Centennial Oscillations in an Ocean-ice Coupled Model

Irregular centennial oscillations, with a spectral peak at 106 years, were obtained from anocean-ice coupled model for the North Atlantic with realistic coastline and bottom topography.The model/s thermohaline circulation is forced by mixed boundary conditions, i.e., a Haney-typel-elaxation condition for temperature, but an equivalent virtual salt flux condition for salinity.Allforcing fields are taken from the observed monthly mean climatological wind stress and buoyancyfluxes.The oscillations appeared in the form of a surface-intensified triPOle in both the sea surfacetemperature and salinity fields located in the vicinity of the Labrador Sea. The oscillations involvea delicate interplay between heat and fresh water advection by meridional overturning circulation,horizontal gyres, vertical convection, and the seasonal cycle. The oscillations al.e primarily controLled by the salinity component of the circulation; however, sea ice plays a minor role in driving theoscillations observed in the model. On the other hand,a regular seasonal cycle in the forcing fieldsis an important ingredient for the centennial oscillations.