Search

Paleoclimate changes during the last glacial in the arid central Asia are not as well understood as the monsoon-dominated areas of Asia. Here we report a 75-m-long sediment core over past 120 kyr based on astronomical tuning combined with the optically stimulated luminescence (OSL) dating in the Kashi depression of the western Tarim Basin, Northwest China. Analysis of grain size and highresolution gamma ray (GR) logs from the KT11 borehole across the last glacial period yields a climate history for the Tarim Basin which reflects the variations of its temperature and the hydrological cycles. Comparison of these records with north hemisphere summer insolation, the Greenland ice core temperature, stalagmites and the loess from the nearby region indicates that the deposits in the fluvio-lacustrine system of the Kashi depression responded to climate change at the Younger Dryas (YD), six Heinrich cooling events and the Dansgaard-Oeschger cycles. Our work indicates that the alternations between warm-humid and cold-dry climates were prevalent in the western Tarim Basin during the last glacial period, showing an in-phase pattern with the climate variations of the East Asian Monsoon, controlled ultimately by precession and North Atlantic Ocean climate variability on orbital-millennial time scales. [ABSTRACT FROM AUTHOR]

Abstract: Testate amoebae are a group of shelled protozoa that occur in high density populations in wet environments. More than 1900 testate amoebae species or subspecies have been reported in published literature over the last 200 years, from many regions of the world. Testate amoebae are classified as Lobosea or Filosea respectively, according to the presence of lobose or filiform pseudopodia. Testate amoebae have proved an interesting group of indicator organisms in palaeoenvironmental studies and have also been used as bioindicators of human impact on ecosystems. Until recently, the testate amoebae of China were unknown to most western scientists, but our knowledge has improved greatly over the past 20 years. This paper summarizes the testate amoebae research in China along with relevant data from other countries in Asia, and provides the necessary context for future research. [ABSTRACT FROM AUTHOR]

To explore the relationship between the global cooling, westerlies, and central Asian aridity, we report ∼1.1 Ma local sedimentary environment changes according to physical-chemical parameters from an 800-m core (KT11) from the Kashgar region in the western Tarim Basin, China. Grain size end-member (EM) modelling is employed to quantify the processes of sediment transport and deposition. Four end members with modal values of 272 μm, 144 μm, 45.6 μm and 12.7 μm were extracted and explained 97.9% of the variance in the grain size data, corresponding aeolian dynamics, river energies, delta development and pedogenesis/long-term suspension components transported by wind or water, respectively. Four dominant sedimentation types, including lacustrine facies, delta facies, fluvial facies, and aeolian dunes, were identified through lithology and grain size frequency curves. The 1.1 Ma sedimentary successions experienced delta deposits interbedded with fluvial and aeolian deposits and lacustrines (1.1–0.6 Ma), alternating fluvial and aeolian facies with the occurrence of deltas and lacustrines (0.6–0.15 Ma), and aeolian facies interbedded with deltas and fluvial facies (0.15 Ma-present). Stepwise drying sedimentary conditions and enhanced desertification indicated by increasing rubidium/strontium ratios and proportion of aeolian sands, and decreasing total organic carbon since the past 1.1 Ma, implied intensified westerlies, likely resulted from ice volume expansion and ongoing global cooling according to geological record comparison and simulations during the Last Glacial Maximum compared to preindustrial conditions, which may have controlled the expansion of the permanent deserts in inland Asia. These persistent drying trends and intensified westerly circulation in arid regions during glacial periods after the mid-Pleistocene Transition indicated by larger amplitudes of aeolian sand proportion than prior to 0.6 Ma are similar to those in the interior monsoonal Asia, where the larger-amplitude of median grain size indicated enhanced Asian winter monsoon intensity and drier glacials. • Dominant sedimentation types are identified. • Westerly aridity is reconstructed since mid-Pleistocene. • Concurrently enhanced westerlies and winter monsoon is proposed. • Records and simulations show westerly aridity driven by global cooling. [ABSTRACT FROM AUTHOR]

