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The southwestern Ryukyu Trench represents the ultimate sink of sediments shed from Taiwan into the Philippine Sea, which are mainly transported to the trench by turbidity currents via submarine canyons. Here, we present trench turbidites intercalated with hemipelagites in a gravity pilot core and a piston core acquired on the Ryukyu Trench floor at 6147 m water depth. We performed X-ray fluorescence core scans (ITRAX profiles), magnetic measurements, and organic geochemistry analyses to discriminate turbidites from hemipelagites. We identified 36 turbidites (0.9–4.2 cm thick) based on visual core descriptions and Ca/Fe ratios in the ITRAX profiles. Three of these turbidites show magnetic signatures indicating the presence of pyrrhotite and peaks in the magnetic susceptibility profile, suggesting that Taiwan-sourced sediments are transported to the Ryukyu Trench by long-runout turbidity currents. Pyrrhotite is also present in hemipelagites of the upper part of the retrieved cores, indicating a dominant sediment source in Taiwan over the last several thousand years. Ca/Fe and Zr/Rb ratios in the ITRAX profiles mark distal turbidites (about 1–3 cm thick), and Zr/Rb peaks mainly reflect grain size changes. Detailed analyses of a representative turbidite show good correlation between Ca/Fe and Zr/Rb peaks with upward-coarsening and upward-fining trends that delimit the turbidite. Sedimentary organic matter in hemipelagites is characterized by higher total organic carbon and total nitrogen contents and higher δ13C values than that in turbidites. Our multi-proxy approach employing high-resolution XRF core scans to differentiate turbidites from hemipelagites contributes to establishing a comprehensive view of modern trench sedimentation from Taiwan to the southwestern Ryukyu Trench.

International audience; Microplastics have become widely dispersed throughout the marine environment in and around Japan since the 1960s, which correspond to the onset of mass plastic production and use in this country. Our study documents a possible abrupt microplastics depositional event in continental shelf and deep-sea environments triggered by a tsunami. The sediment layers contaminated by microplastics correspond with sedimentary horizons where 137Cs signals were measured, indicating deposition after 1960s nuclear tests. The microplastics were observed in the 2011 Tohoku-Oki tsunami deposits. Tsunamis can thus contribute to the wide dispersal of microplastics from coastal to deep-sea areas, and these anthropogenic particles can be used to date very recent turbidite deposits.

Recent studies have revealed an intensification of the Indian Summer Monsoon (ISM) over the past 700 years, but its influence on the sediments in the northern Andaman Sea is unclear. To examine this influence, we used radiocarbon-dated sediment core StMY6, acquired 100 km offshore in the northern Andaman Sea from the Ayeyarwady River mouth, and obtained a 700-year-long record of the grain-size distribution and geochemistry of the sedimentary sequence. The ISM influences precipitation surrounding the Ayeyarwady River, and thus the river water and sediment discharges to the northern Andaman Sea near the river mouth in the Ayeyarwady River and the weathering intensity in the river catchment. Based on the system, we propose that higher sedimentation rates and larger modal grain size (the most abundant size in the grain-size distribution of sediments) and lower carbonate concentrations after about AD 1600 can be attributed to higher ISM intensity. Profiles of total organic carbon (TOC) content and carbon/nitrogen (C/N) ratios, however, did not show any trends after about AD 1600, which suggests that the ISM has had little influence on these proxies at this site.

