In this work a large positive salinity perturbation is introduced into the HadCM3 coupled climate model underneath the cold, fresh water of Arctic origin in the Greenland-Iceland-Norwegian (GIN) seas. It is an idealised perturbation designed to show mechanisms of interaction between the GIN seas and the North Atlantic subpolar gyre and meridional overturning circulation (MOC). It is hoped that knowledge of these mechanisms can be used in decadal climate prediction. To minimise noise from the atmosphere the average of a perturbed ensemble of four members is used and compared to the average of a control ensemble of equal size. The introduced salinity perturbation greatly spins up the circulation of the GIN seas gyre, which introduces large temperature anomalies in the GIN seas and alters the characteristics of the water flowing through the Denmark Straits. This change in the overflow propagates downstream with a large impact on the North Atlantic subpolar gyre. There is a dramatic effect on the Labrador Sea, where the circulation is substantially shut down. The response of the MOC is weak at first but starts to strengthen after 1-2 years and is on average 2 Sv stronger for the following five year period. There are two mechanisms that appear to influence the MOC: 1) a fast boundary wave response to the increased overflow at the Denmark Straits and 2) a slower propagation of a positive density anomaly (fresh and cold) from the Denmark Straits. The response of the atmosphere is surprisingly small (less than 5hPa, which is not significant) in the mean sea level pressure despite 1.5m air temperature anomalies larger than 7 degrees Celsius over the GIN seas SST anomalies. There is a significant response in the precipitation (2 mm/day) and the sea-ice seems to respond only passively. In the ten years of the run a small (compared to the initial perturbation) surface salinity anomaly propagates around the subpolar gyre, returning in its eastward branch toward the GIN seas. This behaviour is similar to that of a Great Salinity Anomaly.