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Three long marine cores collected from the southwestern part of the Ulleung Basin in the East Sea were investigated in terms of chronology, from the middle Pleistocene to Holocene. We propose an age–depth model in cores 19ESDP-101, 19ESDP-103, and 19ESDP-104 obtained through precise age data using a suitable statistical method and classified in chronological units according to their accumulation rates. Changes in accumulation rate in cores 19ESDP-103 and 19ESDP-104, located at the entrance to the contact of the Korean Strait and the Ulleung Basin, showed good agreement with glacial and interglacial cycles. Relatively increased accumulation rates are related to ocean currents flowing through the Korea Strait during interglacial periods of Marine Isotope Stage (MIS) 5 and 7. However, core 19ESDP-101 obtained from the Hupo Basin, located in the northern site, showed a high accumulation rate in the glacial periods of MIS 6 and 8. It is interpreted as an increase in the sediment input from the exposed shallow shelf and inland fluvial, despite the fact that ocean currents from the Korea Strait are blocked by the exposed shelf platform as the sea-level falling down. These results show that the continental shelf on the western East Sea has been deposited from various factors related to several sea-level fluctuations from the glacial-interglacial cycle during the middle to late Quaternary. This study contributes to stratigraphic study in the Korean continental shelf environment of the East Sea from the middle Pleistocene to Holocene. [ABSTRACT FROM AUTHOR]

A common optically stimulated luminescence (OSL) method for dating sediments is the single-aliquot regenerative-dose (SAR) protocol, which is widely applied to measure the equivalent dose (D e) in various sedimentary samples. The modified SAR protocol is distinguished from the conventional SAR protocol by the application of additional high-temperature (e.g. 280 °C) optical stimulation at the end of the procedure. In this study, we performed a dose recovery test using fine-grained (4–11 μm) quartz sample derived from coastal sediments and found that the D e values recovered using the modified SAR protocol were significantly overestimated by ∼30% compared with the given dose, except for a preheating temperature of 160 °C. In contrast, D e values recovered using the conventional SAR protocol showed good agreement with the given dose (within ±10%) over a large preheating temperature range (160–260 °C). Differences in the dose-response curves between the conventional and modified SAR protocols may have led to the overestimation of D e values recovered using the latter approach. The lack of proportionality between L x and T x in the modified SAR protocol complicated the construction of the SAR dose-response curve and dose recovery. To avoid these phenomena, which may be highly sample dependent, modified SAR for OSL dating should be applied only to samples dominated by the slow OSL component and with high recuperation levels. • The sensitivity change could be induced by the modified SAR protocol. • The modified SAR protocols may have led to the overestimation of D e values. • It should be applied only to samples dominated by the slow OSL component and with high recuperation levels. [ABSTRACT FROM AUTHOR]

Abstract The Huksan Mud Belt (HMB) is located in the south-eastern Yellow Sea. The radiocarbon (14C) and optically stimulated luminescence (OSL) age datings of the pre-Holocene HMB sediments were compared precisely. OSL dates for the uppermost HMB sediments showed the recent and short-term chronological development of the HMB. OSL and 14C ages of the Holocene sediment (HMB cores 101–103) were relatively consistent. By contrast, the OSL ages of the pre-Holocene sediment unit were considerably older than the 14C ages (by approximately 30%), where the OSL ages corresponded broadly to marine isotope stages (MIS) 5 and 4 (from about 125 ka to > 50 ka). An overall comparison of 14C and OSL dates suggests that the age of the Holocene mud unit is well constrained by 14C dating. However, 14C ages older than 40 ka may be unreliable. The surficial sedimentation rate and depositional ages for a 6.5-m-thick sequence of the uppermost unit (12HMB cores) were determined. Twenty OSL samples gave an age of approximately 8.5 ka. Most of the OSL ages for each site were in stratigraphic order. The surficial sediment ages for the 12 HMB cores were 2.6 ka for P-08, 7.7 ka for P-10, 7.3 ka for P-11, and 0.05 ka for P-14. The approximate surficial sediment ages of the uppermost unit of the HMB-101, -102, and −103 cores were 6.7 ka, 6.8 ka, and 1.1 ka, respectively. The spatiotemporal differences in deposition and erosion of the HMB Holocene muds, supposedly driven by changes in large, strong tidal forces and marine water depth, and an increase in ocean current velocity, could account for the various surficial deposition ages in the area. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop a novel dabigatran etexilate hemisuccinate (DEH) salt-loaded polycap with bioequivalence to the dabigatran etexilate mesylate (DEM)-loaded commercial product. DEH prepared with dabigatran etexilate base (DE) and succinic acid was less hygroscopic but less soluble than DEM. Numerous micronized DEHs and DEH-loaded solid dispersions were prepared employing the spiral jet-milling and spray-drying techniques, respectively. Among the formulations prepared, a micronized DEH prepared with the injection air at 1.5 bar and the grinding air at 2 bar, and a DEH-loaded solid dispersion prepared with 6 g HPMC most improved the drug solubility, respectively. Moreover, the micronized DEH provided more increased drug solubility and dissolution compared with the solid dispersion, even though its drug solubility was still lower than that of DEM. Unlike the situation in other studies, the enhanced solubility and dissolution of DEH was more due to particle size reduction than to a change to the amorphous form. The micronized DEH prepared with Myrj 52S had greater drug solubility than preparations with other surfactants. Among the organic acids investigated, only fumaric acid (128.8 mg) showed a similar pattern in pH changes to the DEM-loaded commercial product. Furthermore, in order to make the environment acidic while preventing the direct contact of the drug with fumaric acid, the polycap was composed of a tablet containing the micronized DEH, Myrj 52S and other ingredients, and separate fumaric acid. This micronized DEH-loaded polycap was dissolution- and bio-equivalent to the DEM-loaded commercial product in beagle dogs. Thus, the novel micronized DEH-loaded polycap would be a promising alternative to the DEM-loaded commercial product. [ABSTRACT FROM AUTHOR]

The objective of this study was to develop a novel prasugrel base microsphere-loaded tablet (PBMST) with enhanced stability as a bioequivalent to the commercial prasugrel hydrochloride-loaded tablet. Numerous prasugrel base-loaded microspheres were prepared with hydroxypropylmethyl cellulose (HPMC), colloidal silica and various acidifying agents using a spray-drying process, and the physicochemical properties, solubility and stability were investigated. The PBMSTs were prepared and their dissolution, pharmacokinetics in beagle dogs and stability were evaluated compared to commercial prasugrel hydrochloride-loaded tablets. Among the acidifying agents tested, phosphoric acid provided the greatest increase in drug solubility, by as much as 110-fold. The prasugrel base-loaded microspheres composed of prasugrel base, HPMC, colloidal silica and phosphoric acid at a weight ratio of 10/10/5/2.5 provided an amorphous drug and reduced particle size of about 11.3 μm. Moreover, it exhibited excellent solubility and improved stability compared to prasugrel base and hydrochloride. Moreover, PBMST drug dissolution was improved in comparison to the prasugrel base-loaded tablet (PBT), with similar dissolution to the commercial prasugrel hydrochloride-loaded tablet at pH 1.2 and 4.0. PBMST provided significantly higher plasma concentrations of AUC and C max in beagle dogs compared to PBT. In particular, the AUC of PBMST was approximately four times greater than PBT, leading to improved oral bioavailability. There were no significant differences observed for all pharmacokinetic parameters between PBMST and the commercial prasugrel hydrochloride-loaded tablet, suggesting their bioequivalence in beagle dogs. Furthermore, the prepared PBMSTs were stable for at least six months. Therefore, this novel prasugrel base microsphere-loaded tablet could be a potential alternative for enhancing the stability and bioavailability of prasugrel. [ABSTRACT FROM AUTHOR]

