Investigation of the Effects of CACO3 Saturation State & Temperature on the Calcification Rate & Skeletal Properties of Benthic Marine Calcifiers

智力优势：大气二氧化碳浓度的人为升高增加了海洋的酸度，从而降低了海水相对于碳酸钙(CaCO3)的饱和状态。越来越令人担忧的是，这些变化对钙化有机体形成贝壳和骨骼的能力的潜在影响。最近的研究，包括PiRies和他的同事对一系列海底海洋钙化物的试点工作，跨越了广泛的分类学、矿物学和生态学范围，揭示了海洋生物对CO2诱导的海洋酸化表现出广泛的钙化反应，包括正、负、抛物线、阈值和中性反应。海洋钙化物的外壳和骨架由不同形态(多晶型)的碳酸钙组成，最常见的是文石、高镁方解石和低镁方解石。这些多晶型在海水中的溶解度有很大不同，因此，它们对二氧化碳诱导的海洋酸化的潜在反应也有很大不同。对初步研究中所调查的生物体所分泌的贝壳进行的X射线衍射分析表明，在二氧化碳浓度升高的情况下，其贝壳中方解石(较难溶解的CaCO3形式)与文石(较易溶解的形式)的比例增加，而方解石的镁钙比下降。这些观察表明，一些海洋钙剂可能部分地适应了CaCO3饱和度的下降，因为它以牺牲较易溶的形式(文石、高镁方解石)为代价，增加了较少溶解的CaCO3(低镁方解石)的比例。然而，海洋生物贝壳和骨骼的这种矿物学和成分变化很可能会改变它们的结构和生物力学特性。该项目试图在初步研究结果的基础上，培育一套在过去(280ppm)、现在(385ppm)和预测未来(540、840ppm)二氧化碳和三种不同温度下的海底海洋钙化动物，以研究以下方面的变化：(1)它们的钙化速率和线性延伸；(2)各种CaCO3晶型在贝壳/骨骼中的相对丰度和微米尺度分布；(3)它们贝壳/骨骼的超微结构和晶体形态；以及(4)它们的生物力学特性。这项研究还将以试点实验为基础，利用更彻底的重复研究设计，更精确地限制实验海水处理的化学参数，调查3种不同温度下的钙化反应，并采用“工业化前”的二氧化碳水平(280ppm)。这项拟议的研究结果应该会促进我们对海底海洋钙化生物如何应对未来二氧化碳引起的海水温度和CaCO3饱和状态变化的理解。通过研究生物对晚古生代以来大气PCO2的响应，这项研究应该有助于我们理解大气PCO2与大规模灭绝事件的联系，以及海洋钙化物在整个地质时代的多形矿物学的长期变化。最后，将观测到的对不同PCO2-T情景的生物响应与已经为非生物成因碳酸盐建立的生物响应进行比较，将有助于我们理解海洋钙化器建造外壳和骨骼的机制。BROADER影响：拟议的研究结果将为政策制定者和立法者提供决策依据，这些决策者和立法者致力于通过为一系列海洋钙化器建立PCO2-T容忍度来缓解二氧化碳诱导的变暖和海洋酸化的影响。拟议研究的结果将通过同行评议出版物、会议介绍、公众宣传、主计委网站和主流媒体广泛传播。皮里斯是一位早期的职业科学家，他正在开发的研究计划将通过研究提供的资源和活动得到实质性的加强。这项研究还将促进研究生Ann Mooney(太平洋岛民)和Isaac Westfield以及博士后研究员Karl Castillo(非洲裔伯利兹人)的教育、培训和专业发展，其中两人属于在海洋科学中代表性不足的少数群体。最后，拟议的研究将为在PI下进行研究的几名本科生创造宝贵的培训和教育经验。

INTELLECTUAL MERIT: Anthropogenic elevation of atmospheric pCO2 is increasing the acidity of the oceans, thereby reducing the saturation state of seawater with respect to calcium carbonate (CaCO3). Of mounting concern is the potential impact of these changes on the ability of calcifying organisms to form their shells and skeletons. Recent studies, including pilot work conducted by PI Ries and his colleagues on a suite of benthic marine calcifiers spanning broad taxonomic, mineralogical, and ecological ranges, have revealed that marine organisms exhibit a wide range of calcification responses to CO2-induced ocean acidification, including positive, negative, parabolic, threshold, and neutral responses. Marine calcifiers build their shells and skeletons from various forms (polymorphs) of CaCO3, most commonly aragonite, high-Mg calcite, and low-Mg calcite. These polymorphs differ greatly in their solubility in seawater and, therefore, in their potential response to CO2-induced ocean acidification. X-ray diffraction analysis of shells secreted by the organisms investigated in the pilot study reveals that the proportion of calcite (the less soluble form of CaCO3) to aragonite (the more soluble form) within their shells increases under elevated pCO2, while the Mg:Ca ratio of their calcite declines. These observations suggested that some marine calcifiers may partially adapt to a declining CaCO3 saturation state by accreting a greater proportion of the less-soluble form of CaCO3 (low-Mg calcite) at the expense of the more soluble forms (aragonite, high-Mg calcite). However, it is likely that such mineralogical and compositional changes in the shells and skeletons of marine organisms would alter their structural and biomechanical properties. The project seeks to build upon the results of the pilot study by rearing a suite of benthic marine calcifiers under past (280 ppm), present (385 ppm), and predicted future (540, 840 ppm) pCO2 and under three distinct temperatures to investigate changes in: (1) their rates of calcification and linear extension; (2) the relative abundance and micron-scale distribution of the various CaCO3 polymorphs within their shells/skeletons; (3) the ultrastructure and crystal morphology of their shells/skeletons; and (4) their biomechanical properties. The research would also build upon the pilot experiments by utilizing a more thoroughly replicated study design, by more precisely constraining the chemical parameters of the experimental seawater treatments, by investigating calcification responses under 3 different temperature regimes, and by employing a "pre-industrial" pCO2 level (280 ppm). The results of the proposed research should advance our understanding of how benthic marine calcifiers shall respond to future CO2-induced changes in seawater temperature and CaCO3 saturation state. And by investigating the response of organisms over the range of atmospheric pCO2 that has occurred since late Paleozoic time, this research should inform our understanding of the putative links atmospheric pCO2, mass extinction events, and secular variation in the polymorph mineralogy of marine calcifiers throughout geologic time. Finally, comparison of the observed biological responses to variable pCO2-T scenarios with that already established for abiogenic carbonates will advance our understanding of the very mechanisms by which marine calcifiers build their shells and skeletons.BROADER IMPACTS: The results of the proposed research will inform the decisions of policy makers and legislators working to mitigate the impacts of CO2-induced warming and ocean acidification by establishing pCO2-T tolerances for a range of marine calcifiers. Results of the proposed research would be widely disseminated through peer-reviewed publication, conference presentations, public outreach, the PI's website, and mainstream media outlets. PI Ries is an early career scientist whose developing research program would be materially enhanced by the resources and activities afforded via the research. This research would also promote the education, training, and professional development of graduate students Ann Mooney (a native Pacific Islander) and Isaac Westfield, and postdoctoral fellow Karl Castillo (a native Belizean of African descent), two of whom belong to minority groups that are underrepresented in the marine sciences. Finally, the proposed research would create valuable training and educational experiences for several undergraduates conducting research under the PI.