Past and ongoing precipitations of Mn-carbonate (rhodochrosite) have occurred in the freshwater Lake Ohnuma, which is situated about 8 km south of the Hokkaido-Komagatake volcano, southwest Hokkaido (northern Japan). Lake sediments from a surface and a longer ∼4 m core contain the sedimentary rhythms of rhodochrosite laminae and volcanic deposits which were identified by nondestructive micro-XRF fluorescence analyses. The three tephra ash layers from the Hokkaido-Komagatake volcano, characterized by peaks of Al, Si, K, Ca, and Ti, correspond to regionally recognized tephras (1640, 1929 and 1996 CE) based on ashfall isopachs and 137Cs, 210Pb and 14C ages determined from the two cores. The sedimentation rate showed a drastic change around 1929 CE; ∼0.3 cm/yr for 1640–1929 CE and ∼2.7 cm/yr for 1929–2012 CE. The Mn content record of Lake Ohnuma sediments, composed of rhodochrosite laminae, showed a periodic variation with a decadal–centennial scale over the interval 1640–2012 CE. Sediment petrography and hydrochemical measurements suggest that the metastable phase of rhodochrosite was deposited during summer after being precipitated, followed by the crystal growth of rhodochrosite within the anoxic sediments. On the basis of these results, high Mn content is interpreted as an indicator of strengthened summer stratification associated with reduced rainfall runoff. The Ti/Si ratios are representative of the relative abundance of detrital inputs from the watershed. The combined signals of elevated Mn content and Ti/Si ratio for 1935–2012 CE indicate eutrophication and hypoxia in the lake and enhanced land erosion in the watershed, associated with the post-1970s intensive land use such as livestock farming. For 1640–1935 CE, the Lake Ohnuma record shows an antiphase relationship between the Mn content and Ti/Si ratio, which implies that the detrital inputs reflected the strength of the East Asian summer monsoon (EASM), and the reduced rainfall runoff resulted in weaker mixing, followed by depleted O2 in the water column. The antiphase variation in Mn content and Ti/Si ratio suggest weak EASM during the Little Ice Age (∼1850 CE), followed by strong EASM between 1860 and 1929 CE.

Widespread diagenesis of clay minerals occurs in deeply buried marine sediments under high-temperature and high-pressure conditions. For example, the smectite-to-illite (S-I) transformation has been often observed in sediments at in situ temperatures above ~60°C. However, it remains largely unknown whether such diagenetic processes naturally occur in relatively shallow and low-temperature sediments and, if so, what the consequences are of any related chemical reactions to the geochemical characteristics in the deep biosphere. We evaluated the possibility of naturally occurring S-I transformation at temperatures below 40°C in continental slope sediments of the Bering Sea by examining porewater chemistry, clay mineralogy, and chemical composition of clay minerals measured to ~800 m beneath the seafloor (mbsf) in core samples acquired during Integrated Ocean Drilling Program Expedition 323. In porewater from these cores, chloride concentrations decreased with increasing depth from 560 mM near the seafloor to 500 mM at ~800 mbsf; δ18O increased from 0‰ to 1.5‰; and δD decreased from –1‰ to –9‰. These trends are consistent with the addition of water derived from S-I transformation. The discrete low Cl– spikes observed between ~200 mbsf and ~450 mbsf could be attributed to the dissociation of methane hydrate. X-ray diffraction analysis of the clay-size fraction (

Centennial-scale variability of the East Asian winter monsoon during the Holocene is poorly understood because suitable archives and proxies are lacking. Here we present a high-resolution (∼30-yr spacing) planktonic foraminiferal δ O 18 record of Neogloboquadrina incompta (dextral form), which reflects sea surface temperature during the winter season, for the last 6000 yrs from marine sediments in the western North Pacific. Stronger winter monsoons indicated by cooler winter SSTs correspond to weaker summer monsoons indicated by the cave oxygen isotopes in centennial-scale variability. The variability also shows good correlation with δ O 18 records in lake sediments and ice cores from the Yukon Territory, Canada, spanning the last 4500 yrs, suggesting east–west climate coupling across the North Pacific. Furthermore, the climate changes across the North Pacific co-vary over widespread regions, such as the eastern tropical Pacific and the northern Red Sea, and the reconstructed solar activity. The cross-spectral and wavelet analyses show that the East Asian winter monsoon shares some cyclicity with the solar variability. Our results suggest that the solar activity is a fundamental forcing producing the centennial-scale EAWM variability mediated by the large-scale climate linkages.

