NSFGEO-NERC: Quantifying the Modern and Glacial Ocean's Carbon Cycle Including Isotopes

海洋“S”碳循环是地球气候系统的重要组成部分，因为它影响大气中二氧化碳的浓度，二氧化碳是一种温室气体。然而，海洋中的碳循环目前还没有得到很好的理解，部分原因是它受到不同复杂的物理、化学和生物过程的影响。这使对海洋碳储量变化的量化变得复杂，例如当代海洋与最后一次冰川盛期(LGM，约21,000年前)之间的变化，并阻碍了对这种变化原因的机械论理解。以前的研究提出了几种解释末次盛冰期大气二氧化碳浓度较低的原因，包括海冰覆盖增加，深海环流更加缓慢，气温较低，以及浮游植物生长肥沃的粉尘携带的铁通量增加。该项目将提供一种新的数据约束量化这些过程，这将改善我们对过去变化的机械性理解，并可能提高对未来可能预测的理解。一名研究生将接受海洋学、生物地球化学和物理模型方面的培训。该项目将通过俄勒冈州农村初中和高中的25个课外科学、技术、工程和数学俱乐部为代表不足的学生提供支持。这将通过与教师合作，在他们的计划中开发和实施碳循环和气候科学课程来实现。这是一个由国家科学基金会地球科学理事会(NSF/GEO)和英国国家环境研究理事会(NERC)通过NSF/GEO-NERC牵头机构协议共同资助的项目。该协定允许美国和英国提交一个单一的联合提案，并由该机构进行同行审查，该机构的调查员在预算中所占比例最大。在成功地联合确定一项裁决后，每个机构将为与其本国有关的预算和调查员的比例提供资金。现代观测和古气候数据提供了大量有关碳循环变化的信息。这些数据，包括来自冰川沉积物的碳和氮同位素，将被用来约束现代和LGM海洋的基于过程的模型。将应用一种新开发的方法，将溶解的无机碳储存精确和完全地分解成预制的和生物再生的成分。预制碳进一步分为饱和和不平衡组分，每一组分都有物理和生物贡献。将使用微扰实验，其中一次改变一个变量(温度、海冰、环流、可溶铁通量)，并应用碳分解。将考虑循环、混合和生物地球化学方面的不确定性。将在模型中实施钚-钍比(Pa/Th)，并与现代和冰川沉积物数据进行比较，这将对海洋环流提供额外的限制。将研究海洋环流变化对不同碳组分的影响。分解将扩展到溶解氧和碳同位素(D13C)。将测试有关现代和冰川海洋碳储存的假设。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The ocean"s carbon cycle is an important part of Earth's climate system because it impacts the concentration of atmospheric carbon dioxide (CO2), which is a greenhouse gas. However, carbon cycling in the ocean is currently not well understood in part because it is influenced by different complex physical, chemical and biological processes. This complicates quantification of changes in ocean carbon storage such as those between the contemporary ocean and that of the Last Glacial Maximum (LGM, ~21,000 years ago) and hinders mechanistic understanding of the reasons for such changes. Previous studies have suggested several explanations for the lower atmospheric CO2 concentrations during the LGM including, increased sea ice cover, more sluggish deep ocean circulation, cooler temperatures and increased dust-borne iron fluxes that fertilized phytoplankton growth. This project will provide a novel data-constrained quantification of these processes, which will improve our mechanistic understanding of past changes, and may improve understanding of possible future projections. A graduate student will be trained in oceanography, biogeochemical and physical modeling. The project will support underrepresented students through more than 25 afterschool Science Technology Engineering and Mathematics clubs in rural Oregon middle and high schools. This will be achieved by working with teachers to develop and implement a carbon cycle and climate science curriculum into their programs. This is a project that is jointly funded by the National Science Foundation's Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own country. Modern observations and paleoclimate data provide a wealth of information on changes to the carbon cycle. These data including carbon and nitrogen isotopes from glacial sediments will be used to constrain process-based models of the modern and LGM ocean. A newly developed method will be applied that provides a precise and complete decomposition of dissolved inorganic carbon storage into preformed and biologically-regenerated components. Preformed carbon is further separated into saturation and disequilibrium components, each of which has physical and biological contributions. Perturbation experiments will be used in which one variable (temperature, sea ice, circulation, soluble iron fluxes) is changed at a time and the carbon decomposition is applied. Uncertainties in circulation, mixing, and biogeochemistry will be considered. Protactinium Thorium ratios (Pa/Th) will be implemented in the model and compared with modern and glacial sediment data, which will provide additional constraints on ocean circulation. Effects of ocean circulation changes on the different carbon components will be investigated. The decomposition will be extended to dissolved oxygen and carbon isotopes (d13C). Hypotheses regarding modern and glacial ocean carbon storage will be tested.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.