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Interest in the study of microplanktonic organisms in the Arctic has increased owing to their direct participation in the process of sedimentation and sensitive response to changes in environmental and climatic factors. This study presents new data on the taxonomic diversity and content of radiolarian skeletons and agglutinated tintinnid ciliate loricae in the Upper Holocene sediments of the Laptev Sea, East Siberian Sea, and the adjacent part of the Arctic Ocean. We traced the spatial distribution of representative microfauna of these groups in surface sediments and sediment cores. Radiolarian skeletons were found in the surface sediments of the continental slope of the Laptev Sea and adjacent parts of the Arctic Ocean. These belong to the following six species: Stylatractus (?) sp., Actinomma leptoderma leptoderma, Actinomma leptoderma longispina, Streblacantha circumtexta, Spongotrochus glacialis, and Cycladophora davisiana. The radiolarian fauna detected was in deep sea and close to the fauna of the Nansen Basin (Central Arctic). Furthermore, we found tintinnid ciliate loricae belonging to the following seven species: Tintinnopsis ventricosoides, Tintinnopsis fimbriata, Tintinnopsis turbo, Tintinnopsis nitida, Tintinnopsis sp. cf. fusus (?), Tintinnopsis sp., and Stenosemella nivalis. In the study area, the tintinnid ciliate loricae of these species were discovered for the first time and traced mainly in the coastal shelf zone, which can be explained by their ecology. The only exception is that of T. nitida, which was found only on the continental slope of the Laptev Sea. Our findings advance knowledge on the biodiversity of Arctic seas and can be used to monitor ecological and paleoceanographic changes in the Arctic region. [ABSTRACT FROM AUTHOR]

The pollen and algae records derived from core KCES-1 in the East Sea (Japan Sea) reveal vegetation and climate changes during the past 44 ka. From 44 to 36 cal ka BP, forest vegetation in the coastal regions of Ulleung Basin was composed predominantly of subalpine conifer forest, open grassland covered the exposed continental shelves, indicating a cool and dry climate. During the period of 36–28.3 cal ka BP, a warmer and wetter climate caused the contraction of subalpine conifer forest in the coastal regions of Ulleung Basin, and the expansion of marsh in the exposed continental shelves. From 28.3 to 17.6 cal ka BP, the sea-level decline restricted the herbs pollen originates in the exposed shelf of East China Sea and Yellow Sea inflow into the East Sea (Japan Sea), and caused the reduction of herbs pollen in the site location. During the time interval of 17.6–15.1 cal ka BP, a great expansion of subalpine conifer forest can be regarded as the consequence of enhanced East Asian winter monsoon (EAWM). The obvious increase in temperate deciduous broadleaved trees, spores and algae can be attributable to the rising of sea level and the warming of climate from 15.1 to 12.1 cal ka BP. During the period of 12.1 to 5.3 cal ka BP, broadleaved taxa increased, especially during the time period of 9.5–5.3 cal ka BP, evergreen broadleaved trees pollen reach the highest values throughout the core, as a result of the Holocene climate optimum condition. Vegetation changes controlled by humid impacts occurred at the late Holocene, as indicated by an increase in Pinus pollen. [ABSTRACT FROM AUTHOR]

AMS14C dating and analysis of grain size, major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea. Based on the environmentally sensitive grain size, clay mineral and major element assemblages, the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed. These three proxies, mean grain size (>9.71 µm), chemical index of alteration (CIA) and ratio of smectite to kaolinite in particular, show similar fluctuation patterns. Furthermore, 10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene; these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon. The cooling events correlated well with the results of the δ 18 O curves of the Dunde ice core and GISP2, which therefore revealed a regional response to global climate change. Four stages of the East Asia winter monsoon were identified, i.e. 8300-6300 a BP, strong and unstable; 6300-3800 a BP, strong but stable; 3800-1400 a BP, weak and unstable; after 1400 a BP, weak but stable. [ABSTRACT FROM AUTHOR]

