Application of a novel geochemical approach to the alkalinity anomaly method of estimating coral reef calcification rates: implications of ocean acidification

最近人们意识到，由于人为吸收二氧化碳，表层海洋正变得越来越酸，由此导致的碳酸盐矿物饱和状态的降低导致包括珊瑚在内的许多生物的钙化率下降，因此迫切需要建立珊瑚礁的基线钙化率，以衡量未来的变化。测量珊瑚礁钙化的标准方法需要了解相对于近海源水的碱度损耗和水在珊瑚礁上的停留时间。为了计算停留时间，通常需要测量或模拟进出系统的水量。这可能需要大量的时间和金钱，并极大地限制了这种原本强大的方法的效用。在这个项目中，迈阿密大学的两名研究人员——一名珊瑚生态学家和一名放射性同位素地球化学家——将使用一种基于宇宙生成放射性同位素7Be的新型放射化学方法，通过一组简单的廉价测量来估计居住地。同位素7Be通过降雨在大气中输入海洋。降雨事件是自然的“示踪剂释放”实验，在浅水珊瑚礁水域，这种通量导致高度集中的7Be活动，而在近海水域，相同的通量分布在更深的混合层上，导致7Be活动低得多。有了输入通量（通过降水）的知识，这种活动对比的持续时间可以用来确定在1-20天的时间尺度上水在珊瑚礁上的停留时间。这是大多数珊瑚礁系统应该落在的范围。研究小组将采用这种方法来确定加勒比和西大西洋三个研究充分的珊瑚礁系统的钙化率在空间和时间上是如何变化的。更广泛的影响：在全球变暖和海洋酸化的影响下，珊瑚礁是最有可能最先出现压力迹象的生态系统之一。实验室研究表明，由于大气中二氧化碳的增加，珊瑚的钙化程度随着饱和状态的下降呈线性下降。然而，实验室研究也表明，当温度升高时，这种反应可能是非线性的。在未来的50-100年里，珊瑚礁的钙化率很有可能低于维持自身免受正常侵蚀力所需的阈值。为了确定气候变化的影响，需要新的方法来扩大珊瑚礁研究的时空覆盖范围，以便能够判断这些变化是否在全球范围内，是否与观测到的气候和海洋化学变化在时间上一致。该项目将以开发、应用和评估一种方法为特色，该方法将促进珊瑚礁代谢研究的概要性。顺便说一句，这是评估珊瑚礁系统污染事件冲刷的潜在工具，可能对修复工作有益。该项目还将资助一名研究生。这将是一个真正的跨学科机会，因为pi将能够提供地球化学示踪剂和珊瑚生态学方面的培训。

With the recent awareness that the surface oceans are becoming more acidic due to the uptake of anthropogenic CO2, and that the resulting decrease in the carbonate mineral saturation state causes a decline in the calcification rate of many organisms, including corals, there is a pressing need to establish baseline calcification rates of coral reefs against which future changes can be measured. The standard method for measuring coral reef calcification requires knowledge of the alkalinity depletion relative to the offshore source water and the residence time of the water over the reef. To compute the residence time it is generally necessary to measure or model the flux of water into and out of the system. This can require a great deal of time and money and greatly limits the utility of this otherwise powerful method.In this project, two researchers at the University of Miami -- a coral ecologist and a radioisotope geochemist -- will use a novel radiochemical method based on the cosmogenic radioisotope 7Be to estimate the residence from a simple set of inexpensive measurements. The isotope 7Be has an atmospheric input to the ocean via rainfall. Rainfall events act as natural "tracer release" experiments, whereby in shallow coral reef waters this flux results in a highly concentrated 7Be activity, while in offshore waters the same flux is distributed over a much deeper mixed layer resulting in a much lower 7Be activity. With knowledge of the input flux (via precipitation), the persistence of this activity contrast can be used to establish the residence time of water over the reef over a timescale of 1-20 days. This is the range within which most reef systems should fall. The team will employ the method to determine how calcification rate varies spatially and temporally at three well-studied reef systems in the Caribbean and Western Atlantic. Broader impacts: Coral reefs are one of the ecosystems most likely to show the first signs of stress in response to global warming and ocean acidification. Lab studies have shown that coral calcification declines linearly with the decline in saturation state that is resulting from the increase in atmospheric CO2. However, lab studies have also shown that the response can be non-linear when combined with rising temperature. There is a real possibility that calcification on coral reefs will fall below the threshold rate needed to sustain themselves against normal erosive forces in the next 50-100 years. In order to ascertain the impact of climate change new methods are needed to extend the spatial and temporal coverage of coral reef studies so that it can be judged whether the changes are global in scope and temporally coherent with observed changes in climate and ocean chemistry. This project would feature the development, application, and evaluation of a method that would advance the synopticity of reef metabolic studies. As an aside, this is a potential tool for evaluating flushing of pollution events over reef systems and could be beneficial in remediation efforts. The project will also support a graduate student. This will be a true interdisciplinary opportunity, as the PIs will be able to provide training in geochemical tracers and coral ecology.