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In this study, Holocene changes in the riverine, eolian, and erosional supplies to the eastern part of the central Yellow Sea (YS) and their forcing mechanisms were determined on the basis of multiple mineralogical and geochemical indices of three age-dated piston cores from the central Yellow Sea mud (CYSM) deposition. The core records of the indices, including clay minerals, rare earth element fractionation parameters, and conservative trace elements, revealed abrupt changes in the sediment sources, especially ∼9.0 and 4.8 ka. The late last deglaciation and early Holocene sediments (Units 3 and 4, ∼14.1 to ∼9.0 ka) most likely originated from the paleo-Huanghe and the sea bed erosion, together with some contribution from the paleo-Changjiang Shoal sediments that extended northeastward into the YS. After that period, the dominant sediment source gradually changed to the Changjiang during the middle Holocene (∼9.0–4.8 ka, Unit 2), while the supplies from Huanghe and sea bed erosion to the south YS decreased. In the last 4.8 ka (Unit 1), the CYSM largely received Changjiang-derived sediments. Besides, some clay-sized particulates from the Huanghe, sea bed erosion, and Korea rivers might be transported to the CYSM during Unit 1. Possible mechanisms behind such changes in the riverine and erosional sediment sources and contributions include position shifts of river mouths, tidal stress evolutions, shelf sea-level fluctuations, East Asian monsoon climate changes, and the development of the YSWC and coastal circulation systems. [ABSTRACT FROM AUTHOR]

Based on a δO chronology, rare earth elements (REE) and other typical elements in sediments from core MD06-3047 in the western Philippine Sea were analyzed to constrain the provenances of the sediments and investigate quantitative changes in the Asian eolian input to the study area over the last 700 ka. Among the competing processes that might affect REE compositions, sediment provenance is the most important one. Provenance analysis suggests that the study sediments have two provenance end-members; local volcanic sources are dominant, and eolian dust from the Asian continent has a smaller contribution. During glacial periods, eolian input to the western Philippine Sea was enhanced. In contrast, material supply from local volcanics increased during interglacial periods. Changes in eolian input to the study area were probably related to the strength of the East Asian winter monsoon (EAWM) as well as aridity in the Asian continent on an orbital time scale, and were partly influenced by local control factors on shorter time scales. Therefore, we propose that the present study expands the application of the REE-based method for quantitatively estimating the eolian component from the mid-latitude northern Pacific to the low-latitude western Pacific. Additionally, the study preliminarily confirms the influence of EAWM-transported eolian material on sedimentation in the western Philippine Sea since 700 ka. [ABSTRACT FROM AUTHOR]

The Oceanic Anoxic Event 2 (OAE 2) represents one of the most profound global environmental disturbances of the Mesozoic Era, which was associated with a positive carbon isotope excursion due to widespread organic carbon burial. However, the character, evolutionary history, and exact driving mechanisms of OAE 2 are still much debated, exacerbated by the lack of records from climate-sensitive southern high latitudes. Here we present a multi-proxy record of a stratigraphically continuous succession spanning the late Cenomanian to early Turonian at the International Ocean Discovery Program Site U1516 in the Mentelle Basin off southwest Australia, which was located at southern high latitudes (~ 60–62°S) during the Late Cretaceous. Sedimentary records at Site U1516 allow the first detailed insights into source-to-sink processes in the Mentelle Basin and associated paleoenvironmental reconstruction in the southern Indian Ocean during OAE 2. Rare earth element abundances and clay-bound neodymium isotopes of the siliciclastic sediment fractions indicate that southwest Australia was the main detrital source of sediment at Site U1516 during OAE 2, with volcanogenic sediments representing only a minor component. A major provenance shift is observed across OAE 2, indicating an increased sediment contribution from distant sources (i.e., Yilgarn Craton and Albany-Fraser Orogen) relative to proximal sources (i.e., Perth Basin and Leeuwin Block) in southwest Australia, interpreted as reflecting a major reorganization of the drainage system due to enhanced fluvial runoff. Based on these findings, we infer that the OAE 2 interval showing the most prominent δ13C excursion was associated with an intensification of the hydrological cycle in the high-latitude southern hemisphere, with potential impacts on regional ocean chemistry and marine productivity. In particular, we suggest that enhanced terrigenous input and riverine nutrient export likely played a key role in controlling siliceous productivity at nearby ocean margins. As a consequence, the intense burial of organic matter (i.e., black shale) at Site U1516, which occurred episodically throughout OAE 2, possibly resulted from the combination of enhanced riverine-driven marine productivity and increased burial efficiency associated with the development of anoxic/euxinic bottom water conditions. • First detailed investigation of the source-to-sink process of the Mentelle Basin during OAE 2. • Geochemical records indicate dominant detrital contribution from Southwest Australia during OAE 2. • Enhanced hydrological cycle at southern high latitudes occurred during the interval with the most prominent δ13C excursion. • Multi-proxy records suggest a tight link between oceanic and continental changes during OAE 2. [ABSTRACT FROM AUTHOR]

