Holocene Environmental Evolution Recorded By Multiple Indicators In Judian Lake Area

The Judian Lake area adjacent to Laizhou Bay is located in the northern monsoon region of China.It is sensitive to global climate change and provides abundant lake sediment data for the study of past climate and environmental evolution in land-sea interaction areas.Therefore,through the study of sediment grain size of Judian Lake profile,combined with AMS¹⁴C dating,carbonate,magnetic susceptibility,ostracoda,foraminifera,sporopollen and other indicators of comprehensive comparative analysis,this paper reconstructs the climate and environmental evolution in this area since Holocene.The results show that the grain size of the sediments in the Judian Lake section is dominated by silt,the average silt content is 79.70%,and the average clay content is close to sand,which is 9.28%and 11.02%,respectively.At the stage of 8000cal.a BP⁷765cal.a BP,the sand content was higher,the magnetic susceptibility and carbonate content were lower.Microbiological analysis showed that only one foraminifera and 14 freshwater ostracods were found in the top sample.The sporopollen concentration of each family was not high,which indicated that the climate was dry and cold.In 7765cal.a BP⁶905cal.a BP stage,fine particle content increased,magnetic susceptibility and carbonate content showed an increasing trend,marine and freshwater ostracods appeared in large numbers and foraminifera number and differentiation of low-salt species combinations increased;temperature-loving pine,deciduous oak and elm in arbor and shrub pollen were on the high side,while Artemisia,Chenopodiaceae,Humulus and Graminea were subordinate herbs.The undergraduate occupies an absolute advantage,and the content of the aquatic herb Typha increases,indicating that the lake develops obviously and the climate is very warm.In the 6905cal.a BP⁵210cal.a BP stage,the average particle size content fluctuated frequently and changed greatly,the magnetic susceptibility and carbonate content were higher,the number of foraminifera increased greatly,and the symbiotic ostracods showed the characteristics of low differentiation and high dominance,indicating the higher water level of the lake and warm and wet climate;However,during the period of 5990cal.a BP to 5600cal.a BP,the pollen contents of warm-loving trees and shrubs such as Pinus,Herbal pollen such as Artemisia and Chenopodiaceae continued to decrease,sporopollen deficiency zones occasionally appeared,indicating that the climate turned to dry and cold;after that,the sporopollen concentration generally increased,and the climate began to warm again.It can be seen that the climate fluctuated sharply at this stage,with the alternation of warm-wet and cold-dry.In the5210cal.a BP⁴625cal.a BP stage,the clay content and magnetic susceptibility values are the highest in the profile,the carbonate content is not high as a whole,and the number of foraminifera is up to nearly 200.The symbiotic marine ostracods are typical Chinese Beauty Brocade,Chinese Thorn Brocade and Eyespot Curved Back Brocade;The main sporopollen species are herbaceous plants,and the increase of ferns indicates that the climate in this stage is warm and humid,and the degree of warmth and humidity is stronger than that in the previous stage.Therefore,the climate change since the 8000cal.a BP in this area can be summarized as:cold and dry,warm and wet,warm and dry alternative,warm and wet.