Abrupt climatic events recorded by the Ili loess during the last glaciation in Central Asia: Evidence from grain-size and minerals

The loess record of Central Asia provides an important archive of regional climate and environmental changes. In contrast to the widely investigated loess deposits in the Chinese Loess Plateau, Central Asian loess-paleosol sequences remain poorly understood. Here, we present an aeolian loess section in the southern Ili Basin. Based on granularity and mineralogical analyses, we reconstruct climatic changes during the last glaciation. The results indicated that most of the abrupt climatic events (such as Dansgaard-Oeschger events and Heinrich events) were imprinted in this loess section, although their amplitudes and ages showed some differences. Compared with the millennial oscillations recoded in loess and stalagmites in East Asia, the arid Central Asia responded more sensitively to the warming events than to the cooling events. The shifting trajectory of westerlies across Central Asia played an important role in dust deposition during the stadials. The North Atlantic climatic signals may have been transmitted from Central Asia to the East Asian monsoon regions via the westerlies

Carbon and nitrogen accumulation in the Zoige wetland, northeastern Qinghai-Tibetan Plateau over the past 14000 years

As the largest alpine wetland and peat deposition area in China, the Zoige wetland is climatically sensitive. The organic matter (OM) in peat stores copious environmental information. Here, we report new data on the organic geochemistry of a 4.5 m peat profile HY2014 from southern Zoige wetland. Based on closely spaced accelerator mass spectrometry (AMS) 14C dating, we established a high-resolution geochronological framework beginning at 14057 a BP. Moreover, we estimated the sedimentation flux of TOC and TN (SFs) and their influencing factors. Before 10916 a BP, the lake shrunk and peat began to develop under cold and dry conditions, and SFs were at their lowest values due to low productivity. More OM originated from hydrophyte and marsh plants. From 10916 to 3050 a BP, peat was widely and well developed, and the climate was warm and humid, despite a cooling and drying trend. The HY2014 profile experienced an optimum climate during 10916-6000 a BP, when SFs had the highest values that benefited from high productivity, and OM mainly originated from terrestrial plants. After 3050 a BP, the climate was the coldest and driest. The higher SFs over the past 2000 a BP was mainly resulted from the low decomposition rate. The plant community, primary productivity and decomposition rate were closely linked with the temporal variation of SFs. The environment change was mainly controlled by summer solar insolation, and the Zoige wetland was significantly influenced by the Indian summer monsoon

(Figure 5a-b) SFTOC and SFTN reconstructed from the HY2014 profile

Hannibal and St. Joseph Railroad Co.The original of this document is in the Stevens Family Papers, #1210, at the Division of Rare and Manuscript Collections, Cornell University Library, Ithaca, New York 14853

Heavy mineral assemblages and sedimentation rates of eastern Central Asian loess: Paleoenvironmental implications

Central Asian loess deposits record the evolution of aridification across the Asian interior. However, paleoclimatic proxies are strongly influenced by the variation of the dust source and accumulation process. In order to decipher the paleoenvironmental changes, a sensitive paleoclimatic proxy with clear source and accumulation process will be needed. In this study, heavy mineral assemblages and sedimentation rates were investigated in a 30-kyr loess section in the Ili Basin, Xinjiang, northwestern China. During Marine Isotope Stage (MIS) 2, trends in dust sedimentation rate were similar to those of the Chinese Loess Plateau (CLP), in anti-phase with Northern Hemisphere Summer Insolation (NHSI) at 65 degrees N. Amphibole/epidote ratios (contents and mean grain size) were low during cold phases, such as the late Last Glacial Maximum (LGM) and Heinrich Event (H) 1; their ratios were higher during adjacent warm periods; this was attributed to aeolian sorting during transportation. Namely, greater sorting between amphibole and epidote occurred in warmer phases, and weaker sorting occurred in colder phases. The amphibole/epidote ratio could serve as a proxy for wind intensity, and thus the Siberian High (SH) intensity. Amphibole/epidote ratio was a more appropriate proxy to record wind intensity than dust sedimentation rate which was also influenced by sediment availability. A higher amphibole/epidote ratio corresponded to a more negative East Asian stalagmite delta O-18, indicating an anti-phase relationship between the SH and East Asian Summer Monsoon (EASM) during the MIS 2

Late Pleistocene fire in the Ili Basin, Central Asia, and its potential links to paleoclimate change and human activities

Evidence of late Pleistocene fire activity in Central Asia is important for understanding the underlying processes and controls of fire. Here, two microcharcoal records from two separate loess sections covering the last similar to 70 thousand years (kyr) in the Ili Basin are reported. The results show that total microcharcoal concentrations are similar in both records and are correlated with insolation, indicating consistent basin-wide fire trends related to moisture changes driven by insolation; in addition, two anomalous fire events were identified at 45-35 ka and 6-0 ka. We argue that these events are possibly related to ancient human activities, rather than to pure natural factors such as sedimentation, wind, taphonomic change or climate change

Evaluating the paleoclimatic significance of clay mineral records from a late Pleistocene loess-paleosol section of the Ili Basin, Central Asia

In this study, we present clay mineral records from a late Pleistocene loess-paleosol sequence in the Ili Basin, Central Asia, and assess their significance for paleoclimatic reconstruction. The results show that the clay minerals are mainly illite (average 60%) and chlorite (28%), with minor kaolinite (9%) and smectite (3%). Illite was of detrital origin with no obvious modification to its crystal structure. Increases in illite content in the loess are ascribed to wind intensity rather than pedogenesis. High proportions of illite in the clay fraction, and of muscovite in the bulk samples of the paleosol units, may lead to an overestimation of the weathering intensity. Kaolinite was likely inherited from the sedimentary rocks, while chlorite might have been inherited from both sedimentary and metamorphic rocks. The paleoclimatic signals of kaolinite and chlorite were unclear, due to reworking by both fluvial and eolian systems. Smectite was more likely formed by the transformation of biotite and illite, and its variation in the loess sequence was also controlled by wind intensity; this was largely due to aggregation and is unlikely to reflect moisture changes. Although the interpretation of paleoclimate evolution may contain some uncertainties, clay mineralogy does provide the possibility of tracing dust provenance

Late Holocene hydroclimatic changes inferred from a karst peat archive in the western Guizhou Plateau, SW China

The paleoenvironmental implications of Ca-related indices of peat from karst regions are poorly understood. In this study, we analyze a 450-cm peat core drilled from a sub-alpine karst mountain in the western Guizhou Plateau, SW China. This core is analyzed for carbonate contents and loss on ignition (LOI). High-resolution X-ray fluorescence (XRF) core scanning was also performed to see the variation of chemical compositions. Based on these measurements and 12 accelerator mass spectrometry (AMS)C-14 dates, we reconstructed the history of hydroclimatic shifts in SW China and explored the significance of Ca-related indices. The reconstructed hydro climatic conditions were consistent with the stalagmite, lacustrine sediment, and peat records from the regions controlled by the Indian monsoon. Abrupt decreases in precipitation and temperature were clearly shown during the 4.2 ka and Little Ice Age (LIA) cold events. High carbonate contents in the Yejiping peat during the Medieval Warm Period (MWP) were linked to a warm and humid climate. Additionally, wavelet analysis shows that variations in Ca content have 500, 125, 103, 80, 58, 43, 20, and 12-a quasi-periods, which correspond to the Gleissberg, Pacific Decadal Oscillation (PDO), and Schwabe cycles. Our results highlight the importance of Ca related indices in peat deposits from karst depressions and provide a detailed description of the MWP and the LIA