东亚中高纬Heinrich 1事件的表现特征:呼伦湖孢粉记录

Heinrich 1事件是发生于末次冰消期的极端气候突变事件之一,对全球大气环流和陆地生态格局产生了深刻影响.基于对东亚夏季风边缘区最北端呼伦湖 HL08 孔5. 75 m 以上沉积岩芯的 AMS 14C定年技术和 415~275 cm段140个样品的孢粉分析,重建了东亚中高纬地区呼伦湖21500~13000 cal. a B. P.高分辨率植被变化历史,在此基础上揭示了Heinrich 1事件期间呼伦湖区植被响应过程,明确了Heinrich 1事件在东亚中高纬地区的表现特征.结果显示:呼伦湖区Heinrich 1事件发生于16500~15400 cal. a B. P.,以剧烈降温和显著干旱化为表现特征;事件发生期间湖区周围山地发育亚高山草甸,森林植被稀疏;湖盆区域以藜科为主的荒漠草原显著扩张,区域植被盖度降低、生态环境明显恶化;同时,不同植被类型对Heinrich 1事件的响应存在明显差别,亚高山草甸和蒿属为主的典型草原较藜科为主的荒漠草原和桦属为主的落叶阔叶林响应更为快速、敏感.     

Use of caesium-137 measurements to investigate erosion and sediment sources within a small drainage basin in the loess plateau of China

The contributions of sediment from different geomorpholigical units within a small basin in the Loess Plateau have been determined using caesium-137 as a tracer. The mean caesium-137 content of sediment originating from the hill area, where sheet and rill erosion are predominant, was 3–37 Bq kg-1, whereas no caesium-137 was detected in the sediment originating from the gully area where gullying and gravitational erosion are predominant. The mean caesium-137 content of sediment from two flood deposits was 0–23 Bq kg-1 and 0–89 Bq kg-1. The relative contribution from the hill area in the two floods was 7 per cent and 26 per cent, whilst that from the gully area was 93 per cent and 74 per cent.     

Hydrology of Dali Lake in central-eastern Inner Mongolia and Holocene East Asian monsoon variability

Lacustrine records from the northern margin of the East Asian monsoon generate a conflicting picture of Holocene monsoonal precipitation change. To seek an integrated view of East Asian monsoon variability during the Holocene, an 8.5-m-long sediment core recovered in the depocenter of Dali Lake in central-eastern Inner Mongolia was analyzed at 1-cm intervals for total organic and inorganic carbon concentrations. The data indicate that Dali Lake reached its highest level during the early Holocene (11,500–7,600 cal yr BP). The middle Holocene (7,600–3,450 cal yr BP) was characterized by dramatic fluctuations in the lake level with three intervals of lower lake stands occurring 6,600–5,850, 5,100–4,850 and 4,450–3,750 cal yr BP, respectively. During the late Holocene (3,450 cal yr BP to present), the lake displayed a general shrinking trend with the lowest levels at three episodes of 3,150–2,650, 1,650–1,150 and 550–200 cal yr BP. We infer that the expansion of the lake during the early Holocene would have resulted from the input of the snow/ice melt, rather than the monsoonal precipitation, in response to the increase in summer solar radiation in the Northern Hemisphere. We also interpret the rise in the lake level since ca. 7,600 cal yr BP as closely related to increased monsoonal precipitation over the lake region resulting from increased temperature and size of the Western Pacific Warm Pool and a westward shifted and strengthened Kuroshio Current in the western Pacific. Moreover, high variability of the East Asian monsoon climate since 7,600 cal yr BP, marked by large fluctuations in the lake level, might have been directly associated with variations in the intensity and frequency of the El Niño-Southern Oscillation (ENSO) events.     

Millennial- to centennial-scale anti-phase relationship between the Westerlies and the East Asian summer monsoon and its cultural response along the Silk Roads after a great earthquake in southern Altay ~ 3500 cal a BP

It is strongly debated whether the Westerlies and the East Asian summer monsoon (EASM) are in-phase, anti-phase or out-of-phase, and how hydroclimatic changes in the above two climate systems affected trans-Eurasian cultural exchanges during the late Holocene. In this study, we establish a 3500-a-long paleoclimatic sequence based on high-resolution analyses of sedimentological and geochemical data of a well-dated sediment core from Yileimu Lake in southern Altay. High percentages of the >63-µm fraction and high values of Zr/Rb and Rb/Sr ratios indicate strong transport of weakly weathered, coarse sediments into the depocenter of the lake caused by enhanced surface runoff and catchment erosion associated with a wet climate, and vice versa. High values of Ca and total inorganic carbon (TIC) contents imply increased precipitation of endogenic carbonates in the lake water under intense evaporation associated with a dry climate, and vice versa. This new record indicates two wet intervals at 3500–2300 and 600–100 cal a bp , interrupted by a severe and prolonged dry interval from 2300 to 1000 cal a bp , and a mild dry interval with occasionally wet conditions from 1000 to 600 cal a bp. These results are broadly consistent with other paleoclimatic records in Westerlies-dominated Asia and are generally anti-phase with those in the EASM region. We suggest that a strengthening/weakening and southward/northward migration of the Westerlies during a negative/positive phase of the North Atlantic Oscillation (NAO) transported more/less water vapor into arid Asia. Meanwhile, a decreasing/increasing El Niño-Southern Oscillation (ENSO) superimposed on a southward/northward shift of the Intertropical Convergence Zone (ITCZ) triggered a weakening/strengthening and southward/northward movement of the West-Pacific subtropical high (WPSH), resulting in decreasing/increasing EASM intensity. In addition, the wet climate from 3500 to 2300 cal a bp may have contributed to the development of nomadic herding in the eastern Eurasian Steppe and Altay region, and to the opening of the proto-Silk Roads. Potentially, intense seismic activities in the Altay Mountains ~3500 cal a bp may have also promoted the opening of the proto-Silk Roads by forcing the herdsmen to move to the inter-mountainous basins. The strong EASM intensity from 2300 to 1000 cal a bp in eastern China may have contributed to the creation of the ancient Silk Roads by the Han Dynasty.