The purpose of this study was to develop HM30181 mesylate salt (HM30181M)-loaded microcapsules as a novel P-glycoprotein inhibitor for enhancing the oral absorption of paclitaxel. The effect of various carriers including hydrophilic polymers and solvents on the solubility of HM30181M were evaluated. Among the hydrophilic polymers and solvents tested, HPMC and methylene chloride (and ethanol) provided the highest HM30181M solubility. Numerous HM30181M-loaded microcapsules were prepared with HPMC, silicon dioxide and acidifying agents using a spray-drying technique, and their solubility, dissolution and physicochemical properties were evaluated. Furthermore, a pharmacokinetic study was performed after oral administration of paclitaxel alone, simultaneously with HM30181M powder or HM30181M-loaded microcapsules to rats. Among the acidifying agents investigated, phosphoric acid provided the best improvement in the solubility and dissolution of HM30181M. Moreover, the microcapsule composed of HM30181M, HPMC, silicon dioxide and phosphoric acid at a weight ratio of 3:6:3:2 remarkably enhanced the solubility and dissolution of HM30181M compared with the HM30181M powder alone. The microcapsules were spherical in shape, had a reduced particle size of about 7 μm, and contained HM30181M in an amorphous state. Furthermore, this microcapsule significantly enhanced HM30181M absorption, making it about 1.7-fold faster and 1.6-fold greater after simultaneous administration, leading to about 70- and 2-fold improved oral bioavailability of paclitaxel compared with paclitaxel alone and the simultaneous administration with HM30181M powder, respectively. Thus, this novel microcapsule could be a potential candidate for effective P-glycoprotein inhibition during oral administration of paclitaxel. [ABSTRACT FROM AUTHOR]

The comparison of optically stimulated luminescence (OSL) ages of different grain-size fractions has given rise to conflicting results over recent years. To test the reliability and validity of OSL dating of fine- and coarse-grained fractions, 25 samples were collected from a 46-m sediment core taken from the southwestern coast of Korea, which contained two typically fine-grained tidal units separated stratigraphically by a coarse-grained sand and gravel layer. A single aliquot regenerative dose (SAR) procedure was applied to chemically separated fine- (4–11 μm, n = 16) and coarse- (90–212 μm, n = 24) grained quartz. The ages of coarse-grained quartz in the upper unit were relatively consistent with those of fine-grained quartz in the same unit of Holocene age (12–0 ka). In contrast, in the lower unit the coarse quartz fraction OSL ages are 30–60% (mean 46%) lower than the fine quartz fraction ages. OSL ages for all fine-grained quartz in the lower unit (139–110 ka) were in good agreement with the last interglacial sea-level highstand [Marine Isotope Stage (MIS) 5e]. However, all OSL ages for coarse-grained quartz in this lower unit (90–45 ka) were younger, corresponding broadly to the last glacial period (MIS 4 and 3). OSL ages obtained for fine-grained quartz were in agreement with indirect age controls provided by lithological and palynological data, implying that the use of the SAR protocol to date fine-grained quartz is appropriate for age control of coastal sediments extending to the last interglacial period. The discrepancies between the ages of different grain-size fractions may have arisen from early saturation of the natural signal and, in some cases, from contamination of the feldspar signal in the coarse quartz. However, more research is required to assess the reliability of OSL ages for fine-grained quartz obtained from the high-dose linear region of the dose response curve. [ABSTRACT FROM AUTHOR]

This is the first report of an OSL (optically stimulated luminescence) -dated Eemian marine deposit along the southwest coast of Korea. It was discovered on the Baeksu intertidal shoreface/tidal flat system. Based on the analysis of (up to 46-m-long) drilled cores, the Baeksu tidal deposits can be divided into four sedimentary units. In ascending order these are: 1) basal fluvial gravels, 2) Eemian tidal mud, 3) gravel lag/paleosol, and 4) Holocene tidal deposits. The Eemian tidal sequences were encountered at a core interval of −20 to −38 m below mean sea level, the OSL ages ranging from 138 to 110 ka. Pollen analyses reveal a higher AP (arboreal pollen) to NAP (nonarboreal pollen) ratio, suggesting warm climate conditions similar to that of the Holocene. In addition, marine dinoflagellates and salt marsh pollen were found, these palynofloral records thus also attesting to marine influence in the deposits. In expectation that the Eemian tidal mud succession occurs on a wider geographic scale, the deposit is allocated the stratigraphic name Baeksu Formation (Eemian), the stratotype locality being situated at −20 m below the surface at the Baeksu borehole site. The presence of Eemian tidal muds along the west coast of Korea, which correlate with marine strata in the western Yellow Sea and Bohai Sea, explicitly reveals the occurrence of marine incursions into the eastern margin of the paleo(?)-Yellow Sea land during the last interglacial. [ABSTRACT FROM AUTHOR]

We investigated the chronostratigraphy of six boreholes in the Nakdong River delta area in South Korea based on optically stimulated luminescence (OSL) and 14C dating. The standardised growth curves (SGCs) produced from single and multiple boreholes performed well in determining low equivalent dose (D e ; < 40 Gy). 14C dates from shell and wood fragments were mostly representative of depositional time. Based on 14C and OSL ages, the lowermost fluvial sediments showed relatively low sediment accumulation rates (0.1–0.8 m/kyr−1) prior to 12 ka. A hiatal discontinuity ranging from 12 to a maximum of 50 ka resulted in a break in sedimentation between the Last Glacial Maximum and the Holocene. A thick fluvio-estuarine unit in the lower part indicated relatively high accumulation rates (3.3–9.4 m/kyr−1) from 12 to 9 ka, which corresponded to rapid sea level rise. In the middle part, decreased accumulation rates (1.7–5.5 m/kyr−1) from approximately 9 to 6 ka were interpreted as transgressive deepening. Lower accumulation rates (0.9–3.2 m/kyr−1) during the middle to late Holocene were caused by relative sea level fall and a horizontally extended sedimentation area. In the upper part, the highest sediment accumulation rates (3.5–8.3 m/kyr−1) and rapid delta progradation during the last 2.0 ka might have been caused by widespread human influence and monsoonal climatic change. Isochrons of 1-kyr scale were identified based on the lithologic boundary and age results for each borehole, which represent palaeoshoreline positions during the transgressive cycle and boundaries of considerable delta progradation. • The chronostratigraphy in the Nakdong River delta sediments were investigated. • Isochrones of 1-ka scale show boundary of transgressive cycle and delta progradation. • 14C and OSL ages show variable sedimentation rates during the last 12 ka. [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the ability of saucerneol D (SD), a tetrahydrofuran-type sesquilignan isolated from Saururus chinensis, to regulate the expression of inducible nitric oxide synthase (iNOS) in lipopolysaccharide (LPS)-stimulated murine macrophage-like RAW264.7 cells. SD consistently inhibited nitric oxide (NO) production in a dose-dependent manner, with an IC50 of 2.62 µM, and also blocked LPS-induced iNOS expression. SD potently suppressed both the reporter gene expression and DNA-binding activity of nuclear factor-κB (NF-κB). In addition, SD inhibited IκB-α degradation in a concentration- and time-dependent manner. SD also inhibited LPS-induced activation of various mitogen-activated protein kinases, including extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun NH2-terminal kinase (JNK). These findings suggest that SD may inhibit LPS-induced iNOS expression by blocking NF-κB and MAPK activation. [Copyright &y& Elsevier]

Abstract: The Tetori Group is a representative Middle Jurassic to Lower Cretaceous deposit in the northern central part of Honshu, Japan. The Tetori Group is divided into the Kuzuryu, Itoshiro and Akaiwa Subgroups with decreasing age. It consists mainly of a marine sequence in the lower part (Kuzuryu Subgroup) and non-marine sequence in the upper part (Akaiwa Subgroup) with transitional sequence in the middle part (Itoshiro Subgroup). Diagenesis of Tetori Group sandstones comprises compaction, cementation and replacement. Early diagenetic events include mechanical compaction, and pore-filling cementation of calcite, siderite, dolomite and formation of kaolinite. Late diagenesis includes formation of quartz cement and albitization of feldspar, and formation of illite, chlorite, calcite, ankerite and pyrite. Among the diagenetic minerals, carbonate forms the major cement in Tetori Group sandstones. Calcite of each subgroup is subdivided into two or three types based on cathodoluminescence. Tetori Group sandstones of marine, fresh-water, and mixed depositional environments are characterized by distinct chemical compositions of early diagenetic calcites. Late diagenesis seems to have been mainly influenced by detrital compositions of the sequence, burial temperatures and partially hydrothermal processes. Especially, late diagenetic carbonate and authigenic clay minerals seem to have formed mainly from ions released from clay mineral transformations in the adjacent shales. Based on the illite crystallinity (IC), the Kuzuryu Subgroup exhibits higher diagenetic grades than the overlying Itoshiro and Akaiwa Subgroups, indicating that the diagenesis of the Tetori Group was mainly affected by depth of burial. [Copyright &y& Elsevier]

