Testing the veracity of the Mg/Ca palaeotemperature proxy in cultured marine molluscan calcite

测试培养海洋软体动物方解石中 Mg/Ca 古温度代理的准确性

• 批准号: NE/E009875/1
• 负责人: Leon Clarke
• 金额: $ 9.46万
• 依托单位: Bangor University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE009875%2F1
• 关键词: Testing; veracity; Mg; Ca; palaeotemperature

Climate change is an important and pressing issue for all of human society. Scientists need to understand how Earth's climate varies over different timescales so that they can inform politicians and the public about the likely scale and extent of the impacts of any future climate change. To understand climate it is necessary to gather information about how key oceanographic and climatic parameters, e.g. seawater temperature, changed in the recent and geological past. These data then can be used to model, and ultimately predict, how climate varies over different timescales of interest, i.e. years, decades and centuries. Unfortunately, however, instrumental records of these key parameters only extent back 100 years or so, but much critical information can be obtained from earlier times when the climate was in different states. Because direct measurements of the required parameters are not available for the earlier time intervals an indirect approach then must be taken, whereby measurements are made not of the actual climatic or oceanographic parameter but something else that responded in the same way and still is preserved in the recent or geological record. This approach is known as a proxy-based reconstruction, with the proxy being either a physical or chemical signal that can be measured and that also exhibits a relationship with the climatic or oceanographic parameter that needs to be determined. In addition to the physical or chemical proxy an archive material that preserves the information through recent and geological time also is required and these archives include tree rings, corals and marine molluscs. All of these organisms exhibit an incremental growth pattern, e.g. yearly growth bands, such that high temporal resolution records of the proxies and ultimately climatic and oceanographic parameters can be reconstructed. Corals and molluscs secrete calcium carbonate skeletons that include the mineral calcite and it has been shown that elements such as strontium and magnesium can replace, by a process termed substitution, some of the calcium in these minerals and that the amount of substitution can be related to the temperature of the seawater in which they lived. Therefore, the coral and mollusc skeletons are the archive materials and the measurement of the ratios of strontium and magnesium to calcium in the minerals are the proxy measurements, which can be used to reconstruct temperature in this case. Successful use of such a proxy-based approach is reliant, however, on there being sensitive and precise relationships between the proxy and the climatic or oceanographic parameter of interest. We have recently observed significant variation in magnesium to calcium ratios in mollusc shells cultured at constant temperature and therefore we intend to investigate the degree of such variability in more detail in this study. Detailed assessment of the level of variation in magnesium to calcium ratios is necessary so that we can improve the precision of temperature reconstructions made using measurement of this proxy in these organisms. To meet this objective we will grow two mollusc species, with contrasting shell structures, in laboratory aquaria under controlled temperature conditions. The degree of variability of the magnesium to calcium ratio within the new shell material then will be investigated using several analytical techniques, including one that can make the measurements of magnesium and calcium concentrations every one hundredth of a millimetre across and through the shell structure. By understanding how the magnesium to calcium ratio varies within the shells we should be able to adjust our sampling strategy to provide a more precise calibration and hence more precise seawater temperature reconstructions, thereby improving understanding of past and future climate change.

气候变化是整个人类社会的重要问题。科学家需要了解地球气候在不同的时间范围内如何变化，以便他们可以将未来气候变化的影响的可能规模和程度告知政客和公众。要了解气候，有必要收集有关关键海洋学和气候参数的信息，例如海水温度在最近和地质的过去发生了变化。然后，这些数据可用于建模，并最终预测气候如何在感兴趣的不同时间尺度（即数年，几十年和几个世纪）中变化。但是，不幸的是，这些关键参数的工具记录仅限制了100年左右，但是从较早的气候处于不同状态时，可以获得许多关键信息。由于对较早的时间间隔无法直接测量所需参数，因此必须采用间接方法，从而进行测量不是按实际的气候或海洋参数进行的，而是以相同方式响应并仍然保留在最近或地质记录中的其他响应。这种方法被称为基于代理的重建，代理是可以测量的物理信号或化学信号，并且还与需要确定的气候或海洋学参数有关系。除了物理或化学代理外，还需要通过近期和地质时间保留信息的档案材料，这些档案包括树环，珊瑚和海洋软体动物。所有这些生物都表现出增量的生长模式，例如每年的增长带，可以重建代理的高时间分辨率记录以及最终的气候和海洋学参数。珊瑚和软体动物分泌包括矿物方解石在内的碳酸钙骨骼，并且已经表明，诸如锶和镁之类的元素可以用所谓的替代过程代替这些矿物质中的某些钙，并且替代量可以与其居住的海水温度有关。因此，珊瑚和软体动物的骨骼是档案材料，在矿物质中米镁与钙与钙的比率是代理测量值，在这种情况下，可用于重建温度。但是，成功使用这种基于代理的方法是依赖于代理与感兴趣的气候或海洋学参数之间敏感而精确的关系的。我们最近观察到在恒温下培养的软体动物壳中镁与钙比的显着变化，因此我们打算在这项研究中更详细地研究这种可变性的程度。必须详细评估镁与钙比的变化水平，以便我们可以提高使用这些生物中该代理的测量进行的温度重建精度。为了满足这一目标，我们将在受控温度条件下实验室水族箱中种植两个带有壳体结构的Mollusc物种。然后，将使用几种分析技术研究新壳材料中镁与钙比的变异程度，包括可以使镁和钙浓度的测量跨壳结构进行测量。通过了解镁与钙比在壳内如何变化，我们应该能够调整采样策略以提供更精确的校准，从而更加精确的海水温度重建，从而提高人们对过去和未来气候变化的了解。