Search

Although tropical cyclones play a critical role in global climate changes, their long-term variations in the past are not well documented. In this article, a sediment core from the South Yellow Sea was studied in order to reveal the influence of tropical cyclones on depositional processes. Integrating the results of radiocarbon dating and sediment grain-size analysis, we show that the studied sequence was deposited during the Holocene and the sedimentary dynamics were stable and at a relatively low level, with a median grain-size range of 5.3–8.7 µm. It is found that coarse particles were likely transported by highly dynamic depositional events. Based on the findings, a record of paleo-tropical cyclones was derived for the Early Holocene, and several intervals with a reduced influence of tropical cyclones were identified. In addition, it reveals a good agreement between the grain-size results and the changes in solar activity, monsoonal intensity, and the El Niño-Southern Oscillation. Overall, it can be concluded that the influence of tropical cyclones on the sedimentary evolution of the muddy zone of the South Yellow Sea was substantial during the Early Holocene on centennial timescales, and that solar maxima may control the intensity of tropical cyclones via strengthening the walker circulation over the tropical Pacific. [ABSTRACT FROM AUTHOR]

A high-resolution astronomical-tuned magnetostratigraphy was obtained from a continuous 333-m succession recovered at International Ocean Discovery Program (IODP) Hole U1499A in the north margin of the South China Sea (SCS) during joint Legs 367 & 368. A total of 12 magnetic reversals are identified through the Pliocene and Pleistocene. The cycle analysis of natural gamma ray (NGR) data shows an average suite of ca. 33 m and 8 m wavelengths with lesser 1.5-m cycles, which are consistent with the ratios of Milankovitch orbital-climate oscillations caused by long eccentricity (405 kyr), short eccentricity (~100 kyr), and precession (~20 kyr). The astronomical-tuned magnetostratigraphy correlates with nearly all features of the Pliocene-Pleistocene geomagnetic polarity time scale. There was a significant shift to ~100-kyr-dominated cyclicity at ca. 1.3 Ma, which marks the onset of the Mid-Pleistocene Transition, during which the influx of the clay component decreased. A general enrichment in silt-sand influx during the past 0.4 Myr was punctuated by surges in coarser-grained components (lowest NGR) during or at the end of each major global glacial event. Comparison to a high-resolution sediment record spanning the Pliocene-Pleistocene on the southern margin of the SCS (ODP Site 1143) indicates common intervals of changing rates of sediment accumulation. In both regions, there are relatively lower rates of sediment accumulation during the late Zanclean (mid-Pliocene; ca. 4.1 to 3.6 Ma), early Gelasian (ca. 2.5 to 2.0 Ma), early Calabrian (ca. 1.6 to 1.4 Ma) and the earliest Middle Pleistocene (ca. 0.6 Ma). The merger of magnetostratigraphy, cyclostratigraphy and the NGR record to produce a high-resolution profile of bulk sediment accumulation rates and relative clay to sand-silt components is a powerful tool and climate proxy to reconstruct the general history of sediment input into the SCS and its relationships to East Asia monsoon and tectonic evolution. • First astronomical-tuned magnetostratigraphy from South China Sea (SCS) IODP cores • Lower accumulation rates during late Zanclean, early Gelasian and early Calabrian • Mid-Brunhes Event (500 ka) marks the onset of major coarser-grained clastic input. • Astronomical-tuned NGR events correlate to global benthic foraminifer δ18O curve. • Apparent synchronous sediment accumulation trends in northern and southern SCS [ABSTRACT FROM AUTHOR]

We conducted a statistical study to characterize the nonlinear response of the East Asian summer monsoon (EASM) to its potential forcing factors over the last 260 ka on orbital timescales. We find that both variation in solar insolation and global ice volume were responsible for the nonlinear forcing of orbital-scale monsoonal variations, accounting for ~80% of the total variance. Specifically, EASM records with dominated precession variance exhibit a more sensitive response to changes in solar insolation during intervals of enhanced monsoon strength, but are less sensitive during intervals of reduced monsoon strength. In the case of global ice volume with 100-ka variance, this difference is not one of sensitivity but rather a difference in baseline conditions, such as the relative areas of land and sea which affected the land-sea thermal gradient. We therefore suggest that EASM records with dominated precession variance recorded the signal of a shift in the location of the Inter-tropical Convergence Zone, and the associated changes in the incidence of torrential rainfall; while for proxies with dominated 100-ka variance, it recorded changes in the land-sea thermal gradient via its effects on non-torrential precipitation. [ABSTRACT FROM AUTHOR]

Many ancestry informative SNP (AISNP) panels have been published. Ancestry resolution in them varies from three to eight continental clusters of populations depending on the panel used. However, none of these panels differentiates well among East Asian populations. To meet this need, we have developed a 74 AISNP panel after analyzing a much larger number of SNPs for F st and allele frequency differences between two geographically close population groups within East Asia. The 74 AISNP panel can now distinguish at least 10 biogeographic groups of populations globally: Sub-Saharan Africa, North Africa, Europe, Southwest Asia, South Asia, North Asia, East Asia, Southeast Asia, Pacific and Americas. Compared with our previous 55-AISNP panel, Southeast Asia and North Asia are two newly assignable clusters. For individual ancestry assignment, the likelihood ratio and ancestry components were analyzed on a different set of 500 test individuals from 11 populations. All individuals from five of the test populations – Yoruba (YRI), European (CEU), Han Chinese in Henan (CHNH), Rondonian Surui (SUR) and Ticuna (TIC) – were assigned to their appropriate geographical regions unambiguously. For the other test populations, most of the individuals were assigned to their self-identified geographical regions with a certain degree of overlap with adjacent populations. These alternative ancestry components for each individual thus help give a clearer picture of the possible group origins of the individual. We have demonstrated that the new AISNP panel can achieve a deeper resolution of global ancestry. [ABSTRACT FROM AUTHOR]

