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The modern Indian summer monsoon (ISM) is characterized by exceptionally strong interhemispheric transport, indicating the importance of both Northern and Southern Hemisphere processes driving monsoon variability. Here, we present a high-resolution continental record from southwestern China that demonstrates the importance of interhemispheric forcing in driving ISM variability at the glacial-interglacial time scale as well. Interglacial ISM maxima are dominated by an enhanced Indian tow associated with global ice volume minima. In contrast, the glacial ISM reaches a minimum, and actually begins to increase, before global ice volume reaches a maximum. We attribute this early strengthening to an increased cross-equatorial pressure gradient derived from Southern Hemisphere high-latitude cooling. This mechanism explains much of the nonorbital scale variance in the Pleistocene ISM record. [ABSTRACT FROM AUTHOR]

The article discusses research by Z. An et al. which used analysis of the organic carbon content of ancient lake sediments in the Heqing Basin in southwestern China to study the Indian summer monsoon (ISM) annual climate cycle during the Pleistocene period. Previous research indicated that the expansion of glaciers in the Northern Hemisphere (NH) led to a weaker ISM, but the data gathered by An et al. suggests that ISM development during glacial periods was driven by cooling in the Southern Hemisphere (SH).