Quoted from: https://e3sm.org/model/e3sm-model-description/v1-description/v1-ocean-sea-ice-land-ice/ 

During Phase I, MPAS-O underwent continued testing in coupled ocean ice configurations (Petersen et al., 2018a). For the first time, it was also used within a full coupled system configuration. Like all MPAS components, the ocean uses an unstructured grid composed of convex polygons (Ringer et al. 2008) with a generalization of the seminal Arakawa C-grid mimetic discretization (Arakawa and Lamb, 1981; Thurburn et al., 2009; Ringler et al., 2010; Ringler et al., 2013). MPAS-O also includes a vertical discretization based on the Arbitrary Lagrangian Eulerian (ALE) approach that can mimic z-level, sigma, and isopycnal coordinates (Petersen et al., 2015). Three major model development projects were completed during Phase I: extending the ocean domain to include ice shelf cavities around the AIS (Petersen et al. 2018a), leading the verification and validation of the KPP scheme used in the Community Vertical MIXing (CVMIX) collaboration (Van Roekel et al. 2017), and developing an online, scalable, high-performance implementation of Lagrangian particle trajectories to study mesoscale-induced mixing (Wolfram et al. 2017a; 2017b).