Collaborative Research: New approaches to study calcium carbonate dissolution on the sea floor and its impact on paleo-proxy interpretations

海洋对人为CO2的吸收最终将因CaCO3在海底的溶解而减轻。溶解是用于气候预测的模型中碳循环的一个重要组成部分，尽管它发生的位置（水柱与沉积物）的相对重要性以及所涉及的速率和过程尚未完全了解。这项雄心勃勃的实地和实验室研究旨在提高我们对控制深海沉积物中碳酸盐溶解/保存的重要因素的认识。该项目将使用一种新的示踪方法和多种现场取样策略，调查海底溶解速率、其动力学控制因素、溶解发生的沉积物深度、颗粒有机碳氧化所起的作用以及固相蚀变的影响，以便使用基于地球化学的古海洋学代用指标。该项目将促进海底着陆器技术的进一步发展，并提供有关海底状况与碳酸盐溶解速度的关键信息，从而有助于限制海洋中和海洋酸化影响的速度。研究生和本科生将接受培训，研究团队将通过与洛杉矶自然历史博物馆的合作，利用电影和动画将这项工作带给更广泛的观众，研究团队开发了一种新的方法，基于13-C标记的碳酸盐基质来量化碳酸钙溶解速率，该技术明显比基于碱度和/或钙测量的传统方法更灵敏。这为碳酸钙溶解的控制机制和速率开辟了一系列新的机会和见解，碳酸钙溶解是一个具有挑战性的长期地球化学问题。海底碳酸盐溶解率将通过碱度和钙的底栖室通量测量以及TCO2和碱度及其同位素组成的孔隙水模型直接评估。有机碳矿化的潜在影响将通过氧和养分通量测定、孔隙水梯度和建模来测量。标记的13C-富集方解石将作为一个示踪剂的近表面溶解过程时，添加到底栖室和下芯溶解过程中使用13C-标记棒插入到沉积柱。这些标记碳酸盐溶解的原位实验将是此类实验中的第一个。为了补充这些测量，该小组将继续开发一种基于根茎的孔隙水采样器，该采样器在所有海洋深度的多芯取样器上工作。将在巴拿马和加拉帕戈斯之间水柱从过饱和到欠饱和的一个样带中的4 - 6个地点进行海上实地试验。溶解速率的测量，再加上阳离子/钙比在碳酸钙有孔虫壳的分析，将有助于校准溶解古代理解释的影响。此外，沉积物方解石和文石馏分的分析将有助于解释净溶解和沉积物随时间的响应。这项研究的结果应该有助于更好地参数化海洋气候模型（GCM），这对预测海洋酸化的后果和古海洋记录的建模具有重要意义的沉积物变量。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审查标准进行评估，被认为值得支持。

The uptake of anthropogenic CO2 by the ocean will eventually be mitigated by the dissolution of CaCO3 on the sea floor. Dissolution is an important component of the carbon cycle in models used for climate projections though the relative importance of where it occurs (water column versus sediments) and the rates and processes involved are not fully understood. This ambitious field and laboratory study is designed to advance our knowledge of the important factors that control carbonate dissolution/ preservation in deep ocean sediments. Using a novel tracer approach and multiple in situ sampling strategies, the project will investigate sea floor dissolution rates, their kinetic controlling factors, the depth in sediments at which dissolution occurs, the role that oxidation of particulate organic carbon plays, and the ramifications of solid phase alteration for the use of geochemically-based paleoceanographic proxies. The project will foster further development of benthic lander technology and yield key information relating sea floor conditions to carbonate dissolution rate, thereby helping to constrain the rate at which the ocean can neutralize the impacts of ocean acidification. Graduate and undergraduate students will be trained and the research team will use film and animation to bring this work to a broader audience through a collaboration with the Los Angeles Natural History Museum.The research team has developed a new approach to quantify calcium carbonate dissolution rates based on 13-C labeled carbonate substrates, a technique which is significantly more sensitive than traditional approaches based on alkalinity and/or calcium measurements. This has opened a range of new opportunities and insights into the governing mechanisms and rates of calcium carbonate dissolution, a challenging and long-standing geochemical problem. Carbonate dissolution rates on the sea floor will be directly assessed by benthic chamber flux measurements of alkalinity and calcium as well as pore water models of TCO2 and alkalinity and their isotopic composition. The potential impacts of organic carbon remineralization will be measured through oxygen and nutrient flux determinations, pore water gradients and modeling. Labeled 13C-enriched calcite will serve as a tracer of near surface dissolution processes when added to benthic chambers and of down-core dissolution processes using 13C-labeled rods inserted into the sediment column. These in situ experiments of labeled carbonate dissolution will be the first of their kind. To complement these measurements, the team will continue development of a rhizon-based pore water sampler that works on a multi-corer at all ocean depths. Field experiments will be conducted at sea at 4-6 sites in a transect through water column supersaturation to undersaturation between Panama and the Galapagos. Dissolution rate measurements, coupled with analyses of cation/Ca ratios in CaCO3 foraminiferal shells will help calibrate the impact of dissolution on paleo-proxy interpretations. Further, analyses of sediment calcite and aragonite fractions will help explain net dissolution and sediment response with time. The results from this study should help to better parameterize sediment variables in ocean-climate models (GCMs), which has important implications for predicting the consequences of ocean acidification and the modeling of paleoceanographic records. The methodologies and new techniques will surely be adopted by other researchers, therefore impacting the larger geochemical community.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.