Cyclic changes in volume transport of the Tsushima Warm Current (TWC) have been argued from diatom records in the southern Japan Sea off the Japanese islands during the Holocene. Although this phenomenon has not yet been confirmed by various proxy data, determining whether or not these oceanographic changes occurred is crucial for clarifying the nature of oceanographic changes in the southern Japan Sea. Here, we conducted a coupled analysis of Mg/Ca ratios and oxygen isotopes (δ18O) in shallow-dwelling Neogloboquadrina incompta from 13 core-top sediments in southern Japan, and developed a new equation for Mg/Ca temperature calibration (Mg/Ca = 0.311 × exp (0.07 × T)) as a proxy for spring sea surface temperature (SST). Using the newly developed, species-specific Mg/Ca-paleothermometry, we reconstructed SST variability for the past 6800 years from core YK10-7-PC09 in the southern Japan Sea. The Mg/Ca-derived SST record clearly represented five warmer periods at 6200–6000, 4900–4500, 4200–3800, 2600–2100, and 900–400 cal. year BP, almost consistent with previously published diatom records. These warmer events also corresponded to the periods in which warm molluscan assemblages increased at the northern end of the TWC, suggesting that periods of higher SST can be seen as reflecting the increased volume transport of the TWC. We interpreted the results of a model study showing that higher solar irradiance provoked positive Arctic Oscillation (AO)-like spatial patterns and the negative phase of the Pacific Decadal Oscillation (PDO) to mean that increased (reduced) TWC volume transport on the multi-centennial to millennial time scales was caused by high (low) solar insolation via a potential link between AO and PDO. Given that larger and more frequent volcanic eruptions occurred in the mid Holocene than in the late Holocene, volcanic forcing on the TWC volume transport changes would have been more significant during the former, as seen in the highly variable SST from this period and distinct decreases in SST around ~5900 cal. year BP and ~6400 cal. year BP. The millennial-scale fluctuations seen in SSTs in the southern Japan Sea would have had a large impact on the evolution of vegetation and human adaptation in the northern Japanese islands, adjacent to the Japan Sea, over the last 6800 years.

The Nankai Trough off southwest Japan has an ∼1300 yr historical record of great earthquakes, including the most recent, the A.D. 1944 Tonankai (M = 8.2) earthquake. Evaluation of the activity of an individual submarine fault is difficult when only onland observations are available. Submarine core records can pinpoint individual fault activity. Here we present Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment data from the shallow portion. IODP Expedition 316 drilled and cored several holes in the shallow portion of the offshore Tonankai earthquake area, including sites in the hanging wall of a margin-dominating splay fault that has previously been interpreted to have ruptured coseismically during megathrust earthquakes. X-ray computed tomography scanning revealed that the uppermost core at one site contains repeated occurrences of mud breccia. Radioisotope dating of the uppermost mud breccia indicates a deposition time consistent with the 1944 Tonankai earthquake, suggesting that the mud-breccia layers result from episodic brecciation caused by seismic shaking. Mud brecciation provides a potential new tool to reconstruct ancient earthquake history in subduction zones.

The occurrences of polycystine Radiolaria, Phaeodaria, and Acantharia are reported from plankton net samples, which were obtained in the transect covering from the Kuroshio Current off Shikoku Island to Tosa Bay during Cruise KT07-19 in August 2007. We employed 100 μm as the mesh size of the plankton nets, which was coarser than the mesh size of many recent radiolarian studies (e.g., 44 or 63 μm). The obtained specimens in the samples were categorized into 130 polycystine radiolarian, and 17 phaeodarian, and 3 acantharian taxa. The marked similarity of the polycystine radiolarian assemblages encountered in this study to those reported from the tropical and subtropical oceans in the literature clearly indicates the significant influence by the warm Kuroshio Current. Furthermore, the observed polycystine radiolarian assemblages are similar to those of the previous result from the same specific study area. However, the vertical distribution patterns of some of the major polycystine radiolarian and phaeodarian taxa are different from the previous results from the same region. The differences in vertical distribution may be primarily due to the differences in vertical water mass conditions due to different sampling seasons. In spite of the lengthy sample storage for seven months after the sampling in the shore laboratory, many acantharian specimens were still preserved and encountered in the laboratory census, representing the acantharian presence in the summer sea surface waters in the Kuroshio Current area.

In this paper we describe the sedimentary characteristics of the 2004 Indian Ocean tsunami deposits in and around Periya Kalapuwa Lagoon, Sri Lanka. Periya Kalapuwa is a coastal lagoon of about 13 km 2 area and has an average depth of about 1 m. It is separated from the Indian Ocean by coastal barrier sand dunes of up to 9-m elevation through which two inlet channels open the lagoon to the ocean. This region was hit by three waves during the 2004 Indian Ocean tsunami. The second wave was largest (4–6 m) and entered the lagoon not only via the two inlet channels, but also by flowing over the sand dunes. Erosive scars were found on the sand dunes adjacent to the two inlets. Twenty-seven core samples, along with trenching and hand-auger data, show that the tsunami deposits are 9 cm thick on average (up to 35 cm in the lagoon and up to 66 cm on the shore) and are composed mainly of medium sand (mean grain size 1.06 φ) with low mud content (0.61 wt.%), which is similar to the composition of sand from near the erosive scars in the sand dunes (mean grain size 0.94 φ), but different from the lagoon deposits (mean grain size 1.68 φ; mud content 4.7 wt.%). The distribution of the tsunami deposits was limited to within about 1 km from each inlet. The tsunami deposits become thinner and finer grained with increasing distance from the inlets. Most of the tsunami deposits are massive, but some show sedimentary structures: single or multiple-graded bedding structures, parallel laminations defined by layers of heavy minerals, and muddy laminations. Our observations and analyses suggest that the tsunami deposits were formed mainly from sand eroded from sand dunes near the two inlets. We estimated the total volume of tsunami sediments to be 83 000 m 3 . By assuming that the sediments of the tsunami deposits were supplied only by erosion of sand dunes from near the two inlets, this is equivalent to erosion of 83 m 3 of sand per meter of sand dune traversed by the tsunami wave.

