Impacts of insolation and CO2 on the spatial differences of the MIS-9 and MIS-11 climate between monsoonal China and central Asia

Marine oxygen isotope records and ice cores in Antarctica suggest that Marine Isotope Stage (MIS) 9, an interglacial occurring about 300 ka ago, is a strong interglacial and has the highest greenhouse gases (GHG) concentrations during the past 800 ka. Model results also show that MIS-9 is the warmest interglacial among the last nine ones as a result of both its high CO₂ concentration and its high summer insolation in the northern Hemisphere (NH). However, the China loess records show that the paleosol S3 that corresponds to MIS-9 is not necessarily strong as compared to some other paleosol units such as the S4 soil that was formed during MIS-11, suggesting relatively drier climate condition during MIS-9. By contrast, in Tajikistan of southern central Asia, the paleosol S3 is the most developed soil over the past 800 ka, indicating a relatively warm and humid climate conditions. The difference in the paleosol formation and the MIS-9 climate between monsoonal China and central Asia is intriguing. In this study, we combine loess records from monsoonal China and central Asia as well as climate simulation results to understand the spatial difference of the MIS-9 climate in particular in comparison with the climate of MIS-11. The individual and combined contributions of insolation and greenhouse gases are quantified through simulations with the LOVECLIM model and using the factor separation technique. Our results show that the simulated effective moisture conditions between northern China and southern central Asia are consistent with the loess records and field observation. Insolation leads to much more annual mean precipitation than GHG during MIS-9 in southern central Asia, explaining a much wetter MIS-9 there. By contrast, both insolation and GHG lead to more annual mean precipitation and evaporation during MIS-9 in northern China, leading to only a slight difference in the effective moisture between MIS-9 and MIS-11. In addition, compared to MIS-11, the larger obliquity and higher GHG concentration during MIS-9 lead to an anomalous atmospheric circulation pattern similar to negative phase of North Atlantic Oscillation (NAO), favoring precipitation increase in southern central Asia and therefore explain strong soil development in Tajikistan.