Abstract
The effect of precession on paleoclimate changes depends on eccentricity. However, whether and to what degree eccentricity relates to millennial-scale monsoonal changes remain unclear. By investigating climate simulations with a fixed precession condition of 9 ka before the present, we explored the potential influence of eccentricity on early-Holocene changes in the Afro–Asian summer monsoons. Compared with the lower eccentricity of the present day, higher eccentricity in the early Holocene strengthened the continental summer monsoons, Pacific anticyclone, and Hadley circulation, particularly over the ocean. Over Africa, the eccentricity-induced “dry-gets-wetter” condition could be related to the Green Sahara, suggesting a superimposed effect of precession. Over the western Pacific, the tropical response to eccentricity may have been competitive in terms of what an extremely high obliquity may have caused. A downscaled modulation of eccentricity in relation to precession and obliquity cannot be ignored when paleomonsoon records are studied. Regarding early-Holocene monsoonal changes in South Asia, however, a high eccentricity may have had only a secondary effect on enhancing the monsoonal precipitation in the southern edge of the Tibetan Plateau, exhibiting the weak power of candle-like heating. This suggested that sizable monsoonal changes over the northern Indian Ocean and India–Pakistan region are unrelated to early-Holocene eccentricity.
Highlights
We explored the modeling of monsoons in the early Holocene through timeslice experimental simulation at the fixed orbital condition of 9 ka before the present (BP; 9 K simulation), which had an approximate eccentricity of 0.019, obliquity of 24.2°, and perihelion precession of 312°
We explored the role of eccentricity in modulating changes in the Afro–Asian summer monsoons in the early Holocene
We investigated the climate sensitivity of the modeled monsoons to the approximate eccentricity forcing during the Holocene (EH case)
Summary
The effect of precession on paleoclimate changes depends on eccentricity. whether and to what degree eccentricity relates to millennial-scale monsoonal changes remain unclear. Compared with the lower eccentricity of the present day, higher eccentricity in the early Holocene strengthened the continental summer monsoons, Pacific anticyclone, and Hadley circulation, over the ocean. Regarding early-Holocene monsoonal changes in South Asia, a high eccentricity may have had only a secondary effect on enhancing the monsoonal precipitation in the southern edge of the Tibetan Plateau, exhibiting the weak power of candle-like heating. This suggested that sizable monsoonal changes over the northern Indian Ocean and India–Pakistan region are unrelated to early-Holocene eccentricity. The orbitally driven circulation changes occurred broadly in latitudes in the early Holocene, implying the combined effects of precession and obliquity
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