Generation of the ocean's permanent pycnocline in the ice-covered Southern Ocean

永久跃层(PP)是海洋的主要组织特征--一种升高的层结界面，将与大气交换热量和碳的近表面水域与存储这些示踪物长达数千年的深层水域隔开。然而，尽管海洋在气候中的作用是它的基本基础，而且经过几十年的研究，支配PP形成的过程仍然未知。PycnoGen将通过为PP的建立产生第一个以观测为基础的机械论范式来解决这一关键的知识鸿沟。为实现这一目标，该项目将涉及四个目标：(O1)开发一套尖端、耐久的自主机器人系统和分布式传感器网络技术，以测量冰层下的极地海洋；(O2)利用O1中的创新技术，对太平洋冰盖形成的一个有代表性的区域--太平洋冰盖的发源地--进行第一次针对过程的观测；(03)根据在O2的观测结果，确定控制冰盖形成和流经海洋的过程；和(O4)评估PP从其形成区域投射到全球海洋的机制、PP对海洋通风和倾覆的大范围影响，以及该系统对关键气候强迫的敏感性。PicnoGen将通过以下方式在海洋学和气候科学领域留下具有影响力和持久的遗产：(I)通过O1的技术突破，使国际极地海洋观测能力发生阶段性变化；(Ii)制作PP形成的基准观测数据集(O2)，作为从根本上推进气候尺度海洋模型的发射台；以及(Iii)改变我们对海洋-气候系统最重要组成部分之一(O3-O4)的机械理解，对许多高级别的全球气候变化问题产生深远影响。

The permanent pycnocline (PP) is the ocean's main organising feature - an interface of elevated stratification that sets apart near-surface waters exchanging heat and carbon with the atmosphere from deeper waters storing those tracers for as long as millennia. Yet despite its basic underpinning of the ocean's role in climate, and decades of investigation, the processes governing the PP's formation remain unknown. PycnoGen will tackle this critical knowledge gap by generating the first observationally-grounded mechanistic paradigm for the establishment of the PP. To accomplish this, the project will address four objectives: (O1) to develop a suite of cutting-edge, long-endurance autonomous robotic system and distributed sensor network technologies to measure the polar oceans under ice; (O2) to generate first-of-a-kind, process-targeted observations - enabled by the innovative technologies in O1 - of the PP's formation in a representative region of the seasonally ice-covered Southern Ocean, where the PP originates; (O3) to determine the processes controlling the formation of, and flow across, the PP from the observations in O2; and (O4) to assess the mechanisms by which the PP is projected from its formation region into the global ocean, the PP's large-scale impacts on oceanic ventilation and overturning, and the system's sensitivities to key climate forcings. PycnoGen will leave an influential and long-lasting legacy in oceanography and climate science by: (i) generating a step change in international capability for polar ocean observation, through the technological breakthroughs in O1; (ii) producing a benchmark observational data set of the PP's formation (in O2), poised to serve as a launchpad to fundamentally advance climate-scale ocean models; and (iii) transforming our mechanistic understanding of one of the foremost components of the ocean-climate system (in O3-O4), with profound ramifications for many high-ranking global climate change problems.