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

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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.