Calibrating novel palaeotemperature proxies in laboratory aquaria cultured long-lived Arctica islandica mollusc shells

自工业革命以来的大约200年里，人类活动，主要是通过燃烧化石燃料，向地球大气中添加了二氧化碳。二氧化碳是一种重要的温室气体，大气中这种化合物浓度的增加会导致气候变暖。了解地球气候系统对大气二氧化碳浓度变化的时间和空间响应是地球上所有人类社会面临的紧迫问题。进行这种评估的一种方法是回顾过去，重建过去的温度变化，并将这种变化与过去大气成分的记录联系起来。尽管全球变暖具有重要意义，但并不是所有气候科学家感兴趣的地理区域都有过去海水温度变化的长期仪器记录，或者这种仪器记录不足以追溯到足够远的时间。因此，为了将海水温度变化的最新仪器记录放在更长的时间范围内，并能够在没有仪器记录的情况下重建过去的海水温度，重要的是通过应用所谓的基于代理的温度重建方法来更深入地研究历史。在碳酸钙生物矿物(包括珊瑚、软体动物贝壳和一些浮游生物)中加入某些元素的元素和同位素比率，已显示出有潜力作为替代手段，用于重建在有仪器记录之前的那些时间段和没有这种仪器记录的地理区域的海水温度的大小和变化率。长期以来，这种方法一直被应用于低纬度温暖水域的珊瑚，因为它们形成了很容易确定日期的年生长量，但这些生物仅限于温暖的低纬度地区。岛角珊瑚是一种海洋双壳软体动物，生活在北大西洋边缘的中高纬度陆架海域，这一物种的个体被证明可以活到大约400年。此外，这种生物(如暖水珊瑚)的沉积物很容易辨认，并确定每年贝壳生长增量的日期，其组成有可能在日历时间尺度上(通过从已知死亡日期计算年度增长增量)重建过去海水温度的基于代理的记录，包括过去几个世纪甚至上一个千年(使用与树木年轮相同的方法相互关联个体的贝壳)。然而，为了能够生成这些过去海水温度的基于代理的记录，至关重要的是要得到可靠的校准，其中记录了代理测量和海水温度之间的关系的强度，以及识别任何代理的任何限制。这项详细和系统的研究将是首次使用已经在实验室水族箱中在恒定海水温度下、在受控条件下培养的岛藻标本，以得出三个新的温度替代指标的校准。这种实验室实验对于开发恢复过去海水温度的替代物至关重要，因为这种实验允许贝壳在受控条件下生长。一旦确定了这些校准，在后续项目中的下一步将是生成北大西洋不同部分过去海水温度变化的长期时间序列记录。这样的记录将进一步加深气候科学家对与英国和西欧直接相关的地理区域气候过去和未来演变的理解。

For the last approximately 200 years since the Industrial Revolution, human activity, primarily by burning of fossil fuels, has added carbon dioxide to planet Earth's atmosphere. Carbon dioxide is an important greenhouse gas and increasing concentrations of this chemical compound in the atmosphere causes climate warming. Understanding the temporal and spatial response of Earth's climate system to changing atmospheric carbon dioxide concentrations is a pressing issue for all of human society across the planet. One way to make such an assessment is to look back into the past and to reconstruct past temperature changes and to relate such variability to records of past atmospheric composition.Despite the significance of global warming, long instrumental records of changing seawater temperature in the past are not available for all of the geographical regions which interest climate scientists, or such instrumental records do not extend far enough back in time. Therefore, in order to place the most recent instrumental records of seawater temperature change in a longer temporal context, as well as to enable reconstruction of past seawater temperature where instrumental records do not exist, it is important to delve deeper into history by application of what is called a proxy-based temperature reconstruction approach. Elements and isotope ratios of some elements, when incorporated into calcium carbonate biominerals (including corals, mollusc shells and some plankton), have demonstrated potential to be used as the proxy means of reconstructing the magnitude and rates of change of seawater temperatures, for those time periods before the existence of instrumental records and for geographical regions where such instrumental records do not exist. Such an approach has long been applied to low latitude warm-water corals, since they form easily dated annual growth increments, but these organisms are restricted in distribution to the warm low latitudes.Arctica islandica is a marine bivalve mollusc that inhabits those middle to high latitude shelf seas that border the North Atlantic Ocean and individuals of this species have been shown to live for up to ~400 years. Furthermore, this organism (like a warm-water coral) deposits easily identified and dated annual shell growth increments, the composition of which has the potential to enable reconstruction of proxy-based records of past seawater temperature, on a calendar timescale (by counting annual growth increments from a known date of death), for the last few centuries and even for the last millennium (when shells of individuals are cross-correlated using the same approach as is applied to tree rings). However, to be able to generate these proxy-based records of past seawater temperature it is critically important that robust calibrations are derived, which document the strength of the relationship between the proxy measurement and seawater temperature, as well as identifying any limitations with any proxy. This detailed and systematic study will be the first use of specimens of A. islandica, which have already been cultured at constant seawater temperatures in laboratory aquaria, under controlled conditions, to derive calibrations for three novel temperature proxies. Such laboratory experiments are fundamental to the development of proxies for reconstructing past seawater temperatures, because such experiments allow for shell growth under controlled conditions. Once these calibrations have been determined the next step, in a follow-up project, will be to generate long time-series records of past seawater temperature change in different parts of the North Atlantic Ocean. Such records then will further climate scientist's understanding of the past and future evolution of climate in a geographical region which is of direct relevance to the UK and western Europe.