be established in Holocene Antarctic shelf sediments that lack suitable material for radiocarbon dating. Two jumbo piston cores of 10-m length were collected in the Western Bransfield Basin. The cores preserve a strong, stable remanent magnetization and meet the magnetic mineral assemblage criteria recommended for reliable paleointensity analyses. The relative paleomagnetic intensity records were tuned to published absolute and relative paleomagnetic stacks, which yielded a record of the last ∼8500 years for the post-glacial drape. Four tephra layers associated with documented eruptions of nearby Deception Island have been dated at 3.31, 3.73, 4.44, and 6.86 ± 0.07 ka using the geomagnetic paleointensity method. This study establishes the dual role of geomagnetic paleointensity and tephrochronology in marine sediments across both sides of the northern Antarctic Peninsula.     

Heavy metals in freshly deposited sediments of the river Subernarekha, India: an example of lithogenic and anthropogenic effects

Heavy metal distribution patterns in river sediments aid in understanding the exogenic cycling of elements as well as in assessing the effect of anthropogenic influences. In India, the Subernarekha river flows over the Precambrian terrain of the Singhbhum craton in eastern India. The rocks are of an iron ore series and the primary rock types are schist and quartzite. One main tributary, the Kharkhai, flows through granite rocks and subsequently flows through the schist and quartzite layers. The Subernarekha flows through the East Singhbhum district, which is one of India’s industrialised areas known for ore mining, steel production, power generation, cement production and other related activities. Freshly deposited river sediments were collected upstream and downstream the industrial zone. Samples were collected from four locations and analysed in <63-μm sediment fraction for heavy metals including Zn, Pb, Cd and Cu by anodic stripping voltammetry. Enrichment of these elements over and above the local natural concentration level has been calculated and reported. Sediments of the present study are classified by Muller’s geo-accumulation index (I _geo) and vary from element to element and with climatic seasons. During pre-monsoon period the maximum I _geo value for Zn is moderately to highly polluted and for Cu and Pb is moderately polluted, respectively, based on the Muller’s standard. Anthropogenic, lithogenic or cumulative effects of both components are the main reasons for such variations in I _geo values. The basic igneous rock layer through which the river flows or a seasonal rivulet that joins with the main river may be the primary source for lithogenic components.     

Effect of a submerged bay-mouth breakwater on tsunami behavior analyzed by 2D/3D hybrid model simulation

The hybrid numerical model had been developed to simulate a complicated 3D flow around structures generated by tsunami. In the model, the conventional 2D model is adopted for the wide region far from structures and the 3D non-hydrostatic pressure model is used in the limited region adjacent to structures. The applicability of the model is shown by comparisons of the numerical results with the experimental results of the laboratory model tests and the numerical analysis results of the conventional whole 2D simulation. In addition, the effect of a submerged structure at the opening of a breakwater is discussed from the numerical simulations by the hybrid model. The submerged structure improves the stability of the rubble mound and reduces the tsunami inflow into the bay, while it increases the water surface velocity around the opening of the breakwater. The increase of surface velocity causes the increases of impulsive forces by collision with drafts and so on.     

南极菌Pseudoalteromonas sp．S-15-13产胞外多糖的研究及其分子鉴定

本文对影响南极细菌S-15-13生长和胞外多糖产量的主要环境因子进行了研究,同时采用16S rDNA序列分析及系统发育分析方法对其进行了分子鉴定。结果表明：菌株S-15-13最佳产糖条件为：培养时间,56h；培养温度,8℃；碳源,1．0%葡萄糖；NaCl浓度,3．0%；pH,6．0-7．0。16S rDNA序列分析和系统发育分析表明,菌株S-15-13属于假交替单胞菌属(Pseudoaltero- monas)。     

Modelling net erosion responses to enviroclimatic changes recorded upon multisecular timescales

Land use change has been recognized throughout the Earth as one of the most important factors influencing the occurrence of rainfall-driven geomorphological processes. However, relating the occurrence of historical soil erosion rates is difficult because of the lack of long-term research projects in river basins. Also, complex models are not adequate to reconstruct erosion rate changes because they require significant input data not always available on long timescales. Given the problems with assessing sediment yield using complex erosion models, the objective of this study is to explore a parsimonious scale-adapted erosion model (ADT) from the original Thornes and Douglas algorithms, which aims at reconstruction of annual net erosion (ANE) upon multisecular timescales. As a test site, the Calore River basin (3015 km² in southern Italy) provides a peculiar and unique opportunity for modelling erosion responses to climate and land cover changes, where input-data generation and interpretation results were also supported by documented hydrogeomorphological events that occurred before and after land deforestation. In this way, ANE_ADT-values were reconstructed for the period 1675–2004 by using precipitation indexes, complemented by recent instrumental records, and by using land cover statistics from documented agrarian sources. Pulses of natural sedimentation in the predeforestation period have been related to Vesuvius volcanic activity and changes in rainstorm frequency. After deforestation, the basin system became unstable with sudden fluctuations in the hydrogeomorphological regime contributing significantly to increased erosion and, in turn, sediment transport sequences via river drainage towards the Tyrrhenian coast.     

Structural and nutritional heterogeneity of riparian vegetation in Patagonia (Argentina) in relation to seasonal grazing by sheep

Riparian meadows of southern Patagonia are temporally and spatially heterogeneous habitats. They are thought to play a key role in regulating the dynamics of arid grazed steppes of the region. We conducted a 2-year study with sheep to determine the influence of two grazing conditions (deferment and spring grazing) on structural and nutritional parameters of three vegetation types apparently associated with a soil moisture gradient in a riparian meadow in southern Santa Cruz (Argentina). Spring deferment allowed forage accumulation in very moist and intermediate vegetation types by the beginning of the summer and had no detrimental impact on forage quality. Deferment had no effect on biomass accumulation of the drier vegetation type at our study site. Structural attributes of the vegetation appeared to affect spatial grazing patterns of sheep. Soil-related patchiness, rather than sheep grazing, appeared to control vegetation structure and nutritional value. The proportion of more mesic plant communities in riparian habitats of Patagonia could determine the outcome of plant–animal interactions in these systems. Practical recommendations of grazing capacity in paddocks, or more theoretical considerations of ecosystem dynamics of the Patagonian steppes need to explicitly consider the internal patchiness of riparian habitats.