This study traces coastal sand dune development processes in East Asia during the Holocene to understand climate and environmental changes. We used optically stimulated luminescence (OSL) dating to examine periods of activation and stabilization of dunes along the western coast of the Korean Peninsula. The results from the Taean Chollipo, Seocheon Dasari, and Gochang Sabanri dunes were then compared with those from previous studies to establish a broad understanding of coastal dune development in this region. Sedimentation rates were calculated for the three dunes, and their development periods were classified through statistical analysis that included data from previous studies. We defined five main periods of late Holocene dune development (<0.1 ka, 0.2–0.5 ka, 1.2–2.0 ka, 2.5–3.2 ka, and 5.5–6.5 ka). These correlated to periods of sea level decrease and global cooling determined by ice rafted debris records. We concluded that the development of coastal dunes in western Korea was influenced by sea level decreases, and global cooling events were enhanced by the East Asian winter monsoon. In addition, human activity increases also contributed to the development of the dunes. This study showed how coastal sand dunes can be evaluated as important indicators of global climate change. These results improved our understanding of how paleoclimate changes affected environmental conditions in East Asia and how coastal dune development periods can be used to reconstruct paleo-environmental conditions. • Coastal sand dunes are developed along the western coast of the Korean Peninsula. • Five main periods of late Holocene dune development were determined by OSL. • Main periods were -less than 0.1, 0.2–0.5, 1.2–2.0, 2.5–3.2, and 5.5–6.5 ka. • Main periods were agreed with sea level decrease and global cooling in the Holocene. [ABSTRACT FROM AUTHOR]

ABSTRACT Bayhead deltas form at the interface between fluvial and estuarine systems. As such, they are sensitive to processes operating in both the fluvial catchment and the marine realm, including past relative sea‐level changes. The Nakdong valley is a small and confined incised valley containing a bayhead delta that provides a record of fluvial sediment input and accommodation changes. Based on a facies analysis that included 833 sediment textures and 118 optically stimulated luminescence and radiocarbon ages within five cores up to 70 m long, this study reconstructed the development of a fully filled bayhead delta in response to relative sea‐level changes through the early to late Holocene. Sixteen facies are defined and grouped into eight facies associations: alluvial plain; fluvial channel and floodplain; oxidized fluvial channel; tidal flat; tidal bar; central basin and bayhead prodelta; bayhead delta front; and bayhead delta plain. The sequence stratigraphy of the Nakdong valley fill can be divided into three systems tracts: a lowstand systems tract, a transgressive systems tract and a highstand systems tract. Overall sedimentary analyses suggest six depositional stages corresponding to variations between sediment inputs and sea‐level rise of the developing bayhead delta in the Nakdong valley. The depositional model tracks relative sea‐level rise in the Nakdong valley after 12 ka during the early to late Holocene. These analyses on the Nakdong bayhead delta succession illustrate the balance between sediment inputs and periods of accelerating and decelerating relative sea‐level rise during the Holocene. The architecture of the valley fill also records two abrupt disequilibrium events from 9 to 8 ka and 5 to 3 ka, likely resulting from rapid sea‐level rise during the deglacial outburst flooding of the early Holocene and decreased sediment inputs during regional climatic changes associated with the middle Holocene, respectively. [ABSTRACT FROM AUTHOR]

Hong, S.-H.; Chun, S.S.; Kim, J.-C.; Lee, G.-S.; Yoon, H.-H., and Yoo, D.-G., 2020. Sedimentary facies and depositional environment of long sediment cores from the Nakdong incised valley fills, southeastern Korea. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 511–515. Coconut Creek (Florida), ISSN 0749-0208. Two deep-drilled cores were obtained from the Nakdong River delta in 2016. Based on the sediment structure, composition and texture, the deposits can be divided into four depositional units: I) fluvial sediments, II) estuarine sediments, III) coastal sediments, and IV) delta sediments. The lowermost Unit I is about 25 m thick and comprised clast-supported gravel and massive sand. The age dates of the upper part of Unit 1 is 49.7 ± 5.3 ka. Unit II consists of thin silt laminations that vary rhythmically in thickness, suggesting tidal influences in the estuarine environment. The age dates of this unit range from 10.9 ± 0.18 to 9.6 ± 0.11. Unit III is composed of cross-bedded sand, which contains peat materials and shell fragments and is interpreted to rapidly deposited sand bars in coastal environment. The age of Unit III had 9.7 ± 0.18 ka. Unit IV is composed of extremely bioturbated sandy mud and cross-laminated sand. The age dates of Unit IV ranges from 7.4 ± 0.5 to 0.8 ± 0.09 ka, the deposits belonging to the Holocene. These results indicate that depositional units in the study area consists of fluvial deposits of forced regression formed during the MIS 3, estuarine to tidal flat deposits during deglacial transgression, prograding delta deposits during postglacial periods. [ABSTRACT FROM AUTHOR]

Incised-valley infill deposits are closely related to sea level changes during the post-glacial period of the late Quaternary and are an important topic in sea level history. In Asia, there are many large river basins that receive large amounts of sediment from the land, and the infilling deposits of incised valley systems have been well studied. Yeongil Bay is a semi-enclosed, funnel-shaped topographic feature on the east coast of the Korean Peninsula, located in the southwestern part of the East Sea (Sea of Japan). The Hyeongsan River, a small river flowing into Yeongil Bay, is flows perpendicular to the East sea. During the last glacial maximum (LGM), when the sea level was >120–130 m lower than at present in the Korea Strait, inflowing river processes are thought to have formed incised valleys. In this study, the sediment depositional patterns of incised valley fill since the LGM were examined by analyzing the sedimentary facies, optically stimulated luminescence (OSL) dates, and radiocarbon dates by accelerated mass spectrometry (AMS) of three sediment cores in Yeongil Bay. The infilling sequence consists of sediments from channel lag (>12 ka) and meandering river (12–10 ka), wave-dominated estuary (12–7.8 ka), and wave-dominated delta (7.8–0 ka) systems in ascending order. The barrier appear only in the outer part of Yeongil Bay. The barrier emerged from eroding estuary systems at 8.5 ka. Millennial-scale isochrons based on OSL and radiocarbon dates showed that fluvial and estuary systems were deposited in retrogradation and delta systems were deposited in progradation since LGM. The modern delta of the Asian large rivers were initiated by a decreasing rate of sea level rise during the mid-Holocene, and consideration of this is important for RSL. This study emphasizes the importance of accommodation capacity as much as sediment discharge as a factor in the timing of delta initiation. This study provides important insights into the incised-valley infill deposits and past environmental conditions, and may help to gain a better understanding of how coastal environments have changed with sea level changes. • Holocene sedimentary environment changes in Yeongil Bay through OSL, 14C dating, and facies analysis were reconstructed. • Sedimentary facies and high-resolution chronology a depositi characterized a depositional sequence of the incised valley. • The timing and its control factors of the delta initiation were also constrained. [ABSTRACT FROM AUTHOR]

