Maud Rise and Weddell Sea Polynyas in High-Resolution CESM-iHESP simulations

Abstract:

Since the beginning of satellite passive-microwave remote sensing of sea-ice concentration, Weddell Sea Polynyas (WSPs) occurred only in years 1974-1976, and distinct Maud Rise Polynyas (MRPs) only in years 2016-2017. While most Earth System Models (ESMs) produce quasi permanent WSPs, the Community ESM (CESM) produces WSPs intermittently only when running at high-resolution (atmosphere and land 0.25⁰, ocean and sea ice 0.1⁰). The International Laboratory for High-resolution Earth System Prediction (iHESP) partnership recently produced an unprecedented set of high-resolution CESM simulations. Here we analyze the occurrence of MRPs and WSPs in the 250-year historical and future CESM-iHESP simulation from 1850 to 2100, and in the 500-year preindustrial CESM-iHESP simulation. In the former simulation, MRPs and WSPs occur more frequently in the period between year 1950-2020 than observed. We will show that a combination of biases of wind stress curl, external freshwater flux (precipitation and glacial melt water), advection of salinity anomalies, and accumulation of heat at depth in the Weddell Sea leads to an excessive production of polynyas. We will furthermore report on the polynya formation mechanisms, and the impact of the intermittently occurring WSPs on the formation and spreading of Antarctic Bottom Water (AABW) in the long-term preindustrial simulation. Water age will be used as a tracer to track the deep ocean pathway of anomalies due to convection events associated with WSPs. We will also report on large-scale variability patterns in the Pacific Ocean that are seemingly connected if not followed by WSP events.