Search

Abstract: In their recent paper, ; Anti-phase oscillation of Asian monsoons during the Younger Dryas period: Evidence from peat cellulose δ13C of Hani, Northeast China, Palaeogeography, Palaeoclimatology, Palaeoecology 297, 214–222) discuss bulk peat sample cellulose δ13C data from a fen in northeast China as a proxy for East Asian summer monsoon intensity during the Late Glacial period. Based on their own results, cited papers, and an extensive re-interpretation of sedimentological and palynological data from nearby Lake Sihailongwan, construct a hypothesis of contrasting moisture conditions in northern and southern China, with wet conditions in the north during the Younger Dryas period and an anti-phase behaviour of Indian- and East Asian summer monsoon intensity. However, we do not approve of the re-interpretation of our Lake Sihailongwan data by and must strongly reject it. We show here that neither the fen data, nor the Lake Sihailongwan data or any other cited data allow for the sound assumption of an intensified East Asian summer monsoon in northeastern China during the Younger Dryas. The Late Glacial variability of the fen data found by can be easily explained by changes in the plant assemblage down core and thus by the composition of the peat. Furthermore, the use of bulk peat cellulose δ13C data as a precipitation proxy remains unproven for that area. Hence, there is no basis for a model contrasting Indian and East Asian summer monsoons during that period. [Copyright &y& Elsevier]

Abstract The Eocene was an interval of climate evolution, when the extreme high temperatures of the earliest Cenozoic gave way to a global cooling trend. Fine-grained lacustrine sediments of Eocene age from northeastern China represent an excellent archive to study long-term environmental and climatic changes at high-resolution. The Huadian Basin is a Cenozoic, fault-bounded basin in Jilin Province, northeastern China. Though small in area, it contains numerous oil shale- and coal-bearing layers, which provide an abundant Middle to Late Eocene palynoflora. Eighty-five palynomorph genera and one hundred palynomorph species were identified in the Huadian Formation, allowing to distinguish 4 palynozones. The nearest living relatives of the recovered palynomorph taxa suggest the presence of subtropical evergreen and deciduous broad-leaved forests during deposition of the Huadian Formation. Using the coexistence approach (CA), we calculated seven paleoclimatic parameters, which indicate a subtropical warm and humid climate with a mean annual temperature above 13.6 °C and a mean annual precipitation of at least 887 mm. However, the climate became cooler and drier during the transition from the lower Oil Shale Member to the upper Carbonaceous Shale Member. Palaeoclimatic data from the various Middle and Late Eocene basins of northeastern China (i.e., the Huadian, Fushun, Yilan, Hunchun and Jishu basins) were compared with data from North American and European basins. Middle Eocene climate in the Northern Hemisphere was generally warm and humid, and the mean annual temperature and precipitation in northeastern China were similar to those in North America, though slightly lower than those of Europe. Similar trends in temperature and precipitation on different continents support the existence of a global Mid-Eocene cooling event. This paper is the first systematic study of Middle to Late Eocene seasonality in the Huadian Basin. Our results show an apparent differentiation in both temperature and precipitation between summer and winter, supporting the view that the East Asian Monsoon was established in northeastern China already during the Middle to Late Eocene. This Middle and Late Eocene monsoon was likely driven by the development of Pacific trade winds and an alternating, seasonal high- and low-pressure system over Siberia. The climatic changes observed in our dataset, especially the precipitation changes, appear to have played an important role in controlling oil shale formation in the Huadian Basin. A warmer and more humid climate, with abundant precipitation and high subsidence rates, formed a deeper Huadian depositional lake. High productivity and stable stratification provided the abundant organic matter and favorable preservation conditions necessary for oil shale accumulation. Highlights • The Middle-Late Eocene palynoflora were firstly systematically studied in Huadian Basin. • We quantitatively estimated the Middle-Late Eocene climate based on CA method. • A globally cooler phase was recognized in the Middle Eocene. • Climate seasonality in the Middle-Late Eocene supports the EAM was already prevalent in NE China. • Changes in climate, especially precipitation, play an important role in oil shale formation. [ABSTRACT FROM AUTHOR]

The Salawusu River Valley cuts through the Mu Us Desert in north central China, and lies at the interface of the East Asian Summer and Winter Monsoonal regions. Exposed at numerous locations in the valley side are extensive late Quaternary deposits, consisting of interbedded aeolian sands, fluvio-lacustrine units and palaeosols. Due to the importance of the location in potentially elucidating both summer and winter monsoonal regimes, and the quality of the sedimentary record, the region has a rich history of study, and yet even within the Holocene sequence, many conflicting interpretations have arisen based on studies on different sections. This paper aims to synthesize and explore these differences by exploring the lateral continuity of the Holocene sequences along a ~ 45 km reach of the valley, and presenting new, detailed physical and geochemical analyses of three sections, focusing on the lacustrine Holocene Dagouwan Formation. The absence of the lacustrine unit at several locations confirms that rather than representing a single lake, the Dagouwan Formation instead represents a series of palaeolakes, probably at least partially hydrologically isolated from each other by aeolian sands. All begin with sand-dominated deposits during the early−/mid-Holocene, which is interpreted as the result of abundant sand-supply to the north and west, under the influence of an enhanced East Asian Winter Monsoon, and all switch to silt-dominated, more carbonate-rich deposits during the mid−/late-Holocene, which is attributed to an enhanced East Asian Summer Monsoon bringing loessic silts from the Chinese Loess Plateau to the east and south. The timing of this change, perhaps as late as 5.5 ka, supports the idea of a relatively enhancement late mid-Holocene of the summer monsoonal circulation in the region. However, despite the proximity of the sections and consistent analytical approaches, marked differences between the sections occur in all proxies studied. The timing and rate of the switch from sand- to silt-dominated lacustrine deposition varies between the sites by as much as 2000 years within just a few kilometres of each other, and at some sites the switch was gradual, whereas at others it was very rapid. Similar dramatic variations are also seen with organic carbon content, carbonate content, C:N ratio, and especially the δ13C isotopic ratio. These point to the lake basins behaving very differently, and emphasize that consideration must be given to the local geomorphology and palaeolimnological evolution of individual sections. • Differences in lacustrine Holocene monsoon records in northern China are explored. • The occurrence of the lakes is geomorphologically, not climatologically, controlled. • Different sections of similar units represent different lakes with varied histories. • Consistent changes in sediment suggest mid-Holocene decline of winter monsoon. • Study of individual sections or proxies cannot be used to infer regional climate. [ABSTRACT FROM AUTHOR]

The terrestrial mollusk fossils found in Chinese loess strata have been studied for over one hundred years. However, the greatest progress in these studies has been made only in the last two decades. In this paper, we review the advancements, advantages and limitations of terrestrial mollusk studies in Chinese loess deposits. Improvements in research methods and approaches have allowed the extraction of more detailed paleoenvironmental and paleoclimatic information from mollusk assemblages. The broadened research scope and content have yielded many new findings and results. The mollusk record has thus become one of the most important proxies in the paleoenvironmental and paleoclimatic reconstruction of loess-paleosol sequences in China. The greatest progress in the studies of terrestrial mollusks in Chinese loess sequences can be summarized as follows: (1) modern mollusk assemblages can be classified into four ecotypes, based on their temperature and humidity requirements, including eurytopic, semi-aridiphilous and sub-humidiphilous, cold-aridiphilous, and thermo-humidiphilous types; (2) Quaternary mollusk assemblages can be modified into the following three ecological types: glacial loess, interglacial paleosol, and interstadial weakly-developed paleosol assemblages; (3) mollusk records successfully reveal long-term climatic and environmental changes reflective of the history of East Asian monsoonal variations since the Late Cenozoic, and the succession of mollusk species also indicate short-term environmental changes such as millennial climate variability during Last Glacial Maximum and unstable climatic fluctuations during glacial and interglacial periods; and (4) more recently, new analytical approaches have offered increased research potential in areas such as paleotemperature reconstruction using the isotopic compositions of modern and fossil mollusk shells, combined with higher accuracy 14 C dating of Quaternary loess deposits, which will greatly improve future loess paleoenvironmental research. [ABSTRACT FROM AUTHOR]

Under the influence of glacial-interglacial climate change and regional tectonic activities in the Quaternary, the sedimentary environments of the Bohai Sea changed greatly, providing significant information on transgression-regression events, East Asian monsoon changes and regional tectonic activities. This study analyzed the sedimentological characteristics of the BH1302 core (water depth of 12.3 m, length of 70.2 m) in the southern Bohai Sea based on grain size, foraminiferal assemblages, carbon and oxygen isotopes in foraminiferal shells and element geochemistry, and established a chronological framework based on AMS 14C, optically stimulated luminescence dating and Oxcal age-depth model using Bayesian modeling. The results showed that three interglacial transgressions and one interstadial transgression were revealed in BH1302 since the late Quaternary, corresponding to marine isotope stages (MIS) 7, 5, 3 and 1, and three subinterglacial transgressions were further identified during MIS 7. The sedimentary environments of Laizhou Bay transitioned from an estuary environment dominated by rivers to a neritic environment dominated by marine conditions because of subsidence of the Miaodao uplift in late MIS 7.1. Three subinterstadial transgressions occurred in both MIS5 with two subinterstadial in MIS 3, and the highstand sea level of MIS 3 reached approximately −18 ∼ −21 m. Under the influence of sea level fluctuations and the East Asian monsoon, the sedimentary environments of MIS 1 can be divided into a low salinity tidal-flat environment (12.0–7.0 kyr BP), a low salinity neritic environment (7.0–4.5 kyr BP) and a modern neritic environment (∼4.5 kyr BP). • The isotopes in the foraminifera shells have good indications to the impact of freshwater input on the neritic environments. • Except for 4 interglacial transgressions, the paper further identifies 3 sub-interglacial transgressions in the MIS7 period. [ABSTRACT FROM AUTHOR]

Situated in the Salawusu River Valley in the southeast of China's Mu Us Desert, the Milanggouwan stratigraphical section MGS1 has recorded 11 sedimentary cycles, consisting of alternations between dune sands and fluvial or lacustrine facies. This paper analyzed the distribution of grain-size and Zr/Rb ratios in the MGS1, which is located in the arid and semi-arid areas of North China, and grain-size and Zr/Rb ratios are good proxy indicators of East Asian winter and summer monsoons. Results determined the age of the top of MGS1 to be 11.6 ± 0.9 ka BP, and Mz and σ values in the dune sands to be lower than those in the corresponding fluviolacustrine or paleosols. Furthermore, Zr/Rb also exhibited low values in the dune sands and a relatively high content in the fluviolacustrine and paleosols. Both grain-size and Zr/Rb ratios displayed 11 cycles similar to the sedimentation changes, while the Zr/Rb ratios were observed to correlate with Mz and σ. The results suggested that the cycles resulted from the fluctuations between cold-dry and warm-humid climates, and the MGS1 segment experienced at least 11 cold-dry and warm-humid climatic fluctuations. This type of high-frequency climatic fluctuation on a millennial time-scale is related to variations in the strength of the East Asian winter and summer monsoons during the Holocene Period. The dominant periods of the winter monsoon corresponded to the cold events of 8200, 5000, 4000, 2700 and 1400a BP reported in the North Atlantic and other regions in China. [ABSTRACT FROM AUTHOR]

Abstract: Loess deposits in the Eastern Qinling Mountains (central China) provide a detailed archive for reconstructing the paleoenvironment during early hominin occupation. The study of the loess deposits also provides a unique opportunity to understand Pleistocene atmospheric circulation in this transitional climatic zone. However, the provenance and formation of the loess deposits were not well understood until now. In this paper, we report on new geomorphologic investigations and depositional analyses of the loess deposits. The results suggest that Gobi deserts and drylands in northern and northwestern China were one of the dust sources. These loess deposits show similar geochemical composition as the average upper crust (UCC), and may indicate that they experienced multiple sedimentary processes, with the dust being well mixed before deposition. However, the higher 87Sr/86Sr ratios (between 0.719650 and 0.721043) and extremely low ɛNd(0) values (between −11.98 and −18.97), which are different from the typical loess of the Chinese Loess Plateau, demonstrate that proximal clastic sediments that were apparently derived from the weathered Qinling orogen bedrocks, form the other important source for the loess deposits. The chemical Index of Alteration [CIA = Al2O3/(Al2O3 + CaO* + Na2O + K2O) × 100] and Chemical Proxy of Alteration [CPA = 100 × Al2O3/(Al2O3 + Na2O)], both in molar proportions show that the loess has experienced intense pedogenesis. We conclude that the loess deposit has a mixed provenance. The palaeoclimate in the Eastern Qinling Mountains remained mild in the glacial periods due to the topography and unique geographic locations, providing a suitable place for hominine occupation. [Copyright &y& Elsevier]

Abstract: Multi-proxy records (geochemistry, clay mineralogy and paleontology) from three sediment cores from Lake Hovsgol, northwest Mongolia, provide paleoenvironmental changes in continental Asia from the last glacial to the present (during the last 29calka BP). This paper presents the first continuous δ13C and δ18O dataset for ostracod shells (Cytherissa lacustris) from Lake Hovsgol sediments. A positive shift in ostracod δ13C values (from +0.5‰ to +3.2‰) began at ca. 21calka BP, and was associated with a decrease in δ13C values of total organic carbon (from −24.7‰ to −27.3‰) and an increase in the mass accumulation rate of total organic carbon (MAR-TOC). These results suggest that increased lake productivity led to the 13C-enrichment of dissolved inorganic carbon in Lake Hovsgol. In addition, decreases in clay content and the illite crystallinity index (full width at half maximum of the 10Å peak) began at ca. 21calka BP, indicating an increase in surface runoff and a change in sources of clastic materials in the watershed. The highest δ18Oostracod values (up to −4.8‰) at 16–15calka BP indicate the increases in precipitation from the East Asian monsoon. The total pollen amount increased, and Betula, Alnus, and Salix were dominant (up to 53%, 30%, and 6%, respectively) after 16–15calka BP. These findings indicate that broad-leaved trees expanded around Lake Hovsgol. In addition, fossil diatom valves appeared after 16–15calka BP, suggesting climate amelioration, and increased input of soil-derived nutrients and dissolved silica. Between 10 and 5calka BP (Holocene climate optimum), productivity was high in and around the lake (MAR-TOC, up to 47.3mg/cm2 kyr; MAR-diatoms, up to 14.4×108 valves/cm2 kyr; total pollen concentration, up to 9.0×105 grains/cm3). Environmental changes during the last 29kyr in and around Lake Hovsgol are clearly associated with fluctuations in summer insolation and East Asian monsoon intensity. [Copyright &y& Elsevier]