Marine reservoir correction for the Pacific coast of central Japan using C ages of marine mollusks uplifted during historical earthquakes

In this study we utilize marine shell samples from two levels of historically uplifted sessile mollusk assemblages and raised wave-cut benches to evaluate the marine reservoir correction (ΔR) for the Pacific coast of central Japan. Elevation measurements of the uplifted marine shells indicate that the lower assemblage emerged during the 1923 Taisho Kanto earthquake (M7.9), whereas uplift of the upper assemblage is most likely but less confidently ascribed to the 1703 Genroku Kanto earthquake (M8.2). Radiocarbon dating of carefully selected samples from the upper and lower assemblages yielded very similar ΔR values of 82 ± 33 and 77 ± 32 yr, respectively. We regard the former ΔR value as a representative and more reliable value given the uncertainty in correlation of the upper assemblage with the 1703 earthquake. This result is consistent with previously reported ΔR values for the Pacific coast of south-central Japan and areas around the Sea of Japan that are influenced by warm ocean currents. Radiocarbon dating of coseismically uplifted shells can aid in estimating marine reservoir ages in the tectonically active Japan Islands.     

Intensified mid-Holocene Asian monsoon recorded in corals from Kikai Island, subtropical northwestern Pacific

Coupled records of Sr/Ca and oxygen isotope ratios (δ¹⁸O) of coral skeletons have been used to produce quantitative estimates of paleo-sea surface temperature (SST) and δ¹⁸O of surface seawater that can in some cases be converted to sea surface salinity (SSS). Two fossil corals from Kikai Island in the subtropical northwestern Pacific, a location affected by East Asian summer and winter monsoons, were analyzed to investigate differences between mid-Holocene and present-day SST and SSS. At 6180 cal yr BP, SSTs were roughly the same as today, both in summer and winter; δ¹⁸O_seawater and SSS values were higher both in summer (+ 0.5‰, +1.1 psu) and in winter (+ 0.2‰, + 0.6 psu) than modern values. At 7010 cal yr BP, SSTs were slightly cooler both in summer and winter (−0.8 and −0.6 °C), whereas δ¹⁸O_seawater and SSS had higher values in summer (+ 0.3‰, + 0.6 psu) and in winter (+ 0.8‰, + 1.9 psu) than present-day values. These results are consistent with other marine records for the mid-Holocene of the low and midlatitudes in the northwestern Pacific. Such regional conditions indicate that the East Asian summer and winter monsoons were more intense in the mid-Holocene, which was likely a function of the mid-Holocene insolation regime.     

大洋间SST遥联与亚太夏季风异常的关系

用奇异值分解(Singular Value Decomposition,SVD)方法,给出了四季年代际和年际时间尺度上北大西洋和北太平洋海表温度(Sea Surface Temperature,SST)的显著遥相关.用SVD主模态时间系数构造了海温异常指数Ⅰ,分析了它们与同期亚太夏季风和我国东部夏季降水异常的关系.结果表明:两大洋间的SST遥联在年际、年代际时间尺度上都与亚太夏季风相关,其中,年际尺度的两大洋SST遥联与长江流域的降水存在显著相关.     

Shear wave anisotropy in D＂ region beneath the western Pacific

Using seismic shear phases from 47 Tonga-Fiji and its adjacent region events recorded by the CENC and IRIS, and from 26 northeast Asia and north Pacific events recorded by IRIS, we studied the shear wave anisotropy in D" region beneath the western Pacific utilizing the ScS-S differential travel time method and obtained the splitting time values between the radial and transverse components of each ScS wave corresponding to each core-mantle boundary (CMB) reflection point. We found that most shear waves involved horizontally polarized shear wave components traveling faster than vertically polarized shear wave components through the D" region. The splitting time values of ScS wave range from ?0.91 s to 3.21 s with an average value of 1.1 s. The strength of anisotropy varies from ?0.45% to 1.56% with an average value of 0.52%. The observations and analyses show that in the D" region beneath the western Pacific the lateral flow is expected to be dominant and the vertical transverse isotropy may be the main anisotropic structure. This structure feature may be explained by the shape preferred orientation of the CMB chemical reaction products or partial melt and the lattice preferred orientation of the lower mantle materials caused by the lateral flow at lowermost mantle.     

Tsunami and its Hazard in the Indian and Pacific Oceans: Introduction

The 2004 Indian Ocean tsunami caused an estimated 230,000 casualties, the worst tsunami disaster in history. A similar-sized tsunami in the Pacific Ocean, generated by the 1960 Chilean earthquake, commenced international collaborations on tsunami warning systems, and in the tsunami research community through the Tsunami Commission of International Union of Geodesy and Geophysics. The IUGG Tsunami Commission, established in 1960, has been holding the biannual International Tsunami Symposium (ITS). This volume contains selected papers mostly presented at the 22nd ITS, held in the summer of 2005. This introduction briefly summarizes the progress of tsunami and earthquake research as well as international cooperation on tsunami warning systems and the impact of the 2004 tsunami. Brief summaries of each paper are also presented.     