Abstract: We present a paleoclimatic reconstruction of the mid-Holocene by geochemical analysis of a sediment core MZ01 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). Our results show that the downcore geochemical variations in the sediments of the core provide a link to historical climate changes. Relatively higher ratios of CIA, Ba/Sr and a lower ratio of CaO/MgO coincide with major regional warm and humid climate episodes, and vice versa. Therefore, these geochemical indicators are useful in reconstructing the paleoclimate in eastern China. Using the geochemical records of core MZ01, which are well constrained by AMS 14C dating, we found that from 8300yr BP to 4200yr BP the regional climate was moderately warm and humid, and from 4200yr BP to 2300yr BP the climate was cool and dry, with large fluctuations between cool–dry (3700yr BP, 2850yr BP and 2400yr BP) and warm-wet (3250yr BP and 2650yr BP). Since 2300yr BP, our records indicate that the climate has gradually become warmer, although a cold event centered at around 250yr BP (the Little Ice Age, LIA) interrupted this warming trend. We also found significant 238yr cycles in our CIA records that imply a possible solar influence on the regional climate changes since the mid-Holocene. [Copyright &y& Elsevier]

Sediment accumulation in continental margins during the Quaternary Period was substantially influenced by both sea-level fluctuations and climate changes. However, the response of sediment accumulation to these changes on an orbital timescale, remains poorly understood, for two main reasons: the scarcity of sedimentary records with a high-resolution chronology, and the difficulty in distinguishing the role of sea-level from regional climate signals. Here we present the results of sediment color reflectance (c*), grain size and total organic carbon (TOC) content of core BH08 (212.4 m in length, spanning the last ~1 Myr) recovered from the Bohai Sea, China. The chronology of core BH08 on the orbital timescale is constrained by both magnetostratigraphy and astronomical tuning. Sedimentary facies analysis suggests that the sedimentary sequence is dominated by the alternation of a deltaic system and floodplain deposition. Principal components analysis of the grain-size data reveals two principal components (PCs), including PC1, reflecting the 31–500 μm fraction, and PC2, reflecting the 18–66 μm fraction. Comparison of sample scores on PC1, PC2 and c* with the alternation of sedimentary environments reveals that PC1 and c* reflect cycles of deltaic and floodplain deposition at ~100-kyr and ~40-kyr periodicities, while PC2 exhibits a ~20-kyr periodicity, in addition to the ~100-kyr and ~40-kyr cycles. We infer that PC1 and c* are mainly sea-level dependent, whereas PC2 is controlled by the combination of changes in monsoon climate and sea level. We suggest that Milankovitch-scale monsoon climate fluctuations controlled the sediments supply to the Bohai Sea during the last ~1 Myr, while the redistribution of sediments by marine processes (e.g., tidal currents) has partially obscured the monsoonal signal in the grain-size proxy (e.g., PC1) which instead is sensitive to sea-level change. Our results provide an example of the influence of climate and sea-level on sediment accumulation in a shallow continental margin setting influenced by monsoonal climate in an icehouse world. • A 1-Myr record of orbitally-forced continental margin deposits is presented. • Principal components analysis of grain size reveals sea-level and climate signals. • Sedimentation in the Bohai Sea is influenced by sea level and monsoonal climate. • Monsoon signal could be obscured by marine process (e.g., tidal currents). [ABSTRACT FROM AUTHOR]

The Bering Sea, as a transition between the Arctic and the Pacific oceans, plays an important role in global climate change and biogeochemical cycles. Here we examined a variety of biomarkers in a core (BR07) from the northern continental slope of the Bering Sea in order to reconstruct summer sea surface temperature (SST) and sea ice extent during the period 11–2 ka (thousands of calendar years ago). The TEX 86 L -derived SST gradually decreased (ca. 1.6 °C) from early to mid-Holocene (11.3–8.0 ka), but did not show a cooling or warming trend afterwards. Our SST data do not support the hypothesis of a Holocene seesaw in temperature between the North Atlantic and the North Pacific. Several algal biomarkers, including IP 25 and its derived indicators for sea ice, brassicasterol for diatoms and dinosterol for dinoflagellates, suggest that the sea ice extent gradually increased from early to late Holocene, interrupted by rapid changes at ca. 2.8–2.6 and 5.5–5.0 ka. The synchronous evolution between IP 25 and SST indicates a strong coupling between sea ice cover and climate change in the Holocene. [ABSTRACT FROM AUTHOR]

