Collaborative Proposal: Exploring Hypotheses of Southern Hemisphere Westerly Wind Changes on Southern Ocean Circulation and Biogeochemistry

合作提案：探索南半球西风变化对南大洋环流和生物地球化学的假设

• 批准号: 1537496
• 负责人: John Chiang
• 金额: $ 3.3万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-10-01 至 2018-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1537496&HistoricalAwards=false
• 关键词: Collaborative; Proposal; Exploring; Hypotheses; Southern

The circulation of the Southern Ocean plays a prominent role in regulating Earth's climate, in particular connecting the deep ocean to the surface. This connection holds particular importance for the Earth's carbon cycle as upwelling of waters from the deep ocean brings stored carbon of the deep to the surface, eventually entering into the atmosphere as carbon dioxide. Increased upwelling is thought to have brought about the initial rise in atmospheric CO2 concentrations during the last deglaciation, caused by changes to the surface westerlies and resulting changes to the wind-driven upwelling. This project investigates a recent hypothesis for how the westerlies changed during this time period affects Southern ocean circulation and carbon cycle, through the use of a state-of-the-art climate model. The predictions of this hypothesis will be contrasted against those made by the "annular-mode" view for westerly changes that dominates current thinking, and both compared against available paleoproxy observations. The research provides concrete tests
to each hypothesis, and the process will help advance our understanding of how southern hemisphere westerlies affect the ocean climate and carbon cycle. The project will also enhance collaboration between two US-based scientists with an overseas collaborator based in Taiwan.Previous studies have largely assumed that paleo-westerly changes were zonally uniform, analogous to the so-called "annular mode" behavior that dominates year-to-year variations in the southern hemisphere westerlies today. However, in reality there are insufficient paleoproxy data to confirm this interpretation, and in a recent study one of the PIs proposed an alternative hypothesis for westerly changes through the modulation of the South Pacific Split Jet. The Split Jet is a regional feature of the South Pacific whereby the core of the westerlies split into two around Australia, and this split extends across the Pacific. Based on dynamical reasoning and comparison to paleoproxy records, the PI argued that the Split Jet feature weakened during Heinrich events, in particular Heinrich event 1 that preceded the last deglaciation. In this study, the consequences for a weaker Split Jet on the Southern ocean circulation and biogeochemistry will be investigated through idealized simulations using the ocean component of the Community Earth System Model version 1 with a simple ocean biogeochemistry module. Focus will be placed on understanding changes to the ocean surface temperature and frontal locations, changes to the upwelling and carbon fluxes. These simulations will be compared and contrasted against simulations where annular-mode like westerly changes is imposed. Through comparison between these simulations with available ocean paleoproxies, an assessment can be made as to which westerly configuration was more likely. If the Split Jet hypothesis turns out to be more correct, it has strong implications for our conceptualization and understanding of Southern ocean climate and circulation changes.

南大洋的环流在调节地球气候方面发挥着重要作用，特别是连接深海和地表。 这种联系对地球的碳循环具有特别重要的意义，因为深海的沃茨涌上来将深海储存的碳带到地表，最终以二氧化碳的形式进入大气。 上升流的增加被认为是在最后一次冰消期导致大气CO2浓度最初上升的原因，这是由地表西风带的变化和由此导致的风驱动的上升流的变化造成的。 该项目通过使用最先进的气候模式，调查了最近关于西风带在这段时间内如何变化影响南大洋环流和碳循环的假设。 这一假说的预测将与主导当前思想的西风变化的“环形模式”观点形成对比，并与现有的古代用资料进行比较。 该研究提供了具体的测试
这一过程将有助于推进我们对南半球西风带如何影响海洋气候和碳循环的理解。 该项目还将加强两名美国科学家与一名驻台湾的海外合作者之间的合作。以前的研究在很大程度上假设古西风带的变化是纬向均匀的，类似于所谓的“环形模式”行为，这种行为主导着今天南半球西风带的逐年变化。 然而，在现实中，没有足够的paleoproxy数据来证实这一解释，并在最近的一项研究中，一个PI提出了一个替代假设西风变化通过调制的南太平洋分裂急流。 分裂急流是南太平洋的一个区域性特徴，西风带的核心在澳大利亚附近一分为二，并延伸至整个太平洋。 根据动力学推理和与古代理记录的比较，PI认为分裂喷流特征在海因里希事件期间减弱，特别是在最后一次冰消之前的海因里希事件1。 在这项研究中，一个较弱的分裂射流对南大洋环流和海洋地球化学的后果将通过理想化的模拟使用社区地球系统模型版本1的海洋组件与一个简单的海洋地球化学模块进行调查。 重点将放在了解海洋表面温度和锋面位置的变化，上升流和碳通量的变化。 这些模拟将进行比较，并与模拟的环形模式，如西风变化。 通过这些模拟与现有的海洋paleoproxies之间的比较，可以作出评估，以西风配置更有可能。 如果分裂喷流假说被证明是更正确的，它对我们的概念化和理解南大洋气候和环流变化有很大的影响。