North Atlantic ocean model results and Yashayaev's new climatology show isopycnal flattening in the region between the shelfslope and Gulf Stream core, reflecting thermohaline effects that are analogous to observed nonlinear baroclinic eddy dynamics in the rotating annulus experiments and the atmosphere. This involves interaction between the Gulf Stream and deep/ shelfslope current system. Realistic modeling of the narrow, thin deep current system penetration to Cape Hatteras and the resulting Gulf Stream interactions --- including mean Gulf Stream path (sometimes called "the Holy Grail of ocean modeling"), variability and model-challenging warm-core eddies that pinch off northern Gulf Stream meanders --- demand low model dissipation and numerical dispersion.

The model uses a two-way coupled duo grid (1/2 deg resolution east of 60 deg W; 1/6 deg resolution west of 60 deg W) and 4th-order-accurate control volume numerics in order to efficiently resolve the dynamics (one model year per ~2 clock days on a 2 GHz P4 PC). This efficiency in addressing major observed dynamics is critical to model-based climate risk assessment for rapid climate change involving coupled shelfslope current, methane hydrate gasification, Gulf Stream and strongly exothermic biogeochemical processes that may fuel observed ongoing deep ocean warming, oxygen depletion and decreasing Arctic Ocean ice cover. Strong positive feedbacks are possible and there is more than enough chemical energy stored in methane hydrates to melt all of the world ocean ice cover.