Multi-proxy sediment properties reveal that three cores (ND-01, ND-02, and ND-03) from the lower delta plain of the Nakdong River Delta, southeast Korea, are characterized by the same stratigraphic lithologic successions consisting of a upper sand unit (10–15 m thick and <1 ka), a middle mud unit (∼20 m thick and 1–9 ka), a lower sand unit (6–9 m thick and 9–10 ka), and a lower mud unit (10–15 m thick and >10 ka) overlying weathered gravelly fluvial sediments and weathered bedrock. The sediment properties of each lithologic unit are controlled by the balance between the marine influence from Holocene sea level rise and the freshwater influence from Nakdong River discharge. In particular, the middle mud unit is characterized by distinct peaks in CaCO 3 content, P/T ratios (the ratio of planktonic foraminifera to the sum of benthic and planktonic foraminifera), total organic carbon and total nitrogen contents, and δ13C org values at 7–8 ka, which indicates that the maximum marine forcing during the sea level rising and the greatest influence of the Tsushima Warm Current during the evolution of the river-mouth coastal depositional system from an estuarine to a deltaic environment. Although the vertical stacking of lithologic successions is stratigraphically consistent within the lower delta plain, the precise temporal evaluation and comprehensive depositional evolution in the Nakdong River Delta including the upper delta plain and the prodelta zones remain a topic of future investigation. [ABSTRACT FROM AUTHOR]

Five shell-gravel layers (2.2–2.9 m in elevation, 70 cm in thickness) formed by storm-induced rip currents along the southern coast of the Korean Peninsula over the past 1300 years are described. The three radiocarbon dates (S1–S3) and the two optically stimulated luminescence (S4 and S5) dates correspond well with the succession of the five shell-gravel layers. The age of S1, CE 720 ± 60, corresponds to the early Medieval Warm Period (MWP). The dates of the three overlying layers (S2–S4), CE 880 ± 110, 950 ± 70, and 995 ± 120, respectively, coincide with the middle MWP. The fifth date of the uppermost shell-gravel layer (S5), CE 1535 ± 40, coincides with the Little Ice Age (LIA) of Western Europe. The characteristics of shell habitats based on 16 shell species from each layer suggest that the first four layers formed in a slightly erosional to dominantly depositional environment during the MWP, whereas the youngest layer formed in a dominantly erosional environment during the LIA. Analyses of grain size distribution, magnetic susceptibility, and geochemistry of the sediments, and gravel morphology indicate that storm activity at this site during the MWP and LIA occurred within active storm periods in the western North Atlantic (WNA). Comparison of the five storm events and related climatic factors suggests that, although the typhoon track type at the site is similar to recurving tracks typical for El Niño conditions in North China and Japan, tracks during the MWP and LIA were likely shifted not only by changes in El Niño conditions but by other climatic factors such as sea surface temperature, the North Pacific High, and the westerly jet stream. However, storm energy under El Niño years during the middle MWP was likely stronger than that produced in normal years during the early MWP. [ABSTRACT FROM AUTHOR]

Cho, A.; Cheong, D.; Kim, J.C.; Shin, S.; Park, Y.-H., and Katsuki, K., 2017. Delta formation in the Nakdong River, Korea, during the Holocene as inferred from the diatom assemblage. The causes and succession of the Nakdong River delta formation related to sea-level change and precipitation in the early-middle Holocene were discussed based on diatom analysis. On the basis of ecology, stratigraphic changes of diatom flora were divided into five divisions, labeled zones I-V. According to the diatom assemblage, the first marine transgression occurred at about 10.5 ka at this research site. At that time, marine species gradually increased, and freshwater species had their highest values. This site was an estuary influenced by inputs of fresh and marine water until 9.8 ka (zone I). Zone II is dominated by bay and offshore species, meaning that sea level rose continuously after about 9.8 ka (zone II) when the Nakdong River mouth region was an inner bay. Then, the environment of this site changed to an outer bay after 8 ka (zone III) because of sea-level rise, which is supported by increasing numbers of oceanic species. At the end of this zone, at 6-7 ka, sea level highstand occurred. A prodelta began forming just after the highstand under slow sea-level rise (zone IV), and the delta front arrived at its present location at 5 ka by voluminous sediment input from the Nakdong River related to high precipitation during the Holocene Climate Optimum (zone V). After 5 ka, the delta front remained around its present site because of stable or decreasing sea level. Compared with other Asia deltas (Yangtze and Mekong), the initiation of the Nakdong River delta was delayed by about 1000-2000 years because of differences in relative sea-level changes. [ABSTRACT FROM AUTHOR]

This study entails the characterization of the depositional environment of the Hupo Basin shelf. By means of sedimentary structure analysis, grain size, textures, sediment color, as well as optically stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) ages, a sediment core (19ESDP-101, 120 m) has been interpreted to be the product of shallow-water contourites. The shallow-water (165 m) contourite deposits observed in the core are divided into seven sedimentary facies grouped into four facies associations (FA): FA1) contourite drift, FA2) contourite drift/channel transition, FA3) contourite channel/drift transition, and FA4) contourite channel. FA1 resulted from the interaction between hemipelagic fallout, low-density gravity flow, and sedimentation under low velocity bottom currents. Compared to FA1, both FA 2 and FA3 are indicative of higher velocity bottom currents, owing to their relative increase in grain size and the presence of subtle indicators of bed-load transport. FA 4 portrayed massive to slightly bedded sand, representing a contourite channel environment with high-energy conditions. Fluctuations in the bottom current activity, related to the intensification and deceleration of the North Korean Cold Current (NKCC), have caused fluctuations between contouritic and hemipelagic-dominated periods. The vertical sedimentary facies stacking patterns observed at the Hupo Basin site suggested that, over time, the depositional processes changed at the site where the core was optained. The facies association stacking pattern suggests the lateral migration of the contourite depositional system and continuous flow of the NKCC. Our findings and interpretations can serve as a much needed reference for shallow-water contourite recognition in modern environments. Moreover, our proposed model can be used to more accurately interpret shallow-water contourite deposits. [ABSTRACT FROM AUTHOR]

Fault gouge, located in highly deformed fault cores, shows substantial particle size reduction and loss of crystallinity, which could affect the physicochemical properties and thus control the slip behavior and earthquake stability of a fault. To systematically investigate the effect of deformed fault gouge on fault slip behavior in laboratory-scale experiments, a fault gouge analog with variable particle size and crystallinity is required. However, the systematic study for formation of a fault gouge analog (i.e., controlling the particle size and crystallinity) was not performed well. In this study, we investigated the effect of the rotation speed of a high-energy ball mill on particle size reduction rate and degree of amorphization. As the rotation speed increased from 500 to 2000 rpm, the comminution rate linearly increased, and reached a reduced particle size limit. The degree of amorphization and its rate also increased with increasing rotation speed. Upon grinding, the X-ray diffraction (XRD) peaks markedly decreased and reached critical amorphization points within 120 min, except for the case of grinding with a rotation speed of 500 rpm. Talc ground with a rotation speed of 500 rpm did not reach steady-state in mechanical amorphization after 360 min of grinding, thus necessitating prolonged grinding for further amorphization. A comparison of talc powders having similar specific surface areas, but ground at different rotation speeds, shows that grinding with a higher rotation speed for a shorter duration preserves the crystalline structure relatively well compared with grinding at a lower rotation speed for a longer duration. These results indicate that optimizing the grinding rotation speed facilitates the formation of talc fault gouge analogs with systematically varying particle size and crystallinity. The specific surface area of talc increased from 6.1 to 365 m2/g, and the degree of crystallinity decreased from approximately 75% to 11%. Our results indicate that an artificial talc fault gouge can be prepared by varying the particle size and crystallinity using a high-energy ball mill. [ABSTRACT FROM AUTHOR]

To trace the environmental change that occurred at a coastal area during the Holocene, we performed radiocarbon dating and geochemical analyses using sedimentary cores recovered from the Beolgyo tidal flats on the south coast of Korea. The δ 13 C values of total organic carbon (TOC), which represent relative inputs of terrestrial (or freshwater) and marine organic sources, revealed a long-term increasing trend from −27.5 to −21.7‰ during the period between 10,000 and 3000 cal BP, suggesting an evolutionary series of fluvial-dominant to marine-dominant environments, coupled with weakened summer monsoon intensity. From 3000 cal BP to the present, the δ 13 C TOC decreased gradually from −21.7 to −24‰, indicating enhancement of freshwater input during this time. The observed long-term environmental change was divided into six stages based on the averages of the total sulfur content (TS%) and the organic carbon to sulfur ratio (C/S), proxies for paleosalinity. On multi-centennial to millennial timescales, higher C/S ratios and lower TS% were linked to higher δ 13 C TOC values, indicating strong freshwater input at Stage 2 (∼8300–7400 cal BP), Stage 4 (∼4500–3300 cal BP), and Stage 6 (∼1100 cal BP to present). Strong freshwater discharge events synchronously occurred at 4300 cal BP and 3600 cal BP along the south coast of Korea. Further testing should be carried out in other East Asian coastal areas. This study suggests that sedimentary δ 13 C TOC values and C/S ratios can be used in Asian coastal regions to trace past freshwater input events and summer monsoon intensity during relatively stable sea level periods (e.g., the middle to late Holocene). [ABSTRACT FROM AUTHOR]

