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

人类向大气排放二氧化碳造成的海洋酸化最终将由沉积碳酸盐溶解来平衡。然而，该反应的时间常数为ca。六千年。因此，在未来几十年，海洋对二氧化碳吸收的反应将基于供应和去除的动力学，而不是系统的热力学。不幸的是，我们对海洋中碳酸盐溶解的基本速率定律缺乏了解。速率定律的阶数仍然被认为是从1到4.5的任何地方;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。文石与方解石溶解的相对重要性，矿物中镁含量的影响，以及有机质作用的标志在现代海洋中仍然是未知的。当然，一个真正有用的速率定律将能够将所有这些因素的相对重要性联合收割机组合成一个预测规则，以预测溶解将如何对海洋酸化作出反应。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组新的实验室和原位实验来解决这个问题，这些实验使用13 C示踪剂标记的生物碳酸盐来测量在广泛的饱和状态下的溶解速率。 他们将收集一套规则，这些规则将控制碳酸盐在下沉颗粒和海洋沉积物中的溶解。这将需要两个次级项目。首先，他们将在实验室中培养几种不同种类的生物碳酸盐生产者，并在强烈的13 C标记的影响下进行。在CaCO 3中富集约30，000 o/oo，他们将在专门建造的高压反应室中在1-2周内的几个时间点测量DI 13 C的变化。原型室的建设完成，它提供了手段，第一次，通过改变海水化学，压力和温度独立控制碳酸盐饱和状态。纯13 C标记的无机碳酸钙的实验将提供无机参考框架，我们的生物碳酸盐的结果。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尼斯金瓶式反应器中使用标记的生物源颗粒，该反应器可部署在常规水力钢丝上。Niskin DIC中13 C在1-2天内的累积将提供与对同类材料进行的更广泛的实验室研究直接相当的初始速率。使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应该允许团队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。制定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影响。这种速率定律位于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，并通过乔纳森·埃雷兹和他的学生的参与促进美以合作。在科学/海洋学研究的代表性不足的高中学生的具体参与是建立在这个项目的努力，以及正在进行的努力，由两个PI传播他们的科学，以广泛的非科学观众。

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.