Establishing a new palaeothermometer from the speleothem archive of phosphate-oxygen isotopes

温度记录对于了解过去和未来的气候至关重要。然而，重建过去的温度动态是极其困难的。在目前可用的过去温度的地面档案中，这些档案往往在空间上受到限制，在校准方面存在模糊性，或者需要大量样本。这些问题阻碍了高分辨率、高密度的地面温度记录网络的发展。这通常被认为是古气候档案中唯一最重要的空白。在这里，我们试图通过开发一种新的古温度计来实现温度重建领域的突破。为此，我们使用洞穴石笋。洞穴群落是层层生长的，可以像树上的年轮一样确定年代。每一层中的化学成分都提供了前所未有的环境信息分辨率，受50万年以上的绝对年龄模型的限制。在兰开斯特环境中心，我们最近开发了一种技术，可以从石笋层中提取磷酸盐。这是该研究领域的一项至关重要的进展，因为磷酸盐-氧同位素已知受温度动态控制。我们对洞穴滴水和现代洞穴方解石中磷氧同位素组成的首次测量提供了明确的证据，表明洞穴温度信号可以被捕获并存储在洞穴记录中。由于浅层洞穴系统的内部温度是已知的反映外部平均气温(加上或减去局部影响)的，这提供了一个令人兴奋的机会，通过它可以建立真正独立的地球温度记录。这项研究旨在建立和测试洞穴温度和洞穴磷氧同位素之间的现代校准。这将提供一个平台，通过该平台，可以自信地从迄今为止前所未有的时空尺度的全球洞穴遗址档案中获得准确的、保存良好的、独立的温度记录。

Temperature records are critical for understanding past and future climate. However, reconstructing past temperature dynamics is incredibly difficult. Of the currently available terrestrial archives of past temperature, these are often spatially limited, suffer from ambiguity around calibration, or require large sample sizes. These issues have prevented the development of a high resolution, high density network of terrestrial temperature records. This is now often considered the single most significant gap in the palaeoclimate archive. Here, we seek to provide a breakthrough in the field of temperature reconstruction by developing a new palaeothermometer. For this, we use speleothems (cave stalagmites). Speleothems grow in layers, which can be dated like the rings in a tree. The chemistry in each layer offers an unprecedented resolution of environmental information, constrained by an absolute age model over 500,000 years. At the Lancaster Environment centre, we have recently developed a technique which allows phosphate to be extracted from the stalagmite layers. This is a critically important advance in the research field, as phosphate-oxygen isotopes are known to be controlled by temperature dynamics. Our first measurements of the phosphate-oxygen isotope composition in cave drip waters and modern cave calcite provide clear evidence that the cave temperature signal can be captured and stored within the speleothem record. As the internal temperature of shallow cave systems are known to reflect the external average air temperature (plus or minus localised effects), this provides an exciting opportunity through which a truly independent terrestrial temperature record may be built. This research aims to build and test a modern-day calibration between cave temperature and speleothem phosphate-oxygen isotopes. This will enable a platform from which precisely dated, well preserved, independent temperature records can be confidently obtained from the global archive of speleothems at a spatial and temporal scale hitherto unprecedented.