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非常困难的。在目前可用的过去温度的陆地档案中，这些档案通常在空间上受到限制，在校准方面存在模糊性，或者需要较大的样本量。这些问题阻碍了高分辨率、高密度地面温度记录网络的发展。这通常被认为是古气候档案中最重要的一个空白。在这里，我们试图通过开发一种新的古温度计，在温度重建领域提供一个突破。为此，我们使用洞穴石笋（洞穴石笋）。洞穴沉积物是分层生长的，可以像树木的年轮一样确定年代。每一层的化学成分都提供了前所未有的环境信息分辨率，受到超过50万年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个至关重要的进展，因为磷酸盐-氧同位素已知受温度动力学控制。我们首次测量洞穴滴水沃茨和现代洞穴方解石中的磷酸盐-氧同位素组成，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沉积物记录中。由于已知浅洞穴系统的内部温度反映了外部平均气温（加上或减去局部效应），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面温度记录。本研究旨在建立和测试洞穴温度和洞穴沉积物磷酸盐氧同位素之间的现代校准。这将使一个平台，从精确的日期，保存完好，独立的温度记录，可以放心地从全球档案的洞穴沉积物在空间和时间尺度前所未有的。

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.