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，酸化有可能影响由文石和方解石矿物制成贝壳的生物群，这些矿物在低pH值水域很难形成贝壳。其中一类是钙质超微浮游生物(触生藻类，包括构成矿物方解石外壳的球藻)，是公海食物链的重要组成部分。实验室实验表明，球藻基团可以适应更酸性的条件，但该群体是否能适应自然环境还不确定。地质记录包含了一系列自然实验，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-始新世最高温度(PETM)是5600万年前一个长约20万年的瞬时变暖事件，它可能是研究大规模温室气体对海洋生态系统影响的最佳古代模型。对深海地点的超微浮游植物的研究表明，在PETM期间出现了新的类群，包括畸形形态类型的增加，这可能表明它们适应了较低的方解石饱和度。此外，地球化学证据表明，在该事件的初始阶段，PH值下降幅度与预计在21世纪发生的类似。从这项研究中获得的洞察力将补充现代实验和生态学研究，使人们能够通过空间和时间绘制逐渐增加的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，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，以及与K-12课堂的接触。关于海洋酸化的许多信息来自对深海钻探岩芯的研究。然而，由于深海在这次事件中也发生了酸化，这是大洋运动的关键早期阶段，很可能是表层海洋酸化最严重的时候，碳酸钙在大多数深海位置都已被溶解。因此，为了研究海洋酸化对超微浮游植物的全面影响，本研究重点研究了大陆架水深处沉积剖面中所含的超微浮游植物。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海岸平原陆架的岩芯中，在那里发现了一些关于这一事件的最浅和最广泛的记录。这些核心剖面提供了高时间分辨率，并保存了PETM早期的高保真记录。该项目将使用来自马里兰州和新泽西州的新的和现有的岩心来研究千年时间尺度上酸化对沿海海洋的发展和影响。其目标是解决以下假设：(1)表层海洋碳酸盐饱和度在PETM的头2万年内达到最低水平，然后缓慢恢复；(2)超微浮游植物对表层酸化的响应是系统性的，现有物种对低饱和度的耐受性增加，随后新物种和形态类型的进化；(3)沿海海洋的富营养化放大了酸化的影响，并在PETM早期阶段对二氧化碳的吸收起到关键作用。将利用密切结合的办法处理这些假设：(A)超微浮游植物组合研究，以确定物种组成和形态如何变化；(B)一套无机和有机替代物，以阐明环境变化的性质，特别是从温度信号中解算酸化作用；(C)模型，以模拟酸碱度、饱和状态和大陆架富营养化的时间变异性。

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.