Ocean Acidification: Collaborative Research: The response of calcareous nannoplankton to ocean acidification during the Paleocene-Eocene thermal maximum

海洋生物面临的最大威胁之一是人为二氧化碳排放有增无减造成的酸化。 在全球范围内，酸化有可能影响以文石和方解石矿物为外壳的生物群，这些矿物在低pH值的沃茨中很难形成外壳。 其中一个群体，钙质微型浮游生物（包括形成方解石外壳的颗石藻在内的附着藻类），是公海食物链的重要组成部分。实验室实验表明，颗石藻可以适应酸性更强的环境，但该群体是否能适应自然环境还不确定。 地质记录包含一系列自然实验，使我们能够解决微型浮游生物对温室气体扰动的生物反应。古新世-始新世热峰（PETM）是5600万年前发生的一次约20万年的短暂变暖事件，可能是大量温室气体对海洋生态系统影响的最佳古代模型。对来自深海的微型浮游生物的研究显示，在PETM期间出现了新的类群，包括畸形形态类型的增加，这可能意味着对较低方解石饱和度的适应。 此外，地球化学证据表明，在事件的初始阶段，pH值下降的幅度与预计在世纪发生的相似。从这项研究中获得的见解将补充现代实验和生态研究，允许通过空间和时间绘制渐进碳酸盐不饱和对现代微型浮游生物祖先的影响。 除了更好地了解海洋酸化的长期后果外，更广泛的影响包括对研究生和本科生的培训，对博士后研究人员的支持，以及对K-12教室的宣传。 然而，由于深海也在该事件期间酸化，这是PETM的关键早期阶段，可能是最大的海洋表面酸化发生的时候，碳酸钙在大多数深海位置溶解。因此，为了研究海洋酸化对微型浮游生物的全面影响，本研究侧重于大陆架水深沉积剖面中的微型浮游生物。一个极好的机会来探索海洋酸化对PETM浮游生物的影响存在于从大陆架上的大西洋海岸平原的一些最浅的和最广泛的事件记录被发现的核心。这些核心部分提供高时间分辨率和保存高保真记录的早期部分的PETM。 该项目将使用来自马里兰州和新泽西的新的和现有的岩心，研究千年时间尺度上沿海海洋酸化的发展和影响。 （2）微型浮游生物对表层酸化的响应是系统性的，现有的能耐受低饱和度的物种数量增加，随后出现新的物种和形态型;（3）在古近世早期阶段，近岸海域的富营养化加剧了局部酸化的影响，并在CO2的吸收中发挥了关键作用。 这些假设将通过以下密切结合的方法加以处理：（a）微型浮游生物组合研究，以确定物种组成和形态如何变化;（B）一套无机和有机代用指标，以阐明环境变化的性质，特别是从温度信号中揭示酸化;（c）模拟陆架pH值、饱和状态和富营养化的时间变化的模型。

One of the most significant threats for marine organisms is acidification as a result of unabated anthropogenic CO2 emission. On a global scale, acidification has the potential to impact biota that make their shells out of the minerals aragonite and calcite, that have a hard time forming shells in low pH waters. One such group, the calcareous nannoplankton (haptophyte algae including coccolithophores that build shells of the mineral calcite), are a vital part of the open-ocean food chain. Laboratory experiments suggest that coccolithophores can adapt to more acidic conditions, but whether the group can adapt in the natural environment is uncertain. The geological record contains a series of natural experiments that allow us to address the biological response of nannoplankton to greenhouse gas perturbations. The Paleocene-Eocene thermal maximum (PETM), a ~200,000 year long transient warming event 56 million years ago, is likely the best ancient model for the impact of massive greenhouse gas on marine ecosystems. Studies of nannoplankton from deep-sea sites show new taxa during the PETM including an increase in malformed morphotypes that could signify adaptation to lower calcite saturation. Moreover, geochemical evidence suggests a similar magnitude pH decline during the initial stages of the event as projected to occur in the 21st century. The insight gained from this study will complement modern experimental and ecological studies, allowing mapping of the impact of progressive carbonate undersaturation on the ancestors of modern nannoplankton through space and time. In addition to better understanding the long-term consequences of ocean acidification, broader impacts include training of students at the graduate and undergraduate level, support of a postdoctoral researcher, and outreach to K-12 classrooms.Much of the information on the PETM derives from the study of cores drilled in the deep sea. However, as the deep ocean also acidified during the event, the key early stage of the PETM and likely when the maximum surface ocean acidification took place, calcium carbonate has been dissolved in most deep-sea locations. Thus to study the full impact of ocean acidification on nannoplankton, this research focuses on nannoplankton contained within sedimentary sections deposited at continental shelf water depths. A superb opportunity to explore the impact of ocean acidification on PETM plankton exists in cores from the shelf on the Atlantic Coastal Plain where some of the shallowest and most expanded records of the event are found. These core sections offer high temporal resolution and preserve a high-fidelity record of the early part of the PETM. This project will use new and existing cores from Maryland and New Jersey to study the development and impact of acidification on the coastal ocean over millennial time scales. The goal is to address the following hypotheses: (1) Surface ocean carbonate saturation reached a minimum within the first twenty thousand years of the PETM then slowly recovered; (2) The response of nannoplankton to surface acidification was systematic with existing species tolerant of low saturation increasing in abundance followed by the evolution of new species and morphotypes; and (3) Eutrophication in the coastal ocean amplified the impact of acidification locally and played a critical role in drawing down CO2 during the early stages of the PETM. These hypotheses will be addressed using closely integrated: (a) nannoplankton assemblage studies to determine how species composition and morphology changed; (b) a suite of inorganic and organic proxies to elucidate the nature of environmental changes and particularly to unravel acidification from temperature signals; and (c) models to simulate the temporal variability of pH, saturation state and eutrophication on the shelf.