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

自工业革命以来的近200年里，人类活动，主要是燃烧化石燃料，增加了地球大气中的二氧化碳。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空响应是整个地球上所有人类社会的一个紧迫问题。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，但过去海水温度变化的长期仪器记录并不适用于气候科学家感兴趣的所有地理区域，或者这些仪器记录的时间不够久远。因此，为了将最近的海水温度变化仪器记录置于更长的时间背景下，并在仪器记录不存在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深入研究历史。某些元素的元素和同位素比率，当纳入碳酸钙生物矿物（包括珊瑚、软体动物壳和一些浮游生物）时，已证明有潜力作为重建海水温度变化幅度和速率的代理手段，用于存在仪器记录之前的那些时期和不存在此类仪器记录的地理区域。这种方法长期以来一直应用于低纬度的温水珊瑚，因为它们形成了很容易确定的年增长增量，但这些生物的分布仅限于温暖的低纬度地区。北极岛是一种海洋双壳类软体动物，生活在与北大西洋接壤的中高纬度大陆架海域，这种物种的个体已经被证明可以活到400岁左右。此外，这种生物（像温水珊瑚一样）沉积的贝壳年增量很容易被识别和确定年代，其组成有可能在日历时间尺度上（通过计算从已知死亡日期开始的年增量）重建过去海水温度的代用记录，过去几个世纪甚至过去一千年（当个体的贝壳使用与树木年轮相同的方法交叉相关时）。然而，为了能够生成这些基于过去海水温度的代理记录，至关重要的是推导出可靠的校准，这些校准记录了代理测量与海水温度之间的关系的强度，以及识别任何代理的局限性。这项详细而系统的研究将是首次使用已在实验室水族箱中恒温培养的岛屿拟南鲷标本，在受控条件下获得三种新的温度代用物的校准。这样的实验室实验对于重建过去海水温度的替代品的发展是至关重要的，因为这样的实验允许壳在受控条件下生长。一旦确定了这些校准，在后续项目中，下一步将是生成北大西洋不同地区过去海水温度变化的长时间序列记录。这样的记录将进一步加深气候科学家对地理区域气候过去和未来演变的理解，这与英国和西欧直接相关。

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.