Tessellons,topography, and glaciations on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau has developed into a vast fortress-like structure that has recently presented a barrier limiting the egress of moisture-bearing air masses. Lower sea levels also affected the climate. This paper examines their effects on the current evidence for the timing of past glaciations, and the development and evolution of permafrost. There are two theories regarding glaciation on the Qinghai-Tibet Plateau(QTP). Kuhle suggested that there was a major, unified ice-cap during the Last Glacial Maximum(LGM), whereas major Chinese glaciologists and others have not found or verified reliable evidence for this per se. There have been limited glaciations during the last 1.1 Ma B.P. but with increasing dominance of permafrost including both primary and secondary tessellons infilled with rock, sand or loess. The East Asia Monsoon was absent in this area during the main LGM, starting at 30 ka B.P. on the plateau, with sufficient precipitation reappearing about 19 ka B.P. to produce ice-wedges. A weak Megathermal event took place between 8.5 and 6.0 ka B.P., followed by Neoglacial events exhibiting peak cold at 5.3–4.7 ka, 3.1–1.5 ka, and the Little Ice Age(LIA) after 0.7 ka. Subsequently,mean annual air temperature has increased by 4 °C.     

Pedogenically degenerated illite and chlorite lattices aid to palaeoclimatic reconstruction for chronologically constrained(8-130 ka) loess-palaeosols of Dilpur Formation,Kashmir,India

Chronologically well-constrained loess-palaeosols(recorded glacial and inter-glacial climate) revealed pedogenesis induced ionic substitutions,caused end-member compositional deviations in illite and chlorite,linked to widespread climatic changes occurred during Late Pleistocene.Further,micro-level climatic resolution is yet to be resolved.Thus,layer-wise X-ray diffraction analyses of clay separates,followed by Rietveld refinement revealed varied cell parameters and interatomic distances.Obtained values for detrital and pedogenic illite and chlorite when plotted against stratigraphic succession show notable changes in the crystallographic axes.The illite lattices associated with inadequately pedogenized palaeosols have been altered into illite/smectite mixed layers,but,the chlorite lattices represent expansion of a-,b-and contraction of c-axes with much greater amount of distortions,suggestive of warm-humid and acidic environment.The detrital 48,44 and 83,74 bonded illite and chlorite with2 sub-types each,when pedogenized retained 48,44 and 34;and 83 and 74 bonds(in their neo-formed 3 and 2 sub-types),respectively.The Al-O bond shows expansion,but,unchanged Si-O and decreased Si-K and K-O bonds show loss of Al and retention of Si and K ions in the illite lattices.The illite with 32 atoms and 48 bonds represent contraction of K-O,Si-K,Al-O and Si-O bonds caused bond reinforcement;however,loss of Al~(3+)reflects all-out illite alteration.Owing to Al-O and K-O bond expansion,major K~+ and Al~(3+) ionic loss occurred during the LGM,however,further ionic loss depends upon the magnitude of the loess-palaeosol weathering that they have suffered.The clilate sensitive Fe,Mg and Al ionic losses for Fe-O,Mg-O and Al_(11)-O_9 bond length expansions were recognized in the chlorite lattices.Such ionic losses are common,but,complete distortion is attributed to Al,Si,Fe and Mg ionic losses,followed by weakening of Al-O,Si-O,Fe-O and Mg-O bonds.Though,Si-O_4 and Fe_1-O_4 bonds,and Si and Fe_(1 st) ions remain intact.Thus,three major glacial episodes of ～5 ka each occurred under alkaline environment,but,intervened by two successive cycles of 55 ka each,encompassing three alternate warm and cold climatic sub-cycles of 12-15 ka.But,the coldness increases with each warm-cold sub-cycle that attained the glacial maxima.Further,these events correlate well with the deep-sea records of the North Atlantic(MIS-1 to MIS-5 e) and CLP loess-palaeosols(～127 ka).     

