Changes of environments and human activity at the Sannai-Maruyama ruins in Japan during the mid-Holocene Hypsithermal climatic interval

Sannai-Maruyama is one of the most famous and best-researched mid-Holocene (mid-Jomon) archaeological sites in Japan, because of a large community of people for a long period. Archaeological studies have shown that the Jomon people inhabi1ted the Sannai-Maruyama site from 5.9 to 4.2 ± 0.1 cal kyr BP However, a continuous record of the terrestrial and marine environments around the site has not been available. Core KT05-7 PC-02, was recovered from Mutsu Bay, only 20 km from the site, for the reconstruction of high-resolution time series of environmental records, including sea surface temperature (SST). C₃₇ alkenone SSTs showed clear fluctuations, with four periods of high (8.4–7.9, 7.0–5.9, 5.1–4.1, and 2.3–1.4 cal kyr BP) and four of low (?8.4, 7.9–7.0, 5.9–5.1, and 4.1–2.3 cal kyr BP) SST. Thus, each SST cycle lasted 1.0–2.0 kyr, and the amplitude of fluctuation was about 1.5–2.0 °C. Total organic carbon (TOC) and C₃₇ alkenone contents, and the TOC/total nitrogen ratio indicate that marine biogenic production was low before 7.0 cal kyr BP, but was clearly increased between 5.9 and 4.0 cal kyr BP, because of stronger vertical mixing. During the period when the community at the site prospered (between 5.9 and 4.2 ± 0.1 cal kyr BP), the terrestrial climate was relatively warm. The high relative abundance of pollen of both Castanea and Quercus subgen. Cyclobalanopsis supports the interpretation that the local climate was optimal for human habitation. Between 5.9 and 5.1 cal kyr BP, in spite of warm terrestrial climates, the C₃₇ alkenone SST was low; this apparent discrepancy may be attributed to the water column structure in the Tsugaru Strait, which differed from the modern condition. The evidence suggests that at about 5.9 cal kyr B.P, high productivity of marine resources such as fish and shellfish and a warm terrestrial climate led to the establishment of a human community at the Sannai-Maruyama site. Then, at about 4.1 ± 0.1 cal kyr BP, abrupt marine and terrestrial cooling, indicated by a decrease of about 2 °C in the C₃₇ alkenone SST and an increase in the pollen of taxa of cooler climates, led to a reduced terrestrial food supply, causing the people to abandon the site. The timing of the abandonment is consistent with the timing (around 4.0–4.3 cal kyr BP) of the decline of civilizations in north Mesopotamia and along the Yangtze River. These findings suggest that a temperature rise of ～2 °C in this century as a result of global warming could have a great impact on the human community and especially on agriculture, despite the advances of contemporary society.     

Distribution of Changjiang Diluted Water detected by satellite chlorophyll-a and its interannual variation during 1998–2007

Sea-viewing Wide Field-of-view Sensor (SeaWiFS) chlorophyll-a distribution in summer in the East China Sea during 1998–2007 was analyzed. Statistical analysis with K-means clustering technique allowed us to define the proper satellite chlorophyll-a concentration indicating the Changjiang Diluted Water (CDW). The spatial distributions of the higher satellite chlorophyll-a concentrations (>0.48 mg m⁻³) corresponded well with the distributions of lower salinity CDW (<30–32) every year. Interannual variation of the CDW area, indicated by the high satellite chlorophyll-a, correlated with the interannual variation of the Changjiang summer freshwater discharge. The correlation analysis indicated that the CDW spread eastward in the East China Sea with a time lag of 1 to 2 months after the discharge.     

The high frequency spectrum of wind-generated waves

The high frequency part (10 Hz50 Hz) of the one-dimensional wave spectrum was measured in a wind-wave channel under accurately controlled conditions. The results are compared with the spectral forms for the capillary range that have been proposed recently byPierson andStacy (1973) andToba (1973). In a general sense, fairly good agreement is found between the present results and those ofPierson andStacy (1973) and ofToba (1973). The spectrum in the capillary range is clearly wind speed dependent, and the spectral density in that range increases with increasing wind speed.However, closer examination shows systematic deviations of the present results from those previously proposed, particularly for high speed winds.     

