中晚全新世南海北部的环境演化与人类活动OA

[Objective]The holocene is the most closely related period to us.Human modifications of the Earth System have been attracting increasing attention.The study of environmental evolution and its driving mechanism and human activities during the holocene will help us to further understand the current climate change law and predict the future climate evolution trend.However,great regional differences exist in when and how human activities as a geological force began to affect the Earth's surface system significantly.The development of human civilization in South China exhibits significant differences from that of the Central Plains and northern regions of China,due to the barrier effect of the Nanling Mountains and its unique climatic,topographical,and ecological characteristics.Both the research data of the Pearl River Basin and systematic research appear insufficient.Therefore,marine sedimentary records and tests are used.The influence of the development of human civilization on the natural environment in South China is reconstructed by combining the ancient data.This study aims to investigate the interplay between environmental evolution and human activities in South China during the mid-late Holocene.[Methods]In this study,we conducted systematic analyses of grain size,major/trace elements,rare earth elements,clay minerals,and AMS 14 C dating on sediments from sites B1047 and B1104 in the muddy shelf area of the northern South China Sea.Through AMS 14 C dating analysis,the sites age was limited to 5.2 ka BP.By analyzing the rare earth elements,the provenance and variation of the middle and late Holocene sediments in the northwestern shelf of the South China Sea were studied.We reconstructed the history and drivers of chemical weathering and heavy metal emissions in the Pearl River Basin since 5.2 ka BP using grain-size,elemental,and clay mineral analyses.These analyses revealed the terrigenous clastic sources since 5.2 ka BP and elucidate the response mechanisms between environmental changes and human activities in this region.[Results]Provenance analyses indicate that sediments are mainly derived from the debris of the Hainan Island along the Pearl River,and the contribution from the Qiongzhou Strait is small.Three grain-size end-members(EMs)were identified through endmember modeling,EM1 and EM2,corresponding to the fine-grained material transported by the oceanic current system,and EM3,corresponding to the coarse-grained material input by rivers from proximal sources.Therefore,these three EMs represented different transport mechanisms.The EM1/EM3 reflects intensity variations of the South China Sea Coastal Current driven by winter monsoon,indicating East Asian Monsoon variability.Chemical weathering intensity is represented by chemical weathering index CIA,Rb/Sr and clay mineral ratio kaolinite/illite.Results show that variations in chemical weathering indicators and clay mineral ratios exhibit frequent fluctuations and a continuously intensifying trend.Finally,enrichment factors(EF)of heavy metals exhibit synchronous enhancement with the chemical weathering indicators after 2.2 ka BP.[Conclusion]The EM1/EM3 in core sediments shows that the East Asian winter monsoon exhibits an overall increasing trend,which is consistent with the high-resolution results of other geological carriers in the East Asian monsoon region.The climate-human interaction evolution since 5.2 ka BP comprises three phases:1)During the period of 5.2-4.5 ka BP,the environmental evolution process in the northern South China Sea was controlled by sea-level decline triggered by climatic cooling.2)4.5-2.2 ka BP showed enhanced chemical weathering coinciding with initial human activity intensification,thereby marking the transition to human-dominated geological processes.Along with the population growth and technological progress,enhanced human activities including deforestation,cultivation,and metallurgical activities,gradually superseded natural processes and profoundly impacted the environment in South China.3)Since 2.2 ka BP,anthropogenic heavy metal emissions have been increasing,which might be related to mining and smelting activities.The regional climate tends to be dry as a whole,but the weathering intensity shows an enhanced characteristic opposite to the cooling trend.It indicates that climatic factors(temperature and precipitation)can no longer explain changes of chemical weathering,river input and terrestrial input in the sediments of the 2.2 ka BP cores alone.A non-synergistic evolution exists between the chemical weathering intensity and the evolution record of the East Asian monsoon.Synchronous increases in heavy metal emissions and chemical weathering parameters demonstrate human impacts surpassing natural climatic controls in South China,while remaining modulated by East Asian monsoon variations.These findings confirm mutual constraints and dependencies between human civilization development and natural environmental changes,thus providing the new evidence for understanding prehistoric human-environment interactions in South China.