Fidelity of speleothem climate proxies: an inter-annual calibration against the instrumental record in Gibraltar and prospects for climate hindcasting

洞穴沉积物（洞穴中发现的石笋、石笋和其他类型的碳酸钙装饰物的名称）是由雨水通过土壤和基岩进入洞穴环境的作用形成的，这些沉积物在数千年内不受干扰地生长。石笋随降雨量的季节变化而分层生长，可以准确地测定其年代。石笋碳酸盐岩中氧同位素18 O和16 O是雨水的继承物，雨水中的18 O/16 O比值是气候环境的重要指标，可提供温度和大气环流的信息。洞穴沉积物中记录的氧同位素变化很容易测量，当与精确的日期相结合时，可以提供关于环境变化的独特信息，可以追溯到数万年前。洞穴沉积物氧同位素记录在重建过去的气候方面具有很大的潜力，但令人惊讶的是，从洞穴沉积物中推断出的气候记录从未与真实的天气记录进行过直接比较，以了解它们的实际工作情况。本项目的目标是将洞穴沉积物气候指标与目前可用的最长的气象和降雨同位素记录进行比较：自1791年以来，一直对直布罗陀的降雨量和温度进行观测，自1961年以来一直测量月降雨同位素的氧同位素组成。对直布罗陀活跃石笋形成的一项试点研究表明，同位素和微量元素存在明显的季节性波动，因此可以非常准确地计算年份和气候信号。这次测试的结果将使直布罗陀过去气候的自然周期能够更有信心地构建，并将有助于在未来建立更准确的天气预报。

Speleothem (a name given to stalagtites, stalagmites and others types of calcium carbonate decorations found in caves) form by the action of rain water percolating through soil and bedrock into the cave environment and these deposits grow undisturbed for many thousands of years. Stalagmites grow as successive layers in response to seasonal changes in rainfall amount and can be accurately dated. Isotopes of oxygen, 18O and 16O, in stalagmite carbonate are inherited from the rainwater and the ratio 18O/16O in rainwater is an important indicator of the climatic environment, providing information on temperature and atmospheric circulation. Oxygen isotope variations record in speleothem are easily measured, and when combined with accurate dates provide unique information on environmental change going back many tens of thousands of years. Speleothem oxygen isotope records have great potential in reconstructing past climates yet surprisingly, the climate record deduced from speloethem has never been directly compared with real weather records to see how well they really work The objective of this project is to compare speleothem climate indicators with the longest combined meteorological and rainfall isotope records currently available: rainfall and temperature observations have been recorded in Gibraltar since 1791 and the oxygen isotope compositions of monthly rain isotope have been measured since 1961. A pilot study of active stalagmite formation in Gibraltar shows clear seasonal oscillations in isotopes and trace elements which allow the years to be counted and the climate signal directly with the historical weather record with great accuracy. The results of this test have will enable the natural cycles in the past climate of Gibraltar to be constructed with more confidence and will help create more accurate weather forecasts in the future.