Collaborative Research: RUI - Dissolution kinetics of biogenic calcium carbonates in the upper water column of the North Pacific

最近的各种研究表明，生物碳酸钙（CaCO3）在水柱中溶解的深度比传统认为的要浅。据推测，这是由于生物介导的过程和/或文石溶解的结果。此外，与工业化前的深度相比，海洋对人为CO2的吸收导致文石和方解石饱和层变浅，这意味着碳酸盐颗粒的溶解将随着时间的推移而增加。这对我们理解非稳态海洋碳循环具有重要意义。在这项研究中，加州州立大学圣马科斯分校、斯克里普斯海洋学研究所和南佛罗里达大学的研究人员将在模拟的原位温度和压力条件下，直接测量天然海水中新鲜生物碳酸盐的溶解速率。他们还将研究可能影响它们在上层水柱（1500米）内溶解的一些过程——包括生物介导的过程和仅仅依赖于总体二氧化碳浓度的过程。实验将使用球粒石藻（单细胞藻类）产生的CaCO3，球粒石藻分泌方解石板（球粒石），这些方解石板互锁形成细胞表面的覆盖物，而真体翼足类动物（软体动物）产生文石保护壳。在我们的北太平洋研究区，这些生物群几乎占了CaCO3出口通量的全部。跨学科的方法将建立在团队成员对碳酸盐生物学和化学的个人知识的基础上，并将采用包括放射性示踪剂、二氧化碳化学（包括专门为这项工作构建的高压pH细胞）和SEM在内的方法/测量的组合来记录和量化溶解。除了一系列严格控制的实验室实验外，该团队还将在CLIVAR重复线16N上进行实地研究，并在亚北极太平洋的加拿大P线时间序列上进行三次年度巡航，对新收集的样本进行实验，与我们的实验室研究平行。海上溶解测量系统在精度、样本量和原位饱和条件下的观测能力方面将具有最先进的能力。使用没有溶解历史的新鲜生物碳酸盐或有机保护涂层的降解，再加上两种高灵敏度的方法（分光光度pH测定和放射性45Ca），这些研究人员应该能够在接近平衡的条件下对上层海洋的溶解速率进行高质量的测量。就更广泛的影响而言，该项目将涉及与加拿大同事的国际合作。它还将为研究生和本科生的培训和支持提供经费。

A variety of recent work suggests that biogenic calcium carbonate (CaCO3) is dissolving at shallower depths in the water column than had been conventionally thought. It has been speculated that this is occurring as a result of biologically mediated processes and/or from the dissolution of aragonite. Moreover, the oceanic uptake of anthropogenic CO2 has resulted in the shoaling of the aragonite and calcite saturation horizons compared to pre-industrial depths, implying that the dissolution of carbonate particles will increase over time. This has significant implications for our understanding of the non-steady state marine carbon cycle.In this study researchers at the California State University at San Marcos, Scripps Institution of Oceanography, and the University of South Florida will measure dissolution rates of fresh biogenic carbonates directly in natural seawater under simulated in situ conditions of temperature and pressure. They will also investigate some of the processes - both biologically-mediated ones and those simply dependent on bulk CO2 concentrations - that may influence their dissolution within the upper water column (1500 m). The experiments will use CaCO3 produced by coccolithophores (single-celled algae) that secrete calcite plates (coccoliths) that interlock to form a covering on the cell surface and by euthecosomatous pteropods (molluscs) that produce protective shells of aragonite. These groups of organisms account for nearly all of the export flux of CaCO3 in our North Pacific study area.The interdisciplinary approach will build on the team members individual knowledge of both carbonate biology and chemistry and will employ a combination of methods/measurements involving radioactive tracers, CO2 chemistry including a high-pressure pH cell constructed especially for this work, and SEM to document and quantify dissolution. In addition to a series of rigorously controlled laboratory experiments, the team will conduct field studies on the CLIVAR repeat line 16N and on three annual cruises on the Canadian Line P time-series in the subarctic Pacific, performing experiments on freshly collected samples that parallel our laboratory studies. The at-sea dissolution measurement system will have state-of-the-art capabilities with respect to precision, sample size, and a capability for observation at in situ saturation conditions.The use of fresh biogenic carbonates with no prior dissolution history or degradation of organic protective coatings coupled with two highly sensitive methods (spectrophotometric pH determinations and radioactive 45Ca) should enable these researchers to make high-quality measurements of dissolution rates at near-equilibrium conditions that occur in the upper ocean.In terms of broader impacts, the project would involve international collaboration with Canadian colleagues. It would also make provision for the training and support of graduate and undergraduate (RUI) students.