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，给地球大气层增加了二氧化碳。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导致气候变暖。了解地球气候系统对不断变化的大气二氧化碳浓度的时空响应是地球上所有人类社会面临的一个紧迫问题。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，但并不是气候科学家感兴趣的所有地理区域都有过去海水温度变化的长期仪器记录，或者这种仪器记录的时间不够久远。因此，为了将最新的海水温度变化的仪器记录在一个较长的时间范围内，以及使过去的海水温度的仪器记录不存在重建，重要的是要深入研究历史的应用程序是什么被称为基于代理的温度重建方法。已证明，将元素和某些元素的同位素比率纳入碳酸钙生物矿物（包括珊瑚、软体动物壳和某些浮游生物）后，有可能用作代用手段，重建仪器记录存在之前的时期和没有仪器记录的地理区域的海水温度变化幅度和速率。这种方法长期以来一直适用于低纬度温水珊瑚，因为它们形成容易确定的年度增长增量，但这些生物仅限于分布在温暖的低纬度地区。Arctica islandica是一种海洋双壳类软体动物，栖息于北大西洋边界的中高纬度陆架海，该物种的个体已被证明可以活长达400年。此外，这种生物（如暖水珊瑚）沉积物很容易识别和确定年度贝壳生长增量的日期，其组成有可能在日历时间尺度上重建过去海水温度的代理记录（通过计算从已知死亡日期起的年增长增量），在过去的几个世纪，甚至在过去的一千年（当个体的外壳使用应用于树木年轮的相同方法交叉相关时）。然而，为了能够生成这些基于代理的过去海水温度的记录，至关重要的是，导出稳健的校准，其记录代理测量值与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。本研究是首次利用A. islandica，它们已经在受控条件下在实验室水族箱中的恒定海水温度下培养，以获得三种新温度代理的校准。这种实验室实验对于开发重建过去海水温度的替代物至关重要，因为这种实验允许在受控条件下进行贝壳生长。一旦确定了这些校准，下一步，在一个后续项目中，将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。这些记录将进一步促进气候科学家对与英国和西欧直接相关的地理区域过去和未来气候演变的理解。

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.