Grain size,La/Yb and Th/Sc of settling particles in the western North Pacific: Evidence for lateral transport of small Asian loess

To understand the transport process of lithogenic particles in the ocean, we measured the grain size distributions of lithogenic particles and measured the opal, La, Yb, Th, and Sc concentrations of the settling particles collected from time-series sediment traps at Sta. KNOT (44°N, 155°E, water depth 5320 m) from June 2002 to May 2004. The annual mean lithogenic particle flux observed at the lower sediment trap (5100 m) was twice as high as that at the upper sediment trap (770 m). The contribution of Asian loess estimated by the La/Yb and the Th/Sc ratios in the lower layer was greater than that in the upper layer. The fluxes of small lithogenic particles with sizes of 3–4 μm at the lower layer (5 to 65 mg/m²/day) were approximately four times larger than that at the upper layer (0.6 to 27 mg/m²/day). These results indicate that the horizontal addition of small particle sizes of Asian loess is a main factor in the increase of lithogenic particles at the lower layer. The temporal variations in the small lithogenic particle flux at the lower layer had a positive correlation with those at the upper layer (r = 0.71). The small lithogenic particle fluxes showed a strong positive correlation with the opal fluxes (r = 0.9). We therefore conclude that the small lithogenic particles were laterally transported and scavenged by the formation of aggregates with opal.     

On the Quasi-Lame''s equation with application to lake seiches

An investigation is made on the damping of gravity oscillations in closed basins by using the singular perturbation method of Hukuda and Mysak. A perturbation solution, pivoting on a small bottom friction parameter ε, is derived for an arbitrary shaped basin with a sloping beach. It is shown that at 0(ε) the gravity oscillations are attenuated at a decay rate equal to the kinetic energy of 0(1) wave field. A simple law of decay rates is proposed for estimating the e-folding time of lake seiches, on the basis of calculations in both circular and elliptical basins with parabolic depth. The theoretical prediction is in good agreement with the long life cycle of a uninodal seiches observed in Lake Vättern, Sweden, as quoted in Defant.     

Dike swarm in Hakone volcano

Subparallel dikes are exposed on a new road-cut along the foot of the southeastern caldera wall of Hakone Volcano. The dikes are concentrated within a zone 1,915 m wide. Altogether 96 dikes trending generally from NW to SE are seen within a total length of the actual outcrops of 855 m measured at right angles to the trend of the dikes. This implies that there are 215 dikes within the zone of the dike swarm. As the average thickness of the dikes is 2.85 m, the zone was stretched for about 650 m in NE-SW direction owing to the intrusion of the dikes. The dikes tend to converge to a small area near the center of the caldera, and also tend to dip steeply toward the central axis of the zone. It is concluded that the dikes intruded along originally vertical fissures radiating from the central vent of the pre-caldera cone, but the zone of the dike swarm was subjected to bulging with the maximum elevation along its central axis owing to successive intrusion of the dikes from below. Stretching and bulging of the flank of a volcanic cone owing to rise of magma along one of radial fissures were observed during the 1940 eruption of Miyake-zima, Izu Islands, Japan.     

http://dx.doi.org/10.1016/j.gsf.2016.10.001

The Francevillian Group in Gabonese Republic was recently established as a typical sedimentary sequence for the Paleoproterozoic.However,its age is rather poorly constrained,mainly based on Rb-Sr and Nd-Sm datings.This study reports new zircon data obtained from Chaillu massif and N'goutou complex,which constrain the protolith age of the basement orthogneisses and the igneous age of an intrusive granite,respectively.Most zircons from the orthogneisses are blue and exhibit oscillatory zoning in cathode-luminescence images.Zircons with lower common lead abundances tend to be distributed close to the concordia curve.Two age clusters around 2860 Ma and 2910 Ma are found in zircons plotted on the concordia curve.Based on the Th/U ratios of zircons,these ages correspond to the protolith ages of the orthogneisses,and the zircons are not metamorphic in origin.Syenites and granites were collected from the N'goutou complex that intrudes into the FA and FB units of the Francevillian Group.The granitoids exhibit chemical composition of A-type granite affinity.Half of zircons separated from the granite are non-luminous,and the remaining half exhibit obscure internal textures under cathode-luminescence observation.All zircon grains contain significant amounts of common lead;the lead isotopic variability is probably attributed to the mixing of two components in the zircons.The zircon radiogenic ~(207)Pb/~(206)Pb ratio is 0.13707 ± 0.0010.corresponding to a ~(207)Pb/~(206)Pb age of 2191 ± 13 Ma.This constrains the minimum depositional age of the FA and FB units.Furthermore,the FB unit consists of manganese-rich carbonate rocks and organic carbon-rich black shales with macroscopic fossils.Based on our age constraints,these organisms appeared in the study area just after the last Paleoproterozoic Snowball Earth event,in concert with global scale oxidation event encompassing the Snowball Earth.     

