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

洞穴石（洞穴中发现的石笋、石笋和其他类型的碳酸钙装饰的名称）是由雨水通过土壤和基岩渗透到洞穴环境中形成的，这些沉积物在不受干扰的情况下生长了数千年。石笋生长成连续的层状，响应季节降雨量的变化，可以准确地定年。碳酸石笋中的氧同位素18O和16O继承自雨水，雨水中的18O/16O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。在洞穴中记录的氧同位素变化很容易测量，当与准确的日期相结合时，就提供了数万年前环境变化的独特信息。洞穴氧同位素记录在重建过去气候方面具有巨大的潜力，但令人惊讶的是，从洞穴中推断出的气候记录从未与真实的天气记录直接比较，以了解它们的实际效果。这个项目的目的是将洞穴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。直布罗陀自1791年以来记录了降雨和温度观测，自1961年以来测量了月雨同位素的氧同位素组成。对直布罗陀活动石笋形成的初步研究表明，同位素和微量元素有明显的季节性振荡，这使得可以计算年份和气候信号直接与历史天气记录相联系，而且非常准确。这一试验的结果将使人们能够更有信心地构建直布罗陀过去气候的自然循环，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.