2008 - 2014年青冰滩72号冰川物质平衡特征分析

物质平衡是冰川与气候相互作用的关键桥梁, 对气候变化非常敏感。基于青冰滩72号冰川2008 - 2014年冰面花杆和雪坑的观测资料, 结合Landsat系列卫星影像, 利用零平衡线法对青冰滩72号冰川的物质平衡进行计算和分析。结果表明： 青冰滩72号冰川2008 - 2014年平均物质平衡梯度为（0.86 ± 0.19） m w.e.?（100m）^-1; 平衡线高度在（4 109 ± 23） ~ （4 317 ± 92） m a.s.l.之间变化, 平均为（4 167.5 ± 33.2） m a.s.l。同时, 青冰滩72号冰川年净物质平衡介于-1.23 m w.e. ~ +0.31 m w.e., 年平均为-0.38 m w.e., 累积物质平衡为-2.27 m w.e.。此外, 与位于天山地区图尤克苏冰川、 乌鲁木齐河源1号冰川平衡线高度和累积物质平衡的比较发现, 青冰滩72号冰川平衡线高度和物质平衡的变化与图尤克苏冰川相似, 而与乌鲁木齐河源1号冰川的差异相对较大。     

A simple model for reconstructing geomagnetic field intensity with <Superscript>10</Superscript>Be production rate and its application in Loess studies

A simple model for reconstructing the paleomagnetic field intensity with ¹⁰Be production rate was used for the first time in Loess ¹⁰Be studies of Luochuan profile. Using the LGM (Last Glacial Maxmium) method, the climatic effects and geomagnetic modulation effects on loess ¹⁰Be was separated and in turn the 80 ka geomagnetic excursion sequence reconstructed, of which the globally remarkable geomagnetic excursion events such as the Laschamp (42 ka), Mono Lake (32 ka) during the Last Glacial period were revealed and the paleo-geomagnetic intensity curve from Loess ¹⁰Be over the past 80 ka was quantitatively reconstructed. The reconstructed paleo-intensity fits well with the paleo-intensity curves (SINT200 and NAPIS75), which indicates the significance of global criterion of the ¹⁰Be paleo-intensity curve and the future direction of loess ¹⁰Be tracing studies. Results show the irregular variability of the East Asian monsoon precipitation in Loess Plateau is the main cause that has resulted in the ambiguity of the geomagnetic modulation of the ¹⁰Be record in the loess, and the intrinsic source component of the loess ¹⁰Be and inherited fraction of magnetic susceptibility (SUS) are characterized by the “quasi-homogeneous distribution” manner. Supported by the Key Innovation Project of the Chinese Academy of Sciences (Grant No. KZCX2-YW-118), the National Natural Science Foundation of China (Grant Nos: 40531003, 40121303, 40523002) and State Key Laboratory of Loess and Quaternary Geology in the Institute of Earth Environment of Chinese Academy of Sciences (Grant No. SKLLQG0712)     

盛冰期数十年尺度东亚季风变化的洞穴石笋记录

据湖北青天洞和南京葫芦洞石笋9个230Th年龄和430个δ18O测试数据,建立了18.4～14.4 kaBP平均分辨率7～8 a的东亚季风时间序列.在共同生长时段(17.5～16和18.4～17.5 kaBP),两个洞穴石笋给出了数十年尺度几乎完全一致的δ18O信号,证明了石笋δ18O记录可靠地反映了大尺度区域性季风环流及其水气同位素分馏变化.17.7和16.1 kaBP左右,石笋δ18O值明显正偏,振幅达2‰,指示两次显著的弱夏季风事件,与北大西洋冰漂碎屑事件H1b和H1a同步发生,可视为东亚季风气候系统对北大西洋H1事件的一种响应,18.3～17.7 kaBP期间,东亚季风区存在强季风降水事件,平均强度相当于Bφlling暖期的1/2,最湿润时甚至接近于Bφlling暖期降水强度,可能与北大西洋经向翻转环流的强度变化有关,这一强降水事件内部干湿旋回变化周期与Gleissberg太阳活动周期极为吻合.     

