A Least-Squares Fit of an Ocean Model to Deglacial Radiocarbon Records

海洋模型与冰下放射性碳记录的最小二乘拟合

• 批准号: 1702417
• 负责人: Olivier Marchal
• 金额: $ 49.3万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1702417&HistoricalAwards=false
• 关键词: Least; Squares; Fit; Ocean; Model

The deep ocean is renewed, or "ventilated", when surface waters present at high latitudes become sufficiently cold and very dense. These waters subsequently spread laterally, filling the various deep oceanic basins, and eventually return to the sea surface. Ventilation is therefore the very process by which the deep ocean communicates with our atmosphere and as such, is thought to play a particularly important role in the climate system. This project will estimate the changes in deep ocean ventilation which took place during the last deglaciation -- the largest manifestation of natural climate change that remains relatively well preserved in the geologic record. It will (i) promote the progress of science by elucidating the contribution of ocean ventilation changes to the deglacial rise in atmospheric concentration of carbon dioxide (CO2) observed in ice cores, (ii) be profitable to the broader scientific community by making freely available the computer codes developed for this project, (iii) support education by engaging three students and by drafting a little pocket book on the methods used for this project and aimed particularly at undergraduate and graduate students, and (iv) benefit society by furthering understanding of the ocean's role in the natural changes of atmospheric CO2 -- the most important greenhouse gas in our atmosphere after water vapor and the subject of major current environmental and societal concerns.In more technical terms, the history of the ventilation of deep oceanic basins over the past 20,000 yr will be estimated from the quantitative combination of ocean radiocarbon (14C) records with an ocean circulation model using recursive least-squares techniques (a Kalman filter and a related smoother). The challenge posed by the application of these powerful but computationally intensive techniques over geologic time scales will be addressed by using a coarse-resolution model with simplified dynamics in concert with efficient filtering and smoothing algorithms. The hypothesis that ocean ventilation changes contributed to the changes in atmospheric CO2 concentration of the last deglaciation will be tested with due regard for the uncertainties and sparse distribution of the radiocarbon records. The work plan of this research will comprise four tasks. (1) An ocean circulation model of intermediate complexity, based on coarse resolution and planetary geostrophy, will be applied. It will have a grid that accommodates the spatial distribution of 14C records and include a simplified sea-ice model and transport equation for 14C. (2) Modern and paleo-data, including more than 1000 14C age estimates from benthic foraminifera and deep-sea corals, will be assembled together with uncertainty estimates. (3) A Kalman filter will be used to combine the model with the data during a forward integration of the model from the Last Glacial Maximum (LGM) to today. (4) A smoother will be used to propagate backwards in time the information provided by the data (including modern data) and hence further constrain past ocean states. From (3-4), an estimate of basin-scale ocean ventilation rates from LGM to today will be derived, one that is consistent with the data and the model, given estimates of their respective error statistics.

当存在高纬度的地表水变得足够冷且非常稠密时，深海被更新或“通风”。这些水随后横向散布，充满了各种深海盆地，并最终返回海面。因此，通风是深海与我们的气氛进行交流的过程，因此被认为在气候系统中起着特别重要的作用。该项目将估计在最后一次脱气期间发生的深海通风的变化 - 自然气候变化的最大表现，在地质记录中仍然相对保存得很好。它将（i）通过阐明在冰芯中观察到的二氧化碳（CO2）的大气浓度的脱气浓度的贡献来促进科学的进步，（ii）通过为该项目提供了尤其是在该项目中开发的，该项目通过涉及该项目的范围，从而使更广泛的科学社区获利，并通过在该项目中开发了几乎没有零件的方法，该计划是通过在零件上进行的。和研究生，以及（iv）通过进一步了解海洋在大气变化中的作用来使社会受益，这是水蒸气后我们大气中最重要的温室气体，并且是当前主要的环境和社会关注的主题。在更多的技术术语中，在过去的20,000亿元循环中估计了海洋循环的通风（在过去的20,000层）中，是海洋循环的通风（估计海洋循环）的历史（递归最小二乘技术（Kalman滤波器和相关的更顺畅）。这些功能强大但计算密集型技术在地质时间尺度上的应用所带来的挑战将通过使用具有高效过滤和平滑算法的简化动力学的粗分辨率模型来解决。海洋通风变化的假设有助于对最后一次脱位的大气二氧化碳浓度的变化进行测试，以适当考虑放射性碳记录的不确定性和稀疏分布。这项研究的工作计划将包括四个任务。 （1）将采用基于粗分辨率和行星地球植物的中间复杂性的海洋循环模型。它将具有一个网格，可容纳14C记录的空间分布，并包括14C的简化海冰模型和传输方程。 （2）现代和古数据，包括底栖有孔虫和深海珊瑚的1000多个14c年龄估计，将与不确定性估计一起组装。 （3）在模型从最后一个冰川最大（LGM）到今天的模型的正向集成期间，将使用Kalman滤波器将模型与数据相结合。 （4）将使用更顺畅的人来及时向后传播数据（包括现代数据）的信息，因此进一步限制了过去的海洋国家。从（3-4）开始，将得出盆地规模的海洋通风率从LGM到今天的估计，鉴于其各自的误差统计数据的估计，它与数据和模型是一致的。