The ocean’s permanent pycnocline—a sharp density barrier that separates surface waters from the deep ocean—forms each winter in the ice-covered Southern Ocean, and no one knows exactly how. This matters because the pycnocline controls how quickly heat and carbon dioxide absorbed at the surface reach the deep ocean, where they can be stored for centuries to millennia. Without understanding its formation, climate models cannot accurately predict how the ocean will take up future emissions or respond to warming. Despite decades of study, the mechanisms that build this layer remain a fundamental gap in climate science. PycnoGen will deploy a new generation of long-endurance autonomous robots and distributed sensors under Antarctic sea ice to capture the first direct observations of the pycnocline as it forms. The project will then determine the physical processes at work and trace how the resulting stratification spreads into the global ocean. If successful, the research will transform climate-scale ocean models, improving projections of ocean carbon storage, deep-water ventilation, and the system’s sensitivity to melting ice and shifting winds. This is fundamental science with no immediate practical application, but it addresses a core uncertainty in how the planet’s largest carbon reservoir behaves.
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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.
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