Abstract
Environmental conditions on the Tibetan Plateau (TP) during the last glacial maximum (LGM) are poorly known. Existing studies of environmental proxies and climate model simulations are contradictory, with interpretations varying between cold-dry and cold-wet environmental conditions which differentially influenced lake volumes, loess deposition and vegetation communities across the TP. Genetic and archaeological studies suggest anatomically modern paleolithic foragers initially occupied the TP between 60 and 30 ka, and may have seasonally occupied the TP during the LGM. Hence, a better understanding for LGM environmental conditions is needed in order to estimate whether paleolithic foragers could have survived on the TP during the extreme LGM cold stage. Here we report the investigation of lacustrine sediments and beach deposits within two paleoshorelines around Dagze Co on the southern TP, ∼22 and ∼42 m higher than the present lake level. Optical age estimates suggest the sediments were deposited during the LGM and mid-Holocene, respectively. TraCE-21 climate model simulation results suggest that net annual LGM precipitation in the Dagze Co basin was lower than the mid-Holocene, but about the same as that of the past 1,000 years. Combining the optical age estimates with TraCE-21 and CAM4 climate model simulation results, we deduce that increased summer precipitation and glacier meltwater supply, combined with decreased lake surface evaporation, produced LGM lake levels ∼22 m higher than present. We also synthesized paleoenvironmental records reported across the TP spanning the LGM. This synthesis suggests that the LGM climate in the northern TP was cold and dry, but that some of the southern TP was cold and wet. These relatively wetter LGM conditions in the southern TP may have favored the growth of cold-resistant plants which, in turn, may have supported larger herbivore populations, and provided food for paleolithic foragers. We conclude that seasonal or short-term human occupation of the TP during the LGM was thus more likely in the southern TP than in the north.
Highlights
A recent study of a human mandible fossil found in Xiahe County, in the northeastern Tibetan Plateau (TP), indicates that Denisovans occupied the TP before 160 ka, much earlier than contemporary Tibetans who arrived in the region much later (Chen et al, 2019; Zhang et al, 2020)
optically stimulated luminescence dating (OSL) dating results show that higher Dagze Co lake levels occurred at during the last glacial maximum (LGM) and mid-Holocene (Table 1; Supplementary Figure S8)
The high LGM lake level of Dagze Co, at an elevation of ∼4,500 m asl in the southern TP, confirms that an ice sheet covering the entire TP did not exist during the LGM
Summary
A recent study of a human mandible fossil found in Xiahe County, in the northeastern TP, indicates that Denisovans occupied the TP before 160 ka (during the penultimate glacial period), much earlier than contemporary Tibetans who arrived in the region much later (Chen et al, 2019; Zhang et al, 2020) Both genetic research (Lu et al, 2016) and archaeological investigations (Zhang et al, 2018a; Zhang et al, 2018b) suggest that anatomically modern human foragers conquered high elevations and at least seasonally colonized the Tibetan Plateau (TP) between 60 and 30 ka. Zhang et al (2017) suggest that low temperatures, hypoxia and low bioproductivity would have impeded yearround hunter-gatherer occupation of the high TP until the development of agriculture after ∼5.2 ka, Dong et al (2020) contend that hunter-gatherer groups in China may have adapted to climate change by mobility and subsistence strategy adjustments before 10,000 BP At present, it appears that Paleolithic foragers first colonized the TP sometime before 30 ka. Whether they stayed on the TP and adapted to the extremely cold LGM climate or needed to move down to surrounding low elevation regions during the LGM before reoccupying the TP again after the last deglacial (Madsen et al, 2006) is still unknown
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