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As a high-sedimentation rate depocenter along the path of the Kuroshio Current, the southwesternmost part of the Okinawa Trough is a key area to understand the Kuroshio history and sediments transportation. A 34.17-m-long sediment core was obtained by the advanced piston corer of Marco Polo/IMAGES XII MARION DUFRESNE during the May 2005 from the Southern Okinawa Trough at site MD05-2908. The recovered sediments were analyzed by AMS 14C dating, coarse size fraction (>63 pm) extraction and moisture content determination in order to study its sedimentation flux and provenance. The depth-age relationship of core MD05-2908 was well constrained by 17 14C dating points. The sediments span across the mid-Holocene (6.8 ka B.P.) and have remarkablely high sedimentation rates between 1.8 and 21.2 m ka-1, which is well consistent with the modern observations from sediment traps. We identified five 70-200 a periods of abnormally rapid sedimentation events at 6790-6600 a B.P., 5690-5600 a B.P., 4820-4720 a B.P., 1090-880 a B.P., and 260-190 a B.P., during which the highest sedimentation rate is up to 21.2 m/ka. In general, the lithology of the sediments were dominated by silt and clay, associated with less than 5% coarse size fraction (>63 pm). As the most significant sediment source, the Lanyang River in northeastern Taiwan annually deliver about 10Mt materials to the coastal and offshore region of northeast Taiwan, a portion of which could be carried northward by currents toward the study area. Therefore, we concluded that the 5 abnormally rapid sedimentation events may be related to intensified rainfall in Taiwan and thus increased materials to our study area at that time. However, a few extreme-rapid sedimentation events cannot be explained by normal river runoff alone. The large earth-quakes or typhoons induced hyperpycnal discharge of fluvial sediment to the ocean may also act as a potential source supply to the Okinawa Trough. [ABSTRACT FROM AUTHOR]

[Display omitted] • Analytical results from fifty submarine sediment samples from six hydrothermal fields along the southern Mid-Atlantic Ridge are presented and discussed. • Sediments comprise calcareous biodetritus, hydrothermal and lithogenic materials and elements scavenged from seawater. • Analytical results imply two separate hydrothermal fluids with REE patterns exhibiting positive and absent Eu anomalies, respectively. • Both sulfide-rich and Si-Fe-Mn oxide-rich MS were precipitated from initial high-temperature hydrothermal fluids. • MS samples suggest different sedimentary processes in the northern and southern segments of the SMAR. In this study, we present mineralogical and geochemical analyses of 50 unconsolidated submarine surface sediments collected from separate locations within six active hydrothermal fields (Zouyu, Taij, Caifan, Deyin, Xunmei, and Tongguan) along the southern Mid-Atlantic Ridge (SMAR) at 12°S–28°S. The samples consisted of 33 metalliferous sediments (MS) and 17 non-metalliferous sediments (non-MS). The study area was divided into a northern segment that contained the Zouyu, Taij, Caifan, and Deyin hydrothermal fields and a southern segment containing the Xunmei and Tongguan hydrothermal fields. The presence of chalcopyrite, octahedral pyrite, and cubic pyrite without streaks on the surface of the sediments reflected a stable high temperature mineralization environment with a small temperature gradient in the Xunmei hydrothermal field. Cubic pyrite with growth striations co-existing with pentagonal dodecahedon-form pyrite indicated an unstable ore-forming environment with large temperature gradient in the early stage and a more stable ore-forming environment in the late stage in the Tongguan hydrothermal field. Major and trace element geochemistry data indicated that the most important material source for the abiogenic component of the sediments along SMAR 12°S–28°S was hydrothermal materials, the second most important source was lithogenic components, and the third source was elements scavenged from seawater. The Xunmei and Tongguan hydrothermal fields may have recorded phase separation, a process that would have resulted in the formation of two separate hydrothermal fluids, thereby forming two types of sulfide-rich MS with rare earth element (REE) patterns with positive and absent Eu anomalies, respectively. The Si-Fe-Mn oxide-rich MS had positive Eu anomalies, which also indicated that these oxides in sediments were directly precipitated from initial hydrothermal fluids at high temperature. The chlorite-rich MS exhibited nearly flat REE patterns similar to the volcanic material-rich samples and mid-ocean ridge basalt (MORB), which reflected the origin of the hydrothermal alteration of volcanic materials. In the northern segment, most of the MS were derived from plume fall-out Fe oxide particles. In addition, the chlorite-rich MS was likely derived from hydrothermal alteration. In the southern segment, the hydrothermal materials in the MS were primarily derived from the collapse of sulfide-bearing chimneys and Si-Fe-Mn oxide debris directly precipitated from hydrothermal fluids. [ABSTRACT FROM AUTHOR]

Abstract Taiwan is particularly sensitive to changes in monsoonal precipitation and to typhoon-induced heavy precipitation events, however, rainfall variability in Taiwan on centennial and millennial time scales during the Holocene has not been well understood. This study describes mid-Holocene rainfall features of Taiwan based on pollen, total organic carbon (TOC), total nitrogen (TN), and C/N ratio records of core MD05-2908. The step-wise increase in sedimentation rate, fern spore percentage and concentration, TOC content, and C/N ratio suggests an increasing terrestrial material supply due to the intensified rainfall in Taiwan since 6800 cal. yr BP. This rainfall pattern shows an inverse pattern to the decreasing East Asian summer monsoon (EASM) strength represented by the multi-proxy records from North China. Variation of the East Asian summer circulation and associated moisture transport may account for the long-term rainfall changes in Taiwan. Superimposed on this trend, we interpreted three prominent rainfall changes, which focus on the periods of 6800–6600, 1090–880 and 490–190 cal. yr BP. These centennial time scale rainfall variations in our records are linked to the intensity of El-Niño Southern Oscillations. Highlights • Pollen evidence enabled to trace the sources of sediments in South Okinawa Trough. • The rainfall variation of Taiwan during the past 6800 years is reconstructed by multi-proxies. • The result leads an improved understanding of the interplay between East Asian Monsoon and ENSO since mid-Holocene. [ABSTRACT FROM AUTHOR]