Astronomically forced variations of climate are well documented in lacustrine and marine settings. However, few studies have examined astronomical forced cycles within Quaternary fluvial-fan successions. To explore whether Milankovitch cyclicity might also be present in fluvial-fan successions, we carried out high-resolution gamma-ray (GR) from downhole logging, magnetic susceptibility (MS), Rb/Sr and total organic carbon (TOC) analysis of a core from an 800-m borehole (KT11) from the Kashgar region in the western Tarim Basin, China. Spectral analyses of the GR, MS and Rb/Sr data reveal cycles with ~70 m, ~30 m and ~14 m wavelengths. These pertain to relative variations in grain size. Electron spin resonance (ESR) dating and magnetostratigraphy imply that the cored interval spans the past 1.1 Myr. This age-span constraint, coupled with the comparison of the ratios of these cycle wavelengths to expected ratios of Milankovitch frequencies, suggests that these cycles represent ~100-kyr short-eccentricity, ~40-kyr obliquity and ~20-kyr precession frequencies, respectively. We constructed an astronomical time scale (ATS) spanning the past 1.13 Myr using the ~100-kyr short-eccentricity period. The average accumulation rate is about 70 cm/kyr for this 800-m core succession, and the evolutive spectrum emphasizes that long-term sedimentation rates were stable. We also applied correlation coefficient (COCO) analysis to identify the astronomical forcing. Thus, we conclude that orbitally forced climate change was the main driver of stratigraphic alternations between sand- and clay-rich intervals in the Kashgar region. During maxima of the 100-kyr short-eccentricity cycles, which correspond to interglacial intervals, more chemical weathering and increased seasonal runoff delivered a larger amount of relatively coarser-grained sediments to the fluvial fan in the Kashgar region, and vice versa. The Mid-Pleistocene Transition (MPT) at ca. 0.9 to 0.65 Ma is also well recorded in our GR and Rb/Sr data, and is characterized by a shift in dominant cycle period from 41 kyr obliquity to 100 kyr eccentricity. After 0.65 Ma, the average TOC content decreases whilst Rb/Sr values increase, which suggests that there was an increase in regional aridity of the Kashgar region in the western Tarim Basin following the MPT. This regional change is synchronous with the trend toward aridification observed throughout central Asia. • Milankovitch forcing is the main driver for the climate changes in the western Tarim Basin over the past 1.13 Myr. • The Mid-Pleistocene Transition (MPT) was recorded in both GR and Rb/Sr series. • The MS proxy apparently shows short eccentricity from whole the 1.13 Myr interval. • The long-term increase in average aridity in the western Tarim Basin beginning at ca. 0.65 Ma [ABSTRACT FROM AUTHOR]

• Peatland degradation caused a significant loss of testate amoeba (TA) biodiversity. • Unexpectedly, this loss was accompanied by an increase in TA biosilicification. • TA biodiversity was not coupled to protozoic biogeochemical silicon (Si) cycling. • New insights into microbial biogeochemical Si cycling on a continental scale. Anthropogenic peatland degradation is a global threat. As peatlands store large amounts of carbon (C) their potential for mitigation of climate change has been emphasized recently. Global C cycling is linked to silicon (Si) fluxes from the continents into the oceans. These fluxes in turn are driven by biosilicification, the incorporation of inorganic Si into living organisms, in terrestrial ecosystems. Biosilicification by testate amoeba (TA) communities and its potential for Si cycling has been highlighted since the beginning of the 21st century. However, the effects of peatland degradation on TA biodiversity and corresponding protozoic biosilicification on a continental scale remained unresolved so far. We show that TA biodiversity in Asian peatlands is strongly affected by the grade of human impact. This biodiversity decline was accompanied by an unexpected increase in protozoic biosilicification. Our findings provide new insights into the interactions between the biodiversity of soil microorganisms and biogeochemical Si cycling. [ABSTRACT FROM AUTHOR]

Testate amoebae (TA) are a common and diverse group of protists and are especially abundant in peatlands. The structure of peatland TA communities is well correlated to surface moisture and water table depth (WTD). For that reason, TA are widely used as proxy indicators in ecological and palaeoecological studies. Peatlands are abundant across Asia, but the diversity and ecology of the TA that inhabit these systems are poorly documented. It is therefore unclear whether TA can be used as palaeohydrological indicators in the manner in which they commonly are in Europe and North-America. There is particular uncertainty as to the efficacy of this approach in the lower latitudes. We compiled existing and new data on testate amoebae from 1124 Sphagnum -dominated samples from 42 individual peatlands covering broad latitudinal (25°–66° N) and longitudinal (68°–129° E) ranges. Using a consensus taxonomic framework, we built a checklist of TA and developed TA-based hydrological transfer functions for Asian peatlands. The results showed that three models, weighted averaging (WA), weighted average partial least squares (WA-PLS), and maximum likelihood (ML), predicted similar WTD values for full samples, while the modern analogue technique (MAT) produced the strongest (R2 boot = 0.58) relationship between observed and estimated water-table depths (WTDs). Removing outlier samples improved the R2 values of observed vs. estimated WTDs, with ML then demonstrating the strongest predictive power (R2 boot = 0.68, RMSEP boot = 8.98 cm). The predictive capability of the developed WTD transfer function is comparable to equivalent models for Europe and North America and thus can be used for palaeohydrological reconstructions for boreal to subtropical peatlands in Asia. • A testate amoebae taxonomic checklist was compiled from Asian peatlands. • We developed continental scale testate amoeba-based hydrological transfer functions. • The water-table depth transfer functions can be used for paleohydrological reconstructions. [ABSTRACT FROM AUTHOR]