Response and feedback of the Indian summer monsoon and the Southern Westerly Winds to a temperature contrast between the hemispheres during the last glacial–interglacial transitional period

Abstract

The hypothesis that an interhemispheric thermal gradient, or a temperature contrast between the hemispheres (TCBH), drives shifts in the latitudinal position of the Intertropical Convergence Zone (ITCZ) and the Southern Westerly Winds (SWW) is considered one of the most important climate change mechanisms proposed in the last few decades. However, the controversy over the shifting magnitude and direction of the ITCZ and the SWW brings uncertainty to the hypothesis. Here, we further examine the shifting characteristics of the ITCZ and its relationship with the intensity variation of the Indian summer monsoon (ISM) based on synthesis and summary of previously published literature data. In particular, we evaluate regional distribution patterns of the dry and wet climatic changes in southern South America during the last glacial–interglacial transitional period, including the Heinrich event 1, the Antarctic Cold Reversal, and the Younger Dryas. The results show that in response to the Northern Hemisphere-wide cooling and the Southern Hemisphere-wide warming (the Northern Hemisphere-wide warming and the Southern Hemisphere-wide cooling) during the period, the ITCZ over the Asian and northern South American continents and the SWW shift poleward (equatorward), while the intensity of the ISM decreases (increases). However, the shifting characteristics of the ITCZ over the vast Pacific Ocean remain unclear, which implies that the relationship between the TCBH and the El Niño-Southern Oscillation in the tropical Pacific Ocean needs to be studied. In addition, there may be a relatively stable core region in the SWW. This core region is located in Central Patagonia at approximately 47°S, where the local climate is wetter during the all transition period, showing the continuous influence of the SWW on this region. The position shift of the SWW in response to the TCBH phase changes seems to behave as a swing process with an axis of approximately 47°S. The poleward swing of the SWW may trigger the self-repairing process of the global climate system after the catastrophic impacts of the meltwater, including the pulling effect of the enhanced upwelling on the Atlantic meridional overturning circulation, the influence of CO2 released from the deep sea, and the impact of the gradual strengthening of the ISM. These results support and reinforce the hypothesis that the TCBH drives global climate change, highlight the global teleconnection characteristics of the key physical processes in the Earth's climate system and the important role of the SWW in this teleconnection, and provide a basis for further simulating the climate connections in the two hemispheres, especially the impact of the SWW on the global climate change.