Simple Summary: The Holocene humidity evolution presents spatial heterogeneity in the Mongolian Plateau where multiple circulation systems converged. Inconsistent records of regional environmental evolution affect accurate assessment of lake ecosystems. Chironomid larvae are one of the most abundant benthic invertebrates in lakes. The taxa composition of their functional groups is largely determined by aquatic habitats. Therefore, analyzing the changes of their functional traits can effectively indicate the hydrological dynamics in the past. In this study, we analyzed the early-middle Holocene (9.0–4.5 cal kyr BP) subfossil chironomid assemblages of a sedimentary sequence from the Darhad Basin in northern Mongolia. At 9.0 cal kyr BP, the community structure suddenly changed from littoral taxa to sublittoral/profundal taxa, reflecting an environmental transition from a river or shallow lake condition to a deep lake environment, which lasted until 4.5 cal kyr BP. Those hydrological patterns are consistent with the humidity evolution in the Westerlies dominated region, except that the onset of wetness occurred one thousand years earlier when comparing our results with previous ones, which may be related to the melting of regional glaciers and permafrost caused by increased summer solar insolation. Under the influence of various circulation systems, the Holocene humidity conditions on the Mongolian Plateau are spatially heterogeneous and the underlying mechanism is still ambiguous. The complexity of climate change may affect the accuracy of assessing lake ecosystem evolution. In this study, based on the precise chronology, a chironomid assemblage sequence from the Darhad Basin in northern Mongolia is analyzed to elucidate the hydroclimate variation during the early-middle Holocene. The results show that the chironomid communities changed suddenly from littoral taxa to sublittoral/profundal taxa at about 9 cal kyr BP, reflecting an environmental transition from a river or shallow lake condition to a deep lake environment. Thereafter, most parts of the paleolake remained at a relatively high level until 4.5 cal kyr BP. This hydrological pattern resembles the typical humidity variations in the Westerlies affected regions, except that the onset of wetter conditions occurred one thousand years earlier as reflected in our results. The melting of glaciers and permafrost in the basin resulting from the early increased summer solar insolation could be a feasible explanation for these time advances. [ABSTRACT FROM AUTHOR]

To reconstruct environmental change during the late Holocene, we investigated sedimentary δ 13 C values from an exposed section on Geoje Island, on the southern coast of Korea. The δ 13 C values ranged from −24.3‰ to −21.2‰ and were divided into five stages based on the average value (−22.5‰). A comparison with the regional climate index revealed that wet periods linked to intensified summer monsoon conditions occurred at Stage 1 (4500–3600 cal BP), Stage 3 (1350–900 cal BP), and Stage 5 (300 cal BP to present). Dry intervals were found at Stage 2 (3600–1350 cal BP) and Stage 4 (900–300 cal BP). We found two different vegetational responses to changes in regional temperature and summer monsoons. Stage 3, corresponding to the MWP, was characterized by an association between the δ 13 C values on the island and the regional temperature, but Stage 4, including the LIA interval, did not show such a relationship. Furthermore, based on comparison with the summer monsoon index, this study suggested that, on the southern coast of Korea, vegetational change was controlled by an MWP-like mode during the warm and wet periods following regional climate change, whereas a LIA-like mode showing independent climate change was dominant during the cold and dry periods. This difference in vegetational changes along the southern coast of Korea and regional (mainly terrestrial-signal based) climate change may be attributed to the influence of sea surface temperature changes in the tropical ocean through the transport of warming seawater by the Kuroshio and Tsushima currents on the East Asian coastal area, including this study area, than on the inner part of the East Asian continent. [ABSTRACT FROM AUTHOR]

The dynamics of the East Asian Summer Monsoon (EASM) and their link to past societies during the Holocene are topics of growing interest. In this study, we present results of pollen, geochemistry, and grain-size analyses from the STP18-03 core sampled from Miryang in the Korean Peninsula, which spans ca. 8.3–2.3 ka BP. In-phase relationships of these proxies revealed an imprint of the Holocene Climate Optimum (HCO) during the early to mid-Holocene and subsequent drying toward the late-Holocene in accordance with decreasing solar insolation. At centennial timescales, our study indicates drier climate during ca. 7.5–7.1, 6.4–6.0, and 4.8–3.6 ka BP. Notably, our finding for ca. 6.4–6.0 ka BP contributes further evidence of a drying event in the Korean Peninsula during this period. We suggest that the Pacific Ocean played a role in the underlying mechanism of hydroclimate change in the region. A strong Kuroshio Current (KC) and long-term El Niño–Southern Oscillation (ENSO)-like variability in the Western Tropical Pacific (WTP) were closely linked to the influence of the EASM over the Korean Peninsula. In particular, dry phases during ca. 4.8–3.6 and 2.8–2.3 ka BP, which were synchronous with a more active ENSO, closely corresponded to lower population levels indicated by a summed probability distribution (SPD) of archaeological records previously assembled in the Korean Peninsula. This finding implies that past human societies of Korea were highly vulnerable to climate deterioration caused by precipitation deficits. [ABSTRACT FROM AUTHOR]

This research note presents evidence for the oldest Middle Pleistocene Eastern Saharan human activity from the area referred to as the Eastern Desert Atbara River (EDAR), Sudan, which is currently threatened by gold mining. Preliminary results of multifaceted analyses indicate the activity of Homo sapiens during MIS 5 as well as Homo erectus during MIS 7–11 or earlier. [ABSTRACT FROM AUTHOR]

Although essential for reconstructing hominin behaviour during the Early Palaeolithic, only a handful of Acheulean sites have been dated in the Eastern Sahara region. This is due to the scarcity of sites for this time period and the lack of datable material. However, recent excavations in the Atbara region (Sudan) have provided unique opportunities to analyse and date Acheulean stone tools. We report here on EDAR 7, part of a cluster of Acheulean and Middle Stone Age (MSA) sites that were recently discovered in the Eastern Desert Atbara River (EDAR) region, located in the Eastern Desert (Sudan) far from the Nile valley. At EDAR 7, a 3.5 metre sedimentary sequence was excavated, allowing an Acheulean assemblage to be investigated using a combination of sedimentology, stone tool studies and optically stimulated luminescence dating (OSL). The site has delivered a complete Acheulean knapping chaine opératoire, providing new information about the Saharan Acheulean. The EDAR 7 site is interpreted as a remnant of a campsite based on the co-occurrence of two reduction modes: one geared towards the production of Large Cutting Tools (LCTs), and the other based on the flaking of small debitage and production of flake tools. Particularly notable in the EDAR 7 assemblage is the abundance of cleavers, most of which display evidence of flake production. Implementation of giant Kombewa flakes was also observed. A geometric morphometric analysis of hand-axes was conducted to verify a possible Late Acheulean assemblage standardisation in the Nubian Sahara. In addition, the analysis of micro-traces and wear on the artefacts has provided information on the use history of the Acheulean stone tools. Sediment analyses and OSL dating show that the EDAR 7 sequence contains the oldest Acheulean encampment remains in the Eastern Sahara, dated to the MIS 11 or earlier. This confirms that Homo erectus occupied the EDAR region during Middle Pleistocene humid periods, and demonstrates that habitable corridors existed between the Ethiopian Highlands, the Nile and the Red Sea coast, allowing population dispersals across the continent and out of it. [ABSTRACT FROM AUTHOR]

