Calcium Carbonate Dissolution Mechanisms in the Ocean

碳酸钙在海水中溶解的速度是海洋碳循环的重要组成部分。它是海洋吸收化石燃料二氧化碳能力的关键因素。它对了解和预测海洋酸化也很重要，并可能在遏制气候变化的新技术中发挥作用。尽管这一重要性，很多仍然是不确定的机制和碳酸钙的溶解速度。该项目将使用新方法进行实验室实验，研究碳酸钙在几种不同条件下的溶解。该项目将支持两名早期职业调查员，包括一名研究生。结果将与公众分享，包括通过动画艺术家的支持。在以前的工作中，该团队及其合作者对我们对海洋中碳酸盐溶解速率规律的理解进行了一些改进。在实验室中使用一种新的碳同位素示踪技术，并在水柱中原位，他们可以比其他技术灵敏20- 200倍地测量溶解速率。这在接近平衡时尤其如此，那里的速率很慢，但也是大多数海洋所在的地方。他们之前的工作表明，速率定律在表面溶解机制的三种不同模式之间有两个临界阈值：在接近平衡时，溶解随着台阶边缘的推进而进行;随着进一步的欠饱和，溶液中的自由能在晶格缺陷处打开快速溶解的蚀坑固体;在离平衡最远的地方，蚀刻坑开始均匀地形成在2-D固体表面上，导致最大的溶解速率。然而，理解的充分化学控制的速率定律，其相互作用与这些表面充满活力的功能尚未确定。该项目将寻求实验和理论上限制海洋碳酸盐溶解速率定律背后的机制。饱和状态将作为化学的其他方面的函数而系统地改变，以测试多年来已成功用于描述淡水中溶解的基元反应。在独立实验中，饱和状态将在硫酸盐浓度、钙/碳酸盐比率和镁/钙比率的范围内变化。原始数据的初始时间依赖性，实验固体的西姆斯微探针剖面将允许确定总沉淀和总溶解速率，并结合溶解碳同位素比随时间变化的斜率的净速率限制。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响进行评估，被认为值得支持审查标准。

The rate at which calcium carbonate dissolves in seawater is an important piece of the ocean carbon cycle. It is a key factor in the oceans’ ability to absorb fossil fuel carbon dioxide. It is also important to understanding and predicting ocean acidification and may play a role in new technologies to curb climate change. Despite this importance, a great deal remains uncertain about the mechanism and rate of calcium carbonate dissolution. This project will conduct laboratory experiments using new methods to study calcium carbonate dissolution at several different conditions. The project will support two early-career investigators including a graduate student. Results will be shared with the public, including through support of an animation artist. In previous work, this team and their collaborators have made several improvements to our understanding of the carbonate dissolution rate law in the ocean. Using a novel carbon isotope tracer technique in the lab, and in situ in the water column, they can measure the dissolution rate 20-200x more sensitively than other techniques. This is especially true near equilibrium where rates are slow, but also where most of the ocean resides. Their previous work demonstrated that the rate law has two critical thresholds between three separate modes of surface dissolution mechanisms: near equilibrium, dissolution proceeds as the advance of step edges; with further undersaturation, the free energy in solution opens fast-dissolving etch pits at lattice defects in the solid; furthest from equilibrium, etch pits begin to form homogeneously on the 2-D solid surface leading to maximal dissolution rates. However, understanding of the full chemical control on the rate law, and its interplay with these surface energetic features has yet to be determined. This project will seek to experimentally and theoretically constrain the mechanism behind the rate law for marine carbonate dissolution. The saturation state will be systematically changed as a function of other aspects of the chemistry to test the elementary reactions that have been successfully used for years to describe dissolution in freshwaters. The saturation state will be varied over a range of sulfate concentrations, calcium/carbonate ratios, and magnesium/calcium ratios in independent experiments. Both the initial time dependence of the raw data, and SIMS microprobe profiles of the experimental solids will allow determination of the gross precipitation and gross dissolution rates in conjunction with the net rate constraints from slopes of dissolved carbon isotope ratios produced versus time.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.