Ikaite: A palaeoenvironmental proxy

为了预测全球变暖的后果，必须了解气候对大气二氧化碳的温度和冰量(即海平面)的反应。过去气候波动的地质记录有能力揭示这三个地球系统参数之间的自然相互作用。古海洋学自创立以来的一大挑战是重建整个更新世冰期的海洋温度或海平面的独立记录，以便了解冰川周期中两个关键气候成分：冰量和温度的敏感性和阶段性。传统的代用有孔虫d18O受到冰量和温度的共同影响，因此缺乏对海水d18O的限制，就无法对任何海相碳酸盐d18O记录进行完整和定量的解释。我们假设，伊卡石(CaCO3.6H2O)是碳酸钙的一种亚稳水合形式，沉淀在富含有机物质的沉积物中，它捕获了周围水域的同位素组成，作为晶体内的水合水(Rickaby等人，20061)，并提供了一种有希望的方法，直接探测d18Osw，而不是末次冰盛期(LGm)。我们提出了一种多学科的方法，将矿物学和生物地球化学实验室实验与野外观察相结合，以表征和了解伊卡石及其同位素在自然环境中的存在及其气候意义。我们的主要目的是为这种新型的伊卡石代理奠定基础，并将其应用于d18Osw的重建，从而重建冰体，并将该代理的应用扩展到不同的时间片和水团。

In order to predict the consequences of global warming, it is essential to understand the climate response in terms of temperature and ice volume (hence sea level) to atmospheric carbon dioxide. The geological record of past climatic fluctuations has the power to reveal the natural interplay between these three Earth system parameters. One of the great challenges in paleoceanography since its inception, has been to reconstruct an independent record of oceanic temperature, or sea level throughout the Pleistocene ice ages in order to obtain an idea of the sensitivity and phasing of two crucial climate components: ice volume and temperature, during the glacial cycles. Foraminiferal d18O, the traditional proxy, is influenced by a combination of both ice volume and temperature so lack of constraint on seawater d18O prevents complete and quantitative interpretation of any marine carbonate d18O record. We have hypothesised that ikaite (CaCO3.6H2O), a metastable hydrated form of calcium carbonate which precipitates in organic rich sediments, captures the isotopic composition of ambient waters as hydration waters within the crystal (Rickaby et al., 20061), and offers a promising method of probing directly the d18Osw for periods other than the Last Glacial Maximum (LGM). We propose a multi-disciplinary approach to integrate mineralogical and biogeochemical laboratory experiments with field observations to characterise and understand the presence and climatic significance of ikaite and its isotopes within the natural environment. Our primary aims are to lay the foundations for, and apply this novel ikaite proxy to the reconstruction of d18Osw, hence ice volume, and extend application of the proxy to different timeslices and water masses.