Projections indicate increasing coastal hazards in the Yellow Sea region owing to relative sea-level rise. Accordingly, regional studies of such change over the Holocene timescale could be helpful in mitigating these threats. Here, we describe the Holocene record of relative sea-level change in the Gochang-Yeonggwang area of South Korea. We compared this record with that of other sites around the coast of the Yellow Sea, including Bohai Bay (China), the Tando Estuary and Gunsan Bay (South Korea), and sites on the east coast of the South Sea and Toyo-oka Basin, Japan. The findings are based on a multi-proxy study, including lithostratigraphy combined with radiocarbon dating and analyses of grain size distribution, magnetic susceptibility, and geochemistry, which facilitated the generation of 89 paleo-sea-level points reconstructed from 28 borehole cores. The early Holocene transgression was found to start later at Gochang-Yeonggwang than at Gunsan Bay, although the distance between them is only 150 km. This result was inferred from substantial differences in sediment delivery owing to Holocene differences in river basin size, topography, and tectonic context. Before ∼7 ka, the slope and highstands from the predicted mean sea-level models at Bohai Bay, Tando Estuary, and Gochang-Yeonggwang were steeper and lower, respectively, from north to south in the Yellow Sea, approaching the slope of the glacio-eustatic sea-level curve. Therefore, the levering effect of transgression in the early Holocene decreased southward in the Yellow Sea. The slight fluctuation in mean sea-level points of the late Holocene resulted from the formation of storm deposit layers in the coastal area, erosion and redeposition in the channel, and geomorphic effects. A partial difference occurred between the relative sea levels at Gochang-Yeonggwang and Toyo-oka. Future relative sea-level research at the southernmost part of the east coast of the Yellow Sea would further improve understanding of the coastal evolution of the region. • The RSL curve slope at ∼8 ka was the steepest among the Yellow Sea east coast sites. • Highstand on RSL is lower than any other east coast site of the Yellow Sea. • Early Holocene transgression levering effect decreased southern of the Yellow Sea east coast. • RSL in the late Holocene was influenced by glacio-eustatic sea-level change. [ABSTRACT FROM AUTHOR]

The deposits of the Jeju Strait shelf can be divided into twelve sedimentary facies that are grouped into four depositional units, which formed in response to late Pleistocene to Holocene sea level changes. The deposits of the shelf can be grouped into four depositional units, each with different sedimentary facies and structures: 1) shelf sand, 2) estuarine sand/mud, 3) fluvial sand/mud, 4) shelf sand/mud. The Unit 1 shows massive to slightly bedded sandy shells with oyster fragments and is regarded as shelf sand developed under the shelf environment during the last interglacial. OSL date of the base of the unit is 124.4 ka. Unit 2 is characterized by thinly periodic parallel laminated mud, suggesting tidal signatures in tidal flats. The sediment color of this unit sediments is also characterized by moderate brownish, strongly suggesting extreme weathering trace after the depositions. OSL dates of this unit range from 81.1 to 74.2 ka. Unit 3 consists of lower cross-bedded sand and laminated mud with fining-upward successions. This unit is interpreted to be products of channel deposits in the fluvial environment. The OSL ages of Unit 3 range from 50.6 to 26.1 ka belonging to the Weichselian glacial period. The Unit 4 is composed of homogeneous mud and massive sand with molluscan shell fragments developed in the modern shelf environment. OSL and 14C-AMS age of Unit 4 ranges from 0.32 to 11.2 ka. [ABSTRACT FROM AUTHOR]

The depositional environments of the Jeju Strait shelf since the last interglacial period are analyzed using sedimentary structures, grain size textures, sediment color, and optically-stimulated luminescence (OSL) and accelerator mass spectrometry (AMS) ages of vibro-cores. The shelf deposits can be divided into 12 sedimentary facies grouped into four depositional units: 1) shelf sand, 2) estuarine sand/mud, 3) fluvial sand/mud, and 4) shelf sand/mud. Each unit is separated by a sharp and unconformable erosion boundary. Unit 1 shows massive to slightly bedded sandy shells with oyster fragments, representing a shelf environment during sea-level highstand. The OSL date of the base of the unit is 124.4 ± 10.0 ka. Unit 2 is characterized by thin periodic parallel laminated mud, suggesting tidal signatures in tidal flats. Sediments are typically moderate brownish, suggesting extreme weathering after deposition. The OSL dates of this unit range from 81.1 ± 5.3 to 74.2 ± 4.7. Unit 3 consists of lower cross-bedded sand and laminated mud with fining-upward successions. It is interpreted as the product of channel deposits in a fluvial environment during a sea-level falling. The OSL ages of Unit 3 range from 50.6 ± 2.9 to 26.1 ± 1.6 ka, belonging to the Weichselian glacial period. The uppermost unit (Unit 4) is composed of homogeneous mud and massive sand with molluscan shell fragments in the modern shelf environment during sea-level highstand. OSL and 14C-AMS ages range from 0.32 ± 0.02 to 11.2 ± 0.1 ka. Consequently, the late Pleistocene-Holocene sedimentary facies in this area consist of marine and non-marine environments, which mainly correspond to sea-level changes. [ABSTRACT FROM AUTHOR]

Fossil benthic and planktonic foraminifera from a part of core ND-02 and the published data of core ND-01 from the Nakdong River delta, southeast Korea were analyzed to evaluate the impact of the Tsushima Warm Current on coastal environments in the Korea/Tsushima Strait between Korea and Japan during the early to middle Holocene. Based on cluster analysis, four sample clusters (A, B, C, and D), suggestive of a landward–seaward gradient of environmental conditions, can be defined. According to the spatio-temporal and cluster distributions of benthic foraminifera in faunal compositions, the landward occurrence of benthic foraminifera was delimited in the inner part of the Nakdong River delta at ∼8–7 ka. The common occurrence of warm-water planktonic foraminifera suggests that this maximum landward expansion of benthic foraminifera within the delta was caused by the intensification of the Tsushima Warm Current in addition to sea level rise during the early to middle Holocene. Changes in both marine biota and sedimentation were reported in the coastal areas of southwestern Japan in that period. They were also caused by a precursor of the enhanced Tsushima Warm Current at ∼8 ka. Thus, the evolution of the Tsushima Warm Current during the early to middle Holocene is important for understanding various phenomena in the coastal environments of the Korea/Tsushima Strait. [ABSTRACT FROM AUTHOR]

Abstract The Sahara Desert episodically became a space available for hominins in the Pleistocene. Mostly, desert conditions prevailed during the interpluvial periods, which were only periodically interrupted by enhanced precipitation during pluvial or interglacial periods. Responding to Quaternary climatic changes, hominin dispersal was channeled through vegetated corridors. This manuscript introduces a recently discovered group of Acheulean and Middle Stone Age sites far from the Nile Valley in the Eastern Desert (Sudan), referred to as Eastern Desert Atbara River (EDAR). The ∼5 m stratigraphy of the area is divided into three units (Units I–III) bounded by erosion surfaces. Each contains archaeological horizons. The EDAR area has rich surface sites with Acheulean horizons under the surface, singular finds of hand-axes within stratigraphic context in exposures, and large Acheulean sites partly exposed and destroyed by the gold mining activity. Optically stimulated luminescence (OSL) dating of Acheulean and MSA horizons from the EDAR 135 site indicates that the sedimentary deposits with stone artifacts were formed during the Middle Pleistocene between Marine Isotope Stages (MIS) 7 (pluvial) and 6 (interpluvial). Based on the OSL dating from the top of Unit IB, Acheulean artifact-bearing sedimentary deposits from overlying Unit IIA are younger than ca. 231 ka. Unit IA is the oldest Acheulean horizon in the EDAR area, not yet dated but definitively older than ca. 231 ka. An MSA horizon found in fluvial sediment was dated to be between 156 and 181 ka by OSL. The EDAR Pleistocene archaeological sites provide evidence for the presence of additional corridor(s) across Nubia, which connects the early hominin dispersals from the Nile and Atbara River systems to the Red Sea coast. [ABSTRACT FROM AUTHOR]

