Understanding the Impact of Recent Ocean Acidification on Bio-Calcification

自工业革命以来，大气中二氧化碳（CO2）的增长速度是前所未有的。在过去的二十年中，人类活动释放的二氧化碳只有一半留在大气中，大约三分之一被海洋吸收。通过最近资助的关于海洋酸化的国家和国际项目，关于最近大气中二氧化碳含量上升对海洋的影响的知识正在增长，但这绝不是完整的。拟议中的项目将利用海洋通量计划（OFP, 1984-2008）在百慕大海域（北纬31度50分，西经64度10分）提供的沉积物捕集器时间序列样本，深入了解过去25年这些变化对海洋钙化浮游生物（有孔虫）的影响。这些结果将与挑战者号（1872-76）和发现号（1901-04）在附近地点收集的海底表层沉积物进行比较。这些比较将提供一个工业化前的基线，用以评估最近OA的影响。此外，学生将有机会在计划实习期间在同一地点进行额外的时间积分海底沉积物采样，以进行比较研究。时间序列沉积物捕集器和海底沉积物样本将共同形成一个独特的样本集，用来量化人为二氧化碳对海洋表层碳酸盐化学和浮游生物钙化的持续影响。该项目将集中回答两个主要问题：(1)最近人为二氧化碳的增加如何影响生物钙化（例如，在这种情况下浮游有孔虫）？这个问题将通过研究一个物种内部的物种组成和大小丰度模式的大小标准化壳质量和尺寸（直径、面积、最大和最小长度）的变化来解决。在重建物种的栖息地深度（使用Mg/Ca和氧同位素计算钙化温度）后，这些贝壳钙化参数将与采样地点的深度分层（0-500 m）海水碳酸盐化学数据集进行比较。(2) OA对海水碳酸盐离子浓度（[CO32-]）有何影响？利用现有的[CO32-]指标，如有孔虫壳的硼钙比和壳质量，可以更好地理解这一问题。该项目将使用独特的样本集（时间序列和海底表面沉积物）生成[CO32-]的年度解析记录。每两周一次的时间序列样本，结合测量的深度分层碳酸盐离子浓度（通过测量的总碱度和溶解无机碳计算）和水文数据（来自百慕大大西洋时间序列研究（北纬31度43′，西经64度10′）和S站（北纬32度50′，西经64度10′）），将为有孔虫B/Ca代理提供额外的经验校准。我们将利用我们对B/Ca与[CO32-]的精细校准来推断[CO32-]在工业化前和工业化后的变化，从而推断最近OA的规模。沉积物收集器样本将通过美国伍兹霍尔百慕大海洋科学研究所(BIOS)/海洋生物实验室（MBL）的项目合作伙伴（Conte博士）获得，挑战者号和发现号探险的海底表面沉积物样本将通过合作机构（伦敦自然历史博物馆（提供支持信））获得。该学生将通过实习、在英国剑桥大学进行微量元素/Ca工作的培训，以及在德国阿尔弗雷德·韦格纳研究所（Alfred Wegner Institute）的Jelle Bijma教授（欧洲海洋酸化项目（EPOCA）和海洋酸化的生物影响（BIOACID）项目的核心成员）的共同监督下，受益于在百慕大进行船上样本采集的培训。

The rate of increase in atmospheric carbon dioxide (CO2) since the industrial revolution has been unprecedented. Over the last two decades, only half of the CO2 released by anthropogenic activities has remained in the atmosphere and about one third has been taken up by the oceans. Knowledge about the impact of recent rises in atmospheric CO2 on our oceans is growing through recently funded national and international programmes on Ocean Acidification (OA) but is by no means complete. The proposed project will provide insights into the impact of such changes during the past 25 years on marine calcifying plankton (foraminifera) using sediment trap time series samples available from the Ocean Flux Program (OFP, 1984-2008) off Bermuda (31degree 50'N, 64degree10'W). The results will be compared with seafloor surface sediments at nearby locations collected during the Challenger (1872-76) and Discovery (1901-04) expeditions. These comparisons will provide a pre-industrial baseline with which to evaluate the impact of recent OA. In addition, the student will have an opportunity to carry out additional sampling of time-integrated seafloor sediment at the same location for comparative study during a planned internship. The time series sediment trap and seafloor sediment samples will collectively form a unique sample set with which to quantify the ongoing impact of anthropogenic CO2 on surface ocean carbonate chemistry and plankton calcification. The project will focus on answering two major questions: (1) how has the recent rise in anthropogenic CO2 impacted bio-calcification (e.g., in this case planktonic foraminifera)? This question will be addressed by studying changes in size normalized shell mass and dimensions (diameter, area and maximum and minimum length of surface dwelling species) along with species composition and size abundance patterns within a species. These shell calcification parameters from a seasonally resolved time series will be compared against depth-stratified (0-500 m) seawater carbonate chemistry datasets at the sampling location after reconstructing species' habitat depths (using Mg/Ca & oxygen isotopes to calculate calcification temperatures). (2) How has seawater carbonate ion concentration ([CO32-]) changed as a consequence of OA? A better understanding of this issue will be gained using existing proxies of [CO32-] such as the boron/calcium ratio of foraminiferal shells and shell mass. The project will generate annually resolved records of [CO32-] using the unique sample set (time series and seafloor surface sediments). The fortnightly samples from an annual seasonal cycle of the time series samples, combined with measured depth-stratified carbonate ion concentration (calculated form measured total alkalinity and dissolved inorganic carbon) and hydrography data (from the Bermuda Atlantic Time Series Study (31 degrees 43' N, 64 degrees 10' W) and Hydrostation 'S' (32 degrees 50' N, 64 degrees 10' W)), will provide additional empirical calibration for the foraminiferal B/Ca proxy. We will exploit our refined calibration of B/Ca vs. [CO32-] to infer pre- and post-industrial changes in [CO32-] and, consequently, the scale of recent OA. The sediment trap samples will be obtained through project partner (Dr. Conte) at Bermuda Institute of Ocean Sciences, (BIOS)/Marine Biological Laboratory (MBL), Woods Hole, USA and the sea floor surface sediment samples from the Challenger and Discovery expeditions will be obtained through collaborating institution (Natural History Museum, London (support letter available)). The student will benefit from training of shipboard sample collection off Bermuda through internship, training at University of Cambridge (UK) for trace element/Ca work and co-supervision from Professor Jelle Bijma at Alfred Wegner Institute (Germany), core-member of the European Project on OCean Acidification (EPOCA) and Biological Impacts of Ocean ACIDification (BIOACID) programmes.