Climate Forcing: Observations From Chinese Loess Plateau And A Perspective Of The Influence Of Ocean-ridge Processes

This study involves improving knowledge of the climatic and environmental changes during the past 3 million years in the region of the Chinese Loess Plateau and the forcing mechanisms of global glacial-interglacial climate oscillations during the Quaternary. Loess sections consisting of loess-paleosol sequence, fluviolacustrine sequence, and the red clay formation were selected for detailed study. Laboratory methods used included analyses of paleomagnetism, {dollar}\sp{lcub}14{rcub}{dollar}C dating, bulk sample mineralogy, grain-size distribution, clay mineralogy, major and trace element geochemistry, iron geochemistry, stable carbon-isotopes, carbonate content, organic matter content, pollen and pedo-micromorphology by photomicroscopy and SEM.;The fluviolacustrine sequence in the Shijiawan section was deposited between 3.05 and 1.9 Ma B.P. with a dominant alluvial facies. The red clay formation was developed under a constant warm-dry climate 2.7 Ma ago. The paleovegetation in the southern Guanzhong basin was of typical sage steppe type during the period of 3.0-2.7 Ma B.P. Evidence suggests that the red clay was derived from the northwest deserts by aeolian transport, indicating dust deposition stated long before the major loess accumulation. The dustfall rate in the late Pliocene is much lower than in the Quaternary, implying that the Siberian cold high was abruptly intensified 2.6 Ma B.P. Pollen evidence, pedological studies and dustfall rate indicate that a profound climatic change and regional climate regime replacement were coincident with the advent of the first Quaternary glaciation. As demonstrated, the Quaternary climate in the loess plateau responded strongly to the world glacial-interglacial signals which are related to the sea level-coastal position-precipitation linkage.;As has been suggested by many workers, the last and rapid deglaciation must be linked to major changes in ocean circulation. It is difficult to explain this change by changes in solar insolation alone. In fact, the albedo changes might have worked to maintain the ice age. A first attempt has been made to examine if ice loading could have contributed to asthenosphere flow and intensified ocean ridge volcanism which in turn could perturb ocean circulation patterns and increase atmospheric CO{dollar}\sb2.{dollar} The first modeling results suggest that the process could be of quantitative significance

Long-term spatial and temporal variation of CO2 partial pressure in the Yellow River, China

10.5194/bg-12-921-2015Biogeosciences124921-93

Muon radiography experiments on the subway overburden structure detection

Muon radiography is an innovative and non-destructive technique for internal density structure imaging, based on measuring the attenuation of cosmic-ray muons after they penetrate the target. Due to the strong penetration ability of muons, the detection range of muon radiography can reach the order of hundreds of meters or even kilometers. Using a portable muon detector composed of plastic scintillators and silicon photomultipliers, we performed a short-duration(1h) flux scanning experiment of the overburden above the platform and tunnel of the Xiaoying West Road subway station under construction. With the observation direction facing up, the detector is placed on the north side of the track and moved eastward from the platform section inside the station to the tunnel section. The scanning length is 264m and a total of 21 locations are observed. By comparing the observed and predicted values of the muon survival ratio at different locations, the experiment accurately detects the jump in thickness at the interface of the platform section and tunnel section. Furthermore, unknown anomalies caused by random placed light brick piles and side passage mouth above the observation locations are detected and confirmed later. This experiment verifies the feasibility of using natural muons to quickly detect abnormal structures of the overburden of tunnel, and shows that muon radiography has broad application prospects in tunnel safety and other similar aspects.Comment: 30 pages, 10 figure

Timing of India-Asia collision: Geological, biostratigraphic, and palaeomagnetic constraints

A range of ages have been proposed for the timing of India-Asia collision; the range to some extent reflects different definitions of collision and methods used to date it. In this paper we discuss three approaches that have been used to constrain the time of collision: the time of cessation of marine facies, the time of the first arrival of Asian detritus on the Indian plate, and the determination of the relative positions of India and Asia through time. In the Qumiba sedimentary section located south of the Yarlung Tsangpo suture in Tibet, a previous work has dated marine facies at middle to late Eocene, by far the youngest marine sediments recorded in the region. By contrast, our biostratigraphic data indicate the youngest marine facies preserved at this locality are 50.6–52.8 Ma, in broad agreement with the timing of cessation of marine facies elsewhere throughout the region. Double dating of detrital zircons from this formation, by U-Pb and fission track methods, indicates an Asian contribution to the rocks thus documenting the time of arrival of Asian material onto the Indian plate at this time and hence constraining the time of India-Asia collision. Our reconstruction of the positions of India and Asia by using a compilation of published palaeomagnetic data indicates initial contact between the continents in the early Eocene. We conclude the paper with a discussion on the viability of a recent assertion that collision between India and Asia could not have occurred prior to ∼35 Ma

Influence of the ratio of planktonic to benthic diatoms on lacustrine organic matter δ13C from Erlongwan maar lake, northeast China

