The impact of synoptic atmospheric forcing on the mean ocean circulation is investigated by comparing simulations of a global eddy-permitting ocean-sea ice model forced with and without synoptic atmospheric phenomena. Consistent with previous studies, transient atmospheric motions such as weather systems are found to contribute significantly to the time-mean wind stress and surface heat loss at mid and high latitudes owing to the nonlinear nature of air-sea turbulent fluxes. Including synoptic atmospheric forcing in the model has led to a number of significant changes. For example, wind power input to the ocean increases by about 50%, which subsequently leads to a similar percentage increase in global eddy kinetic energy. The wind-driven subtropical gyre circulations are strengthened by about 10-15%, whereas even greater increases in gyre strength are found in the subpolar oceans. Deep convection in the northern North Atlantic becomes significantly more vigorous, which in turn leads to an increase in the Atlantic Meridional Overturning Circulation (AMOC) by as much as 55%. As a result of the strengthened horizontal gyre circulations and the AMOC, the maximum global northward heat transport increases by almost 50%. Results from this study show that synoptic atmospheric phenomena such as weather systems play a vital role in driving the global ocean circulation and heat transport, and therefore should be properly accounted for in paleo and future climate studies.