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，由于人为二氧化碳的吸收，表层海洋变得更加酸性，由此导致的碳酸盐矿物饱和状态的下降导致包括珊瑚在内的许多生物的钙化速度下降，因此迫切需要确定珊瑚礁的基准钙化速度，以此来衡量未来的变化。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消耗情况和珊瑚礁上水的停留时间。为了计算停留时间，通常需要测量或模拟进出系统的水的流量。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实用性。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放射性同位素7Be的新放射化学方法，通过一套简单而廉价的测量来估计居住地。同位素7Be通过降雨将大气输入海洋。降雨事件作为自然的“示踪剂释放”实验，在浅海珊瑚礁水域，这一通量导致高度集中的7Be活度，而在近海水域，相同的通量分布在更深的混合层上，导致7Be活度低得多。有了输入通量的知识(通过降水)，这种活动对比的持续性可以用来确定水在珊瑚礁上的停留时间，时间尺度为1-20天。这是大多数珊瑚礁系统应该落在的范围。该团队将使用这种方法来确定加勒比海和西大西洋三个经过充分研究的珊瑚礁系统的钙化率在空间和时间上的变化。更广泛的影响：珊瑚礁是最有可能在应对全球变暖和海洋酸化时表现出压力的第一批迹象之一。实验室研究表明，珊瑚的钙化程度随着大气中二氧化碳含量的增加而降低，呈线性下降。然而，实验室研究也表明，当与气温上升结合在一起时，这种反应可能是非线性的。珊瑚礁上的钙化确实有可能在未来50-100年内降到抵御正常侵蚀力所需的门槛速度以下。为了确定气候变化的影响，需要采用新的方法来扩大珊瑚礁研究的空间和时间范围，以便能够判断这些变化是否具有全球性，并在时间上与观测到的气候和海洋化学变化相一致。该项目的特点是开发、应用和评估一种方法，以促进珊瑚礁新陈代谢研究的同时性。顺便说一句，这是一种潜在的工具，可用于评估珊瑚礁系统上污染事件的冲洗情况，并可能有助于补救工作。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，因为私人投资机构将能够提供有关地球化学示踪和珊瑚生态学的培训。

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.