Abrupt CO2 Change and the Southern Hemisphere Westerlies: Testing the Upwelling Hypothesis

二氧化碳突然变化和南半球西风带：检验上升流假说

• 批准号: 1906143
• 负责人: Christo Buizert
• 金额: $ 55.96万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1906143&HistoricalAwards=false
• 关键词: Abrupt; CO2; Change; Southern; Hemisphere

Carbon dioxide (CO2) is the primary atmospheric greenhouse gas that plays a key role both in current climate change as well as in past natural climate variations such as the ice-age cycle. Understanding the natural causes of CO2 change is an important goal of climate research, with applications in improving climate projections for the future. At the coldest point of the last ice age (around 20,000 years ago) the atmospheric concentration of CO2 was around 90 parts per million (ppm) below the pre-industrial level. Most researchers think that during the ice age this missing carbon was stored in the deep ocean. Around 18,000 years ago, the CO2 concentration in the atmosphere started rising, marking the end of the last ice age. The cause for the CO2 rise is not well understood and heavily debated. A popular hypothesis is that the Southern Hemisphere westerly winds shifted southwards, causing CO2 release from the ocean due to increased ocean upwelling in the Southern Ocean. However, climate models disagree on whether this mechanism actually works. Recent research on Antarctic ice cores has provided evidence for repeated shifts in the position of these westerly winds during the last ice age in response to so-called Dansgaard-Oeschger events. This project will use ice-core samples to measure past changes in atmospheric CO2 at very high resolution during these natural shifts in the Southern Hemisphere westerlies. This will allow a direct test of the upwelling hypothesis for the rise in CO2. Currently, the Southern Hemisphere westerlies are again shifting southwards due to stratospheric ozone depletion and global warming. This may reduce carbon uptake by the world's oceans, exacerbating warming from anthropogenic emissions. These recent trends provide great impetus to better understand the relationship between CO2 and the westerly winds. This project work aims to produce a benchmark CO2 record that will be widely used by climate researchers. The project contributes to development of the STEM (Science, Technology, Engineering and Mathematics) workforce by training a postdoctoral researcher. An ongoing science outreach project will visit around 20 middle school classrooms annually to talk about polar and climate research. The project will measure in decadal temporal resolution the evolution of atmospheric CO2 in the WAIS Divide ice core during key climatic events (Heinrich events 2-5 and Dansgaard-Oeschger events 3-8 and 12) where ice-core markers suggest shifts occurred in the Southern Hemisphere westerlies. Existing ice-core CO2 records imply minor variations during these times, but they lack resolution to be conclusive on this issue. The project includes improvements to the CO2 analytical setup that will enhance sample throughput and analytical precision. The proposed number of samples is 720 (240 unique depths in triplicate) in the interval 27,000 to 40,000 years before present to complement the existing low-resolution CO2 record. The ice-core analyses are integrated with modeling and data-analysis to better understand the Antarctic water isotopic evidence for shifts in the Southern Hemisphere westerly winds and their link to CO2 variations, using existing output from isotope-enabled general circulation models and reanalysis data. In particular, the proposed work investigates the possibility of large wind-driven upwelling events in the Atlantic sector around Antarctica associated with Heinrich events--a previously unrecognized mode of climate variability. This project uses existing ice samples and does not require Antarctic field work.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.

二氧化碳（CO2）是主要的大气温室气体，在当前气候变化以及过去的自然气候变化（如冰年龄循环）中起着关键作用。了解二氧化碳变化的自然原因是气候研究的重要目标，其应用在改善未来气候预测方面的应用。在最后一个冰河时代（大约20，000年前）的最冷点，二氧化碳的大气浓度约为工业前水平的百万分之90（ppm）。大多数研究人员认为，在冰河时代，这种缺失的碳被存储在深海中。大约18，000年前，大气中的二氧化碳浓度开始上升，标志着最后一个冰河时代的终结。二氧化碳崛起的原因尚未得到充分理解和辩论。一个受欢迎的假设是，南半球西风向南移动，导致二氧化碳从海洋中释放，这是由于南大洋中海洋上升的增加而从海洋中释放。 但是，气候模型在这种机制是否确实有效的情况下不同意。最近对南极冰核的研究为响应所谓的Dansgaard-Oeschger事件，在上一个冰河时代的这些西风时反复转变提供了证据。该项目将使用冰核样品在南半球西风的这些自然变化期间以很高的分辨率测量大气二氧化碳的过去变化。 这将允许直接检验CO2上升的上升假设。目前，由于平流层臭氧耗竭和全球变暖，南半球的西风再次向南移动。这可能会减少世界海洋的碳吸收，从而加剧人为排放的变暖。这些最近的趋势为更好地了解二氧化碳与西风之间的关系提供了巨大的动力。该项目的工作旨在生成基准二氧化碳记录，该记录将被气候研究人员广泛使用。该项目通过培训博士后研究员来有助于STEM（科学，技术，工程和数学）劳动力的发展。正在进行的科学外展项目每年将访问约20个中学教室，谈论极地和气候研究。 该项目将在衰老的时间分辨率中测量在关键的气候事件（Heinrich事件2-5和Dansgaard-Oeschger事件3-8和12）中，大气二氧化碳在WAIS划分冰芯中的演变，其中冰核标记表明在南半球西风中发生了变化。现有的ICE-CORE CO2记录意味着在这段时间内差异很小，但在此问题上缺乏解决方案。该项目包括改进CO2分析设置，以增强样品吞吐量和分析精度。拟议的样品数量为720（240个独特的深度，一式三份）在27,000至40，000年之前，以补充现有的低分辨率CO2记录。冰核分析与建模和数据分析集成在一起，以更好地了解南半球西风风的转移的南极水同位素证据及其与CO2变化的链接，使用了同位素支持的一般循环模型和重新分析数据。尤其是，拟议的工作调查了与海因里希事件相关的大西洋部门中大型风向的上升流动事件的可能性，这是一种以前无法识别的气候变化方式。该项目使用现有的冰样品，不需要南极现场工作。该奖项反映了NSF的法定任务，并被认为是通过基金会的知识分子优点和更广泛的影响审查标准来评估值得支持的。