We presented the total and inorganic carbon contents of core samples recovered from the Taiwan Chelungpu fault system, which slipped at the 1999 Chi-Chi earthquake, and reported lower contents of inorganic carbon within the black gouge zone in FZB1136 (fault zone at depth 1136 m in Hole B) and in the black-material disks in FZB1194 and FZB1243.

This study presents a high-resolution, multi-proxy analysis of sediments from IMAGES core MD972146 in the northern South China Sea (SCS). Analyses include detailed measurements of planktonic foraminifer oxygen isotopes, sediment carbonate, total organic carbon (TOC), opal, and phosphorus concentrations, as well as a Holocene interval of planktonic foraminifer sea surface temperature (SST) estimates. The age model of MD972146 was constructed by adopting oxygen isotope stratigraphy and AMS 14C dating, and fine-tuned further by correlation with nearby, well-studied SONNE 17940 and Hulu stalagmite isotope records. The age model indicates that this record covers the past 70,000 yr—from isotope stage 4 to the Holocene—with a nearly constant, very high sedimentation rate of ∼50 cm/kyr. Such sedimentation rates allow for intensive investigations of millennial-scale climate variability expressed in the SCS and its potential global linkages. We constructed a composite terrestrial index (CTI) for MD972146 through a principal component analysis of a suite of the core proxies that are sensitive to terrestrial sediment input. During the last glacial of stage 4 to stage 2, warm interstadials appear to coincide with high terrestrial sediment pulses inferred from the CTI, suggesting humid conditions in the SCS and Southern China. Intervals of high terrestrial input are also correlated with Heinrich events, suggesting an increase of eolian and possibly also of fluvial terrestrial input to the northern SCS. Our high resolution Holocene SST and salinity estimates show warm, stable and humid conditions during short episodes of quasi-periodic, millennial-scale cooling in the North Atlantic, superimposed on generally more humid conditions during the middle Holocene (4–6 ka) compared to the dry late Holocene (0–4 ka). The presented data provide evidence that a variety of mechanisms involving the strength of East Asian summer monsoons, migration of the Intertropical Convergence Zone, and processes that are analogous to those governing the El Nino Southern Oscillation and the Arctic Oscillation might play important roles in modulating tropical climate during the last glacial stages and the Holocene.

10 Be concentration was measured at ODP Site 925 on the Ceara Rise in the equatorial Atlantic. The 10 Be fluxes range from 50 to 270 × 10 7 atoms/cm 2 · kyr with an average over 100 × 10 7 atoms/cm 2 · kyr. The age-corrected 10 Be flux vs. the 9 Be flux ratio shows a nearly constant trend, suggesting the 10 Be is associated with the terrigenous fractions. All the 10 Be through the sediments in this area is either coming directly with the terrigenous fraction or scavenged by the terrigenous fraction. The variations of 10 Be flux in the sediments over 7 Ma could be explained by terrigenous input from Amazon drainage area.

[1] To determine the distribution pattern of water content in the three major fault zones penetrated by the Taiwan Chelungpu-fault Drilling Project (TCDP) hole B, and to assess a rapid, nondestructive water content measurement technique, time domain reflectometry (TDR), we determined the volumetric water content of sequential core samples and found that water content increased toward the center of each of the three fault zones, except in the disk-shaped black material. We observed distinct anomalies in the water content and resistivity profiles, particularly in the shallowest major fault zone (FZB1136), supporting the hypothesis that FZB1136 ruptured during the 1999 Chi-Chi earthquake. This study, the first successful application of the TDR technique to determine water content of core samples, including fault zone samples, collected by an active-fault drilling project, showed that this technique is suitable for measuring water content of fault core samples.

