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.

当高纬度地区的表层沃茨变得足够冷和密度很大时，深海就被更新或“通风”。这些沃茨随后横向扩散，充满各个深海盆地，并最终返回海面。因此，通风是深海与大气层沟通的过程，因此被认为在气候系统中发挥着特别重要的作用。该项目将估计最后一次冰川消退期间发生的深海通风变化----这是自然气候变化的最大表现形式，在地质记录中保存相对完好。它将（一）通过阐明海洋通风变化对冰消期在冰芯中观测到的大气二氧化碳浓度上升的作用，促进科学进步，（二）通过免费提供为该项目开发的计算机代码，使更广泛的科学界受益，（iii）支持教育，让三名学生参与，并起草一本关于该项目所用方法的袖珍小册子，特别针对本科生和研究生，以及（iv）通过进一步了解海洋在大气二氧化碳自然变化中的作用来造福社会--二氧化碳是大气中仅次于水蒸气的最重要的温室气体，也是当前环境和社会关注的主要问题。将利用递归最小二乘法（卡尔曼滤波器和相关的平滑器）将海洋放射性碳（14 C）记录与海洋环流模型定量结合，估计过去20 000年深海盆地的通风历史。这些强大的，但计算密集型的技术在地质时间尺度上的应用所带来的挑战，将通过使用一个粗略的分辨率模型与简化的动态与高效的滤波和平滑算法相结合来解决。假设海洋通风的变化有助于在大气中的CO2浓度的变化的最后一次冰消期将进行测试，适当考虑的不确定性和稀疏分布的放射性碳记录。这项研究的工作计划将包括四项任务。(1)将应用基于粗分辨率和行星地转的中等复杂性海洋环流模型。它将有一个网格，容纳14 C记录的空间分布，并包括一个简化的海冰模型和14 C的传输方程。(2)现代和古数据，包括来自底栖有孔虫和深海珊瑚的1000多个14 C年龄估计，将与不确定性估计一起收集。(3)在对从末次盛冰期（LGM）到今天的模型进行前向积分期间，将使用卡尔曼滤波器将模型与数据联合收割机结合起来。(4)将使用平滑器将数据（包括现代数据）提供的信息及时向后传播，从而进一步限制过去的海洋状态。从（3-4），估计从末次盛冰期到今天的流域尺度的海洋通风率将被导出，一个与数据和模型相一致的，给出了各自的误差统计估计。