Specific accumulation of persistent organochlorines in bluefin tuna collected from Japanese coastal waters

Concentrations of persistent organochlorines (OCs) such as PCBs, DDTs, chlordanes (CHLs), HCHs and HCB were determined in the liver of bluefin tuna (Thunnus thynnus) collected from Japanese coastal waters in order to elucidate accumulation profiles and to evaluate the suitability of this species as a biomonitor for pollution in the open sea ecosystem. Concentrations of PCBs, DDTs and CHLs in bluefin tuna increased significantly with body length (30–190 cm). HCHs and HCB residues were comparable among all the sampling regions, and the levels of these chemicals did not show correlation with body length. These results suggest significance of dietary uptake of PCBs, DDTs and CHLs compared to the intake via the gill. On the other hand, equilibrium partitioning with ambient water is a major determinant of the levels of HCHs and HCB in tuna. Body-length normalized values (BLNV) of PCBs, DDTs and CHLs concentrations in bluefin tuna were calculated using the linear regression equation obtained from the plot of concentrations and body length. BLNV of these chemicals on a lipid wt basis, which was adjusted for 100 cm body length, were indicative of the present state water pollution by PCBs, DDTs and CHLs. These results suggest that bluefin tuna is a suitable bioindicator for monitoring OCs contamination in the open sea ecosystem.     

Variability of the topographic core-mantle torque calculated from core surface flow models

With the prospect of studying the relevance of the topographic core-mantle coupling to the variations of the Earth’s rotation and also its applicability to constraining the core surface flow, we investigate the variability of the topographic torque estimated by using core surface flow models accompanied by (a) uncertainty due to the non-uniqueness problem in the flow inversion, and (b) variance originating in that of geomagnetic secular variation models employed in the inversion. Various flow models and their variances are estimated by inverting prescribed geomagnetic models at the epoch 1980. The subsequent topographic torque is then calculated by using a core-mantle boundary topography model obtained by seismic tomography. The calculated axial and equatorial torques are found subject to the variability of order 10¹⁹ and 10²⁰  Nm, respectively, on which (b) is more effective than (a). The variability of the torque is attributed even to (a) and (b) of the large-scale flows (degrees 2 and 3). Yet, it still seems unlikely for the decadal polar motion with the observed amplitude to be excited exclusively by the equatorial topographic torque associated with any of reasonable core surface flow models. It is also confirmed that, with the topography model adopted here, the axial topographic torque on a rigid annulus in the core (coaxial with the Earth’s rotation axis) associated with any of reasonable flow models is larger by two orders of magnitude than the plausible inertial torque on such cylinders. This implies that any core surface flow model consistent with the topographic coupling does not exist, unless the topography model is appropriately modified. Nevertheless, the topographic coupling might provide not only a weak constraint for explaining the decadal LOD variations, but also the possibility to probe the core surface flow and the core dynamics.     

汶川MS8.0级地震成因三“层次”分析——基于深部电性结构

2008年5月12日汶川M_S8级地震的发生不是局部地区孤立的构造事件,研究汶川地震的孕震机制,应该把局部分析和区域分析相结合,关注地壳上地幔直至地幔过渡带的深部结构.基于近年来在东北、华北和汶川地震附近地区进行的深部结构电磁探测结果,结合地震学等其他资料,从太平洋板块的俯冲、印度板块的碰撞和松潘甘孜地块的推挤三个“层次”探讨分析汶川特大地震的成因.太平洋板块向亚洲大陆的俯冲作用,导致中国大陆东部地幔过渡带深度较普遍地存在着停滞的板片,它对汶川地震的影响不可忽视.印度板块与青藏高原的碰撞,使组成高原的各地块发生向北和向东的运动,各地块向东的运动作用于南北地震带中南段,影响到该区域的地震活动.松潘甘孜地块向四川地块的推挤,使松潘甘孜地块运动方向和龙门山断裂带形成“丁”字形结构,龙门山断裂带显示为较陡直的电性边界,加剧了汶川地震前的应力积累,可能是汶川地震发生的最直接的诱因.