The origin and expansion of millennial-scale climate changes in the Earth's climate system, widely presented in different paleo records, remain important issues in the scientific community. In this study, we present a highly resolved record of the East Asian monsoon (EAM) over 123 to 30 ka, obtained from a new archive of millennial/centennial climate variability in the mid-latitudes of the Northern Hemisphere. We used sediments from the semi-enclosed Sea of Japan, which is a region with unique land, ocean, and atmospherice interactions. We obtained color lightness (CL) records of a sediment core recovered from the northwestern part of the Sea of Japan with a high temporal resolution comparable to that of the Chinese EAM records using the original photocolorimeter. The chronology of the studied core was established by correlating the Heinrich events with the measured CL, magnetic susceptibility, and chlorin content with color L* and magnetic susceptibility records of the well-dated Sea of Japan core MD01–2407 and subsequently by correlating the abrupt drops in CL with well-dated Greenland and Chinese interstadials within the established Heinrich events. To infer a new record of EAM evolution, we used the CL record of the studied core over 30–123 ka, when the sea level dropped below the present sea level <90 m, the deep-water ventilation did not change profoundly relative to the present and sediment geochemistry was mainly controlled by millennial-timescale climate changes, such as the Dansgaard–Oeschger (DO) cycles. By comparing the DO cycles inferred from different natural archives, such as δ18O records of Greenland ice core and Chinese caves and CL record of the Sea of Japan sediments, we discussed similarities and some peculiarities of the DO cycles evolution and its millennial scale variabilities recorded in the high, middle, and low latitudes of the Northern Hemisphere over 30–123 ka. • High resolution record of sediment color from the Japan Sea (JS) over last 120 ka. • Correlation of Dansgaard-Oeschger cycles between JS, Greenland and Asia monsoon. • DO cycles 17–5 recorded in three archives show oscillation typical for Greenland. • DO cycle 23 and 25 show different changes between records of three archives. • Such differences were likely ruled by special Pacific responses to N Atlantic changes. [ABSTRACT FROM AUTHOR]

Sedimentary architecture dominated by transgression–regression cycles in the shallow Bohai shelf region contains information about global sea-level, climate and local tectonics. However, previous studies of transgression–regression cycles in this region at orbital timescales that extend back to the early Pleistocene are sparse, mainly because of the shortage of well-dated long cores. Although transgression–regression sedimentary cycles in the region have been interpreted in terms of local tectonics, sea-level, and climate change, the detailed structure of marine transgressions and their significance for Quaternary global sea-level variations remains to be examined. In this study, we present an integrated sedimentological, geochemical and paleontological study of a 212.4 m (∼1 Ma) core (BH08) recovered from the Bohai Sea, China, for which an astronomically-based age model is available. Correspondence between marine-terrestrial sedimentary cycles and global sea-level fluctuations suggests that stacking of marine and terrestrial sediments was driven mainly by glacio-eustatic sea-level fluctuations in a context in which tectonic subsidence was largely balanced by sediment supply over the last ∼1 Ma. We report a dominant 100-kyr cycle beginning at ∼650 ka, which reflects the worldwide influence of the mid-Pleistocene transition (MPT) in sea-level records. We find that neritic deposits after the MPT were relatively thicker than before the MPT, which indicates an important control of the MPT on sedimentary architecture through lengthening of the duration of sea-level highstands. [ABSTRACT FROM AUTHOR]

We present a paleoclimatic reconstruction for the Holocene by clay mineral analyses of sediments from core MZ02 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). The clay minerals mainly consist of illite (66%–79%) and chlorite (12%–19%), with minor kaolinite (7%–13%) and smectite (0–6%). Provenance analysis suggests that the illite-dominated clay minerals were derived mainly from the detrital outputs of the Changjiang, Minjiang, and small rivers from Taiwan Island. Our study indicates that the sea level rise since the last glacial, the strength of the Taiwan Warm Current (TWC) and Chinese Coastal Current (CCC) have controlled the dispersal and deposition of clay minerals on the ECS, that in turn determined the clay mineral compositions in the core sediments. During 13,000–9500 BP, due to the lower sea level and shorter distance between these three estuaries and core MZ02, fine sediments on the inner shelf of the ECS were primarily supplied by mixed provenances from the Changjiang, Taiwanese, and Minjiang rivers. During the early Holocene (9500–6200 BP), stronger sediment reworking and erosion at the shelf edge was responsible for the increased lateral transport of fine sediments in the ECS, which lead to a dominance of the sediment source from the Changjiang, while the Taiwanese and Minjiang rivers only provided minor components of detrital sediment to the shelf. Increased strength of TWC might have played an important role in the sediment dispersal and deposition on the inner shelf of the ECS during 6200–2400 BP, with a dominance of more than 60% sediments transported from Taiwanese rivers. Furthermore, our study implies that the Asian monsoon and the weakening of TWC were linked to the abrupt increase of Changjiang and Minjiang derived terrigenous detritus materials since 2400 BP. [ABSTRACT FROM AUTHOR]

