Ocean Acidification - Collaborative Research: Measuring the kinetics of CaCO3 dissolution in seawater using novel isotope labeling, laboratory experiments, and in situ experiments

人为向大气排放二氧化碳造成的海洋酸化最终将由沉积的碳酸盐溶解来平衡。然而，这种反应的时间常数约为6000年。因此，在未来的几十年里，海洋对二氧化碳吸收的反应将基于供给和去除的动力学，而不是基于系统的热力学。不幸的是，我们对海洋中碳酸盐溶解的基本速率规律还缺乏了解。速率定律的阶数仍然被认为在1到4.5之间；这个范围代表了系统对饱和状态微小变化的灵敏度的主要差异。文石和方解石溶解的相对重要性，矿物中Mg含量的影响，以及有机物作用的标志，在现代海洋中都是未知的。当然，一个真正有用的速率定律将能够把所有这些因素的相对重要性结合起来，形成一个关于溶解如何对海洋酸化作出反应的预测规则。在这项研究中，加州理工学院和南加州大学的研究人员将通过一套新的实验室和原位实验来解决这个问题，这些实验使用13C示踪剂标记生物碳酸盐来测量各种饱和状态下的溶解速率。他们将整理出一套规则来控制碳酸盐在下沉颗粒和海洋沉积物中的溶解。这将需要两个子项目。首先，他们将在实验室中在强13C标签的影响下培养几种不同种类的生物碳酸盐生产者。在CaCO3富集约30,000o/o的情况下，他们将在专门建造的高压反应室中测量DI13C在1-2周内几个时间点的变化。原型室的构建完成，首次提供了通过独立改变海水化学、压力和温度来控制碳酸盐饱和状态的手段。用纯13C标记的无机CaCO3实验将为我们的生物碳酸盐实验结果提供无机参考框架。其次，为了检查基于实验室的速率数据，他们还将在一个简单的Niskin瓶反应器中使用标记的生物颗粒，该反应器将部署在常规的水线上。Niskin DIC中13C在1-2天内的积累将提供一个与同类材料的更广泛的实验室研究直接可比的初始速率。利用圣佩德罗盆地作为这些原位实验的试验台，将在一系列为期3天的巡航中对一系列饱和状态进行采样。这种高灵敏度的方法将使研究小组能够在二氧化碳浓度上升的情况下，解开海水中碳酸盐溶解的各种成分。更广泛的影响。建立一个更好的碳酸盐溶解速率定律将对海洋化学、海洋生物学、古海洋学以及对海洋酸化的潜在社会反应等领域产生广泛的影响。这个速率定律是海洋碳酸盐循环的核心。此外，这项工作将使至少两名研究生受益，并通过Jonathan Erez和他的学生的参与促进美以合作。在本项目的努力中，充分考虑了代表性不足的高中生对科学/海洋学研究的具体参与，以及两个pi正在进行的向广泛的非科学受众传播其科学的努力。

Ocean acidification by anthropogenic CO2 emissions to the atmosphere will ultimately be balanced by sedimentary carbonate dissolution. The time constant for this reaction, however, is ca. 6,000 years. So, in the coming decades, the ocean's response to CO2 uptake will be based on the kinetics of supply and removal, not on the thermodynamics of the system. Unfortunately our understanding of the basic rate law for carbonate dissolution in the ocean is lacking. The order of the rate law is still argued to be anywhere from 1 to 4.5; this range represents a major difference in the sensitivity of the system to small changes in saturation state. The relative importance of aragonite vs. calcite dissolution, the influence of Mg content in the minerals, and the sign of the role of organic matter are all still unknowns in the modern ocean. Of course, a truly useful rate law would be able to combine the relative importance of all of these factors into a predictive rule for how dissolution will respond to ocean acidification. In this study, researchers at the California Institute of Technology and the University of Southern California will address this problem with a novel set of laboratory and in situ experiments that use 13C tracer labeled biogenic carbonates to measure the dissolution rate under a wide range of saturation states. They will assemble a set of rules that will govern carbonate dissolution in sinking particles and in marine sediments. This will require two sub-projects. First, they will culture several different species of biogenic carbonate producers in the lab under the influence of a strong 13C label. With enrichments of around 30,000o/oo in the CaCO3, they will measure the change in DI13C at several time points over 1-2 weeks in specially built high-pressure reaction chambers. The construction of a prototype chamber is completed and it provides the means, for the first time, to control carbonate saturation state by changing seawater chemistry, pressure, and temperature independently. Experiments with pure 13C labeled inorganic CaCO3 will provide the inorganic reference frame for our biogenic carbonate results. Secondly, to check the lab-based rate data, they will also use labeled biogenic particles in a simple Niskin bottle based reactor that will be deployable on regular hydrowire. The accumulation of 13C in the Niskin DIC over 1-2 days will provide an initial rate that is directly comparable to the more extensive laboratory study on the same sorts of materials. Using the San Pedro Basin as a test bed for these in situ experiments will sample a range of saturation states in a series of 3-day cruises. This high-sensitivity approach should allow the team to unpack the various components of carbonate dissolution in seawater under rising CO2 concentrations. Broader Impacts. Producing a better rate law for carbonate dissolution will have broad implications for the fields of marine chemistry, marine biology, paleoceanography, and for potential societal response to ocean acidification. This rate law sits at the heart of the marine carbonate cycle. In addition, this work will benefit at least two graduate students and promote US-Israel collaborations via the inclusion of Jonathan Erez and his students. The specific involvement of underrepresented high school students in scientific/oceanographic research is built into the efforts of this project as well as ongoing efforts by both PIs to communicate their science to a broad array of non-scientific audiences.