During and shortly after the 2017 Pohang Earthquake (Mw 5.4), sand blows were observed around the epicenter for the first time since the beginning of instrumental seismic recording in South Korea. We carried out field surveys plus satellite and drone imagery analyses, resulting in observation of approximately 600 sand blows on Quaternary sediment cover in this area. Most were observed within 3 km of the epicenter, with the farthest being 15 km away. In order to investigate the ground’s susceptibility to liquefaction, we conducted a trench study of a 30 m-long sand blow in a rice field 1 km from the earthquake epicenter. The physical characteristics of the liquified sediments (grain size, impermeable barriers, saturation, and low overburden pressure) closely matched the optimum ground conditions for liquefaction. Additionally, we found a series of soft sediment deformation structures (SSDSs) within the trench walls, such as load structures and water-escaped structures. The latter were vertically connected to sand blows on the surface, reflecting seismogenic liquefaction involving subsurface deformation during sand blow formation. This genetic linkage suggests that SSDS research would be useful for identifying prehistoric damage-inducing earthquakes (Mw > 5.0) in South Korea because SSDSs have a lower formation threshold and higher preservational potential than geomorphic markers formed by surface ruptures. Thus, future combined studies of Quaternary surface faults and SSDSs are required to provide reliable paleoseismological information in Korea. [ABSTRACT FROM AUTHOR]

Understanding past relative sea-level (RSL) changes is crucial for predicting future coastal evolution, particularly within the context of accelerated melting of polar ice sheets due to global warming. RSL records are scarce in many regions along the Pacific coast. Here, we present a Holocene RSL curve for the west coast of South Korea based on detailed analyses of four sediment cores and the synthesis of existing sea-level index points without correction by tectonic, sediment compaction and other effects. Our record shows that the local sea level rose rapidly during the early Holocene and then fell gradually toward the present position during the late Holocene. An apparent sea-level highstand of ca. 1–2 m occurred 7–4 cal kyr B.P. A rapid sea-level rise of ~1.4 cm yr −1 during the early Holocene is a manifestation of polar ice sheet decay, while the apparent mid-Holocene sea-level highstand appears to be a signal of the hydro-isostasy of the far-field continental shelf. The result was confirmed by a glacial isostatic adjustment (GIA) model. Holocene RSL change on the west coast of South Korea was closely linked to global temperature and ice sheet decay, especially during the early Holocene. There is a close relationship between sea-level change in the study area and Laurentide Ice Sheet (LIS) decay. [ABSTRACT FROM AUTHOR]

To understand historical climate change in western Pacific coastal areas, a sediment core (SOJ-2) from the stable sedimentary environment of the Songjiho Lagoon on the east coast of South Korea was obtained for centennial-resolution palynological analysis. The ages of the SOJ-2 core is well controlled by carbon 14 dating with high-resolution accelerator mass spectrometry (AMS), and the results indicated a general warm to cold climate trend from the mid-Holocene to the present, which can be divided into two different stages: a warmer stage between 6842 and 1297 cal yr BP and a colder stage from 1297 cal yr BP to the present, with fluctuations during these stages. The climate was wetter from 6842 to 6227 cal yr BP and 4520 to 1297 cal yr BP and was drier from 6227 to 4520 cal yr BP. The climate changed to cold and dry during the period from 1297–425 cal yr BP. The impact of human activity on the climate began at approximately 1297 cal yr BP and became pronounced starting in 425 cal yr BP. The general cooling trend may represent a response to decreasing solar insolation; however, the relative dryness or wetness of the climate may have been co-determined by westerlies and the East Asian summer monsoon (EASM). The climate had a teleconnection with the North Atlantic region, resulting from changes in solar activity. Nevertheless, EI Niño–Southern Oscillation (ENSO) activity played an important role in impacting the EASM changes in western Pacific coastal areas. [ABSTRACT FROM AUTHOR]

A sediment core (14DH-C01) obtained from the mouth of Gomso Bay, on the west coast of South Korea, was used to obtain high-resolution palynomorph, grain-size, and 14C age data to investigate the Holocene sedimentary environment. The results indicated a transgressive depositional process with four stages controlled by sea-level change, as follows: river-dominated fluvial deposition from the early Holocene to 8.48 cal ka BP; tide-dominated tidal channel fill transgression from 8.48 to 8.08 cal ka BP; tide- to wave-dominated tidal channel fill transgression from 8.08 to 6.98 cal ka BP; and wave-dominated marine transgression from 6.98 cal ka BP to the present. Tidal channel filling was the primary mid-Holocene depositional process, accounting for the high sedimentation rate observed. The different hydrodynamics of the river-dominated, tide-dominated, tide- to wave-dominated, and wave-dominated processes following the changes in sea level may have controlled the transgressive depositional process. This transgressive sedimentary model differs from those of other large river mouth areas (e.g., the Changjiang River) since the mid-Holocene, perhaps resulting from the limited sediment supply in the study area. [ABSTRACT FROM PUBLISHER]

Paleo-relative sea level (paleo-RSL) records in the far-field are essential for constraining models for global sea level change. We compared the early Holocene RSL history on the central east coast of the Yellow Sea with those of Bohai Bay, the northernmost point, and Gunsan Bay, south of the study area. A multi-proxy approach, including lithostratigraphy, biostratigraphy, combined with radiocarbon and OSL dating, facilitated the generation of 28 sea level index points (SLIPs) using 11 borehole samples. Excavation of basal peat of the 10.3 ka in the study area established that the observed RSL of the transgression in the early Holocene was −14.88 m, which was much shallower than −27.9 m in Gunsan Bay at 9.8 ka and was similar to −17.3 m in Bohai Bay at 9.7 ka. The observed RSL and the prediction curves of the study area were compared with those of other areas. In Gunsan Bay, the early Holocene GIA prediction curves are consistent with those observed, which seems to be the result of a "low setting" of the crust thickness and mantle viscosity. Therefore, it is presumed that the significant difference in the elevations observed between the study area and Gunsan Bay is caused by the levering effect owing to the difference in the tectonic characteristics. Conversely, other observed groups during 7.6–6 ka have a similar slope to the prediction curve of the Early Holocene in the study site, and it is thought that the sediments of the early Holocene were eroded and re-deposited along the channel. These results are of great importance as data of sea level variability in the far field due to glacial collapse and as data for the GIA modeling process. • The RSL in the early Holocene is 13 m shallower than Gunsan on the west coast. • During the 8.2 ka event, the RSL difference between the two sites is 5 m. • GIA models suggest the different costal levering effects between two sites. • Different GIA responses of Gyeonggi Massif and Ockcheon Belt to IESL. [ABSTRACT FROM AUTHOR]

Age-controlled palynostratigraphy has revealed changes in the depositional environment, vegetation, and climate of the southwestern Korean Peninsula since marine isotope stage (MIS) 5a. During MIS 5a (ca. 74–81 ka), the Jeju Strait shelf was an inner shelf with deposition influenced by the Jeju Warm Current (JWC), surrounded by land covered by mixed conifer and deciduous broadleaf forests under warm temperate conditions. The paleoenvironment during MIS 4 (57–71 ka) remains unknown due to a lack of palynomorphs from this stage. During mid–late MIS 3 (ca. 29–50 ka), the Jeju Strait shelf was an inner shelf influenced by cold-water masses from the Korean Coastal Current combined with weaker influences by the JWC, and the surrounding land was covered by mixed conifer and deciduous broadleaf forests that were less dense than in MIS 5a under warm and relatively dry conditions. A cold, slightly wet climate during MIS 2 (ca. 12–29 ka) led to the extension of predominantly cold-tolerant conifer forests due to lowstand sea levels, although inland East Asia remained cold and dry. During MIS 1 (ca. 0–12 ka), cold-tolerant conifer forests persisted into the early Holocene, and were subsequently replaced by mixed conifer and deciduous broadleaf forests as a warm climate was restored in the mid–late Holocene, when the depositional environment became an outer shelf due to highstand sea levels, as it remains today. • We reconstructed Jeju Strait shelf depositional environments since marine isotope stage 5a. • Sea surface temperature-dependent dinoflagellate cysts reflect the relative influences of two currents in the Jeju Strait. • Changes in bisaccate/deciduous broadleaf pollen ratios correspond to sea-level changes. [ABSTRACT FROM AUTHOR]