Abstract: Sediments from the continental shelf/coastal region bear significant signals of sea-level, climate change as well as local tectonic information. This study presents a high-resolution magnetostratigraphic and rock magnetic study of a 212.4m core (BH08, with a basal age of 1.06Ma) recovered from the shallow (<30m below sea level) Bohai Sea, China. Astronomical tuning based on the sediment redness (a*) of core BH08 allows the construction of a high-resolution chronology that is assisted by magnetostratigraphic data. Sedimentology and associated proxies (grain size and redness) indicate that the cyclic alternation of neritic/littoral sandy deposits and terrestrial silts/clayey silts was mainly controlled by changes in sea-level and associated base-level at glacial–interglacial timescales. The a* record of the core can be correlated with marine δ18O records at 40- and 100-kyr cycles, indicating that the sediments in the study area are continuous at least at orbital timescales regardless of significant base-level variations. This is likely due to continued subsidence in the basin and creation of accommodation space. The significant lower sedimentary accumulation rates since 750ka might be due to the deviation of the depositional locus from core site because of extreme low sea-level stands during the glacials since the Mid-Pleistocene transition (MPT). Especially the glacial sea-level lowstands might have resulted in bypassing or erosion of sediments on the BH08 core site during peak glacials (MIS 6, MIS 10 and MIS 16), limiting the sediment preservation potential. This study documents the longest Quaternary sedimentary succession in the Bohai Sea and provides, for the first time, a clear link between sedimentation in the area and glacial–interglacial climate-driven sea-level changes. This study also highlights the feasibility of astronomical tuning to obtain high-resolution chronology for shallow shelf deposits, which is otherwise very difficult to be achieved on the basis of magnetostratigraphic data alone. [Copyright &y& Elsevier]

Abstract: Chinese loess is a unique continental archive of Quaternary climate change, and its elemental components or ratios can provide significant insights into variations in the East Asian palaeomonsoon at tectonic to millennial timescales. However, high-resolution elemental analyses of loess deposits have seldom been reported. To investigate geochemical variations of loess sediments at millennial and centennial timescales, and their potential for recording abrupt climate change, powder and U-channel (long plastic single-boxes used to sub-sample the center of split core sections) samples were collected from the Gulang loess section on the northwestern Chinese Loess Plateau for conventional and scanning X-ray fluorescence (XRF) analyses. Results suggest that although ten elements (Al, Si, K, Ca, Ti, Fe, Zn, Rb, Sr and Zr,) can be detected robustly using scanning XRF method, only five elements (Si, Ca, Fe, Sr and Zr) can be employed confidently to infer the chemical weathering and grain size sorting effects. Comparison of scanning XRF-derived elemental data with magnetic susceptibility, grain size and speleothem records indicates that high-resolution elemental records have great potential for evaluating rapid fluctuations of the East Asia monsoon. [Copyright &y& Elsevier]

