The exchange of atmospheric plus oceanic mass between ocean basins is investigated using a global barotropic ocean model. We find two particular cases of exchange between two basins. At periods of 4--6 days, the exchange is between the Atlantic and Pacific basins, and represents a known oscillation forced by atmospheric pressure. This mode represents a failure of the inverse-barometer relationship due to the large scale and high frequency of atmospheric forcing, and the presence of continents. Significant exchange between Atlantic and Pacific also occurs at longer periods. The second case is most prominent at periods longer than 30 days (strongest at periods longer than 100 days), and represents a mass exchange between the Southern Ocean and the Pacific. The Southern Ocean part of this exchange is clearly related to the Southern Mode of fluctuations in Antarctic circumpolar transport, forced by Southern Ocean wind stress. The reason for the exchange being with the Pacific rather than other basins is explored, and is found to be related to the balance of wind stress by form stress in Drake Passage: exchange with the Atlantic and Indian oceans becomes dominant if Drake Passage topography is removed. While recognizing the limitations of a barotropic model, we contend that it is necessary to understand the barotropic adjustment process in order to make sense of longer timescale processes. Accordingly, we end with speculation on the possible importance of the barotropic results for global sea level and tropical dynamics.