Carbonate preservation in pelagic sediments: Developing a new aragonite preservation proxy

海洋酸化被广泛地称为“另一个二氧化碳问题”。人为二氧化碳（CO2）的海洋入侵导致海水pH值降低，碳酸钙（CaCO3）饱和度降低。珊瑚钙化率随其周围水域CaCO3饱和状态的降低而降低。海洋浮游生物，如翼足类动物（也被称为海蝴蝶），当受到CaCO3不饱和海水的影响时，显示出外壳溶解的证据。与珊瑚类似，如果翼足类动物无法适应持续不饱和的水域，它们未来的地理分布可能会受到限制。虽然可以直接观察到海洋酸化对现代海洋中生物群的一些影响，但随着大气中人为二氧化碳的持续增加，预测变化的速度会有多快，以及生物将如何应对这些变化，这些都是挑战。利用地质记录重建过去海洋CaCO3的饱和状态，对于理解现代海洋酸化的潜在未来结果非常重要，因为它提供了碳酸盐系统的自然变异性和敏感性的记录，以及理解扰动的基线。这个项目由密歇根州格兰谷州立大学的一位教授领导，其目标是通过研究海洋沉积物中翼足类贝壳化石的保存情况，开发一种新的替代方法，来量化地球过去海洋酸化事件的程度和影响。深海沉积物中CaCO3保存的可靠定量指标将有助于识别由海洋酸化或碱化事件驱动的底栖生物（如珊瑚、钙化藻类）和浮游海洋群落（如翼足类、颗石藻、有孔虫）的地理和水文变化。这种代理还将有助于了解海洋环流变化、水团边界变化、海洋碳酸盐化学在千年时间尺度上的变化，以及其他可能导致CaCO3溶解的因素，如CaCO3和有机碳到深海的通量的变化。资金支持四名本科生进行数据生成、数据分析和向科学界传播结果。这项研究的结果通过外展活动和科学博客上的帖子向公众传播。

Ocean acidification is widely referred to as "the other CO2 problem." Marine invasion of anthropogenic carbon dioxide (CO2) causes reduced pH and lowers the calcium carbonate (CaCO3) saturation of seawater. Coral calcification rates decrease as the CaCO3 saturation state of their ambient waters decreases. Marine plankton such as pteropods (also known as sea butterflies) show evidence of shell dissolution when subjected to seawater under-saturated with respect to CaCO3. Similar to corals, if pteropods prove unable to adapt to living in continuously under-saturated waters, their geographic distribution may be limited in the future. While some of the effects of ocean acidification on biota in the modern ocean can be directly observed, forecasting how fast changes will occur as anthropogenic CO2 continues to increase in the atmosphere and how organisms will respond to these changes presents challenges. Reconstructing the marine saturation state of CaCO3 in the past, using the geological record, is important for understanding the potential future outcomes of modern ocean acidification because it provides a record of natural variability and sensitivity of the carbonate system, and a baseline from which to understand perturbations.The goal of this project, led by a professor at Grand Valley State University in Michigan, is to develop a new proxy for quantifying the degree and effect of ocean acidification events in Earth's past by studying the preservation of fossilized pteropod shells in marine sediments. A reliable and quantitative indicator of CaCO3 preservation in deep sea sediments will help discern geographic and hydrographic shifts in benthic (e.g. corals, calcifying algae) and planktonic ocean communities (e. g. pteropods, coccolithophores, foraminifers) driven by ocean acidification or alkalization events. Such a proxy will also aid in understanding ocean circulation changes, water mass boundary changes, changes in ocean carbonate chemistry on millennial timescales, and other factors that may cause dissolution of CaCO3 such as changes in fluxes of CaCO3 and organic carbon to the deep sea. Funding supports four undergraduates in data generation, data analysis, and dissemination of results to the scientific community. The results of this study are disseminated to the public in outreach events and postings on science blogs.