A comparison of late Quaternary forest changes in New Caledonia and northeastern Australia

A pollen record from Lake Xere Wapo, southeast New Caledonia, is the longest continuous terrestrial record to be recovered from the tropical southwest Pacific and reveals a series of millennial scale changes in vegetation over the last 130,000 yr. A comparison of the Lake Xere Wapo record with the key northeast Australian record of Lynch's Crater reveals regional patterns of change. From 120,000 to 50,000 yr ago the vegetation around Lake Xere Wapo alternated between rainforest and maquis with fire an important disturbance factor. In the last 50,000 yr fire is almost absent from the record and the vegetation assumes a character unprecedented in the preceding 100,000 yr, dominated by Dacrydium and Podocarpus pollen. The most compelling aspect of the comparison with Lynch's Crater is that the much-discussed Araucaria decline at around 45,000 yr ago in northern Queensland is matched by a similar decline in the Lake Xere Wapo record.     

The variations of stable carbon isotope ratio of land plant-derived n-alkanes in deep-sea sediments from the Bering Sea and the North Pacific Ocean during the last 250,000 years

Two piston cores, one located far from the continents (The North Pacific Ocean: ES core), and another located comparatively closer to the continents (The Bering Sea: BOW-8a core) were investigated to reconstruct environmental changes on source land areas. The results show significant contribution of terrestrial organic matter to sediments in both cores. The δ¹³C values of n-C₂₇, n-C₂₉, and n-C₃₁ alkanes in sediments from the North Pacific ES core show significant glacial to interglacial variation whereas those from the Bering Sea core do not. Variations of δ¹³C values of land plant n-alkanes are related to the environmental or vegetational changes in the source land areas. Environmental changes, especially, aridity, rainfall, and pCO₂ during glacial/interglacial transitional periods can affect vegetation, and therefore C₃ / C₄ plant ratios, resulting in δ¹³C changes in the preserved land plant biomarkers. Maximum values of δ¹³C as well as maximum average chain length values of long chain n-alkanes in the ES core occur mostly at the interglacial to glacial transition zones reflecting a time lag related to incorporation of living organic matter into soil and transportation into ocean basins via wind and/or ability of C₄ plants to adapt for a longer period before being replaced by C₃ plants when subjected to gradual climatic changes. Irregular variations with no clear glacial to interglacial trends in the BOW-8a core may result from complex mixture of aerosols from westerly winds and riverine organic matter from the Bering Sea catchments. In addition, terrestrial organic matter entering the Bering Sea could originate from multiple pathways including eolian, riverine, and ice rafted debris, and possibly be disturbed by turbidity and other local currents which can induce re-suspension and re-sedimentation causing an obliterated time relation in the Bering Sea biomarker records.     

The NPO/ NAO and interdecadal climate variation in China

This article discusses the interannual variation of the North Atlantic Oscillation (NAO) and North Pacific Oscillation (NPO), its relationship with the interdecadal climate variation in China which is associated with the climate jump in the Northern Hemisphere in the 1960’s, using the data analyses. It is clearly shown that both the amplitudes of the NAO and NPO increase obviously in the 1960’s and the main period of the oscillations changes from 3-4 years before the 1960’s to 8-15 years after the 1960’s. Therefore, interdecadal climate variation in China or the climate jump in the 1960’s is closely related to the anomalies of the NAO and NPO.     

西太平洋暖池次表层海温异常 与ENSO循环的相互作用

利用1964～1993年的太平洋次表层海温资料,进一步分析研究了西太平洋暖池次表层海温异常与ENSO循环的关系。合成及相关分析的结果进一步表明,西太平洋暖池次表层海温的暖（冷）异常及其东传对ENSO的发生起着十分重要、且更直接的作用。然而,赤道西太平洋异常纬向风是造成次表层海温异常东传的重要原因,而纬向风的异常又是由于东亚冬季风异常活动所引起的,这间接地说明了异常东亚冬季风对西太平洋暖池次表层海温距平东传的重要作用。通过研究还发现,ENSO发生后,北半球副热带地区将有次表层暖（冷）海温距平沿着10～20oN纬带西传,这是导致西太平洋暖池次表层海温发生异常的重要原因之一。也就是说,西太平洋暖池次表层海温异常与ENSO循环之间是相互影响、相互作用的。