The mid-latitudes of East Asia are characterized by the interaction between the Asian summer monsoon and the westerly winds. Understanding long-term climate change in the marginal regions of the Asian monsoon is critical for understanding the millennial-scale interactions between the Asian monsoon and the westerly winds. Abrupt climate events are always associated with changes in large-scale circulation patterns; therefore, investigations into abrupt climate changes provide clues for responses of circulation patterns to extreme climate events. In this paper, we examined the time scale and mid-Holocene climatic background of an abrupt dry mid-Holocene event in the Shiyang River drainage basin in the northwest margin of the Asian monsoon. Mid-Holocene lacustrine records were collected from the middle reaches and the terminal lake of the basin. Using radiocarbon and OSL ages, a centennial-scale drought event, which is characterized by a sand layer in lacustrine sediments both from the middle and lower reaches of the basin, was absolutely dated between 8.0–7.0 cal kyr BP. Grain size data suggest an abrupt decline in lake level and a dry environment in the middle reaches of the basin during the dry interval. Previous studies have shown mid-Holocene drought events in other places of monsoon marginal zones; however, their chronologies are not strong enough to study the mechanism. According to the absolutely dated records, we proposed a new hypothesis that the mid-Holocene dry interval can be related to the weakening Asian summer monsoon and the relatively arid environment in arid Central Asia. Furthermore, abrupt dry climatic events are directly linked to the basin-wide effective moisture change in semi-arid and arid regions. Effective moisture is affected by basin-wide precipitation, evapotranspiration, lake surface evaporation and other geographical settings. As a result, the time scales of the dry interval could vary according to locations due to different geographical features.
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机译：东亚的中纬度地区以亚洲夏季风和西风之间的相互作用为特征。了解亚洲季风边缘地区的长期气候变化对于了解亚洲季风与西风之间的千禧年尺度相互作用至关重要。突发的气候事件总是与大规模循环模式的变化有关。因此，对突然的气候变化的研究为循环模式对极端气候事件的响应提供了线索。在本文中，我们研究了亚洲季风西北缘的石羊河流域突然发生的全新世中期干旱事件的时间尺度和全新世中期气候背景。从盆地的中游和末湖收集了全新世中期湖相记录。使用放射性碳和OSL年龄，百年尺度的干旱事件的绝对年代在8.0-7.0 cal BP之间，其特征是盆地中下游的湖相沉积物中有沙层。粒度数据表明，在干旱间隔期间，湖水位突然下降，流域中游处于干旱环境。先前的研究表明，季风边缘地区其他地方发生了全新世中期干旱事件。但是，它们的年代顺序不足以研究这种机制。根据绝对的过时记录，我们提出了全新的假说，全新世中期的干旱间隔可能与亚洲夏季风减弱和干旱的中亚地区相对干旱的环境有关。此外，突然的干旱气候事件与半干旱和干旱地区流域范围内有效水分的变化直接相关。有效水分受流域范围内的降水，蒸散量，湖面蒸发和其他地理环境的影响。结果，由于不同的地理特征，干燥间隔的时间尺度可能根据位置而变化。
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