Abstract: Three wetland sediment sections from two different locations (core CL-4 in the Chollipo area, and trenches HS and HY in the Pyeongtaek area) in west-central Korea yield crucial information on the timing and spatial pattern of century-scale climatic changes and subsequent surficial responses during the Holocene. In the Chollipo area, a lake environment developed from 7360 to 5000 calibrated years before present (cal.yrBP), the deposition of organic materials increased from 5000 to 2600cal.yrBP, and peatland have formed since 2600cal.yrBP. In the Pyeongtaek area, fluvial sediment was deposited prior to about 7000cal.yrBP. From 7000cal.yrBP onward, thick peat sequences started to develop. These two patterns of surficial responses to climate change through the Holocene are different from one another. While this might be due to the dissimilarity in geomorphic conditions, the approximate simultaneity of the environmental changes in the two areas shows that they both can be correlated with major climatic changes. Two such areas that have undergone major changes indicate that the hydrological factors including precipitation and strength of water flow were most responsible for the landscape and geomorphic evolution. The upward trend in relative sea level also played a primary role for environmental change in the coastal areas. [Copyright &y& Elsevier]

Abstract: The Eurimji site in Jecheon City, Chungcheong Province holds major importance for Korean cultural heritage because it is assumed to be the oldest man-made reservoir for rice field irrigation in Korea. A multiproxy study provides the first scientific dating of the levee construction. The authors retrieved two sediment cores from the levee (core ER-1, 18.00 m long) and the reservoir bottom (core ER-3-1, 6.98 m long). Several plant fragment layers were observed between layers of dark gray clay–silt sediment in unit 2 of both cores. The spacing and thickness of these plant layers was relatively uniform (from 50 to 90 cm, and 5 to 6 cm, respectively). These features are interpreted to represent part of a man-made sedimentary sequence created using the consolidation-settlement drain method (tamped-earth or rammed-earth method) commonly used for dam or fortress construction in ancient times, as the features are not characteristic of natural river sedimentary processes. In this alternating sequence, bulk carbon from the sediment yielded AMS 14C dates of 2000–1400 14C yr BP, and the plant materials yielded dates of 1300–1200 14C yr BP. If workers at that time used two different materials such as available plant materials and clays for levee construction, the plant material is preferred for 14C age dating. This is because the origin of the carbon in the sediments is ambiguous, but the source of the plant materials has been confidently determined to be equivalent to the time of the levee construction. Therefore, the levee was constructed between 1200 and 1100 14C yr BP (AD 800–900), which is later than previously thought (i.e., AD 300 or AD 550). The results of our study also indicate that wetlands existed in the area before the construction of the Eurimji levee. [Copyright &y& Elsevier]

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley yielded a good example of a river-valley sequence influenced by the complex interplay between the bottom morphology of the steep paleo-valley, varying sediment supply, and Holocene sea-level change associated with coastal currents. The late Quaternary stratigraphic sequence in the Nakdong River Estuary, approximately 60–70 m thick, forms a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuarine, coastal/shoreface, and deltaic. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed before 12 ka. The transgressive systems tract (TST), showing a succession of retrograding or backstepping depositional arrangements, can be divided into two depositional systems (Unit II and III). The riverine sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 7 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the Holocene deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 7 ka. • Sequence analysis using borehole samples and high-resolution seismic data. • Four main depositional systems (fluvial, estuary, coastal/shoreface, and delta). • The fluvial depositional system, regraded as the LST, occupied the incised-valley. • The TST is characterized by a succession of retrograding or backstepping deposits. • Deltaic system was initiated by aggradational and progradational stacking patterns. [ABSTRACT FROM AUTHOR]

The properties and preparation of talc have long been investigated due to its diverse industrial applications, which have expanded recently. However, its comminution behavior is not yet fully understood. Therefore, having better control of the particle size and properties of talc during manufacturing is required. In this study, we investigate the effect of the ball size in a high-energy ball mill on the comminution rate and particle size reduction. High-energy ball milling at 2000 rpm produces ultrafine talc particles with a surface area of 419.1 m2/g and an estimated spherical diameter of 5.1 nm. Increasing the ball size from 0.1 mm to 2 mm increases the comminution rate and produces smaller talc particles. The delamination of (00l) layers is the main comminution behavior when using 1 mm and 2 mm balls, but both the delamination and rupture of (00l) layers occurs when using 0.1 mm balls. The aggregation behavior of ground talc is also affected by the ball size. Larger aggregations form in aqueous solution when ground with 0.1 mm balls than with 1 mm or 2 mm balls, which highlights the different hydro-phobicities of ground talc. The results indicate that optimizing the ball size facilitates the formation of talc particles of a suitable size, crystallinity, and aggregation properties. [ABSTRACT FROM AUTHOR]

In this study, we present a high-resolution multi-proxy record (pollen, magnetic susceptibility, and mean grain size) from Bigeum Island, South Korea, which mainly showed early Holocene paleoenvironmental change. Bigeum pollen records indicated that early Holocene climate variations in coastal East Asia were principally controlled by the Atlantic meridional overturning circulation. Most importantly, the 8.2 ka cooling event was clearly recognized for the first time in coastal East Asia, where few high-resolution proxy data, such as ice core and stalagmite δ18O records, are available. The insular vegetation in the study site was extremely susceptible to even short-term climate changes, such as the 8.2 ka cooling event, which allowed a detailed climate reconstruction from pollen data. Early Holocene climate teleconnections between coastal East Asia and other regions were identified through regional comparisons of Greenland, China, Brazil, Spain, Madagascar, and Korea. Coastal East Asia is one of world’s most populated regions and will be particularly vulnerable to future climate change. Accurate and detailed paleoclimate proxy data, such as the Bigeum pollen record, will therefore be increasingly important in this region. [ABSTRACT FROM AUTHOR]

Paleomagnetic and rock magnetic investigations were performed on a 64-cm-thick section of nonmarine unconsolidated muddy sediment from the Gosan Formation on Jeju Island, Korea. This sediment was recently dated to have been deposited between 22 and 17 kyr BP calibrated, with a sedimentation rate of 13-25 cm/kyr, based on many radiocarbon ages. Interestingly, stepwise alternating field (AF) demagnetization revealed characteristic natural remanent magnetizations with anomalous directions, manifested by marked deviations from the direction of today’s axial dipole field, for some separate depth levels. On the other hand, stepwise thermal (TH) demagnetization showed more complex behavior, resulting in the identification of multiple remanence components. For all TH-treated specimens, consistently two different components are predominant: a low-temperature component unblocked below 240-320 °C entirely having normal-polarity apparently within the secular variation range of the Brunhes Chron, and a high-temperature component with unblocking temperatures (Tubs) between 240-320 and 520-580 °C that have anomalous directions, concentrated in the ~ 13-34-cm-depth interval (~ 17-19 ka in inferred age) and possibly below ~ 53 cm depth (before ~ 20 ka). Rock magnetic results also infer the dominance of low-coercivity magnetic particles having ~ 300 and ~ 580 °C Curie temperature as remanence carriers, suggestive of (titano)maghemite and/or Ti-rich titanomagnetite and magnetite (or Ti-poor titanomagnetite), respectively. A noteworthy finding is that AF demagnetizations in this study often lead to incomplete separation of the two remanence components possibly due to their strongly overlapping AF spectra. The unusual directions do not appear to result from self-reversal remanences. Then, one interpretation is that the low-temperature components are attributable to post-depositional chemical remanences, associated possibly with the later formation of the mineral phase having Tub ~ 300 °C, whereas the high-temperature components are of primary detrital origin that survived later chemical influence. Accordingly, the unusual directions might record geomagnetic instability within the ~ 17-22 ka period manifested by multiple excursional swings, partly associated with the Tianchi/Hilina Pali excursion. However, further work is needed to verify this interpretation and distinguish it from alternative explanations that invoke rock magnetic complexities as the cause of the unusual directions. [ABSTRACT FROM AUTHOR]