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

海洋生物面临的最严重威胁之一是由于人为二氧化碳排放未减少而导致的酸化。在全球范围内，酸化有可能影响那些用矿物文石和方解石制作贝壳的生物群，这些矿物在低pH值水域很难形成贝壳。其中一类，钙质纳米浮游生物（包括形成矿物方解石外壳的球石藻），是开放海洋食物链的重要组成部分。实验室实验表明，颗石藻可以适应更酸性的条件，但该群体是否能适应自然环境尚不确定。地质记录包含了一系列的自然实验，使我们能够解决纳米浮游生物对温室气体扰动的生物反应。古新世-始新世极热期（PETM）是5600万年前一个长达20万年的短暂变暖事件，可能是大规模温室气体对海洋生态系统影响的最佳古代模型。对深海纳米浮游生物的研究表明，在始新世新新世，包括畸形形态的增加，这可能意味着适应较低的方解石饱和度。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21世纪发生的幅度相似。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碳酸盐逐渐不饱和对现代纳米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，更广泛的影响还包括培训研究生和本科生，支持博士后研究人员，以及扩展到K-12教室。关于始新世新石器时代的许多信息来自对深海钻探的岩心的研究。然而，由于深海在事件期间也酸化了，这是PETM早期的关键阶段，也可能是表层海洋酸化最大的时候，碳酸钙在大多数深海地区都被溶解了。因此，为了研究海洋酸化对纳米浮游生物的全面影响，本研究将重点放在大陆架水深沉积剖面中所含的纳米浮游生物上。探索海洋酸化对PETM浮游生物影响的绝佳机会存在于大西洋沿岸平原大陆架的岩心中，在那里发现了一些最浅和最广泛的事件记录。这些岩心剖面提供了高时间分辨率，并保存了PETM早期的高保真度记录。该项目将使用来自马里兰州和新泽西州的新的和现有的核心来研究千年时间尺度上酸化对沿海海洋的发展和影响。目标是解决以下假设：(1)表层海洋碳酸盐饱和度在始新世纪的前2万年达到最低，然后缓慢恢复；(2)纳米浮游生物对表层酸化的响应是系统性的，耐低饱和度的现有物种数量增加，然后是新种和新型的进化；(3)近岸海洋富营养化放大了局部酸化的影响，并在始新世新世早期吸收CO2方面发挥了关键作用。这些假设将通过紧密结合的方法加以解决：(a)纳米浮游生物组合研究，以确定物种组成和形态如何变化；(b)一套无机和有机替代指标，以阐明环境变化的性质，特别是从温度信号中揭示酸化；(c)模拟大陆架pH值、饱和状态和富营养化的时间变化模式。

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.