Centennial oscillations in an ocean-ice coupled model

Irregular centennial oscillations, with a spectral peak at 106 years, were obtained from an ocean-ice coupled model for the North Atlantic with realis tic coastline and bottom topography. The model's thermohaline circulation i s forced by mixed boundary conditions, i.e., a Haney-type relaxation condit ion for temperature, but an equivalent virtual salt flux condition for sali nity. All forcing fields are taken from the observed monthly mean climatolo gical wind stress and buoyancy fluxes. The oscillations appeared in the form of a surface-intensified tripole in b oth the sea surface temperature and salinity fields located in the vicinity of the Labrador Sea. The oscillations involve a delicate interplay between heat and fresh water advection by meridional overturning circulation, hori zontal gyres, vertical convection, and the seasonal cycle. The oscillations are primarily controlled by the salinity component of the circulation; how ever, sea ice plays a minor role in driving the oscillations observed in th e model. On the other hand, a regular seasonal cycle in the forcing fields is an important ingredient for the centennial oscillations.