The landward changes in grain size and thickness of the 26 December 2004 Indian Ocean tsunami deposit on Phra Thong Island and in the Khao Lak Area, south-western Thailand, are summarized in this chapter. The maximum heights of the tsunami on Phra Thong Island and Khao Lak were 7 and 10 m, respectively. The tsunami produced 1- to 4-m-high erosional scarps at the shoreline in these areas. The tsunami deposit is a sheet of sand ranging from a few centimetres to 22-cm thick over a distance of 1500 m inland. It thins near its distal margin, but the thickness is strongly affected by local topography and lacks a consistent trend. The deposit is composed of medium to very fine sand, and fines inland, reflecting loss of energy. It is graded or massive. Sets of graded units result from multiple waves.

International audience; The iron content and the asymmetry of iron and magnesium ions in chlorites are examined for the Chelungpu Fault in Taiwan, which is a seismogenic fault. The samples are collected from the cores drilled for the Taiwan Chelungpu Fault Drilling Project (TCDP, borehole B). Three fault zones are recognized as candidates for the source of seismogenic materials. The fault zones are composed of fractured-damaged rocks, breccia, gray gouge, black gouge, and black material. Chlorite from each type of rock was analyzed by using X-ray diffraction (XRD). The iron content and asymmetry of the iron and magnesium ions in the chlorites were estimated from the XRD peak ratios. The hydroxide and silicate layers of chlorite in the black gouge and black material have low iron contents. Many studies have suggested that a temperature rise occurred at the fault zones. In addition, the temperature rise can result in the production of iron oxides such as magnetite or maghemite, as reported by other studies. However, the temperature rise cannot explain the low value of iron content in the chlorites. Another reason for the low value of iron content is the variation in the pH of the fluid, which can be controlled by radical reactions. Therefore, on the basis of chlorite characteristics, the reactions at the seismogenic fault are due not only to the thermal decomposition resulting from the temperature rise and but also to rock-fluid interactions.

[1] The Taiwan Chelungpu-Fault Drilling Project was undertaken in 2002 to investigate the faulting mechanism of the 1999 Mw 7.6 Taiwan Chi-Chi earthquake. Hole B penetrated the Chelungpu fault, and core samples were recovered from between 948.42- and 1352.60-m depth. Three major zones, designated FZB1136 (fault zone at 1136-m depth in hole B), FZB1194, and FZB1243, were recognized in the core samples as active fault zones within the Chelungpu fault. Nondestructive continuous physical property measurements, conducted on all core samples, revealed that the three major fault zones were characterized by low gamma ray attenuation (GRA) densities and high magnetic susceptibilities. Extensive fracturing and cracks within the fault zones and/or loss of atoms with high atomic number, but not a measurement artifact, might have caused the low GRA densities, whereas the high magnetic susceptibility values might have resulted from the formation of magnetic minerals from paramagnetic minerals by frictional heating. Minor fault zones were characterized by low GRA densities and no change in magnetic susceptibility, and the latter may indicate that these minor zones experienced relatively low frictional heating. Magnetic susceptibility in a fault zone may be key to the determination that frictional heating occurred during an earthquake on the fault.

[1] The Taiwan Chelungpu-fault Drilling Project (TCDP) was undertaken in 2002 to investigate the faulting mechanism of the 1999 Taiwan Chi-Chi earthquake. Hole B penetrated the Chelungpu fault, and recovered core samples from between 948.42 m and 1352.60 m depth. Three zones, marked 1136mFZ, 1194mFZ and 1243mFZ, were recognized in the core samples as active fault-zones within the Chelungpu fault. Multi-Sensor Core Logger measurements revealed lower densities and higher magnetic susceptibilities within the black gouge zones in all three fault zones. Even though the fault zone that slipped during the 1999 earthquake has not been identified, higher magnetic susceptibilities indicate that frictional heating has taken place in the Chelungpu fault.

Earthquake, we performed X-ray computed tomography imaging of core samples from Hole B of the Taiwan Chelungpu Fault Drilling Project. We established the relationship between the degree of X-ray attenuation and wet bulk density and obtained a porosity profile through the major fault zone at 1,136 m depth. The shear zones within the fault zone generally showed high porosity, and the porosity of the shear in the black gouge zone, which previous research suggests was the slip plane for the 1999 earthquake, was deduced to be 33.0%. This high porosity might indicate dilative shear deformation during the earthquake.