Paleoclimate simulations of the mid-Holocene and last glacial maximum by FGOALS

Paleoclimate simulations of the mid-Holocene (MH) and Last Glacial maximum (LGM) by the latest versions of the Flexible Global Ocean-Atmosphere-Land System model, Spectral Version 2 and Grid-point Version 2 (FGOALS-s2 and g2) are evaluated in this study. The MH is characterized by changes of insolation induced by orbital parameters, and the LGM is a glacial period with large changes in greenhouse gases, sea level and ice sheets. For the MH, both versions of FGOALS simulate reasonable responses to the changes of insolation, such as the enhanced summer monsoon in African-Asian regions. Model differences can be identified at regional and seasonal scales. The global annual mean surface air temperature (TAS) shows no significant change in FGOALS-s2, while FGOALS-g2 shows a global cooling of about 0.7 C that is related with a strong cooling during boreal winter. The amplitude of ENSO is weaker in FGOALS-g2, which agrees with proxy data. For the LGM, FGOALS-g2 captures the features of the cold and dry glacial climate, including a global cooling of 4.6 C and a decrease in precipitation by 10%. The ENSO is weaker at the LGM, with a tendency of stronger ENSO cold events. Sensitivity analysis shows that the Equilibrium Climate Sensitivity (ECS) estimated for FGOALS ranges between 4.23 C and 4.59 C. The sensitivity of precipitation to the changes of TAS is～2.3% C-1 , which agrees with previous studies. FGOALS-g2 shows better simulations of the Atlantic Meridional Overturning Circulation (AMOC) and African summer monsoon precipitation in the MH when compared with FGOALS-g1.0; however, it is hard to conclude any improvements for the LGM.     

LGM lake records from China and an analysis of climate dynamics using a modelling approach

Lake-geological studies in China have reported that there were much higher lake levels and much fresher water than today at the last glacial maximum (LGM) in western China. A compilation of lake data in this study showed LGM conditions much drier than today in eastern China but somewhat wetter in western China. These E–W differential patterns of climate conditions were completely different from the modern dry-wet conditions with a N–S differential distribution. In this study palaeoclimate simulations by an AGCM coupled with land surface process model were used to explore the possible mechanisms of LGM climate in China. The results confirmed that the dry conditions in eastern China resulted from less summer precipitation due to the Pacific Subtropical High occupying eastern China and the decline in the summer monsoon. The wet conditions in western China were produced by a decrease in evaporation due to a low temperature on land surface at the LGM and increase in precipitation. Two experiments of the palaeoclimate simulations with different land surface of modern and palaeo-vegetations have been designed to test the discrepancies of simulated LGM climate with in precipitation and P–E fields. The results suggested that the feedback from the Asian land surface within the climate system would amplify and modify external forcing, leading to marked climate changes in China.     

An assessment of variations in mercury deposition to Antarctica over the past 34,000 years

We performed a comparison analysis of the variations .in Mercury ( Hg) concentrations and the precipitation proxies ( e. g. , 18 O values and 10 Be concentrations) in the Dome C ice core. The results showed that there were significant correlations between Hg and δ 10O values, 10Be concentrations, indicating that the accumulation rate in Dome C is one of the key factors controlling the variations of Hg concentrations in the past 34 ,000 years, and implying that Hg concentrations in ice core can be used as another reliable proxy of precipitation rate in Antarctica. Based upon the high-resolution δ 18O values, we estimated the variations in mercury deposition flux to Antarctica over the past 34,000 years. The highest mercury deposition flux is about 3. 80 pg cm-2 yr-1 during the Last Glacial Maxium (LGM) as high as 3. 5 times of the mercury deposition flux ( about 1. 08 pg cm -2 yr -1) in Holocene due to the fluctuations in natural mercury emissions such as the oceanic biological emissions.