%%% PSpence ABSTRACT %%%

The influence of ENSO-related changes in the Atlantic-to-Pacific freshwater budget on the North Atlantic meridional
overturning is examined using the UVic Earth System Climate Model. The initial analysis of freshwater fluxes in the NCEP50 
reanalysis product and GPCP data set reveals that the transport of water vapour out of the tropical Atlantic drainage basin is 
enhanced during El Nino phases and reduced during La Nina phases; a one standard deviation in the southern oscillation index 
alters the tropical Atlantic freshwater balance by about 0.09 Sv. 
A weaker link with ENSO is found in the ERA40 reanalysis although its usefulness is 
severely limited by a strong, and spurious, trend in tropical precipitation. Model results suggest that 
tropical Atlantic salinity anomalies generated with the frequency and amplitude of ENSO tend not to
impact deep water formation as they are diluted en route to the North Atlantic. Lower frequency, decadal timescale anomalies, however, do have an 
impact, albeit weak, on the rate of North Atlantic Deep Water formation. 
In addition, and contrary to earlier results, it is found that even a shift of the tropical Atlantic freshwater balance towards permanent
El Nino conditions only slightly mitigates the transient reduction of North Atlantic Deep Water formation associated with the 
increase of anthropogenic greenhouse gases. 
Taken together, the results suggest that the poleward propagation of salinity anomalies from the tropical Atlantic,
associated with changes in ENSO, should not be considered a significant mechanism for the variability of the North Atlantic meridional
overturning in the present and foreseeable future climate.
