Stalagmite growth rates are usually considered to reflect changes in paleoclimate and paleoenvironment.However,how exactly growth rates are affected by climate and environment is still unclear.We launched a monitoring...Stalagmite growth rates are usually considered to reflect changes in paleoclimate and paleoenvironment.However,how exactly growth rates are affected by climate and environment is still unclear.We launched a monitoring and modeling program that lasted approximately 4 years on two active drip sites in Heshang Cave,central China.We collected comprehensive quantitative data on growth rates,cave temperature,CO2 concentration,drip rate and drip-water chemistry to better understand the relationship between stalagmite growth and cave environment.By laying out glass substrates,we successfully grew stalagmite calcite crystals with rhombic characteristics,and quantified growth rates by measuring the long and short axes of calcite crystals under a microscope.Combined with coeval environmental data,we explicitly examined the roles of cave temperature,drip rate and drip-water chemistry in controlling the micro-scale growth of stalagmite calcite.Results show that growth of stalagmite calcite crystals at two drip sites exhibited similar seasonal variations - generally faster in the summer months,at ～3 μm d-1,and slower during the late winter to early spring,at ～1.5 μm d-1.Variations in calcite growth rates were mainly determined by changes in cave temperature,with the growth rate increasing by 8.1%/°C and 6.6%/°C at the two locations.This indicates the potential use of stalagmite growth rates as a seasonal-resolution paleo-temperature proxy in some ventilated caves.On the other hand,the effect of drip rate and drip-water Ca2+ and SIC values on growth rates were not significant.展开更多
文摘为探究岩溶关键带碳循环机制,揭示洞穴通风对洞穴环境变化的响应机制,在2018年国庆期间对贵州绥阳大风洞洞内空气环境指标(温度、湿度、CO 2浓度)和滴水水化学指标(温度,pH值,EC,Ca 2+,HCO-3)进行为期7 d的连续自动监测,并运用系统分析方法对各要素进行了综合分析。结果表明:(1)受游客数量、洞道结构的影响,洞穴空气CO 2浓度表现出明显的昼夜变化特征;与2#(神泉玉露)点相比,1#(夜明珠)点位于大风洞主洞道,洞腔体积较大,洞道较宽,洞穴空气CO 2浓度增加幅度及变化幅度表现为2#>1#。(2)洞穴通风效应与洞穴滴水水化学相关性显著。洞穴通风与lg P CO 2(w)呈反相关,与pH值,SIc和SId为正相关;受监测点洞道结构、通风效应和滴水水量的影响,洞穴通风与1#点的Ca 2+和HCO-3浓度变化呈反相关关系,与2#点的相关性不显著。(3)不同通风模式下,不同监测点的水气CO 2分压差及沉积环境存在差异。当ΔT v>0时,洞穴属于积极通风状态,洞穴空气CO 2浓度降低,ΔP CO 2>0,有利于洞穴景观的沉积;反之,洞穴沉积物趋向于产生溶蚀作用。
基金supported by the National Natural Science Foundation of China(40531004 and 41072262)
文摘Stalagmite growth rates are usually considered to reflect changes in paleoclimate and paleoenvironment.However,how exactly growth rates are affected by climate and environment is still unclear.We launched a monitoring and modeling program that lasted approximately 4 years on two active drip sites in Heshang Cave,central China.We collected comprehensive quantitative data on growth rates,cave temperature,CO2 concentration,drip rate and drip-water chemistry to better understand the relationship between stalagmite growth and cave environment.By laying out glass substrates,we successfully grew stalagmite calcite crystals with rhombic characteristics,and quantified growth rates by measuring the long and short axes of calcite crystals under a microscope.Combined with coeval environmental data,we explicitly examined the roles of cave temperature,drip rate and drip-water chemistry in controlling the micro-scale growth of stalagmite calcite.Results show that growth of stalagmite calcite crystals at two drip sites exhibited similar seasonal variations - generally faster in the summer months,at ～3 μm d-1,and slower during the late winter to early spring,at ～1.5 μm d-1.Variations in calcite growth rates were mainly determined by changes in cave temperature,with the growth rate increasing by 8.1%/°C and 6.6%/°C at the two locations.This indicates the potential use of stalagmite growth rates as a seasonal-resolution paleo-temperature proxy in some ventilated caves.On the other hand,the effect of drip rate and drip-water Ca2+ and SIC values on growth rates were not significant.
