Collaborative Research: Experimental Investigations of Coral Biomineralization: Understanding the Biomineralization Response to Ocean Acidification

地球大气中二氧化碳(CO2)浓度的上升正在改变海洋的碳酸盐化学。模型表明，随着二氧化碳水平在下个世纪继续上升，地表水碳酸盐离子浓度可能会比工业化前的水平下降近50%。在实验室研究中，海洋钙化生物的多个分类群对海水碳酸盐浓度的变化表现出高度的敏感性。珊瑚的反应尤其有据可查：在受控的实验条件下，随着海水碳酸盐离子浓度的降低，珊瑚的钙化率显示出可测量的下降。这些观察结果对面对全球变化的珊瑚礁生态系统的健康和生存能力具有重大影响。然而，由于我们对珊瑚钙化的基本机制知之甚少，对珊瑚钙化对下个世纪海水饱和状态变化的响应的预测是有限的。例如，考虑到目前珊瑚生物矿化的模型，钙化对外部碳酸盐离子浓度的变化表现出任何敏感性是令人费解的。为了解答这个谜题，来自伍兹霍尔海洋研究所和迈阿密大学罗森斯蒂尔海洋与大气科学学院的科学家们将解决两个关键问题：(1)发生晶体生长的内部钙化流体的饱和状态(S)是什么，它如何响应外部海水碳酸盐浓度的变化？(2)藻类共生体是否与珊瑚钙化对海水碳酸盐的敏感性有关？他们还将测试一种假设，即文石成核在蛋白质的催化下，发生在接近环境饱和的水平，是珊瑚矿化循环中对pH敏感的步骤。PIS将进行一系列实验室降水和珊瑚培育实验，旨在加深我们对珊瑚如何钙化的了解，并为预测珊瑚对海洋酸化的反应奠定基础。他们将利用微米和纳米尺度的晶体形态，以及由虫黄藻类和偶氮黄藻类珊瑚附着的文石晶体的地球化学特征，来解释钙化空间内的条件。在更广泛的影响中，跨学科研究将通过阐明建造珊瑚礁的基本机制以及未来气候变化对具有巨大经济和科学意义的生态系统的潜在影响，使社会受益。他们的发现也将对解释珊瑚和其他生物骨骼中的稳定同位素代用品(d18O，d11B)具有更广泛的意义。PIS还将指导学生并继续其广泛的外展计划

Rising concentrations of carbon dioxide (CO2) in Earth's atmosphere are changing the carbonate chemistry of the ocean. Models indicate that as CO2 levels continue to rise over the next century, surface water carbonate ion concentration may decrease by almost 50% relative to pre-industrial levels. In laboratory studies, multiple taxa of marine calcifying organisms exhibit high sensitivity to changes in seawater carbonate concentration. The response of scleractinian corals is particularly well documented: under controlled experimental conditions, coral calcification rates show a measurable decline with decreasing seawater carbonate ion concentration. These observations have significant implications for the health and survivability of coral reef ecosystems in the face of global change. Predictions of the response of coral calcification to changes in seawater saturation state expected over the next century are limited however, by how little we know of the fundamental mechanisms of coral calcification. For instance, that calcification displays any sensitivity at all to changes in external carbonate ion concentration is puzzling, given current models of coral biomineralization. To answer this puzzle, scientists from Woods Hole Oceanographic Institution and Rosenstiel School of Marine and Atmospheric Science at the University of Miami will address two key questions: (1) What is the saturation state(s) of the internal calcifying fluid in which crystal growth occurs and how does it respond to changes in external seawater concentrations of carbonate? (2) Are algal symbionts implicated in the sensitivity of coral calcification to seawater carbonate? They will also tests the hypothesis that aragonite nucleation, catalyzed by proteins, and occurring at near ambient saturation levels, is the pH-sensitive step in the coral mineralization cycle. The PIs will conduct a series of laboratory precipitation and coral culturing experiments designed to increase our understanding of how corals calcify, and to lay the groundwork for predictions of the coral response to ocean acidification. They will utilize micro- and nanoscale crystal morphology, and geochemical signatures of aragonite crystals accreted by zooxanthellate and azooxanthellate corals, to interpret conditions within the calcifying space. Among the broader impacts, the interdisciplinary research will benefit society by elucidating the fundamental mechanisms by which coral reefs are built and the potential impacts of future climate changes on ecosystems of enormous economic and scientific importance. Their findings also will have broader implications for interpretation of stable isotope proxies (d18O, d11B) in coral and other biogenic skeletons. The PIs will also mentor students and continue their extensive outreach programs