This study investigates Holocene sedimentary evolution and hypoxia development using borehole cores CJK06 and CJK09, in combination with other published core data. Based on lithology and microfossil (benthic foraminifera) characteristics, seven types of sedimentary facies were identified from the base upward: river, tidal flat, tide-influenced river, transgressive lag, estuary, inner-shelf, and prodelta. Isochronous correlation among the cores was established relying on accelerator mass spectrometry 14C dates. Facies succession indicates that a weak progradation occurred in coastal environments (12–10 ka BP) due to the Younger Dryas-induced deceleration of sea-level rise; rapid deposition locally occurred in the southern marginal area of tide-dominated estuary environments (10–8 ka BP), likely due to the junction of the Yangtze and Qiantangjiang River currents; and marine current-induced fluid mudflows prevailed in the shallow marine environments (8–1 ka BP), with the cooling climates of 5–1 ka BP. Furthermore, prodelta and shallow marine environments co-occurred with an uneven progradation of the delta within the last 1 ka, while deposition occurred just inside the more southern, delta-influenced area. The occurrence of euryhaline benthic foraminifera suggests that an enhanced freshwater discharge of the mid-Holocene (8–5 ka BP) was followed by a sharp decline in the late Holocene (5–1 ka BP) with climate change. The occurrence of cold-water benthic foraminifera indicates a severe cold-water condition during the mid-Holocene due to the intrusion of upwelling currents triggered by the propelling force of warm currents and summer monsoon winds. In addition, the occurrence of low-oxygen foraminiferal assemblages reveals that hypoxia has developed since 10 ka BP in stages consistent with the sedimentary evolution: localized hypoxia formation coincident with the southern depocenter during the early Holocene (10–8 ka BP); severe hypoxia with enhanced freshwater discharge and upwelling current intrusion during the mid-Holocene; and weakened hypoxia of the late Holocene, mainly due to the sharp decline in freshwater discharge. Within 1 ka BP, freshwater discharge from the approaching river mouth and increased nutrient inputs from enhanced human activities on land have contributed to the prevalence of hypoxia, especially in the southern deltaic area. Overall, it was revealed that the freshwater discharge modulated with climate variations and delta progradation plays a primary role in controlling the sedimentary evolution and hypoxia development during the mid-late Holocene. • Gravity flows (fluid mudflow) prevailed during the late Holocene (5–1 ka BP). • Holocene freshwater discharge was enhanced (8–5 ka BP) and then sharply declined. • Severe upwelling current intrusion occurred during the mid-Holocene (8–5 ka BP). • Hypoxia boomed during the mid-Holocene (8–5 ka BP). [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) have become the dominating burden in the Arctic ecosystems, but their transport pathways and relative importance of different sources in the Arctic remained unclear, and this would be further complicated by climate change. Here we interpreted 27 PAHs in 34 surface sediments from the northern Bering-Chukchi margin. We integrated source apportionment methods (including diagnostic ratios, principal component analysis, hierarchical analysis, and positive matrix factorization (PMF) model) together with geochemistry parameters, which reveal a gradually clear picture of the spatial patterns of different sources. The total PAH concentrations (50.4 to 896.0 ng/g dw) exhibited a "hilly" shape with the increase of latitude, showing the highest level of PAHs in the northeast Chukchi Sea. The total BaP toxic equivalent quotient (TEQ) for carcinogenic compounds was from 1.06 to 33.3 ng TEQ/g. Most PAHs showed positive correlations with silt content, total organic carbon, stable carbon isotopes and black carbon (p < 0.01 or 0.05). Generally, source apportionment methods revealed an increasing petrogenic source of PAHs with latitudes. The PMF model further differentiated two petrogenic (36.7%), two pyrogenic (softwood and fossil fuel combustion, 35.5%) and one in-situ biogenic source (Perylene, 27.8%). An extremely high petrogenic signal was captured in the Canada Basin margin, possibly originating from the Mackenzie River via ice drifting with Beaufort Gyre, while another petrogenic source may come from coal deposit erosion by deglaciation. Softwood combustion (characterized by Retene) exhibited exclusively higher contribution in the northeast Chukchi Sea and might result from the increasing wildfire in Alaska due to climate change, whereas fossil fuel combustion exhibited similar contributions across different latitudes. Our results revealed natural PAHs as important "inside sources" in the Arctic, which are highly sensitive to global warming and deserves more attention. Unlabelled Image • Characterized 27 PAHs and geochemistry in surface sediment from the northern Bering-Chukchi margin. • Differentiated and quantified the distribution patterns of different PAH sources from the study sites. • PAHs were attributed to five sources with different transport pathways: two petrogenic, one biogenic, two pyrogenic. • There was high signals of petrogenic PAHs associated with Mackenzie River input in Canada Basin margin. [ABSTRACT FROM AUTHOR]