21 ka以来东亚夏季风区南部和北部气候变化的模拟与重建对比

古气候重建和模拟研究相结合可有效揭示气候变化的机制,但针对东亚夏季风区的相关研究还有待深入。文章基于现代观测数据及古气候记录的定量化重建结果,评估过去21 ka气候瞬变模拟(Transient Climate Evolution simulation over last 21000 years,简称TraCE-21ka)对现代东亚气候及古夏季风演变的再现能力,对比分析其异同并探索东亚夏季风区南部(SEASM)和北部(NEASM)特征时期的气候变化及可能的驱动机制。结果表明:TraCE-21ka模拟和定量化重建结果相对一致,即末次冰盛期偏干冷,全新世早中期偏暖湿,但模拟的变化幅度小于重建。相对于SEASM,NEASM变化幅度较显著。同时,SEASM的温度及降水和NEASM的温度在整个全新世期间模拟和重建的结果一致性较高,但NEASM模拟和重建的降水在晚全新世一致而早全新世不一致。相对于重建降水的南部和北部显著不同步变化,即南部降水在早全新世高而北部在中全新世高,模拟降水的南、北差异性较小,且为全新世持续减弱夏季风演变的结果。这种重建与模拟间的不同可能来源于地表过程对气候演变敏感度的区域性差异,也可能来源于粗分辨率模拟所造成的系统性气候偏移。

Comparative analysis of simulation and reconstruction of climate change in the south and north of the East Asian summer monsoon region over the last 21 ka

East Asian Summer Monsoon(EASM) is an integral part of the global climate system, its associated precipitation and temperature is important to maintain a living environment in populous East Asia. Paleoclimate change documented in numerous geological and biological records of East Asia widely attribute to the evolution of EASM. In addition, transient climate model can properly simulate the characteristics and seasonal cycle of Asian monsoon system. So the comparative analysis of deposition records and paleoclimate simulation can effectively reveal the mechanism of climate and environment change over the last 21 ka. However, the relevant studies on the East Asian summer monsoon region is still insufficient. For example, it is unclear whether there are significant regional differences between the pollen-based reconstruction and transient climate simulation, especially for the Holocene. In this paper, the key Asian summer monsoon region we analyzed are the Southern East Asian Summer Monsoon(SEASM:28°~37°N, 115°~122°E) and Northern East Asian Summer Monsoon(NEASM:35°~45°N, 95°~108° E). Based on the results of modern observations of Global Precipitation Climatology Centre(GPCC) and National Centers for Environmental Prediction(NCEP), firstly we evaluated the capability of TraCE-21ka simulation to reproduce the climatic characteristics of modern East Asia. Furthermore, we collect relevant pollen-based reconstruction of precipitation and temperature of SEASM including Chaohu, Gu Chenghu and Ping Wang, pollen-based reconstruction of precipitation of NEASM including Qinghai and Da Lianhai, deposition-based reconstruction of temperature of NEASM including Qinghai. So that, we can effectively reveal the characteristics and possible mechanisms of the climate change between SEASM and NEASM based on reconstruction and simulation over the past 21 ka. The results show that TraCE-21ka simulation and quantitative reconstruction are relatively consistent. Compared with modern precipitation and temperature, they both indicate that the Last Glacial Maximum(LGM, 18~22 ka) was dryer and colder, and the Holocene Optimum(HO, 6~10 ka) was warmer and wetter. For the variability analysis, they both indicate that the variation range of NEASM is greater than SEASM. Expressed as, the precipitation of NEASM respectively increased by 30%~100% and 10%~120% in the HO, and the temperature of NEASM respectively increased by 20%~30% and 20%~130% in the HO;the precipitation of NEASM respectively decreased by 10%~30% and 50% in the LGM, and the temperature of NEASM respectively decreased by 20%~50% and 60%~200% in the LGM. The precipitation of SEASM respectively increased by 0%~20% and 20%~30% in the HO, and the temperature of SEASM respectively increased by 0%~10% and 5%~15% in the HO;the reconstructed precipitation of SEASM decreased by 0%~20% and the temperature decreased by 10%~30% in the LGM. So the variability of simulation is generally smaller than that of reconstruction, and the simulation may underestimate the true change of paleoclimate. At the same time, both the simulation and reconstruction show that temperature and precipitation of SEASM and the temperature of NEASM are highly consistent throughout the Holocene, but precipitation of NEASM is consistent in the Late Holocene and inconsistent in the Early Holocene. According to reconstruction of significant asynchronously precipitation evolution between SEASM and NEASM, shown as highly precipitation of Early Holocene SEASM and highly precipitation of Middle Holocene NEASM, here the simulated precipitation differences between SEASM and NEASM is relatively smaller, and it is the dominance of insolation on the continuously weakening of Holocene summer monsoon. In addition, the differences between reconstruction and simulation may be due to two reasons. From the perspective of reconstruction, the differences may be due to the regional sensitivity of surface processes to climate change. From the perspective of simulation, it may be that the spatial resolution of TraCE-21ka simulation is too low and there is systematic climate migration which can not correspond exactly to the reconstruction.