Seasonal microclimate control of calcite fabrics, stable isotopes and trace elements in modern speleothem from St Michaels Cave, Gibraltar
Seasonal microclimate control of calcite fabrics, stable isotopes and trace elements in modern speleothem from St Michaels Cave, Gibraltar
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DOI：
10.1144/sp336.17
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发表时间：
2010-01-01
期刊：
影响因子：
--
通讯作者：
Durell, Richard
中科院分区：
文献类型：
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作者：
Mattey, David P.;Fairchild, Ian J.;Durell, Richard
在新圣迈克尔的洞穴，直布罗陀，三个滴水网站的详细监测，揭示了一个强有力的连贯性的季节性模式的滴水化学，尽管每个网站有显着不同的流动路径和排放模式。方解石饱和度与洞穴空气pCO（2）的定期季节变化密切相关，这是由洞穴内部和外部空气之间的温差驱动的季节性反向通风引起的。CO2脱气和方解石沉淀的耦合模型将共存的滴水、洞穴空气CO2和洞穴沉积物方解石中的季节性三角洲C-13变化与由洞穴通风驱动的pCO（2）的大变化联系起来。稳定同位素比值之间的关系，Sr/Ca和洞穴沉积物织物每年形成的方解石纹层是一致的脱气方解石沉淀过程中，快速脱气控制三角洲C-13滴水DIC和方解石，而速度慢得多的方解石沉淀导致季节性周期的Sr在一个更复杂的方式。通过展示一个密切监测的洞穴中的现代洞穴沉积物中的层压洞穴沉积物结构加上微量元素和同位素循环的原因，这项研究提供了当地小气候和洞穴沉积物地球化学提供的代理记录之间的明确联系。在直布罗陀，低洞穴空气pCO（2）在夏季是不寻常的相比，已被揭示的洞穴监测在其他地方进行，并表明，需要谨慎时，连接配对的洞穴构造到特定的季节，没有知识的本地过程中运行的洞穴。
Detailed monitoring of three drip sites in New St Michael's Cave, Gibraltar, reveals a strongly coherent seasonal pattern of dripwater chemistry despite each site having significantly different flow paths and discharge patterns. Calcite saturation is closely linked to regular seasonal variations in cave air pCO(2) caused by seasonally reversing ventilation driven by temperature difference between the cave interior and the air outside. A coupled model of CO2 degassing and calcite precipitation links seasonal delta C-13 variations in coexisting dripwater, cave air CO2 and speleothem calcite to large variations in pCO(2) that are driven by cave ventilation. The relationships between stable isotope ratios, Sr/Ca and speleothem fabrics across annually formed calcite laminae are consistent with a degassing-calcite precipitation process in which rapid degassing controls the delta C-13 of both drip water DIC and calcite whereas a much slower rate of calcite precipitation causes seasonal cycles of Sr in a more complex manner. By demonstrating the causes of laminated speleothem fabrics plus trace element and isotope cycles in modern speleothem from a closely monitored cave, this study provides clear links between the local microclimate and the proxy record provided by speleothem geochemistry. In Gibraltar, low cave air pCO(2) in summer is unusual compared to what has been revealed by cave monitoring carried out elsewhere and shows that caution is needed when linking paired speleothem fabrics to specific seasons without knowledge of local processes operating in the cave.