The Chinese Loess Plateau (CLP) is a large, spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the East Asian monsoon. Many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions. Although spatial and temporal variations in the grain sizes of CLP sediments are fundamental to this effort, controversy over the origin of the dominant coarse quartz silt has limited interpretations. Reexamination of the spatial pattern of grain-size distribution across the CLP and a field-scale experiment conducted in the Gobi Desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal Mu-Us, Tengger, and Badain Jaran sandy deserts. Our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in Central Asia and identify this process as the most consistent with the wellrecognized systematic northwest-southeast depositional pattern of the CLP. We suggest that only abraded coarse quartz grains transported short distances by long-term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau. These results decouple the production and transport of coarse silt and finer silt and clay particles, which have a more distant and wider provenance, changing the constraints on previous paleoclimatic reconstructions. © 2013 Geological Society of America

Permafrost is degrading under current warming conditions, disrupting infrastructure, releasing carbon from soils, and altering seasonal water availability. Therefore, it is important to quantitatively map the change in the extent and depth of permafrost. We used satellite images of land-surface temperature to recognize and map the zero curtain, i.e., the isothermal period of ground temperature during seasonal freeze and thaw, as a precursor for delineating permafrost boundaries from remotely sensed thermal-infrared data. The phase transition of moisture in the ground allows the zero curtain to occur when near-surface soil moisture thaws or freezes, and also when ice-rich permafrost thaws or freezes. We propose that mapping the zero curtain is a precursor to mapping permafrost at shallow depths. We used ASTER and a MODIS-Aqua daily afternoon land-surface temperature (LST) timeseries to recognize the zero curtain at the 1-km scale as a “proof of concept.” Our regional mapping of the zero curtain over an area around the 7000 m high volcano Ojos del Salado in Chile suggests that the zero curtain can be mapped over arid regions of the world. It also indicates that surface heterogeneity, snow cover, and cloud cover can hinder the effectiveness of our approach. To be of practical use in many areas, it may be helpful to reduce the topographic and compositional heterogeneity in order to increase the LST accuracy. The necessary finer spatial resolution to reduce these problems is provided by ASTER (90 m).

Some of the largest cataclysmic floods of the Quaternary followed multiple breaches of glaciers damming the headwaters of the Maly Yenisei river in southern Siberia. The shorelines of the impounded lake in Darhad basin suggest at least four depths of 290, 175, 145, and 65 m. Fossil evidence, together with previous ¹⁴C and luminescence dating, indicates the existence of a deep lake during MIS 3; the eroded character of the highest shoreline suggests that the deepest lake was older. ¹⁰Be dating of moraines in the surrounding mountains has documented major glacial advances during MIS 2, although no published direct dating has confirmed a highstand of the lake then. To address this problem, we extracted lake sediments from a 92.6 m deep borehole, sampled beach sands from the nearby basin edge, and dated them both using luminescence methods. We also dated, with ¹⁰Be, the eroded remnants of the end moraine deposited by the last glacier that dammed Darhad basin, as well as other moraines in the mountains surrounding the basin. These numerical ages confirm that a deep lake existed in Darhad basin at ~20 ka and that a large glacier crossed the Maly Yenisei and dammed Darhad basin at ~21 ka. The deep lake persisted episodically until ~14 ka. The ¹⁰Be dating in the surrounding mountains shows that the MIS 2 glaciers subsequently retreated but stalled or re-advanced at ~12, 10, and 1.5 ka. ¹⁰Be dating from the central massif of Mongolia is consistent with this chronology and confirms that MIS 3 equilibrium-line altitudes were slightly (~75 m) lower or approximately the same as those of the MIS 2. The temporal and spatial patterns of glacial advances in southern Siberia and central Mongolia coincided with those of glacial advances in similar climate conditions of the Altai mountains.

The Yenisei, the largest river flowing to the Arctic Ocean, repeatedly hosted cataclysmic floods during the Pleistocene. The largest of the known floods likely originated from palaeolakes in northern Mongolia, at the headwaters of the Little, or Maly, Yenisei. These ancient floods are among the greatest known globally. They left giant gravel dunes and wide abandoned channels in the Kyzyl basin, and high terraces in the gorges upstream. However, few detailed field studies of the flood deposits and no measurements of their ages have been made thus far. The largest palaeolakes were impounded during major glaciations by outlet glaciers from the East Sayan ice field in southern Siberia. The shorelines suggest four distinct palaeolake depths of 290, 175, 145, and 65 m. The timing and location of the glacier impounding the deepest lakes are uncertain but at its maximum, the Tengis outlet glacier was likely capable of impounding the 175 m lake. The dating of glacial deposits in and around the basin reveals that the maximum late Pleistocene glaciers were during Marine Oxygen Isotope Stage (MIS) 3. The ages for deep-lake sediments exposed in the basin behind the dam’s location support this finding. During MIS 2 the Tengis glacier was large enough to impound at least the 145 m lake. However, the existence of a deep MIS 2 palaeolake in the basin has been challenged, because no evidence has been published of MIS 2 lake sediments from the cutbank outcrops and deep drilling cores. Additionally, the end moraines of the Tengis glacier, separated from the deeply eroded lateral moraines by the Maly Yenisei, remain undated; therefore it is uncertain exactly when this glacier crossed the river. This review is part I of a two-part article; Part II presents new age data to constrain the ages of the glacial dam.