Strong summer monsoon during the cool MIS-13

The δ18O record in deep-sea sediments show a significant reduced amplitude of the ice volume variations before Marine Isotope Stage 11, about 400 ka ago, with less warm interglacials and less cold glacials. The deuterium temperature and the greenhouse gases records in the Antarctic ice cores show the same feature. As the reduction in the amplitude of climate and greenhouse gases concentration variations before 400 ka BP is present in both deep-sea and ice cores, it is tempting to conclude that this is a worldwide phenomenon. This is not necessarily true, at least as far as some of the records, in particular of China and Europe, are concerned. The loess in northern China, the sedimentary core in the eastern Tibetan Plateau and the palaeosols in southern China all record an unusually warm and wet climate during Marine Isotope Stage 13, indicating an extremely strong East Asian summer monsoon. The pollen record from Europe shows that the climatic conditions during the interglacials previous to Marine Isotope Stage 11 are at least as warm as the younger interglacials. During Marine Isotope Stage 13, unusually strong African and Indian monsoon are recorded in the sediments of the equatorial Indian Ocean and of the Mediterranean Sea. Other extreme climate events are also recorded in sediment cores of the equatorial Atlantic, the Pacific, the subtropical South Atlantic Ocean and in the Lake Baikal of Siberia. Correspondence to: Q. Z. Yin ([email protected]) The need to better understand the global climatic system leads inevitably to the close inspection of paleoclimatic archives to provide a long-term perspective from which any future change may be more effectively assessed. Such climatic variations of the past are perhaps best illustrated by the oxygen isotopic composition of calcium carbonate in marine organism tests which leads to the definition of Marine Isotopic Stages (MIS). These fluctuations are explained in terms of changing global ice volumes. They are characterized by warmer periods (interglacials which are assigned odd numbers) and colder periods (glacials which are assigned even numbers) defining the glacial-interglacial cycles of the last few millions years. Based on such records, two major transitions have been identified for the Quaternary climate. The mid-Pleistocene revolution (MPR) is characterized by an increase in mean global ice volume, and a change in the dominant period from 41 to 100 ka (Imbrie et al., 1993; Raymo et al., 1997). Its timing is often considered to be at about 900 ka BP. A second distinct climate change, the mid-Brunhes event (MBE, Jansen et al., 1986), roughly corresponds to the transition between MIS-12 and MIS-11 about 430 ka ago. The MBE is characterized by a further increase of ice-volume variations with four large-amplitude 100-ka glacial-interglacial cycles from then to present day (Fig. 1). The intermediate period between MPR and MBE is characterized by a less-clear pattern, with significantly weaker amplitude of ice-volume variations than after MBE. The deuterium measurements in the EPICA dome C ice core (EPICA, 2004; Jouzel et al., 2007) show also the same characteristics with less cold glacial maxima and very significantly less warm interglacials during the period before MIS-11 than after (Fig. 1). Not only the deuterium temperature record shows a reduced amplitude but also the CO2 and CH4 variations (Siegenthaler et al., 2005; Spahni et al., 2005). Explaining the reduction in the amplitude of these variations before MIS-11 is certainly one of the exciting challenge for the paleoclimate community over the next years. Published by Copernicus Publications on behalf of the European Geosciences Union. 30 Q. Z. Yin and Z. T. Guo: Monsoon MIS-13 Fig. 1. Comparison of the loess proxy data with marine benthic δ18O and Antarctic deuterium temperature records. From the top to the bottom panel, the curves are the benthic δ18O stack (Lisiecki and Raymo, 2005), EPICA Dome C ice core temperature anomaly (Jouzel et al., 2007), the stacked FeD/FeT ratio (Guo et al., 2000), magnetic susceptibility (Kukla, 1987) and grain size data (Vandenberghe et al.,