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A comprehensive and integrative view of East Asian monsoon evolution during the Holocene is still under debate, and additional high-resolution proxy records from climatically sensitive locations are requisite to solve this complex issue. In this paper, we present three well-dated mud/peat cores from a paleo-pingo depression in the Sanjiang Plain, a climatically sensitive region to monsoon variation, to reveal the paleoenvironmental history of the wetland and discuss the regional impacts from monsoon evolution. A paleolake developed in the study area before 5.5 ka BP, and a peatland initiated thereafter consequent upon the gradual shrinking of the paleolake. This transition lasted until 4.5 ka BP, when the paleolake changed entirely to a wetland. Considering the prevalent monsoon climate in the Sanjiang Plain, we suggest that the lake-to-wetland transition from 5.5 to 4.5 ka BP indicates a rapid decline of the East Asian summer monsoon in addition to autogenic basin infilling processes. Such a remarkable monsoon weakening event has been documented across northern China, and we associate this with ocean–atmosphere interactions throughout low-latitude regions. [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]

Abstract: The role of ocean feedback on monsoon variations at 6 and 9.5kyr Before Present (BP) compared to present-day is investigated by using sets of simulations computed with the IPSL–CM4 ocean–atmosphere coupled model and simulations with the atmospheric model only with the SST prescribed to the present-day simulation for the coupled model. This work is complementary to the study by Marzin and Braconnot (2009) who have analyzed in detail the response of Indian and African monsoons to changes in insolation at 6 and 9.5kyr BP using the IPSL–CM4 coupled model. The monsoon rainfall was intensified at 6 and 9.5kyr BP compared to 0kyr BP as a result of the intensified seasonal cycle of insolation in the Northern Hemisphere. In this paper, the impact of the ocean feedback is analysed for the Indian, East-Asian and African monsoons. The response of the ocean to the 6 and 9.5kyr BP insolation forcing shares similarities between the two periods, but we highlight local differences and a delay in the response of the surface ocean between 6 and 9.5kyr BP. The ocean feedback is shown to be positive for the early stage of the African monsoon. A dipole of SST in the tropical Atlantic favouring the earlier build-up of the monsoon in the 6 and 9.5kyr BP coupled simulations. However, it is strongly negative for the Indian and East Asian monsoons, and of stronger amplitude at 9.5 than at 6kyr BP over India. In these Asian regions, the convection is more active over the ocean than over the continent during the late monsoon season due to the ocean feedback. The results are consistent with previous studies about 6kyr BP climate. In addition, it is shown that the ocean feedback is not sufficient to explain the relative amplifications of the different monsoon systems within the three periods of the Holocene, but that the mechanisms such as the effect of the precession on the seasonal cycle of monsoons as discussed in Marzin and Braconnot (2009) are more plausible. [Copyright &y& Elsevier]