Rare earth elements (REEs) of 91 fine-grained bottom sediment samples from five major rivers in Korea (the Han, Keum, and Yeongsan) and China (the Changjiang and Huanghe) were studied to investigate their potential as source indicator for Yellow Sea shelf sediments, this being the first synthetic report on REE trends for bottom sediments of these rivers. The results show distinct differences in REE contents and their upper continental crust (UCC)-normalized patterns: compared to heavy rare earth elements (HREEs), light rare earth elements (LREEs) are highly enriched in Korean river sediments, in contrast to Chinese river sediments that have a characteristic positive Eu anomaly. This phenomenon is observed also in primary source rocks within the river catchments. This suggests that source rock composition is the primary control on the REE signatures of these river sediments, due largely to variations in the levels of chlorite and monazite, which are more abundant in Korean bottom river sediments. Systematic variations in ΣLREE/ΣHREE ratios, and in (La/Yb)–(Gd/Yb)UCC but also (La/Lu)–(La/Y)UCC and (La/Y)–(Gd/Lu)UCC relations have the greatest discriminatory power. These findings are consistent with, but considerably expand on the limited datasets available to date for suspended sediments. Evidently, the REE fingerprints of these river sediments can serve as a useful diagnostic tool for tracing the provenance of sediments in the Yellow Sea, and for reconstructing their dispersal patterns and the circulation system of the modern shelf, as well as the paleoenvironmental record of this and adjoining marginal seas. [ABSTRACT FROM AUTHOR]

Based upon analyses of grain-size, rare earth element (REE) compositions, elemental occurrence phases of REE, and U-series isotopic dating, the sediment characteristics and material sources of the study area were examined for the recently formed deep-sea clays in the eastern Philippine Sea. The analytical results are summarized as follows. (1) Low accumulation rate, poor sorting and roundness, and high contents of grains coarser than fine silt indicate relatively low sediment input, with localized material source without long distance transport. (2) The REE Contents are relatively high. Shale-normalized patterns of REE indicate weak enrichment in heavy REE (HREE), Ce-passive anomaly, and Eu-positive anomaly. (3) Elemental occurrence phases of REE between the sediments with and without crust are similar. REE mainly concentrate in residual phase and then in ferromanganese oxide phase. The light REE (LREE) enrichment, Ce-positive anomaly, and Eu-positive anomaly occur in residual phase. Ferromanganese oxide phase shows the characteristics of relatively high HREE content and Ce-passive anomaly. (4) There are differences in each above mentioned aspect between the sediments with and without ferromanganese crust. (5) Synthesizing the above characteristics and source discriminant analysis, the study sediments are deduced to mainly result from the alteration of local and nearby volcanic materials. Continental materials transported by wind and/or river (ocean) flows also have minor contributions. [ABSTRACT FROM AUTHOR]

We analyzed rare earth elements (REEs) and Sr Nd isotope compositions of siliciclastic components in a sediment core from the middle Okinawa Trough (OT), to elucidate spatiotemporal variations in the sediment provenance, and their underlying mechanisms for the last 20 ky. Our results show that the trough deposits were characterized by different proportions of Changjiang- and Taiwan-derived (especially, the western rivers) sediments over time, from which we infer dramatic changes in sea-level, intensity of the Kuroshio Current (KC) inflow, and the East Asian monsoon since the last glacial maximum (LGM). In contrast to previous studies, the sea-level lowstand proximity of the paleo-Changjiang to the middle OT, and the contemporaneous enhancement of the East Asian winter monsoon (EAWM) may have played pivotal roles in supplying terrigenous inputs and forming middle OT deposits during the last glacial period, whereas the paleo-Huanghe was of lesser importance. After the early Holocene (especially the late Holocene cold period between ~4.8 and ~2.7 cal ky BP), a remarkable shift in the combined records of REEs and Nd isotopes reveals a causal link between variations in the Taiwan source and the KC inflow, coupled with climate changes in the East China Sea (ECS). This study suggests that Sr Nd isotope compositions and REEs are useful proxies for understanding the links between river development and paleoenvironmental/paleoclimatic changes in East Asian marginal regions. • Sr Nd isotopic records provide new insights into the sediment source in Okinawa Trough (OT). • Changjiang has played a leading role in forming the middle OT deposits during the last glacial period. • Taiwan-sourced sediments in the OT deposits are linked to Kuroshio/Taiwan Warm Current dynamics. • Our study provides that the comprehensive accumulation history of OT deposits over the last 20 ky. [ABSTRACT FROM AUTHOR]

