Search

• Lake evolution of Sumxi Co has been reconstructed from lacustrine carbonate isotopes. • Hydrological conditions were mainly dominated by regional precipitation on the northwestern QTP. • Millennial hydroclimate events were responding to globally cooling events and solar irradiance. Climatic and hydrological changes on the Qinghai-Tibetan Plateau (QTP) are controlled by the Asian summer monsoon and the mid-latitude westerlies, which directly affect a large population in Asia. However, the millennial temporal and spatial patterns of Holocene hydroclimate variations on the QTP remain unclear due to the lack of high-quality paleoclimatic records. This paper examines high-resolution stable oxygen and carbon isotopes of authigenic carbonate (δ18O carb and δ13C carb) covering the past 5,000 years taken from Sumxi Co, a hydrologically closed lake lies outside the direct influence of the large ice caps on the northwestern QTP. The hydrological environment of Sumxi Co inferred from the covariance between δ18O carb and δ13C carb values was unstable during the middle to late Holocene, with abrupt increases in lake-levels during the 5.0–4.0 cal ka BP, 3.2–3.1 cal ka BP, 1.8–1.3 cal ka BP, and 0.7 cal ka BP to present. Past millennial hydrological fluctuations coincide temporally with the occurrences of glacier advances on the northwestern QTP, implying increased regional moisture and precipitation during cold periods in the region. The 'cold and wet' hydroclimatic pattern is comparable in other records to the arid areas of central Asia dominated by westerlies before the current anthropogenic warming. The four millennial-scale humid events are synchronous with reduced solar irradiance within dating errors, supporting the hypotheses that the regional pattern of hydroclimatic evolution in arid central Asia responds dominantly and directly to changes in solar activity. This external forcing may be amplified by North Atlantic cooling events and southward shifts of the intertropical convergence, which have further modulated the position of mid-latitude westerlies and the strength of the Indian summer monsoon. [ABSTRACT FROM AUTHOR]

Abstract: Holocene climate records obtained from the Asian summer monsoon domain suggest a regionally-delineated response to changing summer monsoon. The interaction between the East Asian summer monsoon (EASM) and the Indian summer monsoon (ISM), two subsystems of the Asian summer monsoon, has been considered as a factor that explains those inconsistent Holocene climate records. However, this assumption is not valid when the relationship between the two subsystems is not clear. This paper presents a literature review regarding climate simulation of the Asian summer monsoon for testing the long-term relationship. The absolutely-dated Holocene speleothem records in the EASM domain and the ISM domain were compared to verify the simulation results. In addition, a unified monsoon index, which has a unified solid dynamic basis and is appropriate for different monsoon regions, was used in order to identify the modern relationship between the two subsystems. The speleothem records show more synchronous than asynchronous on the Holocene millennial-scale monsoon evolution, furthermore the two subsystems respond to the Younger Dryas (YD) and 8.2ka events in a similar way. However, these monsoon simulations roughly suggest that the two subsystems respond to Holocene climate change in different ways. While the simulations were mostly performed in a certain period of the Holocene, the speleothem records provided a relatively continuous Asian summer monsoon history. Therefore, time scales could affect the comparison between simulations and speleothem records. Then, we further discussed the interaction between the Asian monsoon subsystems according to simulations and modern monsoon indices. Overall, the relationship between the two subsystems is more complicated than synchronous or asynchronous, which is a dynamic relationship and related to the atmosphere–land–ocean–vegetation interaction. In addition, the relationship can vary over different time scales, and the links between time scales should be paid more attention to. Besides, the interaction between the westerly winds and the Asian summer monsoon in the mid-latitudes of East Asia will profoundly affect those areas in response to Holocene climate change. It is recommended that further research should be emphasized in dynamic mechanisms between the Asian summer monsoon subsystems and between the Asian monsoon and the westerly winds. [Copyright &y& Elsevier]

Speleothem records from NE Asia are essential to understand the spatial patterns of the Asian Summer Monsoon (ASM) variability. In this paper, we present a new high-resolution and chronologically well-resolved speleothem record from Liu-li (LL) cave, NE China, through δ18O, δ13C and Sr/Ca ratio characterizing a dynamic ASM history over the past 6680 years. The LL δ18O record shows a long-term trend to higher values, following the North Hemisphere summer insolation (NHSI), with the exception of the last 2 kyr characterized by a negative δ18O excursion. The '2-kyr shift' is evident in NE Asia over the past 2 kyr, originally inferred from the speleothem δ18O negative excursion in South China, as well as in many other proxy records from East China, but it merely manifests a flat trend in most of the western East Asian Summer Monsoon (EASM) and Indian Summer Monsoon (ISM) regions, rather than a negative excursion. On multi-centennial to millennial timescales, the intensification of the Tsushima Warm Current (TWC) can amplify rainfall on both sides of the Japan Sea. A close comparison between the monsoon reconstruction and the cultural changes in NE Asia suggests contemporary climatic and cultural regime-shifts, implying an important role of the ASM weakening in the collapse of Neolithic and Early Bronze cultures in this region. • The records we present and the comparison with many regional paleoclimate records offers new evidences of the distribution of the '2-kyr shift'. • On multi-centennial to millennial timescales, the covariation of different records in NE Asia suggests that the intensification of the Tsushima Warm Current can amplify rainfall on both sides of the Japan Sea. • The contemporary climatic and cultural regime-shifts suggest that the monsoon weakening might play an important role in the collapse of the Neolithic and Early Bronze cultures from this region. [ABSTRACT FROM AUTHOR]