末次冰消期临沂石笋微量元素记录及其气候意义

Stalagmite Trace Element Records and Implications for Paleoclimate Change in Linyi During the Last Deglaciation

结合山东临沂LY石笋(发育年代17~11.4ka BP)δ18 O记录,分析了LY石笋微量元素变化特征、影响因素及其指代的气候环境变化信息。LY石笋Sr/Ca、238 U和(234 U/238 U)0变化与石笋δ18 O记录、65°N夏季太阳辐射曲线在千年尺度上变化趋势一致,较好地保存了末次冰消期早期气候环境由冷干向暖湿过渡的信息。Heinrich Event 1时期(17~14.7ka BP),石笋Sr/Ca比值和238 U含量表现为相对高值,(234 U/238 U)0表现为相对低值;Blling-Allerd时期(14.7~12.7ka BP),石笋Sr/Ca比值和238 U含量迅速减少至低值,(234 U/238 U)0呈逐渐增加的趋势;Younger Dryas时期(12.7~11.4ka BP),石笋微量元素无明显波动,Sr/Ca比值和238 U含量表现为相对低值,(234 U/238 U)0表现为相对高值。研究认为LY石笋Sr/Ca比值主要受与降雨量相关的渗流水滞留时间、水-岩相互作用和先期碳酸盐沉淀的影响,可以指示外界降雨量的变化。LY石笋238 U和(234 U/238 U)0则主要受与有效降水量有关的洞穴上覆土壤湿度和氧化还原条件的影响,大气粉尘活动可能是导致石笋238 U、(234 U/238 U)0变化与δ18 O曲线不完全协同的原因。此外,LY石笋Sr/Ca和(234 U/238 U)0变化可能还受石笋生长速率的影响,具体影响机制还有待进一步研究。

Combined with theδ18 O record of stalagmite LY from Linyi,Shandong Province which has been continuously deposited from 17 to 11.4 ka BP,the variation characteristics,influence factors and environmental significance of trace-element records from stalagmite LY were discussed.Variations in the Sr/Ca,238 U and(234 U/238 U)0 of stalagmite LY correlate well with theδ18 O record of stalagmite LY and follow the 65°N summer insolation on millennial scales.Trace elements of stalagmite LY recorded the transition from cold-dry climatic phases to warm-wet climatic phases during the early period of the last deglaciation.Higher values of Sr/Ca and 238 U and lower values of(234 U/238 U)0 occurred during the Heinrich Event 1(17~14.7 ka BP).During the B lling-Aller d(14.7~12.7 ka BP),Sr/Ca and 238 U decreased quickly to low values,while(234 U/238 U)0 showed an increasing trend.During the Younger Dryas(12.7~11.4 ka BP),no obvious fluctuation occurred in trace-element records of stalagmite LY,with lower values in the Sr/Ca and 238 U while higher values in the(234 U/238 U)0.The Sr/Ca ratios of stalagmite LY were mainly influenced by water-rock interaction,residence time of seepage water and prior calcite precipitation,which are associated with rainfall variations.Soil moisture and redox condition associated with effective rainfall are the main control factors of the 238 U values and(234 U/238 U)0 ratios of stalagmite LY,and atmospheric dust activities might cause the decoupling between 238 U,(234 U/238 U)0 andδ18 O of stalagmite LY.In addition,Sr/Ca and(234 U/238 U)0 ratios of stalagmite LY might also be influenced by variations in growth rate of stalagmite LY,and the specific mechanisms remain to be further studied.