Asian monsoon climate during the Last Glacial Maximum: palaeo‐data–model comparisons

Abstract

The Last Glacial Maximum (LGM) (23-19 ka BP) in the Asian monsoon region is generally described as cool and dry, due to a strong winter monsoon. More recently, however, palaeo-data and climate model simulations have argued for a more variable LGM Asian monsoon climate with distinct regional differences. We compiled, evaluated, and partly re-assessed proxy records for the Asian monsoon region in terms of wet/dry climatic conditions based on precipitation and effective moisture, and of sea surface temperatures. The comparison of the palaeo-data set to LGM simulations by the Climate Community System Model version 3 (CCSM3) shows fairly good agreement: a dry LGM climate in the western and northern part due to a strengthened winter monsoon and/or strengthened westerly winds and wetter conditions in equatorial areas, due to a stronger summer monsoon. Data-model discrepancies are seen in some areas and are ascribed to the fairly coarse resolution of CCSM3 and/or to uncertainties in the reconstructions. Differences are also observed between the reconstructed and simulated northern boundaries of the Intertropical Convergence Zone (ITCZ). The reconstructions estimate a more southern position over southern India and the Bay of Bengal, whereas CCSM3 simulates a more northern position. In Indochina, the opposite is the case. The palaeo-data indicate that climatic conditions changed around 20-19 ka BP, with some regions receiving higher precipitation and some experiencing drier conditions, which would imply a distinct shift in summer monsoon intensity. This shift was probably triggered by the late LGM sea-level rise, which led to changes in atmosphere-ocean interactions in the Indian Ocean. The overall good correspondence between reconstructions and CCSM3 suggests that CCSM3 simulates LGM climate conditions over subtropical and tropical areas fairly well. The few high-resolution qualitative and quantitative palaeo-records available for the large Asian monsoon region make reconstructions however still uncertain. Global ice volumes had obtained their maximum, global sea level was at ∼130 m below present (Clark et al. 2009), and forested areas had become reduced bs_bs_banner

Global monsoon change during the Last Glacial Maximum: a multi-model study

“…Six models have simulated the shifting except MRI-CGCM3. The shift of the Asian monsoon domain is consistent with the palaeo-data (Chabangborn et al 2014) and opposite to the simulated northward shift of the Asian summer monsoon circulation under CO 2 doubling (Kitoh et al 1997). Braconnot et al (2007b) also found that some of the models participated in PMIP2 simulated a southward shift of the intertropical convergence zone (ITCZ) over the continents and the Indian Ocean, which was in agreement with the results found from marine data (Leduc et al 2007).…”

“…Proxy data revealed a stronger East Asian winter monsoon but weaker summer monsoon during glacial periods (Jiang and Lang 2010;Wang 2009). Chabangborn et al (2014) found that paleo-data and climate model simulation were agreed in a dry LGM climate in the western and northern part of the Asian monsoon region due to a stronger winter monsoon, and/or wetter conditions in equatorial areas of the Asian monsoon region due to a strengthened summer monsoon. However, the sparse reconstruction data in the global monsoon region make it difficult to pin down the uncertainty.…”

Evolution of the Indian summer monsoon during the interval 32.7–11.4cal. ka BP: Evidence from the Baoxiu peat, Yunnan, southwest China

“…Significantly, based on a review of 75 time series datasets from monsoonal central Asia, Herzschuh (2006) argued that the LGM was characterized by dry or moderately dry climate conditions. Furthermore, modeling provides strong evidence for dry and cold climate conditions during the LGM period in the Asian monsoon region (Jiang and Lang, 2010;Jiang et al, 2011;Chabangborn et al, 2014).…”

Hydrological and ecosystem response to abrupt changes in the Indian monsoon during the last glacial, as recorded by sediments from Xingyun Lake, Yunnan, China

“…In the past few decades, abrupt changes of the ISM have been inferred from marine sediments in the Arabian Sea (Schulz et al, 1998;Leuschner and Sirocko, 2000;Altabet et al, 2002;Govil and Naidu, 2010;Deplazes et al, 2013); the Bay of Bengal and the Andaman Sea (Colin et al, 1998) and speleothems from Socotra Island (Burns et al, 2003;Shakun et al, 2007), India (Sinha et al, 2005) and China (Cai et al, 2006). However, relatively few terrestrial paleoclimatic records of the ISM are from monsoon-dominated regions (Cook et al, 2013;Chabangborn et al, 2014;Dixit et al, 2014). In addition, the environmental significance of stable isotope records from stalagmites remains highly debated (Wang et al, 2001;Yuan et al, 2004;Maher, 2008;Clemens et al, 2010;Pausata et al, 2011;Liu et al, 2014;Tan, 2014).…”