Tracking Southern Ocean sea ice extent and frontal positions: Novel techniques based on oxygen isotope and Mg/Ca analyses of foraminifera

跟踪南大洋海冰范围和锋面位置：基于氧同位素和有孔虫 Mg/Ca 分析的新技术

• 批准号: 2002425
• 负责人: David Lund
• 金额: $ 39.73万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-06-01 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2002425&HistoricalAwards=false
• 关键词: Tracking; Southern; Ocean; sea; ice

Understanding the drivers of glacial-interglacial carbon dioxide (CO2) cycles is one of the most important questions in the field of paleoclimatology. It has long been known that Earth’s ice sheets expand when atmospheric CO2 is low and melt as CO2 rises, but the underlying climate mechanisms remain unclear. Expanded sea ice coverage in the Southern Ocean around Antarctica may have limited the release of carbon from the deep ocean during natural cold periods such as the Last Glacial Maximum (LGM; ~20,000 years ago). Greater sea ice extent and northward movement of oceanic fronts may have also led to carbon storage in the deep ocean. Reliable paleoclimate records from the Southern Ocean are thus essential to understanding the controls on atmospheric CO2 over long timescales. The proposed study will develop new methods to produce such records, using chemical analyses of microscopic fossils from marine sediment cores. The educational impact of the proposed work includes support for a graduate student and an undergraduate at the University of Connecticut. The proposed work will focus on developing a new proxy for sea ice extent based on the oxygen isotope ratios (d18O) of benthic and planktonic foraminifera. Sea ice formation in the Southern Ocean is characterized by near-freezing surface conditions and negative buoyancy forcing, which creates a unique vertical profile in d18O. Preliminary data from the published literature shows that the d18O difference between recent planktonic and benthic foraminifera yields an estimate of sea ice extent consistent with modern observations. We also plan to develop a novel proxy for subtropical front position based on foraminiferal magnesium/calcium (Mg/Ca) and d18O analyses. Contemporary measurements of sea-surface temperature and the d18O of seawater capture the position of the subtropical front, implying that reconstructions based on Mg/Ca and d18O can be used to track frontal position in the geologic past. Motivated by these initial results, we propose to use a transect of cores from ~55ºS to 35ºS in the Atlantic sector of the Southern Ocean to: 1) estimate sea ice extent and surface buoyancy forcing during the LGM, and 2) reconstruct the position of the subtropical front during the LGM to constrain inter-basin exchange between the Atlantic and Indian Oceans. The proposed work could transform our understanding of the Southern Ocean by adding two new methods to the paleoclimate toolkit. The d18O sea ice proxy will complement existing diatom-based methods and it can be used in regions where diatoms are sparse. Similarly, development of the subtropical front technique will lay the groundwork for studies of the deglaciation when changes in frontal position have been invoked to explain rising atmospheric CO2. Given the relevance of the techniques to research questions across a range of timescales, we anticipate our results will be of broad interest to the paleoclimate community.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.

了解冰川间 - 冰川二氧化碳（CO2）周期的驱动因素是古气候学领域中最重要的问题之一。早就知道，当大气中的二氧化碳升高并随着二氧化碳的升高而融化时，地球的冰片会扩大，但是潜在的气候机制尚不清楚。南极附近南洋的海冰覆盖范围扩大可能会限制在自然寒冷时期（例如最后一次冰川最大值）（LGM; 〜20,000年前）从深海中释放出来。海冰范围更大和海洋阵线的北向运动也可能导致深海中的碳储存。因此，来自南大洋的可靠古气候记录对于理解长时间大气中的大气二氧化碳的控制至关重要。拟议的研究将使用来自海洋沉积物核心的微观化石进行化学分析，开发出新的方法来产生此类记录。拟议工作的教育影响包括支持研究生和康涅狄格大学的本科生。拟议的工作将重点介绍基于底栖和浮游有孔虫的氧同位素比（D18O）的海冰范围的新代理。南大洋的海冰形成的特征是近乎冻结的表面条件和负浮力强迫，这在D18O中产生了独特的垂直轮廓。来自已发表的文献的初步数据表明，近期浮游物和底栖有孔虫之间的D18O差异得出了与现代观察结果一致的海冰范围的估计。我们还计划基于有孔虫镁/钙（Mg/Ca）和D18O分析开发用于亚热带前部位置的新型代理。海水温度和海水D18O的现代测量值捕获了亚热带阵线的位置，这意味着基于MG/CA和D18O的重建可以用于跟踪地质过去的额叶位置。在这些最初的结果的激励下，我们提议在南大西洋大西洋地区使用核心从〜55ºS到35ºS的交易，以：1）估计LGM期间的海冰范围和表面浮力强迫，以及2）重建LGM在LGM中限制bassin Inter-Basin Interbasin Interbasin Internation Inder the Inder Inderantic Onder and Inderantic Oceans之间的位置。拟议的工作可以通过在古气候工具包中添加两种新方法来改变我们对南洋的理解。 D18O Sea Ice代理将补充现有的基于硅藻的方法，并且可以在硅藻稀疏的区域使用。同样，当额叶位置的变化被调解以解释大气二氧化碳的上升时，亚热带前端技术的发展将为研究脱气的基础奠定基础。鉴于这些技术与在各个时间尺度上研究问题的相关性，我们预计我们的结果将对古气候社区产生广泛的兴趣。该奖项反映了NSF的法定任务，并被认为是通过基金会的智力优点评估和更广泛影响的评估来审查标准。

项目成果

Tracking Southern Ocean Sea Ice Extent With Winter Water: A New Method Based on the Oxygen Isotopic Signature of Foraminifera

用冬季水追踪南大洋海冰范围：一种基于有孔虫氧同位素特征的新方法

• DOI: 10.1029/2020pa004095
• 发表时间: 2021
• 期刊: Paleoceanography and Paleoclimatology
• 影响因子: 3.5
• 作者: Lund, David C.;Chase, Zanna;Kohfeld, Karen E.;Wilson, Earle A.
• 通讯作者: Wilson, Earle A.