Effects of acidification and warming on long-term ocean carbon cycling constrained by observations

与海洋酸化相关的化学变化将使重要的海洋物种（如颗石藻、有孔虫和翼足类动物）更难构建它们的碳酸钙（CaCO3）身体部位，而现有的CaCO3将更容易溶解。因此，酸化可能会减少未来海洋中碳酸钙的产生。另一方面，较高的温度导致更快的代谢率，这可能会增加初级和CaCO3的产生。表层海水比深层海水变暖得更快，导致分层增加，而进入阳光照射的表层海洋（光区）的营养物质输入减少。这可能导致浮游生物种类组成的变化，有利于球石藻，从而增加CaCO3的产量。由于CaCO3与有机颗粒的聚集和结合，CaCO3产量的任何变化也可能影响从海洋表面到深海的有机碳通量。本研究利用一种经改进的模型，对现有观测资料进行校准，考察了这些影响在长时间尺度（数百至数千年）上对未来全球CaCO3生产和碳循环的相对重要性。CaCO3的产生增加了大气CO2，因此其未来的演变可能是对气候的重要反馈。该反馈的符号和不确定性将被评估。现有的适合千年时间尺度模拟的全球海洋生物地球化学循环模型将通过增加一个基于过程的粒子聚集和下沉公式而得到改进。该模型将考虑CaCO3的两种矿物形式，方解石和文石，以及蛋白石、陆源和有机物质作为聚集体的组成部分。微粒有机碳（POC）的全球数据集将通过分析和校准大容量过滤测量、瓶子、传输计和卫星数据（包括误差估计）来创建。该数据集将与大量现有的其他全球尺度生物地球化学观测数据一起用于校准模型，并估计不确定参数以及(a)海洋酸化对CaCO3产生的影响和(b)颗粒聚集的不同结构公式。将应用贝叶斯数据同化方案，该方案旨在量化有关降雨比控制的三种假设机制（从透光区输出的CaCO3 / POC）。将进行概率预测，以量化每种机制对长期海洋碳循环的影响及其对大气二氧化碳浓度的反馈。将评价现有观测对预估的约束能力。该项目旨在更好、更定量地了解控制海洋中CaCO3和碳的全球循环及其耦合的多变量过程。在广泛使用的中等复杂地球系统模型中改进海洋生物地球化学循环将增强研究和教育的基础设施。改进后的模型将向公众开放，有利于未来对长期碳循环过程的研究，如对人为影响或古气候的研究。全球POC数据集也将向公众开放。将以气候变化和海洋酸化为主题，组织为期3天的K-12教育工作者研讨会。通过改进对人为碳排放对海洋生物地球化学循环影响的评估（包括不确定性），社会可能从该项目的成果中受益。

The chemical changes associated with ocean acidification will make it more difficult for important marine species (such as coccolithophores, foraminifera, and pteropods) to build their calcium carbonate (CaCO3) body parts, and existing CaCO3 will dissolve more easily. Thus acidification will likely decrease the production of CaCO3 in the future ocean. Warmer temperatures, on the other hand, lead to faster metabolic rates, which will likely increase primary and CaCO3 production. Faster warming of surface waters than deeper waters leads to increased stratification and less nutrient input into the sunlit surface ocean (photic zone). This may cause shifts in plankton species composition favoring coccolithophores and thus increasing CaCO3 production. Any change in CaCO3 production may also affect organic carbon fluxes from the surface to the deep ocean due to the aggregation and association of CaCO3 with organic particles. This research examines the relative importance of these effects on future global CaCO3 production and carbon cycling on long time scales (hundreds to thousands of years) using an improved model calibrated with existing observations. CaCO3 production increases atmospheric CO2, thus its future evolution may be an important feedback on climate. The sign and uncertainty of this feedback will be evaluated.An existing global model of ocean biogeochemical cycles suitable for millennial time scale simulations will be improved by adding a process based formulation of particle aggregation and sinking. The model will consider two mineral forms of CaCO3, calcite and aragonite, as well as opal, terrigenous, and organic matter as components of the aggregates. A global dataset of particulate organic carbon (POC) will be created by analyzing and calibrating large volume filtration measurements, bottle, transmissometer and satellite data including error estimates. This dataset, together with a large array of existing other global-scale biogeochemical observations will be used to calibrate the model and estimate uncertain parameters as well as different structural formulations of (a) the effect of ocean acidification on the production of CaCO3 and (b) particle aggregation. A Bayesian data assimilation scheme, designed to quantify three hypothetic mechanisms regarding the control of the rain ratio (CaCO3 over POC export from the euphotic zone), will be applied. Probabilistic projections will be carried out to quantify the effect of each mechanism on long term ocean carbon cycling and its feedback on atmospheric CO2 concentrations. The ability of the existing observations to constrain the projections will be evaluated. The project aims to lead to a better, more quantitative understanding of multi-variable processes that control global cycling of CaCO3 and carbon in the ocean and their coupling. Improving ocean biogeochemical cycling in a widely used Earth System Model of intermediate complexity will enhance infrastructure for research and education. The improved model will be made publicly available and benefit future research of long-term carbon cycle processes such as studies of anthropogenic effects or paleoclimate. The global POC dataset will also be made publicly available. A 3-day workshop for K-12 educators will be organized with climate change and ocean acidification as its main topics. Society may benefit from the outcome of this project through an improved assessment (including uncertainties) of the effects of anthropogenic carbon emissions on ocean biogeochemical cycles.