Estimation of suspended sediment sources using 137Cs and 210Pbex in unmanaged Japanese cypress plantation watersheds in southern Japan

To analyse suspended sediment sources in unmanaged Japanese cypress plantation watersheds, field measurements and fingerprinting of the suspended sediment was conducted in the Shimanto River basin in southern Japan. For sediment fingerprinting, ¹³⁷Cs and ²¹⁰Pb_ex were detected by means of gamma‐ray spectrometry in the surface soil of the forest floor, stream bank and truck trail and mobilized sediment by interrill erosion. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the forest floor materials were considerably higher than those of the stream bank and truck trail. The ¹³⁷Cs and ²¹⁰Pb_ex activities associated with the suspended sediment were found to vary with the sampling period. Evidently, the suspended sediment can comprise materials generated from the forest floor by interrill erosion and those from the truck trail and/or stream bank. The multivariate sediment‐mixing model using ¹³⁷Cs and ²¹⁰Pb_ex showed that the contribution of the forest floor varied periodically, ranging from 23–56% in the Hinoki 156 subwatershed and from 18–85% in the Hinoki 155 subwatershed. The difference in the average contribution of the forest floor between Hinoki 156 (46%) and Hinoki 155 (69%) may relate to the presence of truck trail networks in the watershed. The truck trail network can play roles of sediment source and pathway for sediment from forest floor to stream channel due to the concentrated overland flow on the truck trail during heavy rainfall events. These results indicate that the forest floor should be recognized as a major source of suspended sediment in unmanaged Japanese cypress plantation watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

Lithology, Biostratigraphy, and Magneto stratigraphy of Gas Hydrate-Bearing Sediments in the Eastern Nankai Trough

Abstract: Stratigraphic controls on the formation and distribution of gas hydrates were examined for sediments from a BH-1 well drilled in the landward slope of the Nankai Trough, approximately 60 km off Omaezaki, Japan. Three lithologic units were recognized in the 250 m-thick sequence of sediments: Unit 1 (0–70 mbsf) consists of calcareous silt and clay with thin volcanic ash layers, Unit 2 (70–150 mbsf) consists of calcareous silt and clay with volcanic ash and thin sand layers, and Unit 3 (150–250 mbsf) consists of weakly consolidated calcareous silt and clay with thick and frequent sand layers. Soupy structures and gas bubbles in the sediments indicate the presence of two hydrate zones between 40 and 130 mbsf and below 195 mbsf. Nannofossil biostratigraphy and magnetostratigraphy indicate that the sequence recovered at the BH-1 well is mostly continuous and represents sediments deposited from 0 to 1.5 Ma. Calculation of the sedimentation rate reveals a condensed section between 65 and 90 mbsf. The inferred distribution of gas hydrates in the BH-1 well appears to be strongly controlled by the stratigraphy and lithology of the sediments. Thick, gently inclined sand layers in Unit 3 provide a conduit for the migration of gases from deeper regions, and are considered responsible for the formation of the hydrate zone below 195 mbsf. At shallower levels, thin, gently inclined sand layers are also considered to allow for the migration of gases, leading to the formation of the upper hydrate zone between 40 and 130 mbsf. The overlying sub-horizontal silt and clay of the condensed section, truncating the underlying gently inclined sand and silt/clay layers, may provide an effective trap for gases supplied through the sand layers, further contributing to hydrate formation in the upper hydrate zone.     

Calculating downward longwave radiation under clear and cloudy conditions over a tropical lowland forest site: an evaluation of model schemes for hourly data

Field measurements of radiation fluxes—notably downwelling longwave radiation flux (LW flux)—are as yet rare or nonexistent outside a very select number of sites in the tropics. Data gaps can only be filled through the use of estimation schemes based on measurements of other meteorological variables, and there is a need for recommendations on best practice in this area. We selected 18 contrasting semi-empirical estimation schemes for downward longwave radiation, based on air emissivities, combined with six different sky cover estimation schemes and compared the expected longwave flux with hourly observations from a flux tower at Caxiuan? in Brazil. Of all schemes tested, the Dilley–Kimball emissivity scheme combined with Kasten and Czeplak’s sky cover scheme during the day and Dilley and O’Brien’s model B scheme at night proved to be the most reliable, yielding estimates of LW flux generally within 20?W/m² of measurements across all time points.     