The variability of the winter monsoon is one of the key components of the Asian monsoon, significantly influencing paleoenvironmental evolution in East Asia. However, whether the winter or the summer monsoon is the dominated factor controlling sedimentary dynamics of the muddy areas of the continental shelves of the East China Sea is debated, due to lack of consistency between various winter monsoon proxies in previous studies. In this work, the sediments of the upper part of core ECS-DZ1 with several marine surface samples were studied in terms of sediment grain size and radiocarbon dating, and changes in sedimentary dynamics of the northern muddy area of the ECS over the past 5000 years were documented. The main findings are as follows: (1) regional sedimentary dynamics were low and did not significantly change since the middle Holocene; (2) coarse particles are the dominated component in the sediments; (3) a proxy can be derived to indicate changes in winter monsoon. Based on this reconstructed winter monsoon record, we found that this record was generally negatively correlated to the stalagmite-based summer monsoon variability over the past 3500 years, but positively correlated before that. Moreover, this record can be well correlated to changes in the Kuroshio Current and the Bond ice-rafting debris events in the North Atlantic on millennial timescales, inferring large-scale and common atmospheric dynamics across the Asian continent over the past 5000 years. Therefore, we concluded that the winter monsoon is the predominant factor controlling sedimentary dynamics in the northern part of the ECS and proposed that the contribution of coarse particles may be one of potential indices to identify the role of the winter and the summer monsoons in sedimentary evolution. [ABSTRACT FROM AUTHOR]

Discriminating the provenance of fine-grained sediments is crucial for reconstructing paleogeography, sedimentary processes, and paleoclimate. In this paper, we investigate the South Bohai Coast to better understand source-to-sink systems in East Asia. This region is influenced by both distant sources such as the large-scale Yellow River and small local river sources flowing from the Luzhong Mountain area. Two Holocene sedimentary cores, dated using optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) 14C chronology, were used to investigate the provenance of the fine-grained sediments over the last 7 kyrs. Clay mineralogy and relevant non-linear modeling were employed for provenance discrimination. The results show that the fine-grained sediments along the South Bohai Coast were mainly derived from the Yellow River during the periods of 7.0–5.4 ka and 4.5–2.6 ka, respectively, while the input from the Luzhong Mountain-derived rivers was greater during 5.4–4.5 ka and 2.6–0.2 ka, respectively. Fluvial activities and marine-terrestrial interaction driven by climate factors such as East Asian winter monsoon, temperature, and precipitation in river basins, dominantly influenced the provenance of fine-grained sediments from 7.0 to 2.6 ka. Anthropogenic impact on provenance increased after 2.6 ka. The chronology of the two cores showed extremely rapid sedimentation rate transitions at 5.2 ka and 1.5 ka, respectively, very likely attributed to anthropogenic-induced rapid progradation. Our study provides a model for better understanding the paleoenvironmental and paleogeographic evolution of a coastal area where multiple sources exist. • Anthropogenically high sedimentation rate in the South Bohai Coast in late Holocene. • Provenance discrimination of the fine-grained sediments in the South Bohai Coast since the mid-Holocene. • The major source of the fine-grained sediments in the South Bohai Coast changed episodically. [ABSTRACT FROM AUTHOR]

Abstract: Since the mid-Pliocene, East Asian climates have experienced significant changes. One view suggests that significant uplift of the Tibetan Plateau during this period could have been responsible for these dramatic changes in the strength of the East Asian monsoon and for Asian interior aridification, while some other authors attribute these changes to the ongoing global cooling and rapid growth of the Arctic ice-sheet. Up to the present, which factor dominates the major changes of East Asian climate in the mid-Pliocene is still a contentious issue. This study presents an analysis of several climate proxies including grain-size, (CaO* +Na2O+MgO)/TiO2 ratio, Na/Ka ratio and dust accumulation rates of the Xifeng Red Clay sequence in the eastern Chinese Loess Plateau and the Xihe Pliocene loess-soil sequence in West Qinling. They reveal that aridity in the continental interior and winter monsoon circulation both intensified, whereas the East Asian summer monsoon showed a weakening rather than intensifying trend since the mid-Pliocene. These changes are also supported by the other multi-proxy records from various regions in East Asia. Previous numerical modeling studies have demonstrated that uplift of the Tibetan Plateau would have simultaneously enhanced continental-scale summer and winter monsoon strength as well as central Asian aridity. The mid-Pliocene climate changes in East Asia are therefore unlikely to be a response to Plateau uplift. On the contrary, our recent modeling results give support to the view that ongoing cooling could have intensified both the aridity of the interior and the strength of the winter monsoon, but weakened the summer monsoon in East Asia. [Copyright &y& Elsevier]