This study analyzed grain size and elemental concentrations (Al, Mg, Fe, and rare earth elements (REEs)) in 91 surface sediments to elucidate sediment provenance in the Yellow Sea. Elemental concentrations were normalized by Al concentration ( C element / C Al ) to minimize the sediment grain-size effect (GSE). However, noticeable linear relationships between Al concentration (or mean grain size) and the ratio (e.g., Mg/Al or Fe/Al) appeared unexpectedly in pair diagrams. The spatial distribution patterns of Fe/Al and Mg/Al ratios were also similar to the pattern of mean grain size. This implies that the GSE was not removed completely, even after the normalization process. Thus, great care must be taken when applying the ratios of C element / C Al as a proxy of sediment provenance. To improve provenance discrimination of the sediments in the Yellow Sea, the difference between the REE distribution patterns of Chinese and Korean river sediments, expressed as δ ( δ = REE ∗ (La) − REE ∗ (Lu)), was calculated, and the spatial distribution patterns of the δ values were mapped. The δ values gradually increased from the western to the eastern part of the Yellow Sea, except for low δ values in the southeastern part of the Yellow Sea. This result indicates that the majority of Chinese and Korean river sediments are accumulating near to their respective coasts, except for a deposit along the southwestern coast of Korea in which a considerable amount of sediment from Chinese rivers has been accumulating. [ABSTRACT FROM AUTHOR]

Abstract: Rare earth elements (REE) along with selected major and trace elements were measured in laminated Ethmodiscus rex diatom mats and associated sediments (diatomaceous clay and pelagic clay) in two sediment cores collected from the Parece Vela Basin of the eastern Philippine Sea. REE distributions are characterized by strong enrichment of middle REE (MREE) and heavy REE (HREE) over light REE (LREE) and slight enrichment of MREE over HREE. This distribution pattern suggests that REE compositions of the laminated E. rex diatom mats were not the product of E. rex blooms, an inference also supported by the fact that Ti-normalized REE concentrations are not clearly different from those in the diatomaceous clay and pelagic clay. Comparison of REE patterns with the vertical distribution of authigenic phases in the sediment indicates that LREE were dominantly associated with detrital materials, whereas MREE and HREE were selectively enriched by Mn oxyhydroxides and authigenic phosphates. In the pelagic clay, a weak negative Ce anomaly cannot be linked to oxic depositional conditions but instead is attributed to the retention of a negative Ce anomaly associated with authigenic phosphates. In the laminated E. rex diatom mats, a weak positive Ce anomaly is consistent with depositional sulfidic anoxic conditions and is interpreted to represent enhanced scavenging of reduced aqueous Ce3+ by barite in a strongly reducing environment. Moreover, variably negative to positive Ce anomalies in the diatomaceous clay may reflect the concurrent operation of the two processes controlling Ce accumulation in the laminated E. rex diatom mats and pelagic clay. The study cores show a ubiquitous positive Eu anomaly owing to the presence of volcanic materials. The smaller Eu anomaly in the laminated E. rex diatom mats and diatomaceous clay relative to that in the pelagic clay may be attributed to the release of reduced Eu2+ from mineral phases to the sediment pore water under strongly reducing conditions. Previous studies have shown that the advection of Lower Circumpolar Water (LCPW) strengthened during the Last Glacial Maximum (LGM), which should have resulted in better ventilation of the deep eastern Philippine Sea. Evidence presented here for more reducing bottomwater conditions during the laminated E. rex diatom mats formation implicates elevated primary productivity and enhanced organic sinking fluxes as primary controls on redox changes in the eastern Philippine Sea during the LGM. Enhanced primary productivity and more reducing bottomwaters during the laminated E. rex diatom mats deposition resulted in a larger respired carbon pool in the deep eastern Philippine Sea, which may have been part of a larger-scale modulation of atmospheric CO2 variation during Pleistocene glacial–interglacial cycles by deep-ocean carbon storage. [Copyright &y& Elsevier]

Discriminating sediment sources quantitatively of several unique shelf-mud deposits in the Yellow Sea has received considerable attention, because they are active sedimentary depocenters that can elucidate the river sediment dispersal patterns and the depositional systems of the sea. Here, we propose a new sediment source proxy model of rare earth elements (REEs) that reflects innate characteristics of their fractionation distribution patterns and provides a reasonable and practical estimation for quantifying sediment source apportionments in the Yellow Sea. REEs of riverine and shelf-mud sediments were granulometrically and chemically partitioned, and the unique characteristics of their fractionation patterns were recorded and numerically indexed. We found distinct differences in the REE fractionation pattern index of riverine sediments, possibly due to the different source rock compositions. Notably, the acid-leached phase of the clay fraction may be a better material for quantitative evaluation of river contributions in the Yellow Sea. Using the REE-source index model presented here, proportional contributions of Chinese river sediments to the central and southeastern Yellow Sea mud deposits were estimated to be 55–80% and 10–40%, respectively, with higher percentage in the leached fraction. Our results elucidate the disagreement between mud budget and river discharge, particularly in Korean coastal mud deposits, as well as the source interpretation of the Yellow Sea shelf-mud deposits, which have been debated since the 1980s. • REEs of the river and shelf sediments were granulometrically and chemically partitioned. • REE fractionation patterns were categorized and indexed to quantify the sediment source. • We proposed a new REE-source index model applicable to the Yellow Sea sediments. • The results provide significant insights on dispersal systems of riverine sediments in the sea. [ABSTRACT FROM AUTHOR]