Abstract
Geological records indicated the termination of the Holocene Thermal Maximum (dramatic drying) occurred progressively later at lower latitudes in both North Africa and East Asia, along with the coherent weakening of local summer monsoon. Here we show that this time-transgressive evolution was dominated by the southward migration of monsoon fringe (shrinking monsoon domain) under monsoon weakening, as illustrated in a transient climate-terrestrial ecosystem model simulation. The monsoon fringe retreating southward during the Holocene, as well as expanding northward during the last deglaciation, occurred synchronously in a belt extending from North Africa to East Asia, which induced a locally humid-arid transition and the subsequent dramatic environment impact. The migration of Afro-Asia monsoon fringe since the Last Glacial Maximum was modulated by the orbital forcing through its impact on land-ocean thermal contrast, aiding by the variation of CO2 concentration.
Highlights
Since the Last Glacial Maximum (LGM), the Afro-Asian monsoon system, including East Asian monsoon, South Asian monsoon and North African monsoon, has experienced a coherent strengthening during the last deglaciation and weakening during the Holocene (Fleitmann et al, 2003; Dykoski et al, 2005; Weldeab et al, 2007; Wang et al, 2008; Shi and Yan, 2019) with the maximum at the Holocene Thermal Maximum (HTM, around 8 ka, kilo years ago before 1950; Haug et al, 2001)
Different from the previous explanations which focusing on the migration of monsoon rainbelt (An et al, 2000; Shanahan et al, 2015), here we clearly show that in the model simulation, the Holocene time-transgressive evolution of hydrology in the Afro-Asian monsoon region was caused by the southward migration of the northern monsoon fringe because of shrinking monsoon domain
Combined the geological records and model simulation, the simulation is not validated for every process by limited records, we propose the recorded dramatic ecoenvironmental variation along northern fringe of Afro-Asian monsoon was caused by the migration of the northern monsoon fringe through the associated intensive variation of precipitation since the LGM
Summary
Since the Last Glacial Maximum (LGM), the Afro-Asian monsoon system, including East Asian monsoon, South Asian monsoon and North African monsoon, has experienced a coherent strengthening during the last deglaciation and weakening during the Holocene (Fleitmann et al, 2003; Dykoski et al, 2005; Weldeab et al, 2007; Wang et al, 2008; Shi and Yan, 2019) with the maximum at the Holocene Thermal Maximum (HTM, around 8 ka, kilo years ago before 1950; Haug et al, 2001). The migration of northern Afro-Asian monsoon fringe, which corresponds to the expansion or shrink of the monsoon domain, may induce the time-transgressive evolution of local precipitation and the subsequent dramatic response of environment for reasons of possible humid-arid transition. We hypothesize the recorded time-transgressive evolution of paleo-hydrology in the Afro-Asian monsoon regions and the dramatic environment variation may be dominated by the migration of monsoon fringe. To test this hypothesis, we investigate the fringe change of the Afro-Asian monsoon and the possible subsequent environment response in a transient climate-terrestrial ecosystem model simulation since the LGM, aided by some other snapshot simulations at the LGM and mid-Holocene. We focus on the monsoon fringe (the limit of monsoon domain) close to the arid region, whose migration was robust and the subsequent environmental impact was dramatic as illustrated bellow
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