An overview of the performance of CMIP6 models in the tropical Atlantic: mean state,variability, and remote impacts

General circulation models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) are examined with respect to their ability to simulate the mean state and variability of the tropical Atlantic and its linkage to the tropical Pacific. While, on average, mean state biases have improved little, relative to the previous intercomparison (CMIP5), there are now a few models with very small biases. In particular the equatorial Atlantic warm SST and westerly wind biases are mostly eliminated in these models. Furthermore, interannual variability in the equatorial and subtropical Atlantic is quite realistic in a number of CMIP6 models, which suggests that they should be useful tools for understanding and predicting variability patterns. The evolution of equatorial Atlantic biases follows the same pattern as in previous model generations, with westerly wind biases during boreal spring preceding warm sea-surface temperature (SST) biases in the east during boreal summer. A substantial portion of the westerly wind bias exists already in atmosphere-only simulations forced with observed SST, suggesting an atmospheric origin. While variability is relatively realistic in many models, SSTs seem less responsive to wind forcing than observed, both on the equator and in the subtropics, possibly due to an excessively deep mixed layer originating in the oceanic component. Thus models with realistic SST amplitude tend to have excessive wind amplitude. The models with the smallest mean state biases all have relatively high resolution but there are also a few low-resolution models that perform similarly well, indicating that resolution is not the only way toward reducing tropical Atlantic biases. The results also show a relatively weak link between mean state biases and the quality of the simulated variability. The linkage to the tropical Pacific shows a wide range of behaviors across models, indicating the need for further model improvement.

     

Historical climate changes in southern Xinjiang

1 Introduction Southern Xinjiang has experienced tremendous changes in climate and eco-environment during historic times, for example, the rise and decline of oases and ancient towns, shrinkages and enlargement of lakes and changes in river system, etc. (Figure 1). All these can be attributable to the natural changes of climate and environment superimposed by human impacts. So, it is interesting and significant to reveal the inter-relation between natural climate changes and human抯 impact …     

The eruptive rate and history of Kuju volcano in Japan during the past 15,000 years

The eruptive history of Kuju volcano on Kyushu, Japan, during the past 15,000 years has been determined by tephrochronology and ¹⁴C dating. Kuju volcano comprises isolated lava domes and cones of hornblende andesite together with aprons of pyroclastic-flow deposits on its flanks. Kuju volcano produced tephras at roughly 1000-yr intervals during the past 5000 years and 70% of the domes and cones have formed during the past 15,000 years. The youngest magmatic activity of Kuju volcano was the 1.6 km³ andesite eruption about 1600 years ago which emplaced a lava dome and block-and-ash flow. Kuju volcano shows a nearly constant long-term eruption rate (0.7–0.4 km³ for 1000 years) during the past 15,000 years. This rate is within the range of estimated average eruption rates of late Quaternary volcanoes in the Japanese Arc, but is about one order of magnitude higher than the eruption rate of Unzen volcano. Kuju volcano has been in phreatic eruption since October 1995. The late Quaternary history of Kuju indicates that it poses a significant volcanic hazard, primarily due to block-and-ash flows from collapsing lava domes.     

Faunal analysis of Neogene planktonic foraminifera from forearc sediments of the Japan Trench, ODP Site 1151, Leg 186

Abstract The present paper describes the general outline of Neogene paleoceanographic changes in the northwestern Pacific by means of planktonic foraminiferal assemblages. Planktonic foraminiferal fossils occur commonly in the upper Miocene to lower Pleistocene sediments of Hole 1151A, Ocean Drilling Program Leg 186 in the forearc basin off northeast Japan, with the exception of 11 barren intervals. These barren intervals are explained as a result of dissolution under organic decomposing processes. Three assemblages of planktonic foraminifers were identified by Q‐mode cluster analysis. The succession of the assemblages can be divided into four paleoceanographic stages: (i) warm‐temperate Tortonian; (ii) cold‐temperate Messinian to lower Pliocene; (iii) warm climatic optimum in the middle part of the Pliocene; and (iv) strong glacial–interglacial oscillation of the upper Pliocene to the lower Pleistocene. Three short warming events—namely, the late Miocene climatic optimum 3, the Miocene–Pliocene boundary and the middle Pliocene events—and a short cooling event of the late Miocene could be determined in the studied section of Site 1151.     

Fundamental characteristics of Multiple Tuned Mass Dampers for suppressing harmonically forced oscillations

Multiple Tuned Mass Dampers (MTMD's) consisting of many tuned mass dampers (TMD's) with distributed natural frequencies are considered for suppressing effectively the harmonically forced single mode response of structures. The fundamental characteristics of MTMD's are investigated analytically with the parameters of the covering frequency range of MTMD's, the damping ratio of each TMD and the total number of TMD's. The effectiveness and the robustness of MTMD's are also discussed in comparison with those of the usual single TMD. It is found that there exists an optimum MTMD for the given total number of TMD's with the optimum frequency range and the optimum damping ratio and that the optimum MTMD is more effective than the optimum single TMD. As for the robustness, it is also clarified that a MTMD can be much more robust than a single TMD while keeping the same level of effectiveness as the optimum single TMD.