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Abstract: Changes in paleorainfall intensity linked to the strength of the East Asian (EA) summer monsoon since 21cal kyr BP are inferred from the organic matter contents of a 15-m sediment core from Tung-Yuan Pond in southern Taiwan. High total organic carbon/total nitrogen (TOC/TN) values in association with increased TOC content suggest that more soil-derived material containing terrestrial organic matter (OM) was delivered to the lake during periods of increased runoff associated with extensive precipitation that resulted from intensified summer monsoons, whereas low values indicate OM possessing a dominant algal origin during weakened summer monsoons. Rainfall intensity in terms of the proportion of terrestrial OM was high in four periods: the last deglaciation (∼17.2 to ∼12.2ka), the early Holocene (∼10.6 to ∼8.6ka), the middle Holocene Thermal Optimum (∼7.7 to ∼5ka) and the late Holocene (∼4.2 to ∼2ka), whereas it was low in the intervening time periods. High TOC/TN values coincide with peak values of summer insolation, and thus the strongest EA summer monsoon during the early and middle Holocene; small drops in these ratios correspond to increasing and decreasing solar radiation in the deglacial period and the late Holocene, respectively. The four intervals with low TOC/TN ratios, as well as episodic drops of the ratios during the deglaciation and the early and late Holocene are concordant with the late last glacial (∼21 to ∼17.2ka), the Oldest (∼14.8ka), the Older (∼13.3ka) and the Younger Dryas (∼13 to ∼11.5ka), the 8.2 cold event (∼8.6–7.7ka) and a late Holocene cold event (∼5–4.2ka), and suggest a weakened EA summer monsoon during these times. Moreover, high frequency hydrological variability occurred during the early Holocene, heavy rainfall persisted during the middle Holocene, and precipitation intensity generally diminished after ∼5ka. The Tung-Yuan Pond sediment record indicates that the TOC/TN ratio can be used as a paleorainfall intensity proxy to trace variations in the EA summer monsoon strength in other small lakes. [Copyright &y& Elsevier]

Abstract: Primary rock magnetism analysis was performed on samples from the Jiulong outcrop across the Anxian–Guanxian fault of the 2008 Wenchuan Earthquake rupture zone. The protolith of hanging wall of this outcrop is the upper Triassic sediments, which formed the fault breccia and gouge by repeated large earthquakes. The footwall of this outcrop contains Jurassic grayish-green and dark-purple sandstones. The average magnetic susceptibility value of the gouge is slightly less than that of potential protolith. Based on the primary rock magnetism, the main magnetic carriers are Fe-sulfides for the gouge, magnetite for the fault breccia, and magnetite and hematite for the Jurassic grayish-green and dark-purple sandstones. Possibly during or after repeated large earthquakes (just like the 2008 Mw 7.9 Wenchuan Earthquake), it transformed the magnetic mineral from magnetite to Fe-sulfides by low thermal decomposition processes along the Anxian–Guanxian earthquake fault, which induces the slightly less average magnetic susceptibility values of the gouge than that of potential protolith. If this magnetic mineral changed only because of repeated large earthquake process, the heating by low velocity seismic slip friction and seismic fluid could possibly have been less than 300°C. If this magnetic mineral of the Anxian–Guanxian earthquake fault is only induced after repeated large earthquakes, the earth surface process acts an important role for the magnetic mineral change. More other further studies should be done to verify the primary magnetic mineral phase change and discriminate the time of this magnetic mineral variation. [Copyright &y& Elsevier]

Abstract: In this study, we synthesized the fossil pollen data from 10 lake sediments and 2 land cores to integrate the alteration of forest covered areas in northern Taiwan with changes in humidity and temperature over the last 2000 years. The abundance of arboreal pollen, fern spores and Tsuga pollen in the pollen and spore assemblages were used as indicators. Our results suggested that the climate in northern Taiwan was stably cool and dry during 2000–1000cal. yr BP, but changed to wet and warm during 1000–500cal. yr BP, which corresponded to the Medieval Warm Period (MWP). In addition, an increased density and dispersal of Tsuga pollen corresponding to 500–200cal. yr BP was observed, which corresponded to the Little Ice Age (LIA). In recent years, a decline in Tsuga pollen density and increased fern spore density has been observed, which indicates an increase in temperature associated with elevated rainfall. Based on the synthesized data set, we conducted GIS mapping of such changes in the north of Taiwan over time. The results revealed that the temporal and spatial climate changes could be inferred from the palynological GIS mapping method, and that the fluctuations in temperature over time matched well with the global climate events, including MWP, LIA and recent warming. [Copyright &y& Elsevier]

Abstract: Characterized by extended seasonal sea-ice cover, the Okhotsk Sea is widely considered one possible source of the North Pacific Intermediate Water (NPIW). Therefore, reconstructing the characteristics of the sediments that resulted from the ice-melting pulses of this northeastern Asian sea during glacial–interglacial cycles is crucial to understanding past climatic changes and NPIW formation in the northwest Pacific Ocean. Here, we produced the detailed mineralogy and geochemistry of the upper 20 m of the sediments of IMAGES Core MD012414, which was drilled in the central part of the Okhotsk Sea. This depth covers the last 500 kyrs. The mineralogical data show that in glacial periods, the sediments were predominantly composed of quartz and plagioclase with a volume of about 80%, indicating that they were mainly from the surrounding landmasses. During interglacial periods, however, biogenetic calcite and amorphous opal drastically increased from less than 5% to a remarkable 40–60%, while the element ratios Mg/Al, Ca/Al and Si/Al also had anomalous increases from 0.2 to 0.5, 0.12 to 1.2 and 3.5 to 10, respectively. These characteristics of the sediments in interglacial periods strongly suggest that the melting of permanent ice opened a gateway, thereby letting the northwest Pacific warmer water flow into the Okhotsk Sea, which subsequently increased biogenetic productivity during the deglacial periods. In addition, in early interglacial periods, the bottom water became anoxic, as evidenced by the presence of dolomite and the enrichment of the Mn/Al and P/Al ratios more than 25 to 200 times. The fact that these trends did not occur in stage 7 strongly suggests that stage 8 may have been a warmer glacial period. [Copyright &y& Elsevier]

Abstract: Pollen record derived from the sediment core of Lake Li-yu Tan, central Taiwan, provides valuable information of vegetation history, climate change, and agricultural activity. Subtropical evergreen forests dominated the uplands surrounding this lake from 2.6 ka BP, indicating the climate was warm. However, the appearance of warm-temperate forest vegetation suggests two relatively cool periods, prior to 2.3 ka BP and between 1.6 and 1.2 ka BP. Based on the presence of cultivated pollen, including Poaceae (>40 μm), Lagerstroemia, and Melia, agricultural activity was expansive between 1.6 and 1.2 ka BP and from 0.6 ka BP. This study also provides the first charcoal record in Taiwan. Natural fires occurred frequently during the interval 2.6 to 1.7 ka BP, as shown by continuous and stable charcoal influxes. Decline in charcoal influxes elucidates that fires decreased during the interval 1.7 to 1.6 ka BP. Fire events resulting from agricultural activity occurred between 1.6 and 1.2 ka BP. The high fluctuation of charcoal influxes during this period also indicates charcoal production by humans, presumably near the lake, based on the appearance of large charcoal particles (>500 μm). Fires decreased gradually from 1.2 ka BP. [Copyright &y& Elsevier]

Abstract: We present a mineralogical and geochemical study of core MD012404, retrieved from the central Okinawa Trough (OT) of the East China Sea. Our studies reveal that the sediment sources of the core have been changed through time during the past 100 ka. Our mineralogical proxies indicate that the sediments source from the Yangtze River correlates well sea-level changes before 24 ka. Our Ti/Al ratios otherwise indicate an increase of sediment supply from eastern Taiwan after 26 ka. The cooler climate of the Last Glacial Maximum (LGM, 23∼19 ka) led to a reduction in fluvial sediments from the Yangtze River. However, subsequent climate warming (after ∼19 ka) resulted in an abrupt increase in fluvial sediments. After the LGM, the Kuroshio intrusion flow into the OT may have increased. We also infer anomalous changes in eolian sources transported by winter monsoons during the LGM and at 80 ka based on an eolian mineralogical indicator (feldspar). We conclude that the sediment source of core MD012404 is primarily of terrestrial origins, but influenced by sea-level changes and variations in the East Asian monsoon. [Copyright &y& Elsevier]

Variations in sea surface temperature (SST), productivity, and biogenic components such as total organic carbon (TOC), carbonate, and opal contents measured from IMAGES (International Marine Global Changes Study) core MD972142 provide information about long-term paleoceanographic changes during the past ~870000 years in the southeastern South China Sea (SCS). MD972142 U37 k'-SSTs varied from 25 to 29°C, paralleling the glacial to interglacial changes. MD972142 biogenic components show relatively high carbonate and opal, and low TOC contents in interglacial stages, and low carbonate and opal and high TOC contents in glacial stages, and these variations appear to be sensitive to regional terrestrial sediment input and productivity. Our analysis indicates that the MD972142 carbonate record is primarily controlled by terrestrial sediment inputs that are associated with sea level fluctuations during past glacial-interglacial stages. The TOC record reflects past glacial-interglacial changes in both monsoon-induced productivity and terrestrial organic matter input in the SCS. The TOC record exhibits several short-term peaks that are associated with lower U37 k' -SSTs (especially in MIS 2 - 4, 10, 12), perhaps implying a much strengthened winter monsoon. The opal record shows relatively high content in most interglacial stages, which appears to be linked to increased summer monsoon upwelling or increased siliceous sediment input by more precipitation and river runoff during warm climate conditions. The TOC and opal contents both show long-term increasing trends since the mid-Brunhes, most noticeably from ~330 kya. The long-term trends observed in this study are most likely attributable to changes in SCS hydrography, productivity, and/or preservation in response to the increased strength of the East Asian monsoon system on possibly tectonic timescales. [ABSTRACT FROM AUTHOR]