Carbon isotope ratio (δ13Corg) values of organic matter in lake sediments are commonly used to reconstruct environmental change, but the factors which influence change are varied and complex. Here we report δ13C values for sediments from Erlongwan maar lake in northeast China. In this record, changes in δ13C cannot be explained by simple changes in aquatic productivity. Instead, values were likely influenced by differences in the ratio between planktonic and benthic algae, as indicated by the remains of diatoms. This is because the variation of δ13Corg in algae from different habitats is controlled by the thickness of the diffusive boundary layer, which is dependent on the turbulence of the water. Compared with benthic algae, which grow in relatively still water, pelagic algae are exposed to greater water movement. This is known to dramatically reduce the thickness of the boundary layer and was found to cause even more severe δ13C depletion. In Erlongwan maar lake, low values were linked to the dominance of planktonic diatoms during the period commonly known as the Medieval Warm Period. Values gradually increased with the onset of the Little Ice Age, which we interpret as being driven by an increase in the proportion of benthic taxa, due to effect of the colder climate. The increase in planktonic diatoms at the end of the Little Ice Age, linked to higher temperature and a reduction in ice cover, resulted in a further decline in δ13Corg

Chemical denudation in the Yellow River and its geomorphological implications

10.1016/j.geomorph.2014.12.004Geomorphology23183-9

Spatial and seasonal variability of organic carbon transport in the Yellow River, China

In this study, we examined the spatial and seasonal variability in the concentrations of dissolved and particulate organic carbon (DOC and POC) of the Yellow River. Weekly samples of water and suspended solids were collected along the main stem channel between July 2011 and July 2012 for the upstream Toudaoguai and Tongguan stations, and between August 2008 and July 2012 for the downstream Lijin station near the river mouth. The DOC export at the upstream two stations was primarily controlled by hydrological events such as melting of ice and snow with high DOC concentrations occurring in spring. In contrast, it was more affected by human activities, mainly reservoir regulation, at the lowermost Lijin station. Lower DOC concentration in the wet season indicates that most of the leachable DOC in surface soils may have largely been flushed away by spring floods. In addition, it is also likely due to dilution effect of the rapidly increased water discharge. As a result of low organic carbon content in the parent soils, the Yellow River sediments were characterized by low POC content (POC%). The averaged POC% at Toudaoguai, Tongguan, and Lijin was 0.48%, 0.47%, and 0.37%, respectively, which is significantly lower than the global mean of around 0.95%. The POC% decreased exponentially with total suspended solids (TSS) concentration. This is likely due to the dilution of riverine POC, because high TSS generally means a higher proportion of coarse sediments that have more mineral matter. During the study period, the total DOC and POC fluxes into the ocean were estimated at 0.06×1012g/yr and 0.41×1012g/yr, respectively. Combining our previous estimate of dissolved inorganic carbon (DIC) export shows that the Yellow River transports a carbon flux of 1.52×1012g/yr into the Bohai Sea, accounting for about 0.19% of the global total riverine carbon flux (DOC+POC+DIC). The extremely low DOC/POC ratio represents the lowest level among major world rivers, which is consistent with its intense soil erosion and highlights the effect of soil erosion on organic carbon export. © 2013 Elsevier B.V.Link_to_subscribed_fulltex

CO<inf>2</inf> outgassing from the Yellow River network and its implications for riverine carbon cycle

©2015. American Geophysical Union. All Rights Reserved.CO2 outgassing across water-air interface is an important, but poorly quantified, component of riverine carbon cycle, largely because the data needed for flux calculations are spatially and temporally sparse. Based on compiled data sets measured throughout the Yellow River watershed and chamber measurements on the main stem, this study investigates CO2 evasion and assesses its implications for riverine carbon cycle. Fluxes of CO2 evasion present significant spatial and seasonal variations. High effluxes are estimated in regions with intense rock weathering or severe soil erosion that mobilizes organic carbon into the river network. By integrating seasonal changes of water surface area and gas transfer velocity (k), the CO2 efflux is estimated at 7.9±1.2TgCyr-1 with a mean k of 42.1±16.9cmh-1. Unlike in lake and estuarine environments where wind is the main generator of turbulence, k is more correlated with flow velocity changes. CO2 evasion in the Yellow River network constitutes an important pathway in its riverine carbon cycling. Analyzing the watershed-scale carbon budget indicates that 35% of the carbon exported into the Yellow River network from land is degassed during fluvial transport. The CO2 efflux is comparable to the carbon burial rate, while both larger than the fluvial export to the ocean. Comparing CO2 evasion with ecosystem productivity in the Yellow River watershed shows that its ecosystem carbon sink has previously been overestimated by >50%. Present efflux estimates are associated with uncertainty, and future work is needed to mechanistically understand CO2 evasion from